Fix building without protochain support. (GH #852)

[libpcap] / pcap-linux.c

/*
 *  pcap-linux.c: Packet capture interface to the Linux kernel
 *
 *  Copyright (c) 2000 Torsten Landschoff <torsten@debian.org>
 *                     Sebastian Krahmer  <krahmer@cs.uni-potsdam.de>
 *
 *  License: BSD
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in
 *     the documentation and/or other materials provided with the
 *     distribution.
 *  3. The names of the authors may not be used to endorse or promote
 *     products derived from this software without specific prior
 *     written permission.
 *
 *  THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 *  IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 *  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 *  Modifications:     Added PACKET_MMAP support
 *                     Paolo Abeni <paolo.abeni@email.it>
 *                     Added TPACKET_V3 support
 *                     Gabor Tatarka <gabor.tatarka@ericsson.com>
 *
 *                     based on previous works of:
 *                     Simon Patarin <patarin@cs.unibo.it>
 *                     Phil Wood <cpw@lanl.gov>
 *
 * Monitor-mode support for mac80211 includes code taken from the iw
 * command; the copyright notice for that code is
 *
 * Copyright (c) 2007, 2008     Johannes Berg
 * Copyright (c) 2007           Andy Lutomirski
 * Copyright (c) 2007           Mike Kershaw
 * Copyright (c) 2008           Gábor Stefanik
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */


#define _GNU_SOURCE

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <limits.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/utsname.h>
#include <sys/mman.h>
#include <linux/if.h>
#include <linux/if_packet.h>
#include <linux/sockios.h>
#include <linux/ethtool.h>
#include <netinet/in.h>
#include <linux/if_ether.h>
#include <linux/if_arp.h>
#include <poll.h>
#include <dirent.h>
#include <sys/eventfd.h>

#include "pcap-int.h"
#include "pcap/sll.h"
#include "pcap/vlan.h"
#include "pcap/can_socketcan.h"

#include "diag-control.h"

/*
 * We require TPACKET_V2 support.
 */
#ifndef TPACKET2_HDRLEN
#error "Libpcap will only work if TPACKET_V2 is supported; you must build for a 2.6.27 or later kernel"
#endif

/* check for memory mapped access avaibility. We assume every needed
 * struct is defined if the macro TPACKET_HDRLEN is defined, because it
 * uses many ring related structs and macros */
#ifdef TPACKET3_HDRLEN
# define HAVE_TPACKET3
#endif /* TPACKET3_HDRLEN */

/*
 * Not all compilers that are used to compile code to run on Linux have
 * these builtins.  For example, older versions of GCC don't, and at
 * least some people are doing cross-builds for MIPS with older versions
 * of GCC.
 */
#ifndef HAVE___ATOMIC_LOAD_N
#define __atomic_load_n(ptr, memory_model)              (*(ptr))
#endif
#ifndef HAVE___ATOMIC_STORE_N
#define __atomic_store_n(ptr, val, memory_model)        *(ptr) = (val)
#endif

#define packet_mmap_acquire(pkt) \
        (__atomic_load_n(&pkt->tp_status, __ATOMIC_ACQUIRE) != TP_STATUS_KERNEL)
#define packet_mmap_release(pkt) \
        (__atomic_store_n(&pkt->tp_status, TP_STATUS_KERNEL, __ATOMIC_RELEASE))
#define packet_mmap_v3_acquire(pkt) \
        (__atomic_load_n(&pkt->hdr.bh1.block_status, __ATOMIC_ACQUIRE) != TP_STATUS_KERNEL)
#define packet_mmap_v3_release(pkt) \
        (__atomic_store_n(&pkt->hdr.bh1.block_status, TP_STATUS_KERNEL, __ATOMIC_RELEASE))

#include <linux/types.h>
#include <linux/filter.h>

#ifdef HAVE_LINUX_NET_TSTAMP_H
#include <linux/net_tstamp.h>
#endif

/*
 * For checking whether a device is a bonding device.
 */
#include <linux/if_bonding.h>

/*
 * Got libnl?
 */
#ifdef HAVE_LIBNL
#include <linux/nl80211.h>

#include <netlink/genl/genl.h>
#include <netlink/genl/family.h>
#include <netlink/genl/ctrl.h>
#include <netlink/msg.h>
#include <netlink/attr.h>
#endif /* HAVE_LIBNL */

#ifndef HAVE_SOCKLEN_T
typedef int             socklen_t;
#endif

#define MAX_LINKHEADER_SIZE     256

/*
 * When capturing on all interfaces we use this as the buffer size.
 * Should be bigger then all MTUs that occur in real life.
 * 64kB should be enough for now.
 */
#define BIGGER_THAN_ALL_MTUS    (64*1024)

/*
 * Private data for capturing on Linux PF_PACKET sockets.
 */
struct pcap_linux {
        long long sysfs_dropped; /* packets reported dropped by /sys/class/net/{if_name}/statistics/rx_{missed,fifo}_errors */
        struct pcap_stat stat;

        char    *device;        /* device name */
        int     filter_in_userland; /* must filter in userland */
        int     blocks_to_filter_in_userland;
        int     must_do_on_close; /* stuff we must do when we close */
        int     timeout;        /* timeout for buffering */
        int     cooked;         /* using SOCK_DGRAM rather than SOCK_RAW */
        int     ifindex;        /* interface index of device we're bound to */
        int     lo_ifindex;     /* interface index of the loopback device */
        int     netdown;        /* we got an ENETDOWN and haven't resolved it */
        bpf_u_int32 oldmode;    /* mode to restore when turning monitor mode off */
        char    *mondevice;     /* mac80211 monitor device we created */
        u_char  *mmapbuf;       /* memory-mapped region pointer */
        size_t  mmapbuflen;     /* size of region */
        int     vlan_offset;    /* offset at which to insert vlan tags; if -1, don't insert */
        u_int   tp_version;     /* version of tpacket_hdr for mmaped ring */
        u_int   tp_hdrlen;      /* hdrlen of tpacket_hdr for mmaped ring */
        u_char  *oneshot_buffer; /* buffer for copy of packet */
        int     poll_timeout;   /* timeout to use in poll() */
#ifdef HAVE_TPACKET3
        unsigned char *current_packet; /* Current packet within the TPACKET_V3 block. Move to next block if NULL. */
        int packets_left; /* Unhandled packets left within the block from previous call to pcap_read_linux_mmap_v3 in case of TPACKET_V3. */
#endif
        int poll_breakloop_fd; /* fd to an eventfd to break from blocking operations */
};

/*
 * Stuff to do when we close.
 */
#define MUST_CLEAR_RFMON        0x00000001      /* clear rfmon (monitor) mode */
#define MUST_DELETE_MONIF       0x00000002      /* delete monitor-mode interface */

/*
 * Prototypes for internal functions and methods.
 */
static int get_if_flags(const char *, bpf_u_int32 *, char *);
static int is_wifi(const char *);
static void map_arphrd_to_dlt(pcap_t *, int, const char *, int);
static int pcap_activate_linux(pcap_t *);
static int setup_socket(pcap_t *, int);
static int setup_mmapped(pcap_t *, int *);
static int pcap_can_set_rfmon_linux(pcap_t *);
static int pcap_inject_linux(pcap_t *, const void *, int);
static int pcap_stats_linux(pcap_t *, struct pcap_stat *);
static int pcap_setfilter_linux(pcap_t *, struct bpf_program *);
static int pcap_setdirection_linux(pcap_t *, pcap_direction_t);
static int pcap_set_datalink_linux(pcap_t *, int);
static void pcap_cleanup_linux(pcap_t *);

union thdr {
        struct tpacket2_hdr             *h2;
#ifdef HAVE_TPACKET3
        struct tpacket_block_desc       *h3;
#endif
        u_char                          *raw;
};

#define RING_GET_FRAME_AT(h, offset) (((u_char **)h->buffer)[(offset)])
#define RING_GET_CURRENT_FRAME(h) RING_GET_FRAME_AT(h, h->offset)

static void destroy_ring(pcap_t *handle);
static int create_ring(pcap_t *handle, int *status);
static int prepare_tpacket_socket(pcap_t *handle);
static int pcap_read_linux_mmap_v2(pcap_t *, int, pcap_handler , u_char *);
#ifdef HAVE_TPACKET3
static int pcap_read_linux_mmap_v3(pcap_t *, int, pcap_handler , u_char *);
#endif
static int pcap_setnonblock_linux(pcap_t *p, int nonblock);
static int pcap_getnonblock_linux(pcap_t *p);
static void pcap_oneshot_linux(u_char *user, const struct pcap_pkthdr *h,
    const u_char *bytes);

/*
 * In pre-3.0 kernels, the tp_vlan_tci field is set to whatever the
 * vlan_tci field in the skbuff is.  0 can either mean "not on a VLAN"
 * or "on VLAN 0".  There is no flag set in the tp_status field to
 * distinguish between them.
 *
 * In 3.0 and later kernels, if there's a VLAN tag present, the tp_vlan_tci
 * field is set to the VLAN tag, and the TP_STATUS_VLAN_VALID flag is set
 * in the tp_status field, otherwise the tp_vlan_tci field is set to 0 and
 * the TP_STATUS_VLAN_VALID flag isn't set in the tp_status field.
 *
 * With a pre-3.0 kernel, we cannot distinguish between packets with no
 * VLAN tag and packets on VLAN 0, so we will mishandle some packets, and
 * there's nothing we can do about that.
 *
 * So, on those systems, which never set the TP_STATUS_VLAN_VALID flag, we
 * continue the behavior of earlier libpcaps, wherein we treated packets
 * with a VLAN tag of 0 as being packets without a VLAN tag rather than packets
 * on VLAN 0.  We do this by treating packets with a tp_vlan_tci of 0 and
 * with the TP_STATUS_VLAN_VALID flag not set in tp_status as not having
 * VLAN tags.  This does the right thing on 3.0 and later kernels, and
 * continues the old unfixably-imperfect behavior on pre-3.0 kernels.
 *
 * If TP_STATUS_VLAN_VALID isn't defined, we test it as the 0x10 bit; it
 * has that value in 3.0 and later kernels.
 */
#ifdef TP_STATUS_VLAN_VALID
  #define VLAN_VALID(hdr, hv)   ((hv)->tp_vlan_tci != 0 || ((hdr)->tp_status & TP_STATUS_VLAN_VALID))
#else
  /*
   * This is being compiled on a system that lacks TP_STATUS_VLAN_VALID,
   * so we testwith the value it has in the 3.0 and later kernels, so
   * we can test it if we're running on a system that has it.  (If we're
   * running on a system that doesn't have it, it won't be set in the
   * tp_status field, so the tests of it will always fail; that means
   * we behave the way we did before we introduced this macro.)
   */
  #define VLAN_VALID(hdr, hv)   ((hv)->tp_vlan_tci != 0 || ((hdr)->tp_status & 0x10))
#endif

#ifdef TP_STATUS_VLAN_TPID_VALID
# define VLAN_TPID(hdr, hv)     (((hv)->tp_vlan_tpid || ((hdr)->tp_status & TP_STATUS_VLAN_TPID_VALID)) ? (hv)->tp_vlan_tpid : ETH_P_8021Q)
#else
# define VLAN_TPID(hdr, hv)     ETH_P_8021Q
#endif

/*
 * Required select timeout if we're polling for an "interface disappeared"
 * indication - 1 millisecond.
 */
static const struct timeval netdown_timeout = {
        0, 1000         /* 1000 microseconds = 1 millisecond */
};

/*
 * Wrap some ioctl calls
 */
static int      iface_get_id(int fd, const char *device, char *ebuf);
static int      iface_get_mtu(int fd, const char *device, char *ebuf);
static int      iface_get_arptype(int fd, const char *device, char *ebuf);
static int      iface_bind(int fd, int ifindex, char *ebuf, int protocol);
static int      enter_rfmon_mode(pcap_t *handle, int sock_fd,
    const char *device);
static int      iface_get_ts_types(const char *device, pcap_t *handle,
    char *ebuf);
static int      iface_get_offload(pcap_t *handle);

static int      fix_program(pcap_t *handle, struct sock_fprog *fcode);
static int      fix_offset(pcap_t *handle, struct bpf_insn *p);
static int      set_kernel_filter(pcap_t *handle, struct sock_fprog *fcode);
static int      reset_kernel_filter(pcap_t *handle);

static struct sock_filter       total_insn
        = BPF_STMT(BPF_RET | BPF_K, 0);
static struct sock_fprog        total_fcode
        = { 1, &total_insn };

static int      iface_dsa_get_proto_info(const char *device, pcap_t *handle);

pcap_t *
pcap_create_interface(const char *device, char *ebuf)
{
        pcap_t *handle;

        handle = PCAP_CREATE_COMMON(ebuf, struct pcap_linux);
        if (handle == NULL)
                return NULL;

        handle->activate_op = pcap_activate_linux;
        handle->can_set_rfmon_op = pcap_can_set_rfmon_linux;

        /*
         * See what time stamp types we support.
         */
        if (iface_get_ts_types(device, handle, ebuf) == -1) {
                pcap_close(handle);
                return NULL;
        }

        /*
         * We claim that we support microsecond and nanosecond time
         * stamps.
         *
         * XXX - with adapter-supplied time stamps, can we choose
         * microsecond or nanosecond time stamps on arbitrary
         * adapters?
         */
        handle->tstamp_precision_list = malloc(2 * sizeof(u_int));
        if (handle->tstamp_precision_list == NULL) {
                pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                    errno, "malloc");
                pcap_close(handle);
                return NULL;
        }
        handle->tstamp_precision_list[0] = PCAP_TSTAMP_PRECISION_MICRO;
        handle->tstamp_precision_list[1] = PCAP_TSTAMP_PRECISION_NANO;
        handle->tstamp_precision_count = 2;

        struct pcap_linux *handlep = handle->priv;
        handlep->poll_breakloop_fd = eventfd(0, EFD_NONBLOCK);

        return handle;
}

#ifdef HAVE_LIBNL
/*
 * If interface {if_name} is a mac80211 driver, the file
 * /sys/class/net/{if_name}/phy80211 is a symlink to
 * /sys/class/ieee80211/{phydev_name}, for some {phydev_name}.
 *
 * On Fedora 9, with a 2.6.26.3-29 kernel, my Zydas stick, at
 * least, has a "wmaster0" device and a "wlan0" device; the
 * latter is the one with the IP address.  Both show up in
 * "tcpdump -D" output.  Capturing on the wmaster0 device
 * captures with 802.11 headers.
 *
 * airmon-ng searches through /sys/class/net for devices named
 * monN, starting with mon0; as soon as one *doesn't* exist,
 * it chooses that as the monitor device name.  If the "iw"
 * command exists, it does
 *
 *    iw dev {if_name} interface add {monif_name} type monitor
 *
 * where {monif_name} is the monitor device.  It then (sigh) sleeps
 * .1 second, and then configures the device up.  Otherwise, if
 * /sys/class/ieee80211/{phydev_name}/add_iface is a file, it writes
 * {mondev_name}, without a newline, to that file, and again (sigh)
 * sleeps .1 second, and then iwconfig's that device into monitor
 * mode and configures it up.  Otherwise, you can't do monitor mode.
 *
 * All these devices are "glued" together by having the
 * /sys/class/net/{if_name}/phy80211 links pointing to the same
 * place, so, given a wmaster, wlan, or mon device, you can
 * find the other devices by looking for devices with
 * the same phy80211 link.
 *
 * To turn monitor mode off, delete the monitor interface,
 * either with
 *
 *    iw dev {monif_name} interface del
 *
 * or by sending {monif_name}, with no NL, down
 * /sys/class/ieee80211/{phydev_name}/remove_iface
 *
 * Note: if you try to create a monitor device named "monN", and
 * there's already a "monN" device, it fails, as least with
 * the netlink interface (which is what iw uses), with a return
 * value of -ENFILE.  (Return values are negative errnos.)  We
 * could probably use that to find an unused device.
 *
 * Yes, you can have multiple monitor devices for a given
 * physical device.
 */

/*
 * Is this a mac80211 device?  If so, fill in the physical device path and
 * return 1; if not, return 0.  On an error, fill in handle->errbuf and
 * return PCAP_ERROR.
 */
static int
get_mac80211_phydev(pcap_t *handle, const char *device, char *phydev_path,
    size_t phydev_max_pathlen)
{
        char *pathstr;
        ssize_t bytes_read;

        /*
         * Generate the path string for the symlink to the physical device.
         */
        if (asprintf(&pathstr, "/sys/class/net/%s/phy80211", device) == -1) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: Can't generate path name string for /sys/class/net device",
                    device);
                return PCAP_ERROR;
        }
        bytes_read = readlink(pathstr, phydev_path, phydev_max_pathlen);
        if (bytes_read == -1) {
                if (errno == ENOENT || errno == EINVAL) {
                        /*
                         * Doesn't exist, or not a symlink; assume that
                         * means it's not a mac80211 device.
                         */
                        free(pathstr);
                        return 0;
                }
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "%s: Can't readlink %s", device, pathstr);
                free(pathstr);
                return PCAP_ERROR;
        }
        free(pathstr);
        phydev_path[bytes_read] = '\0';
        return 1;
}

struct nl80211_state {
        struct nl_sock *nl_sock;
        struct nl_cache *nl_cache;
        struct genl_family *nl80211;
};

static int
nl80211_init(pcap_t *handle, struct nl80211_state *state, const char *device)
{
        int err;

        state->nl_sock = nl_socket_alloc();
        if (!state->nl_sock) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: failed to allocate netlink handle", device);
                return PCAP_ERROR;
        }

        if (genl_connect(state->nl_sock)) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: failed to connect to generic netlink", device);
                goto out_handle_destroy;
        }

        err = genl_ctrl_alloc_cache(state->nl_sock, &state->nl_cache);
        if (err < 0) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: failed to allocate generic netlink cache: %s",
                    device, nl_geterror(-err));
                goto out_handle_destroy;
        }

        state->nl80211 = genl_ctrl_search_by_name(state->nl_cache, "nl80211");
        if (!state->nl80211) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: nl80211 not found", device);
                goto out_cache_free;
        }

        return 0;

out_cache_free:
        nl_cache_free(state->nl_cache);
out_handle_destroy:
        nl_socket_free(state->nl_sock);
        return PCAP_ERROR;
}

static void
nl80211_cleanup(struct nl80211_state *state)
{
        genl_family_put(state->nl80211);
        nl_cache_free(state->nl_cache);
        nl_socket_free(state->nl_sock);
}

static int
del_mon_if(pcap_t *handle, int sock_fd, struct nl80211_state *state,
    const char *device, const char *mondevice);

static int
add_mon_if(pcap_t *handle, int sock_fd, struct nl80211_state *state,
    const char *device, const char *mondevice)
{
        struct pcap_linux *handlep = handle->priv;
        int ifindex;
        struct nl_msg *msg;
        int err;

        ifindex = iface_get_id(sock_fd, device, handle->errbuf);
        if (ifindex == -1)
                return PCAP_ERROR;

        msg = nlmsg_alloc();
        if (!msg) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: failed to allocate netlink msg", device);
                return PCAP_ERROR;
        }

        genlmsg_put(msg, 0, 0, genl_family_get_id(state->nl80211), 0,
                    0, NL80211_CMD_NEW_INTERFACE, 0);
        NLA_PUT_U32(msg, NL80211_ATTR_IFINDEX, ifindex);
DIAG_OFF_NARROWING
        NLA_PUT_STRING(msg, NL80211_ATTR_IFNAME, mondevice);
DIAG_ON_NARROWING
        NLA_PUT_U32(msg, NL80211_ATTR_IFTYPE, NL80211_IFTYPE_MONITOR);

        err = nl_send_auto_complete(state->nl_sock, msg);
        if (err < 0) {
                if (err == -NLE_FAILURE) {
                        /*
                         * Device not available; our caller should just
                         * keep trying.  (libnl 2.x maps ENFILE to
                         * NLE_FAILURE; it can also map other errors
                         * to that, but there's not much we can do
                         * about that.)
                         */
                        nlmsg_free(msg);
                        return 0;
                } else {
                        /*
                         * Real failure, not just "that device is not
                         * available.
                         */
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                            "%s: nl_send_auto_complete failed adding %s interface: %s",
                            device, mondevice, nl_geterror(-err));
                        nlmsg_free(msg);
                        return PCAP_ERROR;
                }
        }
        err = nl_wait_for_ack(state->nl_sock);
        if (err < 0) {
                if (err == -NLE_FAILURE) {
                        /*
                         * Device not available; our caller should just
                         * keep trying.  (libnl 2.x maps ENFILE to
                         * NLE_FAILURE; it can also map other errors
                         * to that, but there's not much we can do
                         * about that.)
                         */
                        nlmsg_free(msg);
                        return 0;
                } else {
                        /*
                         * Real failure, not just "that device is not
                         * available.
                         */
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                            "%s: nl_wait_for_ack failed adding %s interface: %s",
                            device, mondevice, nl_geterror(-err));
                        nlmsg_free(msg);
                        return PCAP_ERROR;
                }
        }

        /*
         * Success.
         */
        nlmsg_free(msg);

        /*
         * Try to remember the monitor device.
         */
        handlep->mondevice = strdup(mondevice);
        if (handlep->mondevice == NULL) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "strdup");
                /*
                 * Get rid of the monitor device.
                 */
                del_mon_if(handle, sock_fd, state, device, mondevice);
                return PCAP_ERROR;
        }
        return 1;

nla_put_failure:
        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
            "%s: nl_put failed adding %s interface",
            device, mondevice);
        nlmsg_free(msg);
        return PCAP_ERROR;
}

static int
del_mon_if(pcap_t *handle, int sock_fd, struct nl80211_state *state,
    const char *device, const char *mondevice)
{
        int ifindex;
        struct nl_msg *msg;
        int err;

        ifindex = iface_get_id(sock_fd, mondevice, handle->errbuf);
        if (ifindex == -1)
                return PCAP_ERROR;

        msg = nlmsg_alloc();
        if (!msg) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: failed to allocate netlink msg", device);
                return PCAP_ERROR;
        }

        genlmsg_put(msg, 0, 0, genl_family_get_id(state->nl80211), 0,
                    0, NL80211_CMD_DEL_INTERFACE, 0);
        NLA_PUT_U32(msg, NL80211_ATTR_IFINDEX, ifindex);

        err = nl_send_auto_complete(state->nl_sock, msg);
        if (err < 0) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: nl_send_auto_complete failed deleting %s interface: %s",
                    device, mondevice, nl_geterror(-err));
                nlmsg_free(msg);
                return PCAP_ERROR;
        }
        err = nl_wait_for_ack(state->nl_sock);
        if (err < 0) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: nl_wait_for_ack failed adding %s interface: %s",
                    device, mondevice, nl_geterror(-err));
                nlmsg_free(msg);
                return PCAP_ERROR;
        }

        /*
         * Success.
         */
        nlmsg_free(msg);
        return 1;

nla_put_failure:
        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
            "%s: nl_put failed deleting %s interface",
            device, mondevice);
        nlmsg_free(msg);
        return PCAP_ERROR;
}
#endif /* HAVE_LIBNL */

static int pcap_protocol(pcap_t *handle)
{
        int protocol;

        protocol = handle->opt.protocol;
        if (protocol == 0)
                protocol = ETH_P_ALL;

        return htons(protocol);
}

static int
pcap_can_set_rfmon_linux(pcap_t *handle)
{
#ifdef HAVE_LIBNL
        char phydev_path[PATH_MAX+1];
        int ret;
#endif

        if (strcmp(handle->opt.device, "any") == 0) {
                /*
                 * Monitor mode makes no sense on the "any" device.
                 */
                return 0;
        }

#ifdef HAVE_LIBNL
        /*
         * Bleah.  There doesn't seem to be a way to ask a mac80211
         * device, through libnl, whether it supports monitor mode;
         * we'll just check whether the device appears to be a
         * mac80211 device and, if so, assume the device supports
         * monitor mode.
         */
        ret = get_mac80211_phydev(handle, handle->opt.device, phydev_path,
            PATH_MAX);
        if (ret < 0)
                return ret;     /* error */
        if (ret == 1)
                return 1;       /* mac80211 device */
#endif

        return 0;
}

/*
 * Grabs the number of missed packets by the interface from
 * /sys/class/net/{if_name}/statistics/rx_{missed,fifo}_errors.
 *
 * Compared to /proc/net/dev this avoids counting software drops,
 * but may be unimplemented and just return 0.
 * The author has found no straigthforward way to check for support.
 */
static long long int
linux_get_stat(const char * if_name, const char * stat) {
        ssize_t bytes_read;
        int fd;
        char buffer[PATH_MAX];

        snprintf(buffer, sizeof(buffer), "/sys/class/net/%s/statistics/%s", if_name, stat);
        fd = open(buffer, O_RDONLY);
        if (fd == -1)
                return 0;

        bytes_read = read(fd, buffer, sizeof(buffer) - 1);
        close(fd);
        if (bytes_read == -1)
                return 0;
        buffer[bytes_read] = '\0';

        return strtoll(buffer, NULL, 10);
}

static long long int
linux_if_drops(const char * if_name)
{
        long long int missed = linux_get_stat(if_name, "rx_missed_errors");
        long long int fifo = linux_get_stat(if_name, "rx_fifo_errors");
        return missed + fifo;
}


/*
 * Monitor mode is kind of interesting because we have to reset the
 * interface before exiting. The problem can't really be solved without
 * some daemon taking care of managing usage counts.  If we put the
 * interface into monitor mode, we set a flag indicating that we must
 * take it out of that mode when the interface is closed, and, when
 * closing the interface, if that flag is set we take it out of monitor
 * mode.
 */

static void     pcap_cleanup_linux( pcap_t *handle )
{
        struct pcap_linux *handlep = handle->priv;
#ifdef HAVE_LIBNL
        struct nl80211_state nlstate;
        int ret;
#endif /* HAVE_LIBNL */

        if (handlep->must_do_on_close != 0) {
                /*
                 * There's something we have to do when closing this
                 * pcap_t.
                 */
#ifdef HAVE_LIBNL
                if (handlep->must_do_on_close & MUST_DELETE_MONIF) {
                        ret = nl80211_init(handle, &nlstate, handlep->device);
                        if (ret >= 0) {
                                ret = del_mon_if(handle, handle->fd, &nlstate,
                                    handlep->device, handlep->mondevice);
                                nl80211_cleanup(&nlstate);
                        }
                        if (ret < 0) {
                                fprintf(stderr,
                                    "Can't delete monitor interface %s (%s).\n"
                                    "Please delete manually.\n",
                                    handlep->mondevice, handle->errbuf);
                        }
                }
#endif /* HAVE_LIBNL */

                /*
                 * Take this pcap out of the list of pcaps for which we
                 * have to take the interface out of some mode.
                 */
                pcap_remove_from_pcaps_to_close(handle);
        }

        if (handle->fd != -1) {
                /*
                 * Destroy the ring buffer (assuming we've set it up),
                 * and unmap it if it's mapped.
                 */
                destroy_ring(handle);
        }

        if (handlep->oneshot_buffer != NULL) {
                free(handlep->oneshot_buffer);
                handlep->oneshot_buffer = NULL;
        }

        if (handlep->mondevice != NULL) {
                free(handlep->mondevice);
                handlep->mondevice = NULL;
        }
        if (handlep->device != NULL) {
                free(handlep->device);
                handlep->device = NULL;
        }

        close(handlep->poll_breakloop_fd);
        pcap_cleanup_live_common(handle);
}

#ifdef HAVE_TPACKET3
/*
 * Some versions of TPACKET_V3 have annoying bugs/misfeatures
 * around which we have to work.  Determine if we have those
 * problems or not.
 * 3.19 is the first release with a fixed version of
 * TPACKET_V3.  We treat anything before that as
 * not having a fixed version; that may really mean
 * it has *no* version.
 */
static int has_broken_tpacket_v3(void)
{
        struct utsname utsname;
        const char *release;
        long major, minor;
        int matches, verlen;

        /* No version information, assume broken. */
        if (uname(&utsname) == -1)
                return 1;
        release = utsname.release;

        /* A malformed version, ditto. */
        matches = sscanf(release, "%ld.%ld%n", &major, &minor, &verlen);
        if (matches != 2)
                return 1;
        if (release[verlen] != '.' && release[verlen] != '\0')
                return 1;

        /* OK, a fixed version. */
        if (major > 3 || (major == 3 && minor >= 19))
                return 0;

        /* Too old :( */
        return 1;
}
#endif

/*
 * Set the timeout to be used in poll() with memory-mapped packet capture.
 */
static void
set_poll_timeout(struct pcap_linux *handlep)
{
#ifdef HAVE_TPACKET3
        int broken_tpacket_v3 = has_broken_tpacket_v3();
#endif
        if (handlep->timeout == 0) {
#ifdef HAVE_TPACKET3
                /*
                 * XXX - due to a set of (mis)features in the TPACKET_V3
                 * kernel code prior to the 3.19 kernel, blocking forever
                 * with a TPACKET_V3 socket can, if few packets are
                 * arriving and passing the socket filter, cause most
                 * packets to be dropped.  See libpcap issue #335 for the
                 * full painful story.
                 *
                 * The workaround is to have poll() time out very quickly,
                 * so we grab the frames handed to us, and return them to
                 * the kernel, ASAP.
                 */
                if (handlep->tp_version == TPACKET_V3 && broken_tpacket_v3)
                        handlep->poll_timeout = 1;      /* don't block for very long */
                else
#endif
                        handlep->poll_timeout = -1;     /* block forever */
        } else if (handlep->timeout > 0) {
#ifdef HAVE_TPACKET3
                /*
                 * For TPACKET_V3, the timeout is handled by the kernel,
                 * so block forever; that way, we don't get extra timeouts.
                 * Don't do that if we have a broken TPACKET_V3, though.
                 */
                if (handlep->tp_version == TPACKET_V3 && !broken_tpacket_v3)
                        handlep->poll_timeout = -1;     /* block forever, let TPACKET_V3 wake us up */
                else
#endif
                        handlep->poll_timeout = handlep->timeout;       /* block for that amount of time */
        } else {
                /*
                 * Non-blocking mode; we call poll() to pick up error
                 * indications, but we don't want it to wait for
                 * anything.
                 */
                handlep->poll_timeout = 0;
        }
}

static void pcap_breakloop_linux(pcap_t *handle)
{
        pcap_breakloop_common(handle);
        struct pcap_linux *handlep = handle->priv;

        uint64_t value = 1;
        /* XXX - what if this fails? */
        (void)write(handlep->poll_breakloop_fd, &value, sizeof(value));
}

/*
 * Set the offset at which to insert VLAN tags.
 * That should be the offset of the type field.
 */
static void
set_vlan_offset(pcap_t *handle)
{
        struct pcap_linux *handlep = handle->priv;

        switch (handle->linktype) {

        case DLT_EN10MB:
                /*
                 * The type field is after the destination and source
                 * MAC address.
                 */
                handlep->vlan_offset = 2 * ETH_ALEN;
                break;

        case DLT_LINUX_SLL:
                /*
                 * The type field is in the last 2 bytes of the
                 * DLT_LINUX_SLL header.
                 */
                handlep->vlan_offset = SLL_HDR_LEN - 2;
                break;

        default:
                handlep->vlan_offset = -1; /* unknown */
                break;
        }
}

/*
 *  Get a handle for a live capture from the given device. You can
 *  pass NULL as device to get all packages (without link level
 *  information of course). If you pass 1 as promisc the interface
 *  will be set to promiscuous mode (XXX: I think this usage should
 *  be deprecated and functions be added to select that later allow
 *  modification of that values -- Torsten).
 */
static int
pcap_activate_linux(pcap_t *handle)
{
        struct pcap_linux *handlep = handle->priv;
        const char      *device;
        int             is_any_device;
        struct ifreq    ifr;
        int             status = 0;
        int             status2 = 0;
        int             ret;

        device = handle->opt.device;

        /*
         * Make sure the name we were handed will fit into the ioctls we
         * might perform on the device; if not, return a "No such device"
         * indication, as the Linux kernel shouldn't support creating
         * a device whose name won't fit into those ioctls.
         *
         * "Will fit" means "will fit, complete with a null terminator",
         * so if the length, which does *not* include the null terminator,
         * is greater than *or equal to* the size of the field into which
         * we'll be copying it, that won't fit.
         */
        if (strlen(device) >= sizeof(ifr.ifr_name)) {
                /*
                 * There's nothing more to say, so clear the error
                 * message.
                 */
                handle->errbuf[0] = '\0';
                status = PCAP_ERROR_NO_SUCH_DEVICE;
                goto fail;
        }

        /*
         * Turn a negative snapshot value (invalid), a snapshot value of
         * 0 (unspecified), or a value bigger than the normal maximum
         * value, into the maximum allowed value.
         *
         * If some application really *needs* a bigger snapshot
         * length, we should just increase MAXIMUM_SNAPLEN.
         */
        if (handle->snapshot <= 0 || handle->snapshot > MAXIMUM_SNAPLEN)
                handle->snapshot = MAXIMUM_SNAPLEN;

        handlep->device = strdup(device);
        if (handlep->device == NULL) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "strdup");
                status = PCAP_ERROR;
                goto fail;
        }

        /*
         * The "any" device is a special device which causes us not
         * to bind to a particular device and thus to look at all
         * devices.
         */
        is_any_device = (strcmp(device, "any") == 0);
        if (is_any_device) {
                if (handle->opt.promisc) {
                        handle->opt.promisc = 0;
                        /* Just a warning. */
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                            "Promiscuous mode not supported on the \"any\" device");
                        status = PCAP_WARNING_PROMISC_NOTSUP;
                }
        }

        /* copy timeout value */
        handlep->timeout = handle->opt.timeout;

        /*
         * If we're in promiscuous mode, then we probably want
         * to see when the interface drops packets too, so get an
         * initial count from
         * /sys/class/net/{if_name}/statistics/rx_{missed,fifo}_errors
         */
        if (handle->opt.promisc)
                handlep->sysfs_dropped = linux_if_drops(handlep->device);

        /*
         * If the "any" device is specified, try to open a SOCK_DGRAM.
         * Otherwise, open a SOCK_RAW.
         */
        ret = setup_socket(handle, is_any_device);
        if (ret < 0) {
                /*
                 * Fatal error; the return value is the error code,
                 * and handle->errbuf has been set to an appropriate
                 * error message.
                 */
                status = ret;
                goto fail;
        }
        /*
         * Success.
         * Try to set up memory-mapped access.
         */
        ret = setup_mmapped(handle, &status);
        if (ret == -1) {
                /*
                 * We failed to set up to use it, or the
                 * kernel supports it, but we failed to
                 * enable it.  status has been set to the
                 * error status to return and, if it's
                 * PCAP_ERROR, handle->errbuf contains
                 * the error message.
                 */
                goto fail;
        }

        /*
         * We succeeded.  status has been set to the status to return,
         * which might be 0, or might be a PCAP_WARNING_ value.
         */
        /*
         * Now that we have activated the mmap ring, we can
         * set the correct protocol.
         */
        if ((status2 = iface_bind(handle->fd, handlep->ifindex,
            handle->errbuf, pcap_protocol(handle))) != 0) {
                status = status2;
                goto fail;
        }

        handle->inject_op = pcap_inject_linux;
        handle->setfilter_op = pcap_setfilter_linux;
        handle->setdirection_op = pcap_setdirection_linux;
        handle->set_datalink_op = pcap_set_datalink_linux;
        handle->setnonblock_op = pcap_setnonblock_linux;
        handle->getnonblock_op = pcap_getnonblock_linux;
        handle->cleanup_op = pcap_cleanup_linux;
        handle->stats_op = pcap_stats_linux;
        handle->breakloop_op = pcap_breakloop_linux;

        switch (handlep->tp_version) {

        case TPACKET_V2:
                handle->read_op = pcap_read_linux_mmap_v2;
                break;
#ifdef HAVE_TPACKET3
        case TPACKET_V3:
                handle->read_op = pcap_read_linux_mmap_v3;
                break;
#endif
        }
        handle->oneshot_callback = pcap_oneshot_linux;
        handle->selectable_fd = handle->fd;

        return status;

fail:
        pcap_cleanup_linux(handle);
        return status;
}

static int
pcap_set_datalink_linux(pcap_t *handle, int dlt)
{
        handle->linktype = dlt;

        /*
         * Update the offset at which to insert VLAN tags for the
         * new link-layer type.
         */
        set_vlan_offset(handle);

        return 0;
}

/*
 * linux_check_direction()
 *
 * Do checks based on packet direction.
 */
static inline int
linux_check_direction(const pcap_t *handle, const struct sockaddr_ll *sll)
{
        struct pcap_linux       *handlep = handle->priv;

        if (sll->sll_pkttype == PACKET_OUTGOING) {
                /*
                 * Outgoing packet.
                 * If this is from the loopback device, reject it;
                 * we'll see the packet as an incoming packet as well,
                 * and we don't want to see it twice.
                 */
                if (sll->sll_ifindex == handlep->lo_ifindex)
                        return 0;

                /*
                 * If this is an outgoing CAN or CAN FD frame, and
                 * the user doesn't only want outgoing packets,
                 * reject it; CAN devices and drivers, and the CAN
                 * stack, always arrange to loop back transmitted
                 * packets, so they also appear as incoming packets.
                 * We don't want duplicate packets, and we can't
                 * easily distinguish packets looped back by the CAN
                 * layer than those received by the CAN layer, so we
                 * eliminate this packet instead.
                 *
                 * We check whether this is a CAN or CAN FD frame
                 * by checking whether the device's hardware type
                 * is ARPHRD_CAN.
                 */
                if (sll->sll_hatype == ARPHRD_CAN &&
                     handle->direction != PCAP_D_OUT)
                        return 0;

                /*
                 * If the user only wants incoming packets, reject it.
                 */
                if (handle->direction == PCAP_D_IN)
                        return 0;
        } else {
                /*
                 * Incoming packet.
                 * If the user only wants outgoing packets, reject it.
                 */
                if (handle->direction == PCAP_D_OUT)
                        return 0;
        }
        return 1;
}

/*
 * Check whether the device to which the pcap_t is bound still exists.
 * We do so by asking what address the socket is bound to, and checking
 * whether the ifindex in the address is -1, meaning "that device is gone",
 * or some other value, meaning "that device still exists".
 */
static int
device_still_exists(pcap_t *handle)
{
        struct pcap_linux *handlep = handle->priv;
        struct sockaddr_ll addr;
        socklen_t addr_len;

        /*
         * If handlep->ifindex is -1, the socket isn't bound, meaning
         * we're capturing on the "any" device; that device never
         * disappears.  (It should also never be configured down, so
         * we shouldn't even get here, but let's make sure.)
         */
        if (handlep->ifindex == -1)
                return (1);     /* it's still here */

        /*
         * OK, now try to get the address for the socket.
         */
        addr_len = sizeof (addr);
        if (getsockname(handle->fd, (struct sockaddr *) &addr, &addr_len) == -1) {
                /*
                 * Error - report an error and return -1.
                 */
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "getsockname failed");
                return (-1);
        }
        if (addr.sll_ifindex == -1) {
                /*
                 * This means the device went away.
                 */
                return (0);
        }

        /*
         * The device presumably just went down.
         */
        return (1);
}

static int
pcap_inject_linux(pcap_t *handle, const void *buf, int size)
{
        struct pcap_linux *handlep = handle->priv;
        int ret;

        if (handlep->ifindex == -1) {
                /*
                 * We don't support sending on the "any" device.
                 */
                pcap_strlcpy(handle->errbuf,
                    "Sending packets isn't supported on the \"any\" device",
                    PCAP_ERRBUF_SIZE);
                return (-1);
        }

        if (handlep->cooked) {
                /*
                 * We don't support sending on cooked-mode sockets.
                 *
                 * XXX - how do you send on a bound cooked-mode
                 * socket?
                 * Is a "sendto()" required there?
                 */
                pcap_strlcpy(handle->errbuf,
                    "Sending packets isn't supported in cooked mode",
                    PCAP_ERRBUF_SIZE);
                return (-1);
        }

        ret = (int)send(handle->fd, buf, size, 0);
        if (ret == -1) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "send");
                return (-1);
        }
        return (ret);
}

/*
 *  Get the statistics for the given packet capture handle.
 */
static int
pcap_stats_linux(pcap_t *handle, struct pcap_stat *stats)
{
        struct pcap_linux *handlep = handle->priv;
#ifdef HAVE_TPACKET3
        /*
         * For sockets using TPACKET_V2, the extra stuff at the end
         * of a struct tpacket_stats_v3 will not be filled in, and
         * we don't look at it so this is OK even for those sockets.
         * In addition, the PF_PACKET socket code in the kernel only
         * uses the length parameter to compute how much data to
         * copy out and to indicate how much data was copied out, so
         * it's OK to base it on the size of a struct tpacket_stats.
         *
         * XXX - it's probably OK, in fact, to just use a
         * struct tpacket_stats for V3 sockets, as we don't
         * care about the tp_freeze_q_cnt stat.
         */
        struct tpacket_stats_v3 kstats;
#else /* HAVE_TPACKET3 */
        struct tpacket_stats kstats;
#endif /* HAVE_TPACKET3 */
        socklen_t len = sizeof (struct tpacket_stats);

        long long if_dropped = 0;

        /*
         * To fill in ps_ifdrop, we parse
         * /sys/class/net/{if_name}/statistics/rx_{missed,fifo}_errors
         * for the numbers
         */
        if (handle->opt.promisc)
        {
                /*
                 * XXX - is there any reason to do this by remembering
                 * the last counts value, subtracting it from the
                 * current counts value, and adding that to stat.ps_ifdrop,
                 * maintaining stat.ps_ifdrop as a count, rather than just
                 * saving the *initial* counts value and setting
                 * stat.ps_ifdrop to the difference between the current
                 * value and the initial value?
                 *
                 * One reason might be to handle the count wrapping
                 * around, on platforms where the count is 32 bits
                 * and where you might get more than 2^32 dropped
                 * packets; is there any other reason?
                 *
                 * (We maintain the count as a long long int so that,
                 * if the kernel maintains the counts as 64-bit even
                 * on 32-bit platforms, we can handle the real count.
                 *
                 * Unfortunately, we can't report 64-bit counts; we
                 * need a better API for reporting statistics, such as
                 * one that reports them in a style similar to the
                 * pcapng Interface Statistics Block, so that 1) the
                 * counts are 64-bit, 2) it's easier to add new statistics
                 * without breaking the ABI, and 3) it's easier to
                 * indicate to a caller that wants one particular
                 * statistic that it's not available by just not supplying
                 * it.)
                 */
                if_dropped = handlep->sysfs_dropped;
                handlep->sysfs_dropped = linux_if_drops(handlep->device);
                handlep->stat.ps_ifdrop += (u_int)(handlep->sysfs_dropped - if_dropped);
        }

        /*
         * Try to get the packet counts from the kernel.
         */
        if (getsockopt(handle->fd, SOL_PACKET, PACKET_STATISTICS,
                        &kstats, &len) > -1) {
                /*
                 * "ps_recv" counts only packets that *passed* the
                 * filter, not packets that didn't pass the filter.
                 * This includes packets later dropped because we
                 * ran out of buffer space.
                 *
                 * "ps_drop" counts packets dropped because we ran
                 * out of buffer space.  It doesn't count packets
                 * dropped by the interface driver.  It counts only
                 * packets that passed the filter.
                 *
                 * See above for ps_ifdrop.
                 *
                 * Both statistics include packets not yet read from
                 * the kernel by libpcap, and thus not yet seen by
                 * the application.
                 *
                 * In "linux/net/packet/af_packet.c", at least in 2.6.27
                 * through 5.6 kernels, "tp_packets" is incremented for
                 * every packet that passes the packet filter *and* is
                 * successfully copied to the ring buffer; "tp_drops" is
                 * incremented for every packet dropped because there's
                 * not enough free space in the ring buffer.
                 *
                 * When the statistics are returned for a PACKET_STATISTICS
                 * "getsockopt()" call, "tp_drops" is added to "tp_packets",
                 * so that "tp_packets" counts all packets handed to
                 * the PF_PACKET socket, including packets dropped because
                 * there wasn't room on the socket buffer - but not
                 * including packets that didn't pass the filter.
                 *
                 * In the BSD BPF, the count of received packets is
                 * incremented for every packet handed to BPF, regardless
                 * of whether it passed the filter.
                 *
                 * We can't make "pcap_stats()" work the same on both
                 * platforms, but the best approximation is to return
                 * "tp_packets" as the count of packets and "tp_drops"
                 * as the count of drops.
                 *
                 * Keep a running total because each call to
                 *    getsockopt(handle->fd, SOL_PACKET, PACKET_STATISTICS, ....
                 * resets the counters to zero.
                 */
                handlep->stat.ps_recv += kstats.tp_packets;
                handlep->stat.ps_drop += kstats.tp_drops;
                *stats = handlep->stat;
                return 0;
        }

        pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE, errno,
            "failed to get statistics from socket");
        return -1;
}

/*
 * Description string for the "any" device.
 */
static const char any_descr[] = "Pseudo-device that captures on all interfaces";

/*
 * A PF_PACKET socket can be bound to any network interface.
 */
static int
can_be_bound(const char *name _U_)
{
        return (1);
}

/*
 * Get a socket to use with various interface ioctls.
 */
static int
get_if_ioctl_socket(void)
{
        int fd;

        /*
         * This is a bit ugly.
         *
         * There isn't a socket type that's guaranteed to work.
         *
         * AF_NETLINK will work *if* you have Netlink configured into the
         * kernel (can it be configured out if you have any networking
         * support at all?) *and* if you're running a sufficiently recent
         * kernel, but not all the kernels we support are sufficiently
         * recent - that feature was introduced in Linux 4.6.
         *
         * AF_UNIX will work *if* you have UNIX-domain sockets configured
         * into the kernel and *if* you're not on a system that doesn't
         * allow them - some SELinux systems don't allow you create them.
         * Most systems probably have them configured in, but not all systems
         * have them configured in and allow them to be created.
         *
         * AF_INET will work *if* you have IPv4 configured into the kernel,
         * but, apparently, some systems have network adapters but have
         * kernels without IPv4 support.
         *
         * AF_INET6 will work *if* you have IPv6 configured into the
         * kernel, but if you don't have AF_INET, you might not have
         * AF_INET6, either (that is, independently on its own grounds).
         *
         * AF_PACKET would work, except that some of these calls should
         * work even if you *don't* have capture permission (you should be
         * able to enumerate interfaces and get information about them
         * without capture permission; you shouldn't get a failure until
         * you try pcap_activate()).  (If you don't allow programs to
         * get as much information as possible about interfaces if you
         * don't have permission to capture, you run the risk of users
         * asking "why isn't it showing XXX" - or, worse, if you don't
         * show interfaces *at all* if you don't have permission to
         * capture on them, "why do no interfaces show up?" - when the
         * real problem is a permissions problem.  Error reports of that
         * type require a lot more back-and-forth to debug, as evidenced
         * by many Wireshark bugs/mailing list questions/Q&A questoins.)
         *
         * So:
         *
         * we first try an AF_NETLINK socket, where "try" includes
         * "try to do a device ioctl on it", as, in the future, once
         * pre-4.6 kernels are sufficiently rare, that will probably
         * be the mechanism most likely to work;
         *
         * if that fails, we try an AF_UNIX socket, as that's less
         * likely to be configured out on a networking-capable system
         * than is IP;
         *
         * if that fails, we try an AF_INET6 socket;
         *
         * if that fails, we try an AF_INET socket.
         */
        fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
        if (fd != -1) {
                /*
                 * OK, let's make sure we can do an SIOCGIFNAME
                 * ioctl.
                 */
                struct ifreq ifr;

                memset(&ifr, 0, sizeof(ifr));
                if (ioctl(fd, SIOCGIFNAME, &ifr) == 0 ||
                    errno != EOPNOTSUPP) {
                        /*
                         * It succeeded, or failed for some reason
                         * other than "netlink sockets don't support
                         * device ioctls".  Go with the AF_NETLINK
                         * socket.
                         */
                        return (fd);
                }

                /*
                 * OK, that didn't work, so it's as bad as "netlink
                 * sockets aren't available".  Close the socket and
                 * drive on.
                 */
                close(fd);
        }

        /*
         * Now try an AF_UNIX socket.
         */
        fd = socket(AF_UNIX, SOCK_RAW, 0);
        if (fd != -1) {
                /*
                 * OK, we got it!
                 */
                return (fd);
        }

        /*
         * Now try an AF_INET6 socket.
         */
        fd = socket(AF_INET6, SOCK_DGRAM, 0);
        if (fd != -1) {
                return (fd);
        }

        /*
         * Now try an AF_INET socket.
         *
         * XXX - if that fails, is there anything else we should try?
         * AF_CAN, for embedded systems in vehicles, in case they're
         * built without Internet protocol support?  Any other socket
         * types popular in non-Internet embedded systems?
         */
        return (socket(AF_INET, SOCK_DGRAM, 0));
}

/*
 * Get additional flags for a device, using SIOCGIFMEDIA.
 */
static int
get_if_flags(const char *name, bpf_u_int32 *flags, char *errbuf)
{
        int sock;
        FILE *fh;
        unsigned int arptype;
        struct ifreq ifr;
        struct ethtool_value info;

        if (*flags & PCAP_IF_LOOPBACK) {
                /*
                 * Loopback devices aren't wireless, and "connected"/
                 * "disconnected" doesn't apply to them.
                 */
                *flags |= PCAP_IF_CONNECTION_STATUS_NOT_APPLICABLE;
                return 0;
        }

        sock = get_if_ioctl_socket();
        if (sock == -1) {
                pcap_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE, errno,
                    "Can't create socket to get ethtool information for %s",
                    name);
                return -1;
        }

        /*
         * OK, what type of network is this?
         * In particular, is it wired or wireless?
         */
        if (is_wifi(name)) {
                /*
                 * Wi-Fi, hence wireless.
                 */
                *flags |= PCAP_IF_WIRELESS;
        } else {
                /*
                 * OK, what does /sys/class/net/{if_name}/type contain?
                 * (We don't use that for Wi-Fi, as it'll report
                 * "Ethernet", i.e. ARPHRD_ETHER, for non-monitor-
                 * mode devices.)
                 */
                char *pathstr;

                if (asprintf(&pathstr, "/sys/class/net/%s/type", name) == -1) {
                        snprintf(errbuf, PCAP_ERRBUF_SIZE,
                            "%s: Can't generate path name string for /sys/class/net device",
                            name);
                        close(sock);
                        return -1;
                }
                fh = fopen(pathstr, "r");
                if (fh != NULL) {
                        if (fscanf(fh, "%u", &arptype) == 1) {
                                /*
                                 * OK, we got an ARPHRD_ type; what is it?
                                 */
                                switch (arptype) {

                                case ARPHRD_LOOPBACK:
                                        /*
                                         * These are types to which
                                         * "connected" and "disconnected"
                                         * don't apply, so don't bother
                                         * asking about it.
                                         *
                                         * XXX - add other types?
                                         */
                                        close(sock);
                                        fclose(fh);
                                        free(pathstr);
                                        return 0;

                                case ARPHRD_IRDA:
                                case ARPHRD_IEEE80211:
                                case ARPHRD_IEEE80211_PRISM:
                                case ARPHRD_IEEE80211_RADIOTAP:
#ifdef ARPHRD_IEEE802154
                                case ARPHRD_IEEE802154:
#endif
#ifdef ARPHRD_IEEE802154_MONITOR
                                case ARPHRD_IEEE802154_MONITOR:
#endif
#ifdef ARPHRD_6LOWPAN
                                case ARPHRD_6LOWPAN:
#endif
                                        /*
                                         * Various wireless types.
                                         */
                                        *flags |= PCAP_IF_WIRELESS;
                                        break;
                                }
                        }
                        fclose(fh);
                }
                free(pathstr);
        }

#ifdef ETHTOOL_GLINK
        memset(&ifr, 0, sizeof(ifr));
        pcap_strlcpy(ifr.ifr_name, name, sizeof(ifr.ifr_name));
        info.cmd = ETHTOOL_GLINK;
        /*
         * XXX - while Valgrind handles SIOCETHTOOL and knows that
         * the ETHTOOL_GLINK command sets the .data member of the
         * structure, Memory Sanitizer doesn't yet do so:
         *
         *    https://bugs.llvm.org/show_bug.cgi?id=45814
         *
         * For now, we zero it out to squelch warnings; if the bug
         * in question is fixed, we can remove this.
         */
        info.data = 0;
        ifr.ifr_data = (caddr_t)&info;
        if (ioctl(sock, SIOCETHTOOL, &ifr) == -1) {
                int save_errno = errno;

                switch (save_errno) {

                case EOPNOTSUPP:
                case EINVAL:
                        /*
                         * OK, this OS version or driver doesn't support
                         * asking for this information.
                         * XXX - distinguish between "this doesn't
                         * support ethtool at all because it's not
                         * that type of device" vs. "this doesn't
                         * support ethtool even though it's that
                         * type of device", and return "unknown".
                         */
                        *flags |= PCAP_IF_CONNECTION_STATUS_NOT_APPLICABLE;
                        close(sock);
                        return 0;

                case ENODEV:
                        /*
                         * OK, no such device.
                         * The user will find that out when they try to
                         * activate the device; just say "OK" and
                         * don't set anything.
                         */
                        close(sock);
                        return 0;

                default:
                        /*
                         * Other error.
                         */
                        pcap_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
                            save_errno,
                            "%s: SIOCETHTOOL(ETHTOOL_GLINK) ioctl failed",
                            name);
                        close(sock);
                        return -1;
                }
        }

        /*
         * Is it connected?
         */
        if (info.data) {
                /*
                 * It's connected.
                 */
                *flags |= PCAP_IF_CONNECTION_STATUS_CONNECTED;
        } else {
                /*
                 * It's disconnected.
                 */
                *flags |= PCAP_IF_CONNECTION_STATUS_DISCONNECTED;
        }
#endif

        close(sock);
        return 0;
}

int
pcap_platform_finddevs(pcap_if_list_t *devlistp, char *errbuf)
{
        /*
         * Get the list of regular interfaces first.
         */
        if (pcap_findalldevs_interfaces(devlistp, errbuf, can_be_bound,
            get_if_flags) == -1)
                return (-1);    /* failure */

        /*
         * Add the "any" device.
         * As it refers to all network devices, not to any particular
         * network device, the notion of "connected" vs. "disconnected"
         * doesn't apply.
         */
        if (add_dev(devlistp, "any",
            PCAP_IF_UP|PCAP_IF_RUNNING|PCAP_IF_CONNECTION_STATUS_NOT_APPLICABLE,
            any_descr, errbuf) == NULL)
                return (-1);

        return (0);
}

/*
 * Set direction flag: Which packets do we accept on a forwarding
 * single device? IN, OUT or both?
 */
static int
pcap_setdirection_linux(pcap_t *handle, pcap_direction_t d)
{
        /*
         * It's guaranteed, at this point, that d is a valid
         * direction value.
         */
        handle->direction = d;
        return 0;
}

static int
is_wifi(const char *device)
{
        char *pathstr;
        struct stat statb;

        /*
         * See if there's a sysfs wireless directory for it.
         * If so, it's a wireless interface.
         */
        if (asprintf(&pathstr, "/sys/class/net/%s/wireless", device) == -1) {
                /*
                 * Just give up here.
                 */
                return 0;
        }
        if (stat(pathstr, &statb) == 0) {
                free(pathstr);
                return 1;
        }
        free(pathstr);

        return 0;
}

/*
 *  Linux uses the ARP hardware type to identify the type of an
 *  interface. pcap uses the DLT_xxx constants for this. This
 *  function takes a pointer to a "pcap_t", and an ARPHRD_xxx
 *  constant, as arguments, and sets "handle->linktype" to the
 *  appropriate DLT_XXX constant and sets "handle->offset" to
 *  the appropriate value (to make "handle->offset" plus link-layer
 *  header length be a multiple of 4, so that the link-layer payload
 *  will be aligned on a 4-byte boundary when capturing packets).
 *  (If the offset isn't set here, it'll be 0; add code as appropriate
 *  for cases where it shouldn't be 0.)
 *
 *  If "cooked_ok" is non-zero, we can use DLT_LINUX_SLL and capture
 *  in cooked mode; otherwise, we can't use cooked mode, so we have
 *  to pick some type that works in raw mode, or fail.
 *
 *  Sets the link type to -1 if unable to map the type.
 */
static void map_arphrd_to_dlt(pcap_t *handle, int arptype,
                              const char *device, int cooked_ok)
{
        static const char cdma_rmnet[] = "cdma_rmnet";

        switch (arptype) {

        case ARPHRD_ETHER:
                /*
                 * For various annoying reasons having to do with DHCP
                 * software, some versions of Android give the mobile-
                 * phone-network interface an ARPHRD_ value of
                 * ARPHRD_ETHER, even though the packets supplied by
                 * that interface have no link-layer header, and begin
                 * with an IP header, so that the ARPHRD_ value should
                 * be ARPHRD_NONE.
                 *
                 * Detect those devices by checking the device name, and
                 * use DLT_RAW for them.
                 */
                if (strncmp(device, cdma_rmnet, sizeof cdma_rmnet - 1) == 0) {
                        handle->linktype = DLT_RAW;
                        return;
                }

                /*
                 * Is this a real Ethernet device?  If so, give it a
                 * link-layer-type list with DLT_EN10MB and DLT_DOCSIS, so
                 * that an application can let you choose it, in case you're
                 * capturing DOCSIS traffic that a Cisco Cable Modem
                 * Termination System is putting out onto an Ethernet (it
                 * doesn't put an Ethernet header onto the wire, it puts raw
                 * DOCSIS frames out on the wire inside the low-level
                 * Ethernet framing).
                 *
                 * XXX - are there any other sorts of "fake Ethernet" that
                 * have ARPHRD_ETHER but that shouldn't offer DLT_DOCSIS as
                 * a Cisco CMTS won't put traffic onto it or get traffic
                 * bridged onto it?  ISDN is handled in "setup_socket()",
                 * as we fall back on cooked mode there, and we use
                 * is_wifi() to check for 802.11 devices; are there any
                 * others?
                 */
                if (!is_wifi(device)) {
                        int ret;

                        /*
                         * This is not a Wi-Fi device but it could be
                         * a DSA master/management network device.
                         */
                        ret = iface_dsa_get_proto_info(device, handle);
                        if (ret < 0)
                                return;

                        if (ret == 1) {
                                /*
                                 * This is a DSA master/management network
                                 * device linktype is already set by
                                 * iface_dsa_get_proto_info() set an
                                 * appropriate offset here.
                                 */
                                handle->offset = 2;
                                break;
                        }

                        /*
                         * It's not a Wi-Fi device; offer DOCSIS.
                         */
                        handle->dlt_list = (u_int *) malloc(sizeof(u_int) * 2);
                        /*
                         * If that fails, just leave the list empty.
                         */
                        if (handle->dlt_list != NULL) {
                                handle->dlt_list[0] = DLT_EN10MB;
                                handle->dlt_list[1] = DLT_DOCSIS;
                                handle->dlt_count = 2;
                        }
                }
                /* FALLTHROUGH */

        case ARPHRD_METRICOM:
        case ARPHRD_LOOPBACK:
                handle->linktype = DLT_EN10MB;
                handle->offset = 2;
                break;

        case ARPHRD_EETHER:
                handle->linktype = DLT_EN3MB;
                break;

        case ARPHRD_AX25:
                handle->linktype = DLT_AX25_KISS;
                break;

        case ARPHRD_PRONET:
                handle->linktype = DLT_PRONET;
                break;

        case ARPHRD_CHAOS:
                handle->linktype = DLT_CHAOS;
                break;
#ifndef ARPHRD_CAN
#define ARPHRD_CAN 280
#endif
        case ARPHRD_CAN:
                handle->linktype = DLT_CAN_SOCKETCAN;
                break;

#ifndef ARPHRD_IEEE802_TR
#define ARPHRD_IEEE802_TR 800   /* From Linux 2.4 */
#endif
        case ARPHRD_IEEE802_TR:
        case ARPHRD_IEEE802:
                handle->linktype = DLT_IEEE802;
                handle->offset = 2;
                break;

        case ARPHRD_ARCNET:
                handle->linktype = DLT_ARCNET_LINUX;
                break;

#ifndef ARPHRD_FDDI     /* From Linux 2.2.13 */
#define ARPHRD_FDDI     774
#endif
        case ARPHRD_FDDI:
                handle->linktype = DLT_FDDI;
                handle->offset = 3;
                break;

#ifndef ARPHRD_ATM  /* FIXME: How to #include this? */
#define ARPHRD_ATM 19
#endif
        case ARPHRD_ATM:
                /*
                 * The Classical IP implementation in ATM for Linux
                 * supports both what RFC 1483 calls "LLC Encapsulation",
                 * in which each packet has an LLC header, possibly
                 * with a SNAP header as well, prepended to it, and
                 * what RFC 1483 calls "VC Based Multiplexing", in which
                 * different virtual circuits carry different network
                 * layer protocols, and no header is prepended to packets.
                 *
                 * They both have an ARPHRD_ type of ARPHRD_ATM, so
                 * you can't use the ARPHRD_ type to find out whether
                 * captured packets will have an LLC header, and,
                 * while there's a socket ioctl to *set* the encapsulation
                 * type, there's no ioctl to *get* the encapsulation type.
                 *
                 * This means that
                 *
                 *      programs that dissect Linux Classical IP frames
                 *      would have to check for an LLC header and,
                 *      depending on whether they see one or not, dissect
                 *      the frame as LLC-encapsulated or as raw IP (I
                 *      don't know whether there's any traffic other than
                 *      IP that would show up on the socket, or whether
                 *      there's any support for IPv6 in the Linux
                 *      Classical IP code);
                 *
                 *      filter expressions would have to compile into
                 *      code that checks for an LLC header and does
                 *      the right thing.
                 *
                 * Both of those are a nuisance - and, at least on systems
                 * that support PF_PACKET sockets, we don't have to put
                 * up with those nuisances; instead, we can just capture
                 * in cooked mode.  That's what we'll do, if we can.
                 * Otherwise, we'll just fail.
                 */
                if (cooked_ok)
                        handle->linktype = DLT_LINUX_SLL;
                else
                        handle->linktype = -1;
                break;

#ifndef ARPHRD_IEEE80211  /* From Linux 2.4.6 */
#define ARPHRD_IEEE80211 801
#endif
        case ARPHRD_IEEE80211:
                handle->linktype = DLT_IEEE802_11;
                break;

#ifndef ARPHRD_IEEE80211_PRISM  /* From Linux 2.4.18 */
#define ARPHRD_IEEE80211_PRISM 802
#endif
        case ARPHRD_IEEE80211_PRISM:
                handle->linktype = DLT_PRISM_HEADER;
                break;

#ifndef ARPHRD_IEEE80211_RADIOTAP /* new */
#define ARPHRD_IEEE80211_RADIOTAP 803
#endif
        case ARPHRD_IEEE80211_RADIOTAP:
                handle->linktype = DLT_IEEE802_11_RADIO;
                break;

        case ARPHRD_PPP:
                /*
                 * Some PPP code in the kernel supplies no link-layer
                 * header whatsoever to PF_PACKET sockets; other PPP
                 * code supplies PPP link-layer headers ("syncppp.c");
                 * some PPP code might supply random link-layer
                 * headers (PPP over ISDN - there's code in Ethereal,
                 * for example, to cope with PPP-over-ISDN captures
                 * with which the Ethereal developers have had to cope,
                 * heuristically trying to determine which of the
                 * oddball link-layer headers particular packets have).
                 *
                 * As such, we just punt, and run all PPP interfaces
                 * in cooked mode, if we can; otherwise, we just treat
                 * it as DLT_RAW, for now - if somebody needs to capture,
                 * on a 2.0[.x] kernel, on PPP devices that supply a
                 * link-layer header, they'll have to add code here to
                 * map to the appropriate DLT_ type (possibly adding a
                 * new DLT_ type, if necessary).
                 */
                if (cooked_ok)
                        handle->linktype = DLT_LINUX_SLL;
                else {
                        /*
                         * XXX - handle ISDN types here?  We can't fall
                         * back on cooked sockets, so we'd have to
                         * figure out from the device name what type of
                         * link-layer encapsulation it's using, and map
                         * that to an appropriate DLT_ value, meaning
                         * we'd map "isdnN" devices to DLT_RAW (they
                         * supply raw IP packets with no link-layer
                         * header) and "isdY" devices to a new DLT_I4L_IP
                         * type that has only an Ethernet packet type as
                         * a link-layer header.
                         *
                         * But sometimes we seem to get random crap
                         * in the link-layer header when capturing on
                         * ISDN devices....
                         */
                        handle->linktype = DLT_RAW;
                }
                break;

#ifndef ARPHRD_CISCO
#define ARPHRD_CISCO 513 /* previously ARPHRD_HDLC */
#endif
        case ARPHRD_CISCO:
                handle->linktype = DLT_C_HDLC;
                break;

        /* Not sure if this is correct for all tunnels, but it
         * works for CIPE */
        case ARPHRD_TUNNEL:
#ifndef ARPHRD_SIT
#define ARPHRD_SIT 776  /* From Linux 2.2.13 */
#endif
        case ARPHRD_SIT:
        case ARPHRD_CSLIP:
        case ARPHRD_SLIP6:
        case ARPHRD_CSLIP6:
        case ARPHRD_ADAPT:
        case ARPHRD_SLIP:
#ifndef ARPHRD_RAWHDLC
#define ARPHRD_RAWHDLC 518
#endif
        case ARPHRD_RAWHDLC:
#ifndef ARPHRD_DLCI
#define ARPHRD_DLCI 15
#endif
        case ARPHRD_DLCI:
                /*
                 * XXX - should some of those be mapped to DLT_LINUX_SLL
                 * instead?  Should we just map all of them to DLT_LINUX_SLL?
                 */
                handle->linktype = DLT_RAW;
                break;

#ifndef ARPHRD_FRAD
#define ARPHRD_FRAD 770
#endif
        case ARPHRD_FRAD:
                handle->linktype = DLT_FRELAY;
                break;

        case ARPHRD_LOCALTLK:
                handle->linktype = DLT_LTALK;
                break;

        case 18:
                /*
                 * RFC 4338 defines an encapsulation for IP and ARP
                 * packets that's compatible with the RFC 2625
                 * encapsulation, but that uses a different ARP
                 * hardware type and hardware addresses.  That
                 * ARP hardware type is 18; Linux doesn't define
                 * any ARPHRD_ value as 18, but if it ever officially
                 * supports RFC 4338-style IP-over-FC, it should define
                 * one.
                 *
                 * For now, we map it to DLT_IP_OVER_FC, in the hopes
                 * that this will encourage its use in the future,
                 * should Linux ever officially support RFC 4338-style
                 * IP-over-FC.
                 */
                handle->linktype = DLT_IP_OVER_FC;
                break;

#ifndef ARPHRD_FCPP
#define ARPHRD_FCPP     784
#endif
        case ARPHRD_FCPP:
#ifndef ARPHRD_FCAL
#define ARPHRD_FCAL     785
#endif
        case ARPHRD_FCAL:
#ifndef ARPHRD_FCPL
#define ARPHRD_FCPL     786
#endif
        case ARPHRD_FCPL:
#ifndef ARPHRD_FCFABRIC
#define ARPHRD_FCFABRIC 787
#endif
        case ARPHRD_FCFABRIC:
                /*
                 * Back in 2002, Donald Lee at Cray wanted a DLT_ for
                 * IP-over-FC:
                 *
                 *      https://www.mail-archive.com/tcpdump-workers@sandelman.ottawa.on.ca/msg01043.html
                 *
                 * and one was assigned.
                 *
                 * In a later private discussion (spun off from a message
                 * on the ethereal-users list) on how to get that DLT_
                 * value in libpcap on Linux, I ended up deciding that
                 * the best thing to do would be to have him tweak the
                 * driver to set the ARPHRD_ value to some ARPHRD_FCxx
                 * type, and map all those types to DLT_IP_OVER_FC:
                 *
                 *      I've checked into the libpcap and tcpdump CVS tree
                 *      support for DLT_IP_OVER_FC.  In order to use that,
                 *      you'd have to modify your modified driver to return
                 *      one of the ARPHRD_FCxxx types, in "fcLINUXfcp.c" -
                 *      change it to set "dev->type" to ARPHRD_FCFABRIC, for
                 *      example (the exact value doesn't matter, it can be
                 *      any of ARPHRD_FCPP, ARPHRD_FCAL, ARPHRD_FCPL, or
                 *      ARPHRD_FCFABRIC).
                 *
                 * 11 years later, Christian Svensson wanted to map
                 * various ARPHRD_ values to DLT_FC_2 and
                 * DLT_FC_2_WITH_FRAME_DELIMS for raw Fibre Channel
                 * frames:
                 *
                 *      https://github.com/mcr/libpcap/pull/29
                 *
                 * There doesn't seem to be any network drivers that uses
                 * any of the ARPHRD_FC* values for IP-over-FC, and
                 * it's not exactly clear what the "Dummy types for non
                 * ARP hardware" are supposed to mean (link-layer
                 * header type?  Physical network type?), so it's
                 * not exactly clear why the ARPHRD_FC* types exist
                 * in the first place.
                 *
                 * For now, we map them to DLT_FC_2, and provide an
                 * option of DLT_FC_2_WITH_FRAME_DELIMS, as well as
                 * DLT_IP_OVER_FC just in case there's some old
                 * driver out there that uses one of those types for
                 * IP-over-FC on which somebody wants to capture
                 * packets.
                 */
                handle->dlt_list = (u_int *) malloc(sizeof(u_int) * 3);
                /*
                 * If that fails, just leave the list empty.
                 */
                if (handle->dlt_list != NULL) {
                        handle->dlt_list[0] = DLT_FC_2;
                        handle->dlt_list[1] = DLT_FC_2_WITH_FRAME_DELIMS;
                        handle->dlt_list[2] = DLT_IP_OVER_FC;
                        handle->dlt_count = 3;
                }
                handle->linktype = DLT_FC_2;
                break;

#ifndef ARPHRD_IRDA
#define ARPHRD_IRDA     783
#endif
        case ARPHRD_IRDA:
                /* Don't expect IP packet out of this interfaces... */
                handle->linktype = DLT_LINUX_IRDA;
                /* We need to save packet direction for IrDA decoding,
                 * so let's use "Linux-cooked" mode. Jean II
                 *
                 * XXX - this is handled in setup_socket(). */
                /* handlep->cooked = 1; */
                break;

        /* ARPHRD_LAPD is unofficial and randomly allocated, if reallocation
         * is needed, please report it to <daniele@orlandi.com> */
#ifndef ARPHRD_LAPD
#define ARPHRD_LAPD     8445
#endif
        case ARPHRD_LAPD:
                /* Don't expect IP packet out of this interfaces... */
                handle->linktype = DLT_LINUX_LAPD;
                break;

#ifndef ARPHRD_NONE
#define ARPHRD_NONE     0xFFFE
#endif
        case ARPHRD_NONE:
                /*
                 * No link-layer header; packets are just IP
                 * packets, so use DLT_RAW.
                 */
                handle->linktype = DLT_RAW;
                break;

#ifndef ARPHRD_IEEE802154
#define ARPHRD_IEEE802154      804
#endif
       case ARPHRD_IEEE802154:
               handle->linktype =  DLT_IEEE802_15_4_NOFCS;
               break;

#ifndef ARPHRD_NETLINK
#define ARPHRD_NETLINK  824
#endif
        case ARPHRD_NETLINK:
                handle->linktype = DLT_NETLINK;
                /*
                 * We need to use cooked mode, so that in sll_protocol we
                 * pick up the netlink protocol type such as NETLINK_ROUTE,
                 * NETLINK_GENERIC, NETLINK_FIB_LOOKUP, etc.
                 *
                 * XXX - this is handled in setup_socket().
                 */
                /* handlep->cooked = 1; */
                break;

#ifndef ARPHRD_VSOCKMON
#define ARPHRD_VSOCKMON 826
#endif
        case ARPHRD_VSOCKMON:
                handle->linktype = DLT_VSOCK;
                break;

        default:
                handle->linktype = -1;
                break;
        }
}

static void
set_dlt_list_cooked(pcap_t *handle)
{
        /*
         * Support both DLT_LINUX_SLL and DLT_LINUX_SLL2.
         */
        handle->dlt_list = (u_int *) malloc(sizeof(u_int) * 2);

        /*
         * If that failed, just leave the list empty.
         */
        if (handle->dlt_list != NULL) {
                handle->dlt_list[0] = DLT_LINUX_SLL;
                handle->dlt_list[1] = DLT_LINUX_SLL2;
                handle->dlt_count = 2;
        }
}

/*
 * Try to set up a PF_PACKET socket.
 * Returns 0 on success and a PCAP_ERROR_ value on failure.
 */
static int
setup_socket(pcap_t *handle, int is_any_device)
{
        struct pcap_linux *handlep = handle->priv;
        const char              *device = handle->opt.device;
        int                     status = 0;
        int                     sock_fd, arptype;
        int                     val;
        int                     err = 0;
        struct packet_mreq      mr;
#if defined(SO_BPF_EXTENSIONS) && defined(SKF_AD_VLAN_TAG_PRESENT)
        int                     bpf_extensions;
        socklen_t               len = sizeof(bpf_extensions);
#endif

        /*
         * Open a socket with protocol family packet. If cooked is true,
         * we open a SOCK_DGRAM socket for the cooked interface, otherwise
         * we open a SOCK_RAW socket for the raw interface.
         *
         * The protocol is set to 0.  This means we will receive no
         * packets until we "bind" the socket with a non-zero
         * protocol.  This allows us to setup the ring buffers without
         * dropping any packets.
         */
        sock_fd = is_any_device ?
                socket(PF_PACKET, SOCK_DGRAM, 0) :
                socket(PF_PACKET, SOCK_RAW, 0);

        if (sock_fd == -1) {
                if (errno == EPERM || errno == EACCES) {
                        /*
                         * You don't have permission to open the
                         * socket.
                         */
                        status = PCAP_ERROR_PERM_DENIED;
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                            "Attempt to create packet socket failed - CAP_NET_RAW may be required");
                } else {
                        /*
                         * Other error.
                         */
                        status = PCAP_ERROR;
                }
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "socket");
                return status;
        }

        /*
         * Get the interface index of the loopback device.
         * If the attempt fails, don't fail, just set the
         * "handlep->lo_ifindex" to -1.
         *
         * XXX - can there be more than one device that loops
         * packets back, i.e. devices other than "lo"?  If so,
         * we'd need to find them all, and have an array of
         * indices for them, and check all of them in
         * "pcap_read_packet()".
         */
        handlep->lo_ifindex = iface_get_id(sock_fd, "lo", handle->errbuf);

        /*
         * Default value for offset to align link-layer payload
         * on a 4-byte boundary.
         */
        handle->offset   = 0;

        /*
         * What kind of frames do we have to deal with? Fall back
         * to cooked mode if we have an unknown interface type
         * or a type we know doesn't work well in raw mode.
         */
        if (!is_any_device) {
                /* Assume for now we don't need cooked mode. */
                handlep->cooked = 0;

                if (handle->opt.rfmon) {
                        /*
                         * We were asked to turn on monitor mode.
                         * Do so before we get the link-layer type,
                         * because entering monitor mode could change
                         * the link-layer type.
                         */
                        err = enter_rfmon_mode(handle, sock_fd, device);
                        if (err < 0) {
                                /* Hard failure */
                                close(sock_fd);
                                return err;
                        }
                        if (err == 0) {
                                /*
                                 * Nothing worked for turning monitor mode
                                 * on.
                                 */
                                close(sock_fd);
                                return PCAP_ERROR_RFMON_NOTSUP;
                        }

                        /*
                         * Either monitor mode has been turned on for
                         * the device, or we've been given a different
                         * device to open for monitor mode.  If we've
                         * been given a different device, use it.
                         */
                        if (handlep->mondevice != NULL)
                                device = handlep->mondevice;
                }
                arptype = iface_get_arptype(sock_fd, device, handle->errbuf);
                if (arptype < 0) {
                        close(sock_fd);
                        return arptype;
                }
                map_arphrd_to_dlt(handle, arptype, device, 1);
                if (handle->linktype == -1 ||
                    handle->linktype == DLT_LINUX_SLL ||
                    handle->linktype == DLT_LINUX_IRDA ||
                    handle->linktype == DLT_LINUX_LAPD ||
                    handle->linktype == DLT_NETLINK ||
                    (handle->linktype == DLT_EN10MB &&
                     (strncmp("isdn", device, 4) == 0 ||
                      strncmp("isdY", device, 4) == 0))) {
                        /*
                         * Unknown interface type (-1), or a
                         * device we explicitly chose to run
                         * in cooked mode (e.g., PPP devices),
                         * or an ISDN device (whose link-layer
                         * type we can only determine by using
                         * APIs that may be different on different
                         * kernels) - reopen in cooked mode.
                         *
                         * If the type is unknown, return a warning;
                         * map_arphrd_to_dlt() has already set the
                         * warning message.
                         */
                        if (close(sock_fd) == -1) {
                                pcap_fmt_errmsg_for_errno(handle->errbuf,
                                    PCAP_ERRBUF_SIZE, errno, "close");
                                return PCAP_ERROR;
                        }
                        sock_fd = socket(PF_PACKET, SOCK_DGRAM, 0);
                        if (sock_fd < 0) {
                                /*
                                 * Fatal error.  We treat this as
                                 * a generic error; we already know
                                 * that we were able to open a
                                 * PF_PACKET/SOCK_RAW socket, so
                                 * any failure is a "this shouldn't
                                 * happen" case.
                                 */
                                pcap_fmt_errmsg_for_errno(handle->errbuf,
                                    PCAP_ERRBUF_SIZE, errno, "socket");
                                return PCAP_ERROR;
                        }
                        handlep->cooked = 1;

                        /*
                         * Get rid of any link-layer type list
                         * we allocated - this only supports cooked
                         * capture.
                         */
                        if (handle->dlt_list != NULL) {
                                free(handle->dlt_list);
                                handle->dlt_list = NULL;
                                handle->dlt_count = 0;
                                set_dlt_list_cooked(handle);
                        }

                        if (handle->linktype == -1) {
                                /*
                                 * Warn that we're falling back on
                                 * cooked mode; we may want to
                                 * update "map_arphrd_to_dlt()"
                                 * to handle the new type.
                                 */
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                        "arptype %d not "
                                        "supported by libpcap - "
                                        "falling back to cooked "
                                        "socket",
                                        arptype);
                        }

                        /*
                         * IrDA capture is not a real "cooked" capture,
                         * it's IrLAP frames, not IP packets.  The
                         * same applies to LAPD capture.
                         */
                        if (handle->linktype != DLT_LINUX_IRDA &&
                            handle->linktype != DLT_LINUX_LAPD &&
                            handle->linktype != DLT_NETLINK)
                                handle->linktype = DLT_LINUX_SLL;
                        if (handle->linktype == -1) {
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                    "unknown arptype %d, defaulting to cooked mode",
                                    arptype);
                                status = PCAP_WARNING;
                        }
                }

                handlep->ifindex = iface_get_id(sock_fd, device,
                    handle->errbuf);
                if (handlep->ifindex == -1) {
                        close(sock_fd);
                        return PCAP_ERROR;
                }

                if ((err = iface_bind(sock_fd, handlep->ifindex,
                    handle->errbuf, 0)) != 0) {
                        close(sock_fd);
                        return err;
                }
        } else {
                /*
                 * The "any" device.
                 */
                if (handle->opt.rfmon) {
                        /*
                         * It doesn't support monitor mode.
                         */
                        close(sock_fd);
                        return PCAP_ERROR_RFMON_NOTSUP;
                }

                /*
                 * It uses cooked mode.
                 */
                handlep->cooked = 1;
                handle->linktype = DLT_LINUX_SLL;
                handle->dlt_list = NULL;
                handle->dlt_count = 0;
                set_dlt_list_cooked(handle);

                /*
                 * We're not bound to a device.
                 * For now, we're using this as an indication
                 * that we can't transmit; stop doing that only
                 * if we figure out how to transmit in cooked
                 * mode.
                 */
                handlep->ifindex = -1;
        }

        /*
         * Select promiscuous mode on if "promisc" is set.
         *
         * Do not turn allmulti mode on if we don't select
         * promiscuous mode - on some devices (e.g., Orinoco
         * wireless interfaces), allmulti mode isn't supported
         * and the driver implements it by turning promiscuous
         * mode on, and that screws up the operation of the
         * card as a normal networking interface, and on no
         * other platform I know of does starting a non-
         * promiscuous capture affect which multicast packets
         * are received by the interface.
         */

        /*
         * Hmm, how can we set promiscuous mode on all interfaces?
         * I am not sure if that is possible at all.  For now, we
         * silently ignore attempts to turn promiscuous mode on
         * for the "any" device (so you don't have to explicitly
         * disable it in programs such as tcpdump).
         */

        if (!is_any_device && handle->opt.promisc) {
                memset(&mr, 0, sizeof(mr));
                mr.mr_ifindex = handlep->ifindex;
                mr.mr_type    = PACKET_MR_PROMISC;
                if (setsockopt(sock_fd, SOL_PACKET, PACKET_ADD_MEMBERSHIP,
                    &mr, sizeof(mr)) == -1) {
                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                            PCAP_ERRBUF_SIZE, errno, "setsockopt (PACKET_ADD_MEMBERSHIP)");
                        close(sock_fd);
                        return PCAP_ERROR;
                }
        }

        /*
         * Enable auxiliary data and reserve room for reconstructing
         * VLAN headers.
         *
         * XXX - is enabling auxiliary data necessary, now that we
         * only support memory-mapped capture?  The kernel's memory-mapped
         * capture code doesn't seem to check whether auxiliary data
         * is enabled, it seems to provide it whether it is or not.
         */
        val = 1;
        if (setsockopt(sock_fd, SOL_PACKET, PACKET_AUXDATA, &val,
                       sizeof(val)) == -1 && errno != ENOPROTOOPT) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "setsockopt (PACKET_AUXDATA)");
                close(sock_fd);
                return PCAP_ERROR;
        }
        handle->offset += VLAN_TAG_LEN;

        /*
         * If we're in cooked mode, make the snapshot length
         * large enough to hold a "cooked mode" header plus
         * 1 byte of packet data (so we don't pass a byte
         * count of 0 to "recvfrom()").
         * XXX - we don't know whether this will be DLT_LINUX_SLL
         * or DLT_LINUX_SLL2, so make sure it's big enough for
         * a DLT_LINUX_SLL2 "cooked mode" header; a snapshot length
         * that small is silly anyway.
         */
        if (handlep->cooked) {
                if (handle->snapshot < SLL2_HDR_LEN + 1)
                        handle->snapshot = SLL2_HDR_LEN + 1;
        }
        handle->bufsize = handle->snapshot;

        /*
         * Set the offset at which to insert VLAN tags.
         */
        set_vlan_offset(handle);

        if (handle->opt.tstamp_precision == PCAP_TSTAMP_PRECISION_NANO) {
                int nsec_tstamps = 1;

                if (setsockopt(sock_fd, SOL_SOCKET, SO_TIMESTAMPNS, &nsec_tstamps, sizeof(nsec_tstamps)) < 0) {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, "setsockopt: unable to set SO_TIMESTAMPNS");
                        close(sock_fd);
                        return PCAP_ERROR;
                }
        }

        /*
         * We've succeeded. Save the socket FD in the pcap structure.
         */
        handle->fd = sock_fd;

#if defined(SO_BPF_EXTENSIONS) && defined(SKF_AD_VLAN_TAG_PRESENT)
        /*
         * Can we generate special code for VLAN checks?
         * (XXX - what if we need the special code but it's not supported
         * by the OS?  Is that possible?)
         */
        if (getsockopt(sock_fd, SOL_SOCKET, SO_BPF_EXTENSIONS,
            &bpf_extensions, &len) == 0) {
                if (bpf_extensions >= SKF_AD_VLAN_TAG_PRESENT) {
                        /*
                         * Yes, we can.  Request that we do so.
                         */
                        handle->bpf_codegen_flags |= BPF_SPECIAL_VLAN_HANDLING;
                }
        }
#endif /* defined(SO_BPF_EXTENSIONS) && defined(SKF_AD_VLAN_TAG_PRESENT) */

        return status;
}

/*
 * Attempt to setup memory-mapped access.
 *
 * On success, returns 1, and sets *status to 0 if there are no warnings
 * or to a PCAP_WARNING_ code if there is a warning.
 *
 * On error, returns -1, and sets *status to the appropriate error code;
 * if that is PCAP_ERROR, sets handle->errbuf to the appropriate message.
 */
static int
setup_mmapped(pcap_t *handle, int *status)
{
        struct pcap_linux *handlep = handle->priv;
        int ret;

        /*
         * Attempt to allocate a buffer to hold the contents of one
         * packet, for use by the oneshot callback.
         */
        handlep->oneshot_buffer = malloc(handle->snapshot);
        if (handlep->oneshot_buffer == NULL) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "can't allocate oneshot buffer");
                *status = PCAP_ERROR;
                return -1;
        }

        if (handle->opt.buffer_size == 0) {
                /* by default request 2M for the ring buffer */
                handle->opt.buffer_size = 2*1024*1024;
        }
        ret = prepare_tpacket_socket(handle);
        if (ret == -1) {
                free(handlep->oneshot_buffer);
                handlep->oneshot_buffer = NULL;
                *status = PCAP_ERROR;
                return ret;
        }
        ret = create_ring(handle, status);
        if (ret == -1) {
                /*
                 * Error attempting to enable memory-mapped capture;
                 * fail.  create_ring() has set *status.
                 */
                free(handlep->oneshot_buffer);
                handlep->oneshot_buffer = NULL;
                return -1;
        }

        /*
         * Success.  *status has been set either to 0 if there are no
         * warnings or to a PCAP_WARNING_ value if there is a warning.
         *
         * handle->offset is used to get the current position into the rx ring.
         * handle->cc is used to store the ring size.
         */

        /*
         * Set the timeout to use in poll() before returning.
         */
        set_poll_timeout(handlep);

        return 1;
}

/*
 * Attempt to set the socket to the specified version of the memory-mapped
 * header.
 *
 * Return 0 if we succeed; return 1 if we fail because that version isn't
 * supported; return -1 on any other error, and set handle->errbuf.
 */
static int
init_tpacket(pcap_t *handle, int version, const char *version_str)
{
        struct pcap_linux *handlep = handle->priv;
        int val = version;
        socklen_t len = sizeof(val);

        /*
         * Probe whether kernel supports the specified TPACKET version;
         * this also gets the length of the header for that version.
         *
         * This socket option was introduced in 2.6.27, which was
         * also the first release with TPACKET_V2 support.
         */
        if (getsockopt(handle->fd, SOL_PACKET, PACKET_HDRLEN, &val, &len) < 0) {
                if (errno == EINVAL) {
                        /*
                         * EINVAL means this specific version of TPACKET
                         * is not supported. Tell the caller they can try
                         * with a different one; if they've run out of
                         * others to try, let them set the error message
                         * appropriately.
                         */
                        return 1;
                }

                /*
                 * All other errors are fatal.
                 */
                if (errno == ENOPROTOOPT) {
                        /*
                         * PACKET_HDRLEN isn't supported, which means
                         * that memory-mapped capture isn't supported.
                         * Indicate that in the message.
                         */
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                            "Kernel doesn't support memory-mapped capture; a 2.6.27 or later 2.x kernel is required, with CONFIG_PACKET_MMAP specified for 2.x kernels");
                } else {
                        /*
                         * Some unexpected error.
                         */
                        pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                            errno, "can't get %s header len on packet socket",
                            version_str);
                }
                return -1;
        }
        handlep->tp_hdrlen = val;

        val = version;
        if (setsockopt(handle->fd, SOL_PACKET, PACKET_VERSION, &val,
                           sizeof(val)) < 0) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "can't activate %s on packet socket", version_str);
                return -1;
        }
        handlep->tp_version = version;

        return 0;
}

/*
 * Attempt to set the socket to version 3 of the memory-mapped header and,
 * if that fails because version 3 isn't supported, attempt to fall
 * back to version 2.  If version 2 isn't supported, just fail.
 *
 * Return 0 if we succeed and -1 on any other error, and set handle->errbuf.
 */
static int
prepare_tpacket_socket(pcap_t *handle)
{
        int ret;

#ifdef HAVE_TPACKET3
        /*
         * Try setting the version to TPACKET_V3.
         *
         * The only mode in which buffering is done on PF_PACKET
         * sockets, so that packets might not be delivered
         * immediately, is TPACKET_V3 mode.
         *
         * The buffering cannot be disabled in that mode, so
         * if the user has requested immediate mode, we don't
         * use TPACKET_V3.
         */
        if (!handle->opt.immediate) {
                ret = init_tpacket(handle, TPACKET_V3, "TPACKET_V3");
                if (ret == 0) {
                        /*
                         * Success.
                         */
                        return 0;
                }
                if (ret == -1) {
                        /*
                         * We failed for some reason other than "the
                         * kernel doesn't support TPACKET_V3".
                         */
                        return -1;
                }

                /*
                 * This means it returned 1, which means "the kernel
                 * doesn't support TPACKET_V3"; try TPACKET_V2.
                 */
        }
#endif /* HAVE_TPACKET3 */

        /*
         * Try setting the version to TPACKET_V2.
         */
        ret = init_tpacket(handle, TPACKET_V2, "TPACKET_V2");
        if (ret == 0) {
                /*
                 * Success.
                 */
                return 0;
        }

        if (ret == 1) {
                /*
                 * OK, the kernel supports memory-mapped capture, but
                 * not TPACKET_V2.  Set the error message appropriately.
                 */
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "Kernel doesn't support TPACKET_V2; a 2.6.27 or later kernel is required");
        }

        /*
         * We failed.
         */
        return -1;
}

#define MAX(a,b) ((a)>(b)?(a):(b))

/*
 * Attempt to set up memory-mapped access.
 *
 * On success, returns 1, and sets *status to 0 if there are no warnings
 * or to a PCAP_WARNING_ code if there is a warning.
 *
 * On error, returns -1, and sets *status to the appropriate error code;
 * if that is PCAP_ERROR, sets handle->errbuf to the appropriate message.
 */
static int
create_ring(pcap_t *handle, int *status)
{
        struct pcap_linux *handlep = handle->priv;
        unsigned i, j, frames_per_block;
#ifdef HAVE_TPACKET3
        /*
         * For sockets using TPACKET_V2, the extra stuff at the end of a
         * struct tpacket_req3 will be ignored, so this is OK even for
         * those sockets.
         */
        struct tpacket_req3 req;
#else
        struct tpacket_req req;
#endif
        socklen_t len;
        unsigned int sk_type, tp_reserve, maclen, tp_hdrlen, netoff, macoff;
        unsigned int frame_size;

        /*
         * Start out assuming no warnings or errors.
         */
        *status = 0;

        /*
         * Reserve space for VLAN tag reconstruction.
         */
        tp_reserve = VLAN_TAG_LEN;

        /*
         * If we're capturing in cooked mode, reserve space for
         * a DLT_LINUX_SLL2 header; we don't know yet whether
         * we'll be using DLT_LINUX_SLL or DLT_LINUX_SLL2, as
         * that can be changed on an open device, so we reserve
         * space for the larger of the two.
         *
         * XXX - we assume that the kernel is still adding
         * 16 bytes of extra space, so we subtract 16 from
         * SLL2_HDR_LEN to get the additional space needed.
         * (Are they doing that for DLT_LINUX_SLL, the link-
         * layer header for which is 16 bytes?)
         *
         * XXX - should we use TPACKET_ALIGN(SLL2_HDR_LEN - 16)?
         */
        if (handlep->cooked)
                tp_reserve += SLL2_HDR_LEN - 16;

        /*
         * Try to request that amount of reserve space.
         * This must be done before creating the ring buffer.
         */
        len = sizeof(tp_reserve);
        if (setsockopt(handle->fd, SOL_PACKET, PACKET_RESERVE,
            &tp_reserve, len) < 0) {
                pcap_fmt_errmsg_for_errno(handle->errbuf,
                    PCAP_ERRBUF_SIZE, errno,
                    "setsockopt (PACKET_RESERVE)");
                *status = PCAP_ERROR;
                return -1;
        }

        switch (handlep->tp_version) {

        case TPACKET_V2:
                /* Note that with large snapshot length (say 256K, which is
                 * the default for recent versions of tcpdump, Wireshark,
                 * TShark, dumpcap or 64K, the value that "-s 0" has given for
                 * a long time with tcpdump), if we use the snapshot
                 * length to calculate the frame length, only a few frames
                 * will be available in the ring even with pretty
                 * large ring size (and a lot of memory will be unused).
                 *
                 * Ideally, we should choose a frame length based on the
                 * minimum of the specified snapshot length and the maximum
                 * packet size.  That's not as easy as it sounds; consider,
                 * for example, an 802.11 interface in monitor mode, where
                 * the frame would include a radiotap header, where the
                 * maximum radiotap header length is device-dependent.
                 *
                 * So, for now, we just do this for Ethernet devices, where
                 * there's no metadata header, and the link-layer header is
                 * fixed length.  We can get the maximum packet size by
                 * adding 18, the Ethernet header length plus the CRC length
                 * (just in case we happen to get the CRC in the packet), to
                 * the MTU of the interface; we fetch the MTU in the hopes
                 * that it reflects support for jumbo frames.  (Even if the
                 * interface is just being used for passive snooping, the
                 * driver might set the size of buffers in the receive ring
                 * based on the MTU, so that the MTU limits the maximum size
                 * of packets that we can receive.)
                 *
                 * If segmentation/fragmentation or receive offload are
                 * enabled, we can get reassembled/aggregated packets larger
                 * than MTU, but bounded to 65535 plus the Ethernet overhead,
                 * due to kernel and protocol constraints */
                frame_size = handle->snapshot;
                if (handle->linktype == DLT_EN10MB) {
                        unsigned int max_frame_len;
                        int mtu;
                        int offload;

                        mtu = iface_get_mtu(handle->fd, handle->opt.device,
                            handle->errbuf);
                        if (mtu == -1) {
                                *status = PCAP_ERROR;
                                return -1;
                        }
                        offload = iface_get_offload(handle);
                        if (offload == -1) {
                                *status = PCAP_ERROR;
                                return -1;
                        }
                        if (offload)
                                max_frame_len = MAX(mtu, 65535);
                        else
                                max_frame_len = mtu;
                        max_frame_len += 18;

                        if (frame_size > max_frame_len)
                                frame_size = max_frame_len;
                }

                /* NOTE: calculus matching those in tpacket_rcv()
                 * in linux-2.6/net/packet/af_packet.c
                 */
                len = sizeof(sk_type);
                if (getsockopt(handle->fd, SOL_SOCKET, SO_TYPE, &sk_type,
                    &len) < 0) {
                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                            PCAP_ERRBUF_SIZE, errno, "getsockopt (SO_TYPE)");
                        *status = PCAP_ERROR;
                        return -1;
                }
                maclen = (sk_type == SOCK_DGRAM) ? 0 : MAX_LINKHEADER_SIZE;
                        /* XXX: in the kernel maclen is calculated from
                         * LL_ALLOCATED_SPACE(dev) and vnet_hdr.hdr_len
                         * in:  packet_snd()           in linux-2.6/net/packet/af_packet.c
                         * then packet_alloc_skb()     in linux-2.6/net/packet/af_packet.c
                         * then sock_alloc_send_pskb() in linux-2.6/net/core/sock.c
                         * but I see no way to get those sizes in userspace,
                         * like for instance with an ifreq ioctl();
                         * the best thing I've found so far is MAX_HEADER in
                         * the kernel part of linux-2.6/include/linux/netdevice.h
                         * which goes up to 128+48=176; since pcap-linux.c
                         * defines a MAX_LINKHEADER_SIZE of 256 which is
                         * greater than that, let's use it.. maybe is it even
                         * large enough to directly replace macoff..
                         */
                tp_hdrlen = TPACKET_ALIGN(handlep->tp_hdrlen) + sizeof(struct sockaddr_ll) ;
                netoff = TPACKET_ALIGN(tp_hdrlen + (maclen < 16 ? 16 : maclen)) + tp_reserve;
                        /* NOTE: AFAICS tp_reserve may break the TPACKET_ALIGN
                         * of netoff, which contradicts
                         * linux-2.6/Documentation/networking/packet_mmap.txt
                         * documenting that:
                         * "- Gap, chosen so that packet data (Start+tp_net)
                         * aligns to TPACKET_ALIGNMENT=16"
                         */
                        /* NOTE: in linux-2.6/include/linux/skbuff.h:
                         * "CPUs often take a performance hit
                         *  when accessing unaligned memory locations"
                         */
                macoff = netoff - maclen;
                req.tp_frame_size = TPACKET_ALIGN(macoff + frame_size);
                /*
                 * Round the buffer size up to a multiple of the
                 * frame size (rather than rounding down, which
                 * would give a buffer smaller than our caller asked
                 * for, and possibly give zero frames if the requested
                 * buffer size is too small for one frame).
                 */
                req.tp_frame_nr = (handle->opt.buffer_size + req.tp_frame_size - 1)/req.tp_frame_size;
                break;

#ifdef HAVE_TPACKET3
        case TPACKET_V3:
                /* The "frames" for this are actually buffers that
                 * contain multiple variable-sized frames.
                 *
                 * We pick a "frame" size of MAXIMUM_SNAPLEN to leave
                 * enough room for at least one reasonably-sized packet
                 * in the "frame". */
                req.tp_frame_size = MAXIMUM_SNAPLEN;
                /*
                 * Round the buffer size up to a multiple of the
                 * "frame" size (rather than rounding down, which
                 * would give a buffer smaller than our caller asked
                 * for, and possibly give zero "frames" if the requested
                 * buffer size is too small for one "frame").
                 */
                req.tp_frame_nr = (handle->opt.buffer_size + req.tp_frame_size - 1)/req.tp_frame_size;
                break;
#endif
        default:
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "Internal error: unknown TPACKET_ value %u",
                    handlep->tp_version);
                *status = PCAP_ERROR;
                return -1;
        }

        /* compute the minimum block size that will handle this frame.
         * The block has to be page size aligned.
         * The max block size allowed by the kernel is arch-dependent and
         * it's not explicitly checked here. */
        req.tp_block_size = getpagesize();
        while (req.tp_block_size < req.tp_frame_size)
                req.tp_block_size <<= 1;

        frames_per_block = req.tp_block_size/req.tp_frame_size;

        /*
         * PACKET_TIMESTAMP was added after linux/net_tstamp.h was,
         * so we check for PACKET_TIMESTAMP.  We check for
         * linux/net_tstamp.h just in case a system somehow has
         * PACKET_TIMESTAMP but not linux/net_tstamp.h; that might
         * be unnecessary.
         *
         * SIOCSHWTSTAMP was introduced in the patch that introduced
         * linux/net_tstamp.h, so we don't bother checking whether
         * SIOCSHWTSTAMP is defined (if your Linux system has
         * linux/net_tstamp.h but doesn't define SIOCSHWTSTAMP, your
         * Linux system is badly broken).
         */
#if defined(HAVE_LINUX_NET_TSTAMP_H) && defined(PACKET_TIMESTAMP)
        /*
         * If we were told to do so, ask the kernel and the driver
         * to use hardware timestamps.
         *
         * Hardware timestamps are only supported with mmapped
         * captures.
         */
        if (handle->opt.tstamp_type == PCAP_TSTAMP_ADAPTER ||
            handle->opt.tstamp_type == PCAP_TSTAMP_ADAPTER_UNSYNCED) {
                struct hwtstamp_config hwconfig;
                struct ifreq ifr;
                int timesource;

                /*
                 * Ask for hardware time stamps on all packets,
                 * including transmitted packets.
                 */
                memset(&hwconfig, 0, sizeof(hwconfig));
                hwconfig.tx_type = HWTSTAMP_TX_ON;
                hwconfig.rx_filter = HWTSTAMP_FILTER_ALL;

                memset(&ifr, 0, sizeof(ifr));
                pcap_strlcpy(ifr.ifr_name, handle->opt.device, sizeof(ifr.ifr_name));
                ifr.ifr_data = (void *)&hwconfig;

                /*
                 * This may require CAP_NET_ADMIN.
                 */
                if (ioctl(handle->fd, SIOCSHWTSTAMP, &ifr) < 0) {
                        switch (errno) {

                        case EPERM:
                                /*
                                 * Treat this as an error, as the
                                 * user should try to run this
                                 * with the appropriate privileges -
                                 * and, if they can't, shouldn't
                                 * try requesting hardware time stamps.
                                 */
                                *status = PCAP_ERROR_PERM_DENIED;
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                    "Attempt to set hardware timestamp failed - CAP_NET_ADMIN may be required");
                                return -1;

                        case EOPNOTSUPP:
                        case ERANGE:
                                /*
                                 * Treat this as a warning, as the
                                 * only way to fix the warning is to
                                 * get an adapter that supports hardware
                                 * time stamps for *all* packets.
                                 * (ERANGE means "we support hardware
                                 * time stamps, but for packets matching
                                 * that particular filter", so it means
                                 * "we don't support hardware time stamps
                                 * for all incoming packets" here.)
                                 *
                                 * We'll just fall back on the standard
                                 * host time stamps.
                                 */
                                *status = PCAP_WARNING_TSTAMP_TYPE_NOTSUP;
                                break;

                        default:
                                pcap_fmt_errmsg_for_errno(handle->errbuf,
                                    PCAP_ERRBUF_SIZE, errno,
                                    "SIOCSHWTSTAMP failed");
                                *status = PCAP_ERROR;
                                return -1;
                        }
                } else {
                        /*
                         * Well, that worked.  Now specify the type of
                         * hardware time stamp we want for this
                         * socket.
                         */
                        if (handle->opt.tstamp_type == PCAP_TSTAMP_ADAPTER) {
                                /*
                                 * Hardware timestamp, synchronized
                                 * with the system clock.
                                 */
                                timesource = SOF_TIMESTAMPING_SYS_HARDWARE;
                        } else {
                                /*
                                 * PCAP_TSTAMP_ADAPTER_UNSYNCED - hardware
                                 * timestamp, not synchronized with the
                                 * system clock.
                                 */
                                timesource = SOF_TIMESTAMPING_RAW_HARDWARE;
                        }
                        if (setsockopt(handle->fd, SOL_PACKET, PACKET_TIMESTAMP,
                                (void *)&timesource, sizeof(timesource))) {
                                pcap_fmt_errmsg_for_errno(handle->errbuf,
                                    PCAP_ERRBUF_SIZE, errno,
                                    "can't set PACKET_TIMESTAMP");
                                *status = PCAP_ERROR;
                                return -1;
                        }
                }
        }
#endif /* HAVE_LINUX_NET_TSTAMP_H && PACKET_TIMESTAMP */

        /* ask the kernel to create the ring */
retry:
        req.tp_block_nr = req.tp_frame_nr / frames_per_block;

        /* req.tp_frame_nr is requested to match frames_per_block*req.tp_block_nr */
        req.tp_frame_nr = req.tp_block_nr * frames_per_block;

#ifdef HAVE_TPACKET3
        /* timeout value to retire block - use the configured buffering timeout, or default if <0. */
        if (handlep->timeout > 0) {
                /* Use the user specified timeout as the block timeout */
                req.tp_retire_blk_tov = handlep->timeout;
        } else if (handlep->timeout == 0) {
                /*
                 * In pcap, this means "infinite timeout"; TPACKET_V3
                 * doesn't support that, so just set it to UINT_MAX
                 * milliseconds.  In the TPACKET_V3 loop, if the
                 * timeout is 0, and we haven't yet seen any packets,
                 * and we block and still don't have any packets, we
                 * keep blocking until we do.
                 */
                req.tp_retire_blk_tov = UINT_MAX;
        } else {
                /*
                 * XXX - this is not valid; use 0, meaning "have the
                 * kernel pick a default", for now.
                 */
                req.tp_retire_blk_tov = 0;
        }
        /* private data not used */
        req.tp_sizeof_priv = 0;
        /* Rx ring - feature request bits - none (rxhash will not be filled) */
        req.tp_feature_req_word = 0;
#endif

        if (setsockopt(handle->fd, SOL_PACKET, PACKET_RX_RING,
                                        (void *) &req, sizeof(req))) {
                if ((errno == ENOMEM) && (req.tp_block_nr > 1)) {
                        /*
                         * Memory failure; try to reduce the requested ring
                         * size.
                         *
                         * We used to reduce this by half -- do 5% instead.
                         * That may result in more iterations and a longer
                         * startup, but the user will be much happier with
                         * the resulting buffer size.
                         */
                        if (req.tp_frame_nr < 20)
                                req.tp_frame_nr -= 1;
                        else
                                req.tp_frame_nr -= req.tp_frame_nr/20;
                        goto retry;
                }
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "can't create rx ring on packet socket");
                *status = PCAP_ERROR;
                return -1;
        }

        /* memory map the rx ring */
        handlep->mmapbuflen = req.tp_block_nr * req.tp_block_size;
        handlep->mmapbuf = mmap(0, handlep->mmapbuflen,
            PROT_READ|PROT_WRITE, MAP_SHARED, handle->fd, 0);
        if (handlep->mmapbuf == MAP_FAILED) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "can't mmap rx ring");

                /* clear the allocated ring on error*/
                destroy_ring(handle);
                *status = PCAP_ERROR;
                return -1;
        }

        /* allocate a ring for each frame header pointer*/
        handle->cc = req.tp_frame_nr;
        handle->buffer = malloc(handle->cc * sizeof(union thdr *));
        if (!handle->buffer) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "can't allocate ring of frame headers");

                destroy_ring(handle);
                *status = PCAP_ERROR;
                return -1;
        }

        /* fill the header ring with proper frame ptr*/
        handle->offset = 0;
        for (i=0; i<req.tp_block_nr; ++i) {
                u_char *base = &handlep->mmapbuf[i*req.tp_block_size];
                for (j=0; j<frames_per_block; ++j, ++handle->offset) {
                        RING_GET_CURRENT_FRAME(handle) = base;
                        base += req.tp_frame_size;
                }
        }

        handle->bufsize = req.tp_frame_size;
        handle->offset = 0;
        return 1;
}

/* free all ring related resources*/
static void
destroy_ring(pcap_t *handle)
{
        struct pcap_linux *handlep = handle->priv;

        /*
         * Tell the kernel to destroy the ring.
         * We don't check for setsockopt failure, as 1) we can't recover
         * from an error and 2) we might not yet have set it up in the
         * first place.
         */
        struct tpacket_req req;
        memset(&req, 0, sizeof(req));
        (void)setsockopt(handle->fd, SOL_PACKET, PACKET_RX_RING,
                                (void *) &req, sizeof(req));

        /* if ring is mapped, unmap it*/
        if (handlep->mmapbuf) {
                /* do not test for mmap failure, as we can't recover from any error */
                (void)munmap(handlep->mmapbuf, handlep->mmapbuflen);
                handlep->mmapbuf = NULL;
        }
}

/*
 * Special one-shot callback, used for pcap_next() and pcap_next_ex(),
 * for Linux mmapped capture.
 *
 * The problem is that pcap_next() and pcap_next_ex() expect the packet
 * data handed to the callback to be valid after the callback returns,
 * but pcap_read_linux_mmap() has to release that packet as soon as
 * the callback returns (otherwise, the kernel thinks there's still
 * at least one unprocessed packet available in the ring, so a select()
 * will immediately return indicating that there's data to process), so,
 * in the callback, we have to make a copy of the packet.
 *
 * Yes, this means that, if the capture is using the ring buffer, using
 * pcap_next() or pcap_next_ex() requires more copies than using
 * pcap_loop() or pcap_dispatch().  If that bothers you, don't use
 * pcap_next() or pcap_next_ex().
 */
static void
pcap_oneshot_linux(u_char *user, const struct pcap_pkthdr *h,
    const u_char *bytes)
{
        struct oneshot_userdata *sp = (struct oneshot_userdata *)user;
        pcap_t *handle = sp->pd;
        struct pcap_linux *handlep = handle->priv;

        *sp->hdr = *h;
        memcpy(handlep->oneshot_buffer, bytes, h->caplen);
        *sp->pkt = handlep->oneshot_buffer;
}

static int
pcap_getnonblock_linux(pcap_t *handle)
{
        struct pcap_linux *handlep = handle->priv;

        /* use negative value of timeout to indicate non blocking ops */
        return (handlep->timeout<0);
}

static int
pcap_setnonblock_linux(pcap_t *handle, int nonblock)
{
        struct pcap_linux *handlep = handle->priv;

        /*
         * Set the file descriptor to non-blocking mode, as we use
         * it for sending packets.
         */
        if (pcap_setnonblock_fd(handle, nonblock) == -1)
                return -1;

        /*
         * Map each value to their corresponding negation to
         * preserve the timeout value provided with pcap_set_timeout.
         */
        if (nonblock) {
                if (handlep->timeout >= 0) {
                        /*
                         * Indicate that we're switching to
                         * non-blocking mode.
                         */
                        handlep->timeout = ~handlep->timeout;
                }
        } else {
                if (handlep->timeout < 0) {
                        handlep->timeout = ~handlep->timeout;
                }
        }
        /* Update the timeout to use in poll(). */
        set_poll_timeout(handlep);
        return 0;
}

/*
 * Get the status field of the ring buffer frame at a specified offset.
 */
static inline u_int
pcap_get_ring_frame_status(pcap_t *handle, int offset)
{
        struct pcap_linux *handlep = handle->priv;
        union thdr h;

        h.raw = RING_GET_FRAME_AT(handle, offset);
        switch (handlep->tp_version) {
        case TPACKET_V2:
                return __atomic_load_n(&h.h2->tp_status, __ATOMIC_ACQUIRE);
                break;
#ifdef HAVE_TPACKET3
        case TPACKET_V3:
                return __atomic_load_n(&h.h3->hdr.bh1.block_status, __ATOMIC_ACQUIRE);
                break;
#endif
        }
        /* This should not happen. */
        return 0;
}

/*
 * Block waiting for frames to be available.
 */
static int pcap_wait_for_frames_mmap(pcap_t *handle)
{
        struct pcap_linux *handlep = handle->priv;
        int timeout;
        struct ifreq ifr;
        int ret;
        struct pollfd pollinfo[2];
        pollinfo[0].fd = handle->fd;
        pollinfo[0].events = POLLIN;
        pollinfo[1].fd = handlep->poll_breakloop_fd;
        pollinfo[1].events = POLLIN;

        /*
         * Keep polling until we either get some packets to read, see
         * that we got told to break out of the loop, get a fatal error,
         * or discover that the device went away.
         *
         * In non-blocking mode, we must still do one poll() to catch
         * any pending error indications, but the poll() has a timeout
         * of 0, so that it doesn't block, and we quit after that one
         * poll().
         *
         * If we've seen an ENETDOWN, it might be the first indication
         * that the device went away, or it might just be that it was
         * configured down.  Unfortunately, there's no guarantee that
         * the device has actually been removed as an interface, because:
         *
         * 1) if, as appears to be the case at least some of the time,
         * the PF_PACKET socket code first gets a NETDEV_DOWN indication
         * for the device and then gets a NETDEV_UNREGISTER indication
         * for it, the first indication will cause a wakeup with ENETDOWN
         * but won't set the packet socket's field for the interface index
         * to -1, and the second indication won't cause a wakeup (because
         * the first indication also caused the protocol hook to be
         * unregistered) but will set the packet socket's field for the
         * interface index to -1;
         *
         * 2) even if just a NETDEV_UNREGISTER indication is registered,
         * the packet socket's field for the interface index only gets
         * set to -1 after the wakeup, so there's a small but non-zero
         * risk that a thread blocked waiting for the wakeup will get
         * to the "fetch the socket name" code before the interface index
         * gets set to -1, so it'll get the old interface index.
         *
         * Therefore, if we got an ENETDOWN and haven't seen a packet
         * since then, we assume that we might be waiting for the interface
         * to disappear, and poll with a timeout to try again in a short
         * period of time.  If we *do* see a packet, the interface has
         * come back up again, and is *definitely* still there, so we
         * don't need to poll.
         */
        for (;;) {
                /*
                 * Yes, we do this even in non-blocking mode, as it's
                 * the only way to get error indications from a
                 * tpacket socket.
                 *
                 * The timeout is 0 in non-blocking mode, so poll()
                 * returns immediately.
                 */
                timeout = handlep->poll_timeout;

                /*
                 * If we got an ENETDOWN and haven't gotten an indication
                 * that the device has gone away or that the device is up,
                 * we don't yet know for certain whether the device has
                 * gone away or not, do a poll() with a 1-millisecond timeout,
                 * as we have to poll indefinitely for "device went away"
                 * indications until we either get one or see that the
                 * device is up.
                 */
                if (handlep->netdown) {
                        if (timeout != 0)
                                timeout = 1;
                }
                ret = poll(pollinfo, 2, timeout);
                if (ret < 0) {
                        /*
                         * Error.  If it's not EINTR, report it.
                         */
                        if (errno != EINTR) {
                                pcap_fmt_errmsg_for_errno(handle->errbuf,
                                    PCAP_ERRBUF_SIZE, errno,
                                    "can't poll on packet socket");
                                return PCAP_ERROR;
                        }

                        /*
                         * It's EINTR; if we were told to break out of
                         * the loop, do so.
                         */
                        if (handle->break_loop) {
                                handle->break_loop = 0;
                                return PCAP_ERROR_BREAK;
                        }
                } else if (ret > 0) {
                        /*
                         * OK, some descriptor is ready.
                         * Check the socket descriptor first.
                         *
                         * As I read the Linux man page, pollinfo[0].revents
                         * will either be POLLIN, POLLERR, POLLHUP, or POLLNVAL.
                         */
                        if (pollinfo[0].revents == POLLIN) {
                                /*
                                 * OK, we may have packets to
                                 * read.
                                 */
                                break;
                        }
                        if (pollinfo[0].revents != 0) {
                                /*
                                 * There's some indication other than
                                 * "you can read on this descriptor" on
                                 * the descriptor.
                                 */
                                if (pollinfo[0].revents & POLLNVAL) {
                                        snprintf(handle->errbuf,
                                            PCAP_ERRBUF_SIZE,
                                            "Invalid polling request on packet socket");
                                        return PCAP_ERROR;
                                }
                                if (pollinfo[0].revents & (POLLHUP | POLLRDHUP)) {
                                        snprintf(handle->errbuf,
                                            PCAP_ERRBUF_SIZE,
                                            "Hangup on packet socket");
                                        return PCAP_ERROR;
                                }
                                if (pollinfo[0].revents & POLLERR) {
                                        /*
                                         * Get the error.
                                         */
                                        int err;
                                        socklen_t errlen;

                                        errlen = sizeof(err);
                                        if (getsockopt(handle->fd, SOL_SOCKET,
                                            SO_ERROR, &err, &errlen) == -1) {
                                                /*
                                                 * The call *itself* returned
                                                 * an error; make *that*
                                                 * the error.
                                                 */
                                                err = errno;
                                        }

                                        /*
                                         * OK, we have the error.
                                         */
                                        if (err == ENETDOWN) {
                                                /*
                                                 * The device on which we're
                                                 * capturing went away or the
                                                 * interface was taken down.
                                                 *
                                                 * We don't know for certain
                                                 * which happened, and the
                                                 * next poll() may indicate
                                                 * that there are packets
                                                 * to be read, so just set
                                                 * a flag to get us to do
                                                 * checks later, and set
                                                 * the required select
                                                 * timeout to 1 millisecond
                                                 * so that event loops that
                                                 * check our socket descriptor
                                                 * also time out so that
                                                 * they can call us and we
                                                 * can do the checks.
                                                 */
                                                handlep->netdown = 1;
                                                handle->required_select_timeout = &netdown_timeout;
                                        } else if (err == 0) {
                                                /*
                                                 * This shouldn't happen, so
                                                 * report a special indication
                                                 * that it did.
                                                 */
                                                snprintf(handle->errbuf,
                                                    PCAP_ERRBUF_SIZE,
                                                    "Error condition on packet socket: Reported error was 0");
                                                return PCAP_ERROR;
                                        } else {
                                                pcap_fmt_errmsg_for_errno(handle->errbuf,
                                                    PCAP_ERRBUF_SIZE,
                                                    err,
                                                    "Error condition on packet socket");
                                                return PCAP_ERROR;
                                        }
                                }
                        }
                        /*
                         * Now check the event device.
                         */
                        if (pollinfo[1].revents & POLLIN) {
                                ssize_t nread;
                                uint64_t value;

                                /*
                                 * This should never fail, but, just
                                 * in case....
                                 */
                                nread = read(handlep->poll_breakloop_fd, &value,
                                    sizeof(value));
                                if (nread == -1) {
                                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                                            PCAP_ERRBUF_SIZE,
                                            errno,
                                            "Error reading from event FD");
                                        return PCAP_ERROR;
                                }

                                /*
                                 * According to the Linux read(2) man
                                 * page, read() will transfer at most
                                 * 2^31-1 bytes, so the return value is
                                 * either -1 or a value between 0
                                 * and 2^31-1, so it's non-negative.
                                 *
                                 * Cast it to size_t to squelch
                                 * warnings from the compiler; add this
                                 * comment to squelch warnings from
                                 * humans reading the code. :-)
                                 *
                                 * Don't treat an EOF as an error, but
                                 * *do* treat a short read as an error;
                                 * that "shouldn't happen", but....
                                 */
                                if (nread != 0 &&
                                    (size_t)nread < sizeof(value)) {
                                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                            "Short read from event FD: expected %zu, got %zd",
                                            sizeof(value), nread);
                                        return PCAP_ERROR;
                                }

                                /*
                                 * This event gets signaled by a
                                 * pcap_breakloop() call; if we were told
                                 * to break out of the loop, do so.
                                 */
                                if (handle->break_loop) {
                                        handle->break_loop = 0;
                                        return PCAP_ERROR_BREAK;
                                }
                        }
                }

                /*
                 * Either:
                 *
                 *   1) we got neither an error from poll() nor any
                 *      readable descriptors, in which case there
                 *      are no packets waiting to read
                 *
                 * or
                 *
                 *   2) We got readable descriptors but the PF_PACKET
                 *      socket wasn't one of them, in which case there
                 *      are no packets waiting to read
                 *
                 * so, if we got an ENETDOWN, we've drained whatever
                 * packets were available to read at the point of the
                 * ENETDOWN.
                 *
                 * So, if we got an ENETDOWN and haven't gotten an indication
                 * that the device has gone away or that the device is up,
                 * we don't yet know for certain whether the device has
                 * gone away or not, check whether the device exists and is
                 * up.
                 */
                if (handlep->netdown) {
                        if (!device_still_exists(handle)) {
                                /*
                                 * The device doesn't exist any more;
                                 * report that.
                                 *
                                 * XXX - we should really return an
                                 * appropriate error for that, but
                                 * pcap_dispatch() etc. aren't documented
                                 * as having error returns other than
                                 * PCAP_ERROR or PCAP_ERROR_BREAK.
                                 */
                                snprintf(handle->errbuf,  PCAP_ERRBUF_SIZE,
                                    "The interface disappeared");
                                return PCAP_ERROR;
                        }

                        /*
                         * The device still exists; try to see if it's up.
                         */
                        memset(&ifr, 0, sizeof(ifr));
                        pcap_strlcpy(ifr.ifr_name, handlep->device,
                            sizeof(ifr.ifr_name));
                        if (ioctl(handle->fd, SIOCGIFFLAGS, &ifr) == -1) {
                                if (errno == ENXIO || errno == ENODEV) {
                                        /*
                                         * OK, *now* it's gone.
                                         *
                                         * XXX - see above comment.
                                         */
                                        snprintf(handle->errbuf,
                                            PCAP_ERRBUF_SIZE,
                                            "The interface disappeared");
                                        return PCAP_ERROR;
                                } else {
                                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                                            PCAP_ERRBUF_SIZE, errno,
                                            "%s: Can't get flags",
                                            handlep->device);
                                        return PCAP_ERROR;
                                }
                        }
                        if (ifr.ifr_flags & IFF_UP) {
                                /*
                                 * It's up, so it definitely still exists.
                                 * Cancel the ENETDOWN indication - we
                                 * presumably got it due to the interface
                                 * going down rather than the device going
                                 * away - and revert to "no required select
                                 * timeout.
                                 */
                                handlep->netdown = 0;
                                handle->required_select_timeout = NULL;
                        }
                }

                /*
                 * If we're in non-blocking mode, just quit now, rather
                 * than spinning in a loop doing poll()s that immediately
                 * time out if there's no indication on any descriptor.
                 */
                if (handlep->poll_timeout == 0)
                        break;
        }
        return 0;
}

/* handle a single memory mapped packet */
static int pcap_handle_packet_mmap(
                pcap_t *handle,
                pcap_handler callback,
                u_char *user,
                unsigned char *frame,
                unsigned int tp_len,
                unsigned int tp_mac,
                unsigned int tp_snaplen,
                unsigned int tp_sec,
                unsigned int tp_usec,
                int tp_vlan_tci_valid,
                __u16 tp_vlan_tci,
                __u16 tp_vlan_tpid)
{
        struct pcap_linux *handlep = handle->priv;
        unsigned char *bp;
        struct sockaddr_ll *sll;
        struct pcap_pkthdr pcaphdr;
        pcap_can_socketcan_hdr *canhdr;
        unsigned int snaplen = tp_snaplen;
        struct utsname utsname;

        /* perform sanity check on internal offset. */
        if (tp_mac + tp_snaplen > handle->bufsize) {
                /*
                 * Report some system information as a debugging aid.
                 */
                if (uname(&utsname) != -1) {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                "corrupted frame on kernel ring mac "
                                "offset %u + caplen %u > frame len %d "
                                "(kernel %.32s version %s, machine %.16s)",
                                tp_mac, tp_snaplen, handle->bufsize,
                                utsname.release, utsname.version,
                                utsname.machine);
                } else {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                "corrupted frame on kernel ring mac "
                                "offset %u + caplen %u > frame len %d",
                                tp_mac, tp_snaplen, handle->bufsize);
                }
                return -1;
        }

        /* run filter on received packet
         * If the kernel filtering is enabled we need to run the
         * filter until all the frames present into the ring
         * at filter creation time are processed.
         * In this case, blocks_to_filter_in_userland is used
         * as a counter for the packet we need to filter.
         * Note: alternatively it could be possible to stop applying
         * the filter when the ring became empty, but it can possibly
         * happen a lot later... */
        bp = frame + tp_mac;

        /* if required build in place the sll header*/
        sll = (void *)(frame + TPACKET_ALIGN(handlep->tp_hdrlen));
        if (handlep->cooked) {
                if (handle->linktype == DLT_LINUX_SLL2) {
                        struct sll2_header *hdrp;

                        /*
                         * The kernel should have left us with enough
                         * space for an sll header; back up the packet
                         * data pointer into that space, as that'll be
                         * the beginning of the packet we pass to the
                         * callback.
                         */
                        bp -= SLL2_HDR_LEN;

                        /*
                         * Let's make sure that's past the end of
                         * the tpacket header, i.e. >=
                         * ((u_char *)thdr + TPACKET_HDRLEN), so we
                         * don't step on the header when we construct
                         * the sll header.
                         */
                        if (bp < (u_char *)frame +
                                           TPACKET_ALIGN(handlep->tp_hdrlen) +
                                           sizeof(struct sockaddr_ll)) {
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                        "cooked-mode frame doesn't have room for sll header");
                                return -1;
                        }

                        /*
                         * OK, that worked; construct the sll header.
                         */
                        hdrp = (struct sll2_header *)bp;
                        hdrp->sll2_protocol = sll->sll_protocol;
                        hdrp->sll2_reserved_mbz = 0;
                        hdrp->sll2_if_index = htonl(sll->sll_ifindex);
                        hdrp->sll2_hatype = htons(sll->sll_hatype);
                        hdrp->sll2_pkttype = sll->sll_pkttype;
                        hdrp->sll2_halen = sll->sll_halen;
                        memcpy(hdrp->sll2_addr, sll->sll_addr, SLL_ADDRLEN);

                        snaplen += sizeof(struct sll2_header);
                } else {
                        struct sll_header *hdrp;

                        /*
                         * The kernel should have left us with enough
                         * space for an sll header; back up the packet
                         * data pointer into that space, as that'll be
                         * the beginning of the packet we pass to the
                         * callback.
                         */
                        bp -= SLL_HDR_LEN;

                        /*
                         * Let's make sure that's past the end of
                         * the tpacket header, i.e. >=
                         * ((u_char *)thdr + TPACKET_HDRLEN), so we
                         * don't step on the header when we construct
                         * the sll header.
                         */
                        if (bp < (u_char *)frame +
                                           TPACKET_ALIGN(handlep->tp_hdrlen) +
                                           sizeof(struct sockaddr_ll)) {
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                        "cooked-mode frame doesn't have room for sll header");
                                return -1;
                        }

                        /*
                         * OK, that worked; construct the sll header.
                         */
                        hdrp = (struct sll_header *)bp;
                        hdrp->sll_pkttype = htons(sll->sll_pkttype);
                        hdrp->sll_hatype = htons(sll->sll_hatype);
                        hdrp->sll_halen = htons(sll->sll_halen);
                        memcpy(hdrp->sll_addr, sll->sll_addr, SLL_ADDRLEN);
                        hdrp->sll_protocol = sll->sll_protocol;

                        snaplen += sizeof(struct sll_header);
                }
        } else {
                /*
                 * If this is a packet from a CAN device, so that
                 * sll->sll_hatype is ARPHRD_CAN, then, as we're
                 * not capturing in cooked mode, its link-layer
                 * type is DLT_CAN_SOCKETCAN.  Fix up the header
                 * provided by the code below us to match what
                 * DLT_CAN_SOCKETCAN is expected to provide.
                 */
                if (sll->sll_hatype == ARPHRD_CAN) {
                        /*
                         * DLT_CAN_SOCKETCAN is specified as having the
                         * CAN ID and flags in network byte order, but
                         * capturing on a CAN device provides it in host
                         * byte order.  Convert it to network byte order.
                         */
                        canhdr = (pcap_can_socketcan_hdr *)bp;
                        canhdr->can_id = htonl(canhdr->can_id);

                        /*
                         * In addition, set the CANFD_FDF flag if
                         * the protocol is LINUX_SLL_P_CANFD, as
                         * the protocol field itself isn't in
                         * the packet to indicate that it's a
                         * CAN FD packet.
                         */
                        uint16_t protocol = ntohs(sll->sll_protocol);
                        if (protocol == LINUX_SLL_P_CANFD) {
                                canhdr->fd_flags |= CANFD_FDF;

                                /*
                                 * Zero out all the unknown bits in
                                 * fd_flags and clear the reserved
                                 * fields, so that a program reading
                                 * this can assume that CANFD_FDF
                                 * is set because we set it, not
                                 * because some uninitialized crap
                                 * was provided in the fd_flags
                                 * field.
                                 *
                                 * (At least some LINKTYPE_CAN_SOCKETCAN
                                 * files attached to Wireshark bugs
                                 * had uninitialized junk there, so it
                                 * does happen.)
                                 *
                                 * Update this if Linux adds more flag
                                 * bits to the fd_flags field or uses
                                 * either of the reserved fields for
                                 * FD frames.
                                 */
                                canhdr->fd_flags &= ~(CANFD_FDF|CANFD_ESI|CANFD_BRS);
                                canhdr->reserved1 = 0;
                                canhdr->reserved2 = 0;
                        } else {
                                /*
                                 * Clear CANFD_FDF if it's set (probably
                                 * again meaning that that field is
                                 * uninitialized junk).
                                 */
                                canhdr->fd_flags &= ~CANFD_FDF;
                        }
                }
        }

        if (handlep->filter_in_userland && handle->fcode.bf_insns) {
                struct pcap_bpf_aux_data aux_data;

                aux_data.vlan_tag_present = tp_vlan_tci_valid;
                aux_data.vlan_tag = tp_vlan_tci & 0x0fff;

                if (pcap_filter_with_aux_data(handle->fcode.bf_insns,
                                              bp,
                                              tp_len,
                                              snaplen,
                                              &aux_data) == 0)
                        return 0;
        }

        if (!linux_check_direction(handle, sll))
                return 0;

        /* get required packet info from ring header */
        pcaphdr.ts.tv_sec = tp_sec;
        pcaphdr.ts.tv_usec = tp_usec;
        pcaphdr.caplen = tp_snaplen;
        pcaphdr.len = tp_len;

        /* if required build in place the sll header*/
        if (handlep->cooked) {
                /* update packet len */
                if (handle->linktype == DLT_LINUX_SLL2) {
                        pcaphdr.caplen += SLL2_HDR_LEN;
                        pcaphdr.len += SLL2_HDR_LEN;
                } else {
                        pcaphdr.caplen += SLL_HDR_LEN;
                        pcaphdr.len += SLL_HDR_LEN;
                }
        }

        if (tp_vlan_tci_valid &&
                handlep->vlan_offset != -1 &&
                tp_snaplen >= (unsigned int) handlep->vlan_offset)
        {
                struct vlan_tag *tag;

                /*
                 * Move everything in the header, except the type field,
                 * down VLAN_TAG_LEN bytes, to allow us to insert the
                 * VLAN tag between that stuff and the type field.
                 */
                bp -= VLAN_TAG_LEN;
                memmove(bp, bp + VLAN_TAG_LEN, handlep->vlan_offset);

                /*
                 * Now insert the tag.
                 */
                tag = (struct vlan_tag *)(bp + handlep->vlan_offset);
                tag->vlan_tpid = htons(tp_vlan_tpid);
                tag->vlan_tci = htons(tp_vlan_tci);

                /*
                 * Add the tag to the packet lengths.
                 */
                pcaphdr.caplen += VLAN_TAG_LEN;
                pcaphdr.len += VLAN_TAG_LEN;
        }

        /*
         * The only way to tell the kernel to cut off the
         * packet at a snapshot length is with a filter program;
         * if there's no filter program, the kernel won't cut
         * the packet off.
         *
         * Trim the snapshot length to be no longer than the
         * specified snapshot length.
         *
         * XXX - an alternative is to put a filter, consisting
         * of a "ret <snaplen>" instruction, on the socket
         * in the activate routine, so that the truncation is
         * done in the kernel even if nobody specified a filter;
         * that means that less buffer space is consumed in
         * the memory-mapped buffer.
         */
        if (pcaphdr.caplen > (bpf_u_int32)handle->snapshot)
                pcaphdr.caplen = handle->snapshot;

        /* pass the packet to the user */
        callback(user, &pcaphdr, bp);

        return 1;
}

static int
pcap_read_linux_mmap_v2(pcap_t *handle, int max_packets, pcap_handler callback,
                u_char *user)
{
        struct pcap_linux *handlep = handle->priv;
        union thdr h;
        int pkts = 0;
        int ret;

        /* wait for frames availability.*/
        h.raw = RING_GET_CURRENT_FRAME(handle);
        if (!packet_mmap_acquire(h.h2)) {
                /*
                 * The current frame is owned by the kernel; wait for
                 * a frame to be handed to us.
                 */
                ret = pcap_wait_for_frames_mmap(handle);
                if (ret) {
                        return ret;
                }
        }

        /*
         * This can conceivably process more than INT_MAX packets,
         * which would overflow the packet count, causing it either
         * to look like a negative number, and thus cause us to
         * return a value that looks like an error, or overflow
         * back into positive territory, and thus cause us to
         * return a too-low count.
         *
         * Therefore, if the packet count is unlimited, we clip
         * it at INT_MAX; this routine is not expected to
         * process packets indefinitely, so that's not an issue.
         */
        if (PACKET_COUNT_IS_UNLIMITED(max_packets))
                max_packets = INT_MAX;

        while (pkts < max_packets) {
                /*
                 * Get the current ring buffer frame, and break if
                 * it's still owned by the kernel.
                 */
                h.raw = RING_GET_CURRENT_FRAME(handle);
                if (!packet_mmap_acquire(h.h2))
                        break;

                ret = pcap_handle_packet_mmap(
                                handle,
                                callback,
                                user,
                                h.raw,
                                h.h2->tp_len,
                                h.h2->tp_mac,
                                h.h2->tp_snaplen,
                                h.h2->tp_sec,
                                handle->opt.tstamp_precision == PCAP_TSTAMP_PRECISION_NANO ? h.h2->tp_nsec : h.h2->tp_nsec / 1000,
                                VLAN_VALID(h.h2, h.h2),
                                h.h2->tp_vlan_tci,
                                VLAN_TPID(h.h2, h.h2));
                if (ret == 1) {
                        pkts++;
                } else if (ret < 0) {
                        return ret;
                }

                /*
                 * Hand this block back to the kernel, and, if we're
                 * counting blocks that need to be filtered in userland
                 * after having been filtered by the kernel, count
                 * the one we've just processed.
                 */
                packet_mmap_release(h.h2);
                if (handlep->blocks_to_filter_in_userland > 0) {
                        handlep->blocks_to_filter_in_userland--;
                        if (handlep->blocks_to_filter_in_userland == 0) {
                                /*
                                 * No more blocks need to be filtered
                                 * in userland.
                                 */
                                handlep->filter_in_userland = 0;
                        }
                }

                /* next block */
                if (++handle->offset >= handle->cc)
                        handle->offset = 0;

                /* check for break loop condition*/
                if (handle->break_loop) {
                        handle->break_loop = 0;
                        return PCAP_ERROR_BREAK;
                }
        }
        return pkts;
}

#ifdef HAVE_TPACKET3
static int
pcap_read_linux_mmap_v3(pcap_t *handle, int max_packets, pcap_handler callback,
                u_char *user)
{
        struct pcap_linux *handlep = handle->priv;
        union thdr h;
        int pkts = 0;
        int ret;

again:
        if (handlep->current_packet == NULL) {
                /* wait for frames availability.*/
                h.raw = RING_GET_CURRENT_FRAME(handle);
                if (!packet_mmap_v3_acquire(h.h3)) {
                        /*
                         * The current frame is owned by the kernel; wait
                         * for a frame to be handed to us.
                         */
                        ret = pcap_wait_for_frames_mmap(handle);
                        if (ret) {
                                return ret;
                        }
                }
        }
        h.raw = RING_GET_CURRENT_FRAME(handle);
        if (!packet_mmap_v3_acquire(h.h3)) {
                if (pkts == 0 && handlep->timeout == 0) {
                        /* Block until we see a packet. */
                        goto again;
                }
                return pkts;
        }

        /*
         * This can conceivably process more than INT_MAX packets,
         * which would overflow the packet count, causing it either
         * to look like a negative number, and thus cause us to
         * return a value that looks like an error, or overflow
         * back into positive territory, and thus cause us to
         * return a too-low count.
         *
         * Therefore, if the packet count is unlimited, we clip
         * it at INT_MAX; this routine is not expected to
         * process packets indefinitely, so that's not an issue.
         */
        if (PACKET_COUNT_IS_UNLIMITED(max_packets))
                max_packets = INT_MAX;

        while (pkts < max_packets) {
                int packets_to_read;

                if (handlep->current_packet == NULL) {
                        h.raw = RING_GET_CURRENT_FRAME(handle);
                        if (!packet_mmap_v3_acquire(h.h3))
                                break;

                        handlep->current_packet = h.raw + h.h3->hdr.bh1.offset_to_first_pkt;
                        handlep->packets_left = h.h3->hdr.bh1.num_pkts;
                }
                packets_to_read = handlep->packets_left;

                if (packets_to_read > (max_packets - pkts)) {
                        /*
                         * There are more packets in the buffer than
                         * the number of packets we have left to
                         * process to get up to the maximum number
                         * of packets to process.  Only process enough
                         * of them to get us up to that maximum.
                         */
                        packets_to_read = max_packets - pkts;
                }

                while (packets_to_read-- && !handle->break_loop) {
                        struct tpacket3_hdr* tp3_hdr = (struct tpacket3_hdr*) handlep->current_packet;
                        ret = pcap_handle_packet_mmap(
                                        handle,
                                        callback,
                                        user,
                                        handlep->current_packet,
                                        tp3_hdr->tp_len,
                                        tp3_hdr->tp_mac,
                                        tp3_hdr->tp_snaplen,
                                        tp3_hdr->tp_sec,
                                        handle->opt.tstamp_precision == PCAP_TSTAMP_PRECISION_NANO ? tp3_hdr->tp_nsec : tp3_hdr->tp_nsec / 1000,
                                        VLAN_VALID(tp3_hdr, &tp3_hdr->hv1),
                                        tp3_hdr->hv1.tp_vlan_tci,
                                        VLAN_TPID(tp3_hdr, &tp3_hdr->hv1));
                        if (ret == 1) {
                                pkts++;
                        } else if (ret < 0) {
                                handlep->current_packet = NULL;
                                return ret;
                        }
                        handlep->current_packet += tp3_hdr->tp_next_offset;
                        handlep->packets_left--;
                }

                if (handlep->packets_left <= 0) {
                        /*
                         * Hand this block back to the kernel, and, if
                         * we're counting blocks that need to be
                         * filtered in userland after having been
                         * filtered by the kernel, count the one we've
                         * just processed.
                         */
                        packet_mmap_v3_release(h.h3);
                        if (handlep->blocks_to_filter_in_userland > 0) {
                                handlep->blocks_to_filter_in_userland--;
                                if (handlep->blocks_to_filter_in_userland == 0) {
                                        /*
                                         * No more blocks need to be filtered
                                         * in userland.
                                         */
                                        handlep->filter_in_userland = 0;
                                }
                        }

                        /* next block */
                        if (++handle->offset >= handle->cc)
                                handle->offset = 0;

                        handlep->current_packet = NULL;
                }

                /* check for break loop condition*/
                if (handle->break_loop) {
                        handle->break_loop = 0;
                        return PCAP_ERROR_BREAK;
                }
        }
        if (pkts == 0 && handlep->timeout == 0) {
                /* Block until we see a packet. */
                goto again;
        }
        return pkts;
}
#endif /* HAVE_TPACKET3 */

/*
 *  Attach the given BPF code to the packet capture device.
 */
static int
pcap_setfilter_linux(pcap_t *handle, struct bpf_program *filter)
{
        struct pcap_linux *handlep;
        struct sock_fprog       fcode;
        int                     can_filter_in_kernel;
        int                     err = 0;
        int                     n, offset;

        if (!handle)
                return -1;
        if (!filter) {
                pcap_strlcpy(handle->errbuf, "setfilter: No filter specified",
                        PCAP_ERRBUF_SIZE);
                return -1;
        }

        handlep = handle->priv;

        /* Make our private copy of the filter */

        if (install_bpf_program(handle, filter) < 0)
                /* install_bpf_program() filled in errbuf */
                return -1;

        /*
         * Run user level packet filter by default. Will be overridden if
         * installing a kernel filter succeeds.
         */
        handlep->filter_in_userland = 1;

        /* Install kernel level filter if possible */

#ifdef USHRT_MAX
        if (handle->fcode.bf_len > USHRT_MAX) {
                /*
                 * fcode.len is an unsigned short for current kernel.
                 * I have yet to see BPF-Code with that much
                 * instructions but still it is possible. So for the
                 * sake of correctness I added this check.
                 */
                fprintf(stderr, "Warning: Filter too complex for kernel\n");
                fcode.len = 0;
                fcode.filter = NULL;
                can_filter_in_kernel = 0;
        } else
#endif /* USHRT_MAX */
        {
                /*
                 * Oh joy, the Linux kernel uses struct sock_fprog instead
                 * of struct bpf_program and of course the length field is
                 * of different size. Pointed out by Sebastian
                 *
                 * Oh, and we also need to fix it up so that all "ret"
                 * instructions with non-zero operands have MAXIMUM_SNAPLEN
                 * as the operand if we're not capturing in memory-mapped
                 * mode, and so that, if we're in cooked mode, all memory-
                 * reference instructions use special magic offsets in
                 * references to the link-layer header and assume that the
                 * link-layer payload begins at 0; "fix_program()" will do
                 * that.
                 */
                switch (fix_program(handle, &fcode)) {

                case -1:
                default:
                        /*
                         * Fatal error; just quit.
                         * (The "default" case shouldn't happen; we
                         * return -1 for that reason.)
                         */
                        return -1;

                case 0:
                        /*
                         * The program performed checks that we can't make
                         * work in the kernel.
                         */
                        can_filter_in_kernel = 0;
                        break;

                case 1:
                        /*
                         * We have a filter that'll work in the kernel.
                         */
                        can_filter_in_kernel = 1;
                        break;
                }
        }

        /*
         * NOTE: at this point, we've set both the "len" and "filter"
         * fields of "fcode".  As of the 2.6.32.4 kernel, at least,
         * those are the only members of the "sock_fprog" structure,
         * so we initialize every member of that structure.
         *
         * If there is anything in "fcode" that is not initialized,
         * it is either a field added in a later kernel, or it's
         * padding.
         *
         * If a new field is added, this code needs to be updated
         * to set it correctly.
         *
         * If there are no other fields, then:
         *
         *      if the Linux kernel looks at the padding, it's
         *      buggy;
         *
         *      if the Linux kernel doesn't look at the padding,
         *      then if some tool complains that we're passing
         *      uninitialized data to the kernel, then the tool
         *      is buggy and needs to understand that it's just
         *      padding.
         */
        if (can_filter_in_kernel) {
                if ((err = set_kernel_filter(handle, &fcode)) == 0)
                {
                        /*
                         * Installation succeeded - using kernel filter,
                         * so userland filtering not needed.
                         */
                        handlep->filter_in_userland = 0;
                }
                else if (err == -1)     /* Non-fatal error */
                {
                        /*
                         * Print a warning if we weren't able to install
                         * the filter for a reason other than "this kernel
                         * isn't configured to support socket filters.
                         */
                        if (errno == ENOMEM) {
                                /*
                                 * Either a kernel memory allocation
                                 * failure occurred, or there's too
                                 * much "other/option memory" allocated
                                 * for this socket.  Suggest that they
                                 * increase the "other/option memory"
                                 * limit.
                                 */
                                fprintf(stderr,
                                    "Warning: Couldn't allocate kernel memory for filter: try increasing net.core.optmem_max with sysctl\n");
                        } else if (errno != ENOPROTOOPT && errno != EOPNOTSUPP) {
                                fprintf(stderr,
                                    "Warning: Kernel filter failed: %s\n",
                                        pcap_strerror(errno));
                        }
                }
        }

        /*
         * If we're not using the kernel filter, get rid of any kernel
         * filter that might've been there before, e.g. because the
         * previous filter could work in the kernel, or because some other
         * code attached a filter to the socket by some means other than
         * calling "pcap_setfilter()".  Otherwise, the kernel filter may
         * filter out packets that would pass the new userland filter.
         */
        if (handlep->filter_in_userland) {
                if (reset_kernel_filter(handle) == -1) {
                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                            PCAP_ERRBUF_SIZE, errno,
                            "can't remove kernel filter");
                        err = -2;       /* fatal error */
                }
        }

        /*
         * Free up the copy of the filter that was made by "fix_program()".
         */
        if (fcode.filter != NULL)
                free(fcode.filter);

        if (err == -2)
                /* Fatal error */
                return -1;

        /*
         * If we're filtering in userland, there's nothing to do;
         * the new filter will be used for the next packet.
         */
        if (handlep->filter_in_userland)
                return 0;

        /*
         * We're filtering in the kernel; the packets present in
         * all blocks currently in the ring were already filtered
         * by the old filter, and so will need to be filtered in
         * userland by the new filter.
         *
         * Get an upper bound for the number of such blocks; first,
         * walk the ring backward and count the free blocks.
         */
        offset = handle->offset;
        if (--offset < 0)
                offset = handle->cc - 1;
        for (n=0; n < handle->cc; ++n) {
                if (--offset < 0)
                        offset = handle->cc - 1;
                if (pcap_get_ring_frame_status(handle, offset) != TP_STATUS_KERNEL)
                        break;
        }

        /*
         * If we found free blocks, decrement the count of free
         * blocks by 1, just in case we lost a race with another
         * thread of control that was adding a packet while
         * we were counting and that had run the filter before
         * we changed it.
         *
         * XXX - could there be more than one block added in
         * this fashion?
         *
         * XXX - is there a way to avoid that race, e.g. somehow
         * wait for all packets that passed the old filter to
         * be added to the ring?
         */
        if (n != 0)
                n--;

        /*
         * Set the count of blocks worth of packets to filter
         * in userland to the total number of blocks in the
         * ring minus the number of free blocks we found, and
         * turn on userland filtering.  (The count of blocks
         * worth of packets to filter in userland is guaranteed
         * not to be zero - n, above, couldn't be set to a
         * value > handle->cc, and if it were equal to
         * handle->cc, it wouldn't be zero, and thus would
         * be decremented to handle->cc - 1.)
         */
        handlep->blocks_to_filter_in_userland = handle->cc - n;
        handlep->filter_in_userland = 1;

        return 0;
}

/*
 *  Return the index of the given device name. Fill ebuf and return
 *  -1 on failure.
 */
static int
iface_get_id(int fd, const char *device, char *ebuf)
{
        struct ifreq    ifr;

        memset(&ifr, 0, sizeof(ifr));
        pcap_strlcpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

        if (ioctl(fd, SIOCGIFINDEX, &ifr) == -1) {
                pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                    errno, "SIOCGIFINDEX");
                return -1;
        }

        return ifr.ifr_ifindex;
}

/*
 *  Bind the socket associated with FD to the given device.
 *  Return 0 on success or a PCAP_ERROR_ value on a hard error.
 */
static int
iface_bind(int fd, int ifindex, char *ebuf, int protocol)
{
        struct sockaddr_ll      sll;
        int                     ret, err;
        socklen_t               errlen = sizeof(err);

        memset(&sll, 0, sizeof(sll));
        sll.sll_family          = AF_PACKET;
        sll.sll_ifindex         = ifindex < 0 ? 0 : ifindex;
        sll.sll_protocol        = protocol;

        if (bind(fd, (struct sockaddr *) &sll, sizeof(sll)) == -1) {
                if (errno == ENETDOWN) {
                        /*
                         * Return a "network down" indication, so that
                         * the application can report that rather than
                         * saying we had a mysterious failure and
                         * suggest that they report a problem to the
                         * libpcap developers.
                         */
                        return PCAP_ERROR_IFACE_NOT_UP;
                }
                if (errno == ENODEV) {
                        /*
                         * There's nothing more to say, so clear the
                         * error message.
                         */
                        ebuf[0] = '\0';
                        ret = PCAP_ERROR_NO_SUCH_DEVICE;
                } else {
                        ret = PCAP_ERROR;
                        pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                            errno, "bind");
                }
                return ret;
        }

        /* Any pending errors, e.g., network is down? */

        if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) {
                pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                    errno, "getsockopt (SO_ERROR)");
                return PCAP_ERROR;
        }

        if (err == ENETDOWN) {
                /*
                 * Return a "network down" indication, so that
                 * the application can report that rather than
                 * saying we had a mysterious failure and
                 * suggest that they report a problem to the
                 * libpcap developers.
                 */
                return PCAP_ERROR_IFACE_NOT_UP;
        } else if (err > 0) {
                pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                    err, "bind");
                return PCAP_ERROR;
        }

        return 0;
}

/*
 * Try to enter monitor mode.
 * If we have libnl, try to create a new monitor-mode device and
 * capture on that; otherwise, just say "not supported".
 */
#ifdef HAVE_LIBNL
static int
enter_rfmon_mode(pcap_t *handle, int sock_fd, const char *device)
{
        struct pcap_linux *handlep = handle->priv;
        int ret;
        char phydev_path[PATH_MAX+1];
        struct nl80211_state nlstate;
        struct ifreq ifr;
        u_int n;

        /*
         * Is this a mac80211 device?
         */
        ret = get_mac80211_phydev(handle, device, phydev_path, PATH_MAX);
        if (ret < 0)
                return ret;     /* error */
        if (ret == 0)
                return 0;       /* no error, but not mac80211 device */

        /*
         * XXX - is this already a monN device?
         * If so, we're done.
         */

        /*
         * OK, it's apparently a mac80211 device.
         * Try to find an unused monN device for it.
         */
        ret = nl80211_init(handle, &nlstate, device);
        if (ret != 0)
                return ret;
        for (n = 0; n < UINT_MAX; n++) {
                /*
                 * Try mon{n}.
                 */
                char mondevice[3+10+1]; /* mon{UINT_MAX}\0 */

                snprintf(mondevice, sizeof mondevice, "mon%u", n);
                ret = add_mon_if(handle, sock_fd, &nlstate, device, mondevice);
                if (ret == 1) {
                        /*
                         * Success.  We don't clean up the libnl state
                         * yet, as we'll be using it later.
                         */
                        goto added;
                }
                if (ret < 0) {
                        /*
                         * Hard failure.  Just return ret; handle->errbuf
                         * has already been set.
                         */
                        nl80211_cleanup(&nlstate);
                        return ret;
                }
        }

        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
            "%s: No free monN interfaces", device);
        nl80211_cleanup(&nlstate);
        return PCAP_ERROR;

added:

#if 0
        /*
         * Sleep for .1 seconds.
         */
        delay.tv_sec = 0;
        delay.tv_nsec = 500000000;
        nanosleep(&delay, NULL);
#endif

        /*
         * If we haven't already done so, arrange to have
         * "pcap_close_all()" called when we exit.
         */
        if (!pcap_do_addexit(handle)) {
                /*
                 * "atexit()" failed; don't put the interface
                 * in rfmon mode, just give up.
                 */
                del_mon_if(handle, sock_fd, &nlstate, device,
                    handlep->mondevice);
                nl80211_cleanup(&nlstate);
                return PCAP_ERROR;
        }

        /*
         * Now configure the monitor interface up.
         */
        memset(&ifr, 0, sizeof(ifr));
        pcap_strlcpy(ifr.ifr_name, handlep->mondevice, sizeof(ifr.ifr_name));
        if (ioctl(sock_fd, SIOCGIFFLAGS, &ifr) == -1) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "%s: Can't get flags for %s", device,
                    handlep->mondevice);
                del_mon_if(handle, sock_fd, &nlstate, device,
                    handlep->mondevice);
                nl80211_cleanup(&nlstate);
                return PCAP_ERROR;
        }
        ifr.ifr_flags |= IFF_UP|IFF_RUNNING;
        if (ioctl(sock_fd, SIOCSIFFLAGS, &ifr) == -1) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "%s: Can't set flags for %s", device,
                    handlep->mondevice);
                del_mon_if(handle, sock_fd, &nlstate, device,
                    handlep->mondevice);
                nl80211_cleanup(&nlstate);
                return PCAP_ERROR;
        }

        /*
         * Success.  Clean up the libnl state.
         */
        nl80211_cleanup(&nlstate);

        /*
         * Note that we have to delete the monitor device when we close
         * the handle.
         */
        handlep->must_do_on_close |= MUST_DELETE_MONIF;

        /*
         * Add this to the list of pcaps to close when we exit.
         */
        pcap_add_to_pcaps_to_close(handle);

        return 1;
}
#else /* HAVE_LIBNL */
static int
enter_rfmon_mode(pcap_t *handle _U_, int sock_fd _U_, const char *device _U_)
{
        /*
         * We don't have libnl, so we can't do monitor mode.
         */
        return 0;
}
#endif /* HAVE_LIBNL */

#if defined(HAVE_LINUX_NET_TSTAMP_H) && defined(PACKET_TIMESTAMP)
/*
 * Map SOF_TIMESTAMPING_ values to PCAP_TSTAMP_ values.
 */
static const struct {
        int soft_timestamping_val;
        int pcap_tstamp_val;
} sof_ts_type_map[3] = {
        { SOF_TIMESTAMPING_SOFTWARE, PCAP_TSTAMP_HOST },
        { SOF_TIMESTAMPING_SYS_HARDWARE, PCAP_TSTAMP_ADAPTER },
        { SOF_TIMESTAMPING_RAW_HARDWARE, PCAP_TSTAMP_ADAPTER_UNSYNCED }
};
#define NUM_SOF_TIMESTAMPING_TYPES      (sizeof sof_ts_type_map / sizeof sof_ts_type_map[0])

/*
 * Set the list of time stamping types to include all types.
 */
static int
iface_set_all_ts_types(pcap_t *handle, char *ebuf)
{
        u_int i;

        handle->tstamp_type_list = malloc(NUM_SOF_TIMESTAMPING_TYPES * sizeof(u_int));
        if (handle->tstamp_type_list == NULL) {
                pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                    errno, "malloc");
                return -1;
        }
        for (i = 0; i < NUM_SOF_TIMESTAMPING_TYPES; i++)
                handle->tstamp_type_list[i] = sof_ts_type_map[i].pcap_tstamp_val;
        handle->tstamp_type_count = NUM_SOF_TIMESTAMPING_TYPES;
        return 0;
}

/*
 * Get a list of time stamp types.
 */
#ifdef ETHTOOL_GET_TS_INFO
static int
iface_get_ts_types(const char *device, pcap_t *handle, char *ebuf)
{
        int fd;
        struct ifreq ifr;
        struct ethtool_ts_info info;
        int num_ts_types;
        u_int i, j;

        /*
         * This doesn't apply to the "any" device; you can't say "turn on
         * hardware time stamping for all devices that exist now and arrange
         * that it be turned on for any device that appears in the future",
         * and not all devices even necessarily *support* hardware time
         * stamping, so don't report any time stamp types.
         */
        if (strcmp(device, "any") == 0) {
                handle->tstamp_type_list = NULL;
                return 0;
        }

        /*
         * Create a socket from which to fetch time stamping capabilities.
         */
        fd = get_if_ioctl_socket();
        if (fd < 0) {
                pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                    errno, "socket for SIOCETHTOOL(ETHTOOL_GET_TS_INFO)");
                return -1;
        }

        memset(&ifr, 0, sizeof(ifr));
        pcap_strlcpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
        memset(&info, 0, sizeof(info));
        info.cmd = ETHTOOL_GET_TS_INFO;
        ifr.ifr_data = (caddr_t)&info;
        if (ioctl(fd, SIOCETHTOOL, &ifr) == -1) {
                int save_errno = errno;

                close(fd);
                switch (save_errno) {

                case EOPNOTSUPP:
                case EINVAL:
                        /*
                         * OK, this OS version or driver doesn't support
                         * asking for the time stamping types, so let's
                         * just return all the possible types.
                         */
                        if (iface_set_all_ts_types(handle, ebuf) == -1)
                                return -1;
                        return 0;

                case ENODEV:
                        /*
                         * OK, no such device.
                         * The user will find that out when they try to
                         * activate the device; just return an empty
                         * list of time stamp types.
                         */
                        handle->tstamp_type_list = NULL;
                        return 0;

                default:
                        /*
                         * Other error.
                         */
                        pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                            save_errno,
                            "%s: SIOCETHTOOL(ETHTOOL_GET_TS_INFO) ioctl failed",
                            device);
                        return -1;
                }
        }
        close(fd);

        /*
         * Do we support hardware time stamping of *all* packets?
         */
        if (!(info.rx_filters & (1 << HWTSTAMP_FILTER_ALL))) {
                /*
                 * No, so don't report any time stamp types.
                 *
                 * XXX - some devices either don't report
                 * HWTSTAMP_FILTER_ALL when they do support it, or
                 * report HWTSTAMP_FILTER_ALL but map it to only
                 * time stamping a few PTP packets.  See
                 * http://marc.info/?l=linux-netdev&m=146318183529571&w=2
                 *
                 * Maybe that got fixed later.
                 */
                handle->tstamp_type_list = NULL;
                return 0;
        }

        num_ts_types = 0;
        for (i = 0; i < NUM_SOF_TIMESTAMPING_TYPES; i++) {
                if (info.so_timestamping & sof_ts_type_map[i].soft_timestamping_val)
                        num_ts_types++;
        }
        if (num_ts_types != 0) {
                handle->tstamp_type_list = malloc(num_ts_types * sizeof(u_int));
                if (handle->tstamp_type_list == NULL) {
                        pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                            errno, "malloc");
                        return -1;
                }
                for (i = 0, j = 0; i < NUM_SOF_TIMESTAMPING_TYPES; i++) {
                        if (info.so_timestamping & sof_ts_type_map[i].soft_timestamping_val) {
                                handle->tstamp_type_list[j] = sof_ts_type_map[i].pcap_tstamp_val;
                                j++;
                        }
                }
                handle->tstamp_type_count = num_ts_types;
        } else
                handle->tstamp_type_list = NULL;

        return 0;
}
#else /* ETHTOOL_GET_TS_INFO */
static int
iface_get_ts_types(const char *device, pcap_t *handle, char *ebuf)
{
        /*
         * This doesn't apply to the "any" device; you can't say "turn on
         * hardware time stamping for all devices that exist now and arrange
         * that it be turned on for any device that appears in the future",
         * and not all devices even necessarily *support* hardware time
         * stamping, so don't report any time stamp types.
         */
        if (strcmp(device, "any") == 0) {
                handle->tstamp_type_list = NULL;
                return 0;
        }

        /*
         * We don't have an ioctl to use to ask what's supported,
         * so say we support everything.
         */
        if (iface_set_all_ts_types(handle, ebuf) == -1)
                return -1;
        return 0;
}
#endif /* ETHTOOL_GET_TS_INFO */
#else  /* defined(HAVE_LINUX_NET_TSTAMP_H) && defined(PACKET_TIMESTAMP) */
static int
iface_get_ts_types(const char *device _U_, pcap_t *p _U_, char *ebuf _U_)
{
        /*
         * Nothing to fetch, so it always "succeeds".
         */
        return 0;
}
#endif /* defined(HAVE_LINUX_NET_TSTAMP_H) && defined(PACKET_TIMESTAMP) */

/*
 * Find out if we have any form of fragmentation/reassembly offloading.
 *
 * We do so using SIOCETHTOOL checking for various types of offloading;
 * if SIOCETHTOOL isn't defined, or we don't have any #defines for any
 * of the types of offloading, there's nothing we can do to check, so
 * we just say "no, we don't".
 *
 * We treat EOPNOTSUPP, EINVAL and, if eperm_ok is true, EPERM as
 * indications that the operation isn't supported.  We do EPERM
 * weirdly because the SIOCETHTOOL code in later kernels 1) doesn't
 * support ETHTOOL_GUFO, 2) also doesn't include it in the list
 * of ethtool operations that don't require CAP_NET_ADMIN privileges,
 * and 3) does the "is this permitted" check before doing the "is
 * this even supported" check, so it fails with "this is not permitted"
 * rather than "this is not even supported".  To work around this
 * annoyance, we only treat EPERM as an error for the first feature,
 * and assume that they all do the same permission checks, so if the
 * first one is allowed all the others are allowed if supported.
 */
#if defined(SIOCETHTOOL) && (defined(ETHTOOL_GTSO) || defined(ETHTOOL_GUFO) || defined(ETHTOOL_GGSO) || defined(ETHTOOL_GFLAGS) || defined(ETHTOOL_GGRO))
static int
iface_ethtool_flag_ioctl(pcap_t *handle, int cmd, const char *cmdname,
    int eperm_ok)
{
        struct ifreq    ifr;
        struct ethtool_value eval;

        memset(&ifr, 0, sizeof(ifr));
        pcap_strlcpy(ifr.ifr_name, handle->opt.device, sizeof(ifr.ifr_name));
        eval.cmd = cmd;
        eval.data = 0;
        ifr.ifr_data = (caddr_t)&eval;
        if (ioctl(handle->fd, SIOCETHTOOL, &ifr) == -1) {
                if (errno == EOPNOTSUPP || errno == EINVAL ||
                    (errno == EPERM && eperm_ok)) {
                        /*
                         * OK, let's just return 0, which, in our
                         * case, either means "no, what we're asking
                         * about is not enabled" or "all the flags
                         * are clear (i.e., nothing is enabled)".
                         */
                        return 0;
                }
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "%s: SIOCETHTOOL(%s) ioctl failed",
                    handle->opt.device, cmdname);
                return -1;
        }
        return eval.data;
}

/*
 * XXX - it's annoying that we have to check for offloading at all, but,
 * given that we have to, it's still annoying that we have to check for
 * particular types of offloading, especially that shiny new types of
 * offloading may be added - and, worse, may not be checkable with
 * a particular ETHTOOL_ operation; ETHTOOL_GFEATURES would, in
 * theory, give those to you, but the actual flags being used are
 * opaque (defined in a non-uapi header), and there doesn't seem to
 * be any obvious way to ask the kernel what all the offloading flags
 * are - at best, you can ask for a set of strings(!) to get *names*
 * for various flags.  (That whole mechanism appears to have been
 * designed for the sole purpose of letting ethtool report flags
 * by name and set flags by name, with the names having no semantics
 * ethtool understands.)
 */
static int
iface_get_offload(pcap_t *handle)
{
        int ret;

#ifdef ETHTOOL_GTSO
        ret = iface_ethtool_flag_ioctl(handle, ETHTOOL_GTSO, "ETHTOOL_GTSO", 0);
        if (ret == -1)
                return -1;
        if (ret)
                return 1;       /* TCP segmentation offloading on */
#endif

#ifdef ETHTOOL_GGSO
        /*
         * XXX - will this cause large unsegmented packets to be
         * handed to PF_PACKET sockets on transmission?  If not,
         * this need not be checked.
         */
        ret = iface_ethtool_flag_ioctl(handle, ETHTOOL_GGSO, "ETHTOOL_GGSO", 0);
        if (ret == -1)
                return -1;
        if (ret)
                return 1;       /* generic segmentation offloading on */
#endif

#ifdef ETHTOOL_GFLAGS
        ret = iface_ethtool_flag_ioctl(handle, ETHTOOL_GFLAGS, "ETHTOOL_GFLAGS", 0);
        if (ret == -1)
                return -1;
        if (ret & ETH_FLAG_LRO)
                return 1;       /* large receive offloading on */
#endif

#ifdef ETHTOOL_GGRO
        /*
         * XXX - will this cause large reassembled packets to be
         * handed to PF_PACKET sockets on receipt?  If not,
         * this need not be checked.
         */
        ret = iface_ethtool_flag_ioctl(handle, ETHTOOL_GGRO, "ETHTOOL_GGRO", 0);
        if (ret == -1)
                return -1;
        if (ret)
                return 1;       /* generic (large) receive offloading on */
#endif

#ifdef ETHTOOL_GUFO
        /*
         * Do this one last, as support for it was removed in later
         * kernels, and it fails with EPERM on those kernels rather
         * than with EOPNOTSUPP (see explanation in comment for
         * iface_ethtool_flag_ioctl()).
         */
        ret = iface_ethtool_flag_ioctl(handle, ETHTOOL_GUFO, "ETHTOOL_GUFO", 1);
        if (ret == -1)
                return -1;
        if (ret)
                return 1;       /* UDP fragmentation offloading on */
#endif

        return 0;
}
#else /* SIOCETHTOOL */
static int
iface_get_offload(pcap_t *handle _U_)
{
        /*
         * XXX - do we need to get this information if we don't
         * have the ethtool ioctls?  If so, how do we do that?
         */
        return 0;
}
#endif /* SIOCETHTOOL */

static struct dsa_proto {
        const char *name;
        bpf_u_int32 linktype;
} dsa_protos[] = {
        /*
         * None is special and indicates that the interface does not have
         * any tagging protocol configured, and is therefore a standard
         * Ethernet interface.
         */
        { "none", DLT_EN10MB },
        { "brcm", DLT_DSA_TAG_BRCM },
        { "brcm-prepend", DLT_DSA_TAG_BRCM_PREPEND },
        { "dsa", DLT_DSA_TAG_DSA },
        { "edsa", DLT_DSA_TAG_EDSA },
};

static int
iface_dsa_get_proto_info(const char *device, pcap_t *handle)
{
        char *pathstr;
        unsigned int i;
        /*
         * Make this significantly smaller than PCAP_ERRBUF_SIZE;
         * the tag *shouldn't* have some huge long name, and making
         * it smaller keeps newer versions of GCC from whining that
         * the error message if we don't support the tag could
         * overflow the error message buffer.
         */
        char buf[128];
        ssize_t r;
        int fd;

        fd = asprintf(&pathstr, "/sys/class/net/%s/dsa/tagging", device);
        if (fd < 0) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                                          fd, "asprintf");
                return PCAP_ERROR;
        }

        fd = open(pathstr, O_RDONLY);
        free(pathstr);
        /*
         * This is not fatal, kernel >= 4.20 *might* expose this attribute
         */
        if (fd < 0)
                return 0;

        r = read(fd, buf, sizeof(buf) - 1);
        if (r <= 0) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                                          errno, "read");
                close(fd);
                return PCAP_ERROR;
        }
        close(fd);

        /*
         * Buffer should be LF terminated.
         */
        if (buf[r - 1] == '\n')
                r--;
        buf[r] = '\0';

        for (i = 0; i < sizeof(dsa_protos) / sizeof(dsa_protos[0]); i++) {
                if (strlen(dsa_protos[i].name) == (size_t)r &&
                    strcmp(buf, dsa_protos[i].name) == 0) {
                        handle->linktype = dsa_protos[i].linktype;
                        switch (dsa_protos[i].linktype) {
                        case DLT_EN10MB:
                                return 0;
                        default:
                                return 1;
                        }
                }
        }

        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                      "unsupported DSA tag: %s", buf);

        return PCAP_ERROR;
}

/*
 *  Query the kernel for the MTU of the given interface.
 */
static int
iface_get_mtu(int fd, const char *device, char *ebuf)
{
        struct ifreq    ifr;

        if (!device)
                return BIGGER_THAN_ALL_MTUS;

        memset(&ifr, 0, sizeof(ifr));
        pcap_strlcpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

        if (ioctl(fd, SIOCGIFMTU, &ifr) == -1) {
                pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                    errno, "SIOCGIFMTU");
                return -1;
        }

        return ifr.ifr_mtu;
}

/*
 *  Get the hardware type of the given interface as ARPHRD_xxx constant.
 */
static int
iface_get_arptype(int fd, const char *device, char *ebuf)
{
        struct ifreq    ifr;
        int             ret;

        memset(&ifr, 0, sizeof(ifr));
        pcap_strlcpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

        if (ioctl(fd, SIOCGIFHWADDR, &ifr) == -1) {
                if (errno == ENODEV) {
                        /*
                         * No such device.
                         *
                         * There's nothing more to say, so clear
                         * the error message.
                         */
                        ret = PCAP_ERROR_NO_SUCH_DEVICE;
                        ebuf[0] = '\0';
                } else {
                        ret = PCAP_ERROR;
                        pcap_fmt_errmsg_for_errno(ebuf, PCAP_ERRBUF_SIZE,
                            errno, "SIOCGIFHWADDR");
                }
                return ret;
        }

        return ifr.ifr_hwaddr.sa_family;
}

static int
fix_program(pcap_t *handle, struct sock_fprog *fcode)
{
        struct pcap_linux *handlep = handle->priv;
        size_t prog_size;
        register int i;
        register struct bpf_insn *p;
        struct bpf_insn *f;
        int len;

        /*
         * Make a copy of the filter, and modify that copy if
         * necessary.
         */
        prog_size = sizeof(*handle->fcode.bf_insns) * handle->fcode.bf_len;
        len = handle->fcode.bf_len;
        f = (struct bpf_insn *)malloc(prog_size);
        if (f == NULL) {
                pcap_fmt_errmsg_for_errno(handle->errbuf, PCAP_ERRBUF_SIZE,
                    errno, "malloc");
                return -1;
        }
        memcpy(f, handle->fcode.bf_insns, prog_size);
        fcode->len = len;
        fcode->filter = (struct sock_filter *) f;

        for (i = 0; i < len; ++i) {
                p = &f[i];
                /*
                 * What type of instruction is this?
                 */
                switch (BPF_CLASS(p->code)) {

                case BPF_LD:
                case BPF_LDX:
                        /*
                         * It's a load instruction; is it loading
                         * from the packet?
                         */
                        switch (BPF_MODE(p->code)) {

                        case BPF_ABS:
                        case BPF_IND:
                        case BPF_MSH:
                                /*
                                 * Yes; are we in cooked mode?
                                 */
                                if (handlep->cooked) {
                                        /*
                                         * Yes, so we need to fix this
                                         * instruction.
                                         */
                                        if (fix_offset(handle, p) < 0) {
                                                /*
                                                 * We failed to do so.
                                                 * Return 0, so our caller
                                                 * knows to punt to userland.
                                                 */
                                                return 0;
                                        }
                                }
                                break;
                        }
                        break;
                }
        }
        return 1;       /* we succeeded */
}

static int
fix_offset(pcap_t *handle, struct bpf_insn *p)
{
        /*
         * Existing references to auxiliary data shouldn't be adjusted.
         *
         * Note that SKF_AD_OFF is negative, but p->k is unsigned, so
         * we use >= and cast SKF_AD_OFF to unsigned.
         */
        if (p->k >= (bpf_u_int32)SKF_AD_OFF)
                return 0;
        if (handle->linktype == DLT_LINUX_SLL2) {
                /*
                 * What's the offset?
                 */
                if (p->k >= SLL2_HDR_LEN) {
                        /*
                         * It's within the link-layer payload; that starts
                         * at an offset of 0, as far as the kernel packet
                         * filter is concerned, so subtract the length of
                         * the link-layer header.
                         */
                        p->k -= SLL2_HDR_LEN;
                } else if (p->k == 0) {
                        /*
                         * It's the protocol field; map it to the
                         * special magic kernel offset for that field.
                         */
                        p->k = SKF_AD_OFF + SKF_AD_PROTOCOL;
                } else if (p->k == 4) {
                        /*
                         * It's the ifindex field; map it to the
                         * special magic kernel offset for that field.
                         */
                        p->k = SKF_AD_OFF + SKF_AD_IFINDEX;
                } else if (p->k == 10) {
                        /*
                         * It's the packet type field; map it to the
                         * special magic kernel offset for that field.
                         */
                        p->k = SKF_AD_OFF + SKF_AD_PKTTYPE;
                } else if ((bpf_int32)(p->k) > 0) {
                        /*
                         * It's within the header, but it's not one of
                         * those fields; we can't do that in the kernel,
                         * so punt to userland.
                         */
                        return -1;
                }
        } else {
                /*
                 * What's the offset?
                 */
                if (p->k >= SLL_HDR_LEN) {
                        /*
                         * It's within the link-layer payload; that starts
                         * at an offset of 0, as far as the kernel packet
                         * filter is concerned, so subtract the length of
                         * the link-layer header.
                         */
                        p->k -= SLL_HDR_LEN;
                } else if (p->k == 0) {
                        /*
                         * It's the packet type field; map it to the
                         * special magic kernel offset for that field.
                         */
                        p->k = SKF_AD_OFF + SKF_AD_PKTTYPE;
                } else if (p->k == 14) {
                        /*
                         * It's the protocol field; map it to the
                         * special magic kernel offset for that field.
                         */
                        p->k = SKF_AD_OFF + SKF_AD_PROTOCOL;
                } else if ((bpf_int32)(p->k) > 0) {
                        /*
                         * It's within the header, but it's not one of
                         * those fields; we can't do that in the kernel,
                         * so punt to userland.
                         */
                        return -1;
                }
        }
        return 0;
}

static int
set_kernel_filter(pcap_t *handle, struct sock_fprog *fcode)
{
        int total_filter_on = 0;
        int save_mode;
        int ret;
        int save_errno;

        /*
         * The socket filter code doesn't discard all packets queued
         * up on the socket when the filter is changed; this means
         * that packets that don't match the new filter may show up
         * after the new filter is put onto the socket, if those
         * packets haven't yet been read.
         *
         * This means, for example, that if you do a tcpdump capture
         * with a filter, the first few packets in the capture might
         * be packets that wouldn't have passed the filter.
         *
         * We therefore discard all packets queued up on the socket
         * when setting a kernel filter.  (This isn't an issue for
         * userland filters, as the userland filtering is done after
         * packets are queued up.)
         *
         * To flush those packets, we put the socket in read-only mode,
         * and read packets from the socket until there are no more to
         * read.
         *
         * In order to keep that from being an infinite loop - i.e.,
         * to keep more packets from arriving while we're draining
         * the queue - we put the "total filter", which is a filter
         * that rejects all packets, onto the socket before draining
         * the queue.
         *
         * This code deliberately ignores any errors, so that you may
         * get bogus packets if an error occurs, rather than having
         * the filtering done in userland even if it could have been
         * done in the kernel.
         */
        if (setsockopt(handle->fd, SOL_SOCKET, SO_ATTACH_FILTER,
                       &total_fcode, sizeof(total_fcode)) == 0) {
                char drain[1];

                /*
                 * Note that we've put the total filter onto the socket.
                 */
                total_filter_on = 1;

                /*
                 * Save the socket's current mode, and put it in
                 * non-blocking mode; we drain it by reading packets
                 * until we get an error (which is normally a
                 * "nothing more to be read" error).
                 */
                save_mode = fcntl(handle->fd, F_GETFL, 0);
                if (save_mode == -1) {
                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                            PCAP_ERRBUF_SIZE, errno,
                            "can't get FD flags when changing filter");
                        return -2;
                }
                if (fcntl(handle->fd, F_SETFL, save_mode | O_NONBLOCK) < 0) {
                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                            PCAP_ERRBUF_SIZE, errno,
                            "can't set nonblocking mode when changing filter");
                        return -2;
                }
                while (recv(handle->fd, &drain, sizeof drain, MSG_TRUNC) >= 0)
                        ;
                save_errno = errno;
                if (save_errno != EAGAIN) {
                        /*
                         * Fatal error.
                         *
                         * If we can't restore the mode or reset the
                         * kernel filter, there's nothing we can do.
                         */
                        (void)fcntl(handle->fd, F_SETFL, save_mode);
                        (void)reset_kernel_filter(handle);
                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                            PCAP_ERRBUF_SIZE, save_errno,
                            "recv failed when changing filter");
                        return -2;
                }
                if (fcntl(handle->fd, F_SETFL, save_mode) == -1) {
                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                            PCAP_ERRBUF_SIZE, errno,
                            "can't restore FD flags when changing filter");
                        return -2;
                }
        }

        /*
         * Now attach the new filter.
         */
        ret = setsockopt(handle->fd, SOL_SOCKET, SO_ATTACH_FILTER,
                         fcode, sizeof(*fcode));
        if (ret == -1 && total_filter_on) {
                /*
                 * Well, we couldn't set that filter on the socket,
                 * but we could set the total filter on the socket.
                 *
                 * This could, for example, mean that the filter was
                 * too big to put into the kernel, so we'll have to
                 * filter in userland; in any case, we'll be doing
                 * filtering in userland, so we need to remove the
                 * total filter so we see packets.
                 */
                save_errno = errno;

                /*
                 * If this fails, we're really screwed; we have the
                 * total filter on the socket, and it won't come off.
                 * Report it as a fatal error.
                 */
                if (reset_kernel_filter(handle) == -1) {
                        pcap_fmt_errmsg_for_errno(handle->errbuf,
                            PCAP_ERRBUF_SIZE, errno,
                            "can't remove kernel total filter");
                        return -2;      /* fatal error */
                }

                errno = save_errno;
        }
        return ret;
}

static int
reset_kernel_filter(pcap_t *handle)
{
        int ret;
        /*
         * setsockopt() barfs unless it get a dummy parameter.
         * valgrind whines unless the value is initialized,
         * as it has no idea that setsockopt() ignores its
         * parameter.
         */
        int dummy = 0;

        ret = setsockopt(handle->fd, SOL_SOCKET, SO_DETACH_FILTER,
                                   &dummy, sizeof(dummy));
        /*
         * Ignore ENOENT - it means "we don't have a filter", so there
         * was no filter to remove, and there's still no filter.
         *
         * Also ignore ENONET, as a lot of kernel versions had a
         * typo where ENONET, rather than ENOENT, was returned.
         */
        if (ret == -1 && errno != ENOENT && errno != ENONET)
                return -1;
        return 0;
}

int
pcap_set_protocol_linux(pcap_t *p, int protocol)
{
        if (pcap_check_activated(p))
                return (PCAP_ERROR_ACTIVATED);
        p->opt.protocol = protocol;
        return (0);
}

/*
 * Libpcap version string.
 */
const char *
pcap_lib_version(void)
{
#if defined(HAVE_TPACKET3)
        return (PCAP_VERSION_STRING " (with TPACKET_V3)");
#else
        return (PCAP_VERSION_STRING " (with TPACKET_V2)");
#endif
}