From Paolo Abeni and me: split pcap_open_live() into a "get a pcap_t

[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> 
 *                     
 *                     based on previous works of:
 *                     Simon Patarin <patarin@cs.unibo.it>
 *                     Phil Wood <cpw@lanl.gov>
 */

#ifndef lint
static const char rcsid[] _U_ =
    "@(#) $Header: /tcpdump/master/libpcap/pcap-linux.c,v 1.140 2008-04-04 19:37:45 guy Exp $ (LBL)";
#endif

/*
 * Known problems with 2.0[.x] kernels:
 *
 *   - The loopback device gives every packet twice; on 2.2[.x] kernels,
 *     if we use PF_PACKET, we can filter out the transmitted version
 *     of the packet by using data in the "sockaddr_ll" returned by
 *     "recvfrom()", but, on 2.0[.x] kernels, we have to use
 *     PF_INET/SOCK_PACKET, which means "recvfrom()" supplies a
 *     "sockaddr_pkt" which doesn't give us enough information to let
 *     us do that.
 *
 *   - We have to set the interface's IFF_PROMISC flag ourselves, if
 *     we're to run in promiscuous mode, which means we have to turn
 *     it off ourselves when we're done; the kernel doesn't keep track
 *     of how many sockets are listening promiscuously, which means
 *     it won't get turned off automatically when no sockets are
 *     listening promiscuously.  We catch "pcap_close()" and, for
 *     interfaces we put into promiscuous mode, take them out of
 *     promiscuous mode - which isn't necessarily the right thing to
 *     do, if another socket also requested promiscuous mode between
 *     the time when we opened the socket and the time when we close
 *     the socket.
 *
 *   - MSG_TRUNC isn't supported, so you can't specify that "recvfrom()"
 *     return the amount of data that you could have read, rather than
 *     the amount that was returned, so we can't just allocate a buffer
 *     whose size is the snapshot length and pass the snapshot length
 *     as the byte count, and also pass MSG_TRUNC, so that the return
 *     value tells us how long the packet was on the wire.
 *
 *     This means that, if we want to get the actual size of the packet,
 *     so we can return it in the "len" field of the packet header,
 *     we have to read the entire packet, not just the part that fits
 *     within the snapshot length, and thus waste CPU time copying data
 *     from the kernel that our caller won't see.
 *
 *     We have to get the actual size, and supply it in "len", because
 *     otherwise, the IP dissector in tcpdump, for example, will complain
 *     about "truncated-ip", as the packet will appear to have been
 *     shorter, on the wire, than the IP header said it should have been.
 */


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/utsname.h>
#include <sys/mman.h>
#include <net/if.h>
#include <netinet/in.h>
#include <linux/if_ether.h>
#include <net/if_arp.h>
#include <poll.h>

/*
 * Got Wireless Extensions?
 */
#ifdef HAVE_LINUX_WIRELESS_H
#include <linux/wireless.h>
#endif

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

#ifdef HAVE_DAG_API
#include "pcap-dag.h"
#endif /* HAVE_DAG_API */

#ifdef HAVE_SEPTEL_API
#include "pcap-septel.h"
#endif /* HAVE_SEPTEL_API */

#ifdef PCAP_SUPPORT_USB
#include "pcap-usb-linux.h"
#endif

#ifdef PCAP_SUPPORT_BT
#include "pcap-bt-linux.h"
#endif

/*
 * If PF_PACKET is defined, we can use {SOCK_RAW,SOCK_DGRAM}/PF_PACKET
 * sockets rather than SOCK_PACKET sockets.
 *
 * To use them, we include <linux/if_packet.h> rather than
 * <netpacket/packet.h>; we do so because
 *
 *      some Linux distributions (e.g., Slackware 4.0) have 2.2 or
 *      later kernels and libc5, and don't provide a <netpacket/packet.h>
 *      file;
 *
 *      not all versions of glibc2 have a <netpacket/packet.h> file
 *      that defines stuff needed for some of the 2.4-or-later-kernel
 *      features, so if the system has a 2.4 or later kernel, we
 *      still can't use those features.
 *
 * We're already including a number of other <linux/XXX.h> headers, and
 * this code is Linux-specific (no other OS has PF_PACKET sockets as
 * a raw packet capture mechanism), so it's not as if you gain any
 * useful portability by using <netpacket/packet.h>
 *
 * XXX - should we just include <linux/if_packet.h> even if PF_PACKET
 * isn't defined?  It only defines one data structure in 2.0.x, so
 * it shouldn't cause any problems.
 */
#ifdef PF_PACKET
# include <linux/if_packet.h>

 /*
  * On at least some Linux distributions (for example, Red Hat 5.2),
  * there's no <netpacket/packet.h> file, but PF_PACKET is defined if
  * you include <sys/socket.h>, but <linux/if_packet.h> doesn't define
  * any of the PF_PACKET stuff such as "struct sockaddr_ll" or any of
  * the PACKET_xxx stuff.
  *
  * So we check whether PACKET_HOST is defined, and assume that we have
  * PF_PACKET sockets only if it is defined.
  */
# ifdef PACKET_HOST
#  define HAVE_PF_PACKET_SOCKETS
# endif /* PACKET_HOST */


 /* 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 TPACKET_HDRLEN
#  define HAVE_PACKET_RING
# endif /* TPACKET_HDRLEN */
#endif /* PF_PACKET */

#ifdef SO_ATTACH_FILTER
#include <linux/types.h>
#include <linux/filter.h>
#endif

#ifndef HAVE_SOCKLEN_T
typedef int             socklen_t;
#endif

#ifndef MSG_TRUNC
/*
 * This is being compiled on a system that lacks MSG_TRUNC; define it
 * with the value it has in the 2.2 and later kernels, so that, on
 * those kernels, when we pass it in the flags argument to "recvfrom()"
 * we're passing the right value and thus get the MSG_TRUNC behavior
 * we want.  (We don't get that behavior on 2.0[.x] kernels, because
 * they didn't support MSG_TRUNC.)
 */
#define MSG_TRUNC       0x20
#endif

#ifndef SOL_PACKET
/*
 * This is being compiled on a system that lacks SOL_PACKET; define it
 * with the value it has in the 2.2 and later kernels, so that we can
 * set promiscuous mode in the good modern way rather than the old
 * 2.0-kernel crappy way.
 */
#define SOL_PACKET      263
#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)

/*
 * Prototypes for internal functions and methods.
 */
static void map_arphrd_to_dlt(pcap_t *, int, int);
#ifdef HAVE_PF_PACKET_SOCKETS
static short int map_packet_type_to_sll_type(short int);
#endif
static int pcap_activate_linux(pcap_t *);
static int activate_old(pcap_t *);
static int activate_new(pcap_t *);
static int activate_mmap(pcap_t *);
static int pcap_can_set_rfmon_linux(pcap_t *);
static int pcap_read_linux(pcap_t *, int, pcap_handler, u_char *);
static int pcap_read_packet(pcap_t *, pcap_handler, u_char *);
static int pcap_inject_linux(pcap_t *, const void *, size_t);
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 void pcap_close_linux(pcap_t *);

#ifdef HAVE_PACKET_RING
#define RING_GET_FRAME(h) (((struct tpacket_hdr**)h->buffer)[h->offset])

static void destroy_ring(pcap_t *handle);
static int create_ring(pcap_t *handle);
static void pcap_close_linux_mmap(pcap_t *);
static int pcap_read_linux_mmap(pcap_t *, int, pcap_handler , u_char *);
static int pcap_setfilter_linux_mmap(pcap_t *, struct bpf_program *);
static int pcap_setnonblock_mmap(pcap_t *p, int nonblock, char *errbuf);
static int pcap_getnonblock_mmap(pcap_t *p, char *errbuf);
#endif

/*
 * Wrap some ioctl calls
 */
#ifdef HAVE_PF_PACKET_SOCKETS
static int      iface_get_id(int fd, const char *device, char *ebuf);
#endif
static int      iface_get_mtu(int fd, const char *device, char *ebuf);
static int      iface_get_arptype(int fd, const char *device, char *ebuf);
#ifdef HAVE_PF_PACKET_SOCKETS
static int      iface_bind(int fd, int ifindex, char *ebuf);
static int      has_wext(int sock_fd, const char *device);
static int      enter_rfmon_mode_wext(pcap_t *handle, int sock_fd,
    const char *device);
#endif
static int      iface_bind_old(int fd, const char *device, char *ebuf);

#ifdef SO_ATTACH_FILTER
static int      fix_program(pcap_t *handle, struct sock_fprog *fcode);
static int      fix_offset(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 };
#endif

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

#ifdef HAVE_DAG_API
        if (strstr(device, "dag")) {
                return dag_create(device, ebuf);
        }
#endif /* HAVE_DAG_API */

#ifdef HAVE_SEPTEL_API
        if (strstr(device, "septel")) {
                return septel_create(device, ebuf);
        }
#endif /* HAVE_SEPTEL_API */

#ifdef PCAP_SUPPORT_BT
        if (strstr(device, "bluetooth")) {
                return bt_create(device, ebuf);
        }
#endif

#ifdef PCAP_SUPPORT_USB
        if (strstr(device, "usb")) {
                return usb_create(device, ebuf);
        }
#endif

        handle = pcap_create_common(device, ebuf);
        if (handle == NULL)
                return NULL;

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

static int
pcap_can_set_rfmon_linux(pcap_t *p)
{
#ifdef IW_MODE_MONITOR
        int sock_fd;
        struct iwreq ireq;
#endif

        if (p->opt.source == NULL) {
                /*
                 * This is equivalent to the "any" device, and we don't
                 * support monitor mode on it.
                 */
                return 0;
        }

#ifdef IW_MODE_MONITOR
        /*
         * Bleah.  There doesn't appear to be an ioctl to use to ask
         * whether a device supports monitor mode; we'll just do
         * SIOCGIWMODE and, if it succeeds, assume the device supports
         * monitor mode.
         *
         * Open a socket on which to attempt to get the mode.
         * (We assume that if we have Wireless Extensions support
         * we also have PF_PACKET support.)
         */
        sock_fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
        if (sock_fd == -1) {
                (void)snprintf(p->errbuf, PCAP_ERRBUF_SIZE,
                    "socket: %s", pcap_strerror(errno));
                return PCAP_ERROR;
        }

        /*
         * Attempt to get the current mode.
         */
        strncpy(ireq.ifr_ifrn.ifrn_name, p->opt.source,
            sizeof ireq.ifr_ifrn.ifrn_name);
        ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
        if (ioctl(sock_fd, SIOCGIWMODE, &ireq) != -1) {
                /*
                 * Well, we got the mode; assume we can set it.
                 */
                close(sock_fd);
                return 1;
        }
        if (errno == ENODEV) {
                /* The device doesn't even exist. */
                close(sock_fd);
                return PCAP_ERROR_NO_SUCH_DEVICE;
        }
        close(sock_fd);
#endif
        return 0;
}

/*
 * With older kernels promiscuous 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 promiscuous 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 promiscuous mode.
 *
 * Even with newer kernels, we have the same issue with rfmon mode.
 */

static void     pcap_close_linux( pcap_t *handle )
{
        struct ifreq    ifr;
#ifdef IW_MODE_MONITOR
        struct iwreq ireq;
#endif

        if (handle->md.must_clear != 0) {
                /*
                 * There's something we have to do when closing this
                 * pcap_t.
                 */
                if (handle->md.must_clear & MUST_CLEAR_PROMISC) {
                        /*
                         * We put the interface into promiscuous mode;
                         * take it out of promiscuous mode.
                         *
                         * XXX - if somebody else wants it in promiscuous
                         * mode, this code cannot know that, so it'll take
                         * it out of promiscuous mode.  That's not fixable
                         * in 2.0[.x] kernels.
                         */
                        memset(&ifr, 0, sizeof(ifr));
                        strncpy(ifr.ifr_name, handle->md.device,
                            sizeof(ifr.ifr_name));
                        if (ioctl(handle->fd, SIOCGIFFLAGS, &ifr) == -1) {
                                fprintf(stderr,
                                    "Can't restore interface flags (SIOCGIFFLAGS failed: %s).\n"
                                    "Please adjust manually.\n"
                                    "Hint: This can't happen with Linux >= 2.2.0.\n",
                                    strerror(errno));
                        } else {
                                if (ifr.ifr_flags & IFF_PROMISC) {
                                        /*
                                         * Promiscuous mode is currently on;
                                         * turn it off.
                                         */
                                        ifr.ifr_flags &= ~IFF_PROMISC;
                                        if (ioctl(handle->fd, SIOCSIFFLAGS,
                                            &ifr) == -1) {
                                                fprintf(stderr,
                                                    "Can't restore interface flags (SIOCSIFFLAGS failed: %s).\n"
                                                    "Please adjust manually.\n"
                                                    "Hint: This can't happen with Linux >= 2.2.0.\n",
                                                    strerror(errno));
                                        }
                                }
                        }
                }

#ifdef IW_MODE_MONITOR
                if (handle->md.must_clear & MUST_CLEAR_RFMON) {
                        /*
                         * We put the interface into rfmon mode;
                         * take it out of rfmon mode.
                         *
                         * XXX - if somebody else wants it in rfmon
                         * mode, this code cannot know that, so it'll take
                         * it out of rfmon mode.
                         */
                        strncpy(ireq.ifr_ifrn.ifrn_name, handle->md.device,
                            sizeof ireq.ifr_ifrn.ifrn_name);
                        ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1]
                            = 0;
                        ireq.u.mode = handle->md.oldmode;
                        if (ioctl(handle->fd, SIOCSIWMODE, &ireq) == -1) {
                                /*
                                 * Scientist, you've failed.
                                 */
                                fprintf(stderr,
                                    "Can't restore interface wireless mode (SIOCSIWMODE failed: %s).\n"
                                    "Please adjust manually.\n",
                                    strerror(errno));
                        }
                }
#endif

                /*
                 * 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->md.device != NULL) {
                free(handle->md.device);
                handle->md.device = NULL;
        }
        pcap_close_common(handle);
}

/*
 *  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 promiscous 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)
{
        const char      *device;
        int             err;
        int             activate_ok = 0;

        device = handle->opt.source;

        handle->inject_op = pcap_inject_linux;
        handle->setfilter_op = pcap_setfilter_linux;
        handle->setdirection_op = pcap_setdirection_linux;
        handle->set_datalink_op = NULL; /* can't change data link type */
        handle->getnonblock_op = pcap_getnonblock_fd;
        handle->setnonblock_op = pcap_setnonblock_fd;
        handle->close_op = pcap_close_linux;
        handle->read_op = pcap_read_linux;
        handle->stats_op = pcap_stats_linux;

        /*
         * NULL and "any" are special devices which give us the hint to
         * monitor all devices.
         */
        if (!device || strcmp(device, "any") == 0) {
                device                  = NULL;
                handle->md.device       = strdup("any");
                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");
                }

        } else
                handle->md.device       = strdup(device);

        if (handle->md.device == NULL) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, "strdup: %s",
                         pcap_strerror(errno) );
                return PCAP_ERROR;
        }

        /*
         * Current Linux kernels use the protocol family PF_PACKET to
         * allow direct access to all packets on the network while
         * older kernels had a special socket type SOCK_PACKET to
         * implement this feature.
         * While this old implementation is kind of obsolete we need
         * to be compatible with older kernels for a while so we are
         * trying both methods with the newer method preferred.
         */

        if ((err = activate_new(handle)) == 1) {
                activate_ok = 1;
                /*
                 * Try to use memory-mapped access.
                 */
                if (activate_mmap(handle) == 1)
                        return 0;       /* we succeeded; nothing more to do */
        }
        else if (err == 0) {
                /* Non-fatal error; try old way */
                if ((err = activate_old(handle)) == 1)
                        activate_ok = 1;
        }
        if (!activate_ok) {
                /*
                 * Both methods to open the packet socket failed. Tidy
                 * up and report our failure (ebuf is expected to be
                 * set by the functions above).
                 */

                if (handle->md.device != NULL) {
                        free(handle->md.device);
                        handle->md.device = NULL;
                }
                return err;
        }

        /* Allocate the buffer */

        handle->buffer   = malloc(handle->bufsize + handle->offset);
        if (!handle->buffer) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                         "malloc: %s", pcap_strerror(errno));
                return PCAP_ERROR;
        }

        /*
         * "handle->fd" is a socket, so "select()" and "poll()"
         * should work on it.
         */
        handle->selectable_fd = handle->fd;

        return 0;
}

/*
 *  Read at most max_packets from the capture stream and call the callback
 *  for each of them. Returns the number of packets handled or -1 if an
 *  error occured.
 */
static int
pcap_read_linux(pcap_t *handle, int max_packets, pcap_handler callback, u_char *user)
{
        /*
         * Currently, on Linux only one packet is delivered per read,
         * so we don't loop.
         */
        return pcap_read_packet(handle, callback, user);
}

/*
 *  Read a packet from the socket calling the handler provided by
 *  the user. Returns the number of packets received or -1 if an
 *  error occured.
 */
static int
pcap_read_packet(pcap_t *handle, pcap_handler callback, u_char *userdata)
{
        u_char                  *bp;
        int                     offset;
#ifdef HAVE_PF_PACKET_SOCKETS
        struct sockaddr_ll      from;
        struct sll_header       *hdrp;
#else
        struct sockaddr         from;
#endif
        socklen_t               fromlen;
        int                     packet_len, caplen;
        struct pcap_pkthdr      pcap_header;

#ifdef HAVE_PF_PACKET_SOCKETS
        /*
         * If this is a cooked device, leave extra room for a
         * fake packet header.
         */
        if (handle->md.cooked)
                offset = SLL_HDR_LEN;
        else
                offset = 0;
#else
        /*
         * This system doesn't have PF_PACKET sockets, so it doesn't
         * support cooked devices.
         */
        offset = 0;
#endif

        /* Receive a single packet from the kernel */

        bp = handle->buffer + handle->offset;
        do {
                /*
                 * Has "pcap_breakloop()" been called?
                 */
                if (handle->break_loop) {
                        /*
                         * Yes - clear the flag that indicates that it
                         * has, and return -2 as an indication that we
                         * were told to break out of the loop.
                         */
                        handle->break_loop = 0;
                        return -2;
                }
                fromlen = sizeof(from);
                packet_len = recvfrom(
                        handle->fd, bp + offset,
                        handle->bufsize - offset, MSG_TRUNC,
                        (struct sockaddr *) &from, &fromlen);
        } while (packet_len == -1 && errno == EINTR);

        /* Check if an error occured */

        if (packet_len == -1) {
                if (errno == EAGAIN)
                        return 0;       /* no packet there */
                else {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                 "recvfrom: %s", pcap_strerror(errno));
                        return -1;
                }
        }

#ifdef HAVE_PF_PACKET_SOCKETS
        if (!handle->md.sock_packet) {
                /*
                 * Unfortunately, there is a window between socket() and
                 * bind() where the kernel may queue packets from any
                 * interface.  If we're bound to a particular interface,
                 * discard packets not from that interface.
                 *
                 * (If socket filters are supported, we could do the
                 * same thing we do when changing the filter; however,
                 * that won't handle packet sockets without socket
                 * filter support, and it's a bit more complicated.
                 * It would save some instructions per packet, however.)
                 */
                if (handle->md.ifindex != -1 &&
                    from.sll_ifindex != handle->md.ifindex)
                        return 0;

                /*
                 * Do checks based on packet direction.
                 * We can only do this if we're using PF_PACKET; the
                 * address returned for SOCK_PACKET is a "sockaddr_pkt"
                 * which lacks the relevant packet type information.
                 */
                if (from.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 (from.sll_ifindex == handle->md.lo_ifindex)
                                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;
                }
        }
#endif

#ifdef HAVE_PF_PACKET_SOCKETS
        /*
         * If this is a cooked device, fill in the fake packet header.
         */
        if (handle->md.cooked) {
                /*
                 * Add the length of the fake header to the length
                 * of packet data we read.
                 */
                packet_len += SLL_HDR_LEN;

                hdrp = (struct sll_header *)bp;
                hdrp->sll_pkttype = map_packet_type_to_sll_type(from.sll_pkttype);
                hdrp->sll_hatype = htons(from.sll_hatype);
                hdrp->sll_halen = htons(from.sll_halen);
                memcpy(hdrp->sll_addr, from.sll_addr,
                    (from.sll_halen > SLL_ADDRLEN) ?
                      SLL_ADDRLEN :
                      from.sll_halen);
                hdrp->sll_protocol = from.sll_protocol;
        }
#endif

        /*
         * XXX: According to the kernel source we should get the real
         * packet len if calling recvfrom with MSG_TRUNC set. It does
         * not seem to work here :(, but it is supported by this code
         * anyway.
         * To be honest the code RELIES on that feature so this is really
         * broken with 2.2.x kernels.
         * I spend a day to figure out what's going on and I found out
         * that the following is happening:
         *
         * The packet comes from a random interface and the packet_rcv
         * hook is called with a clone of the packet. That code inserts
         * the packet into the receive queue of the packet socket.
         * If a filter is attached to that socket that filter is run
         * first - and there lies the problem. The default filter always
         * cuts the packet at the snaplen:
         *
         * # tcpdump -d
         * (000) ret      #68
         *
         * So the packet filter cuts down the packet. The recvfrom call
         * says "hey, it's only 68 bytes, it fits into the buffer" with
         * the result that we don't get the real packet length. This
         * is valid at least until kernel 2.2.17pre6.
         *
         * We currently handle this by making a copy of the filter
         * program, fixing all "ret" instructions with non-zero
         * operands to have an operand of 65535 so that the filter
         * doesn't truncate the packet, and supplying that modified
         * filter to the kernel.
         */

        caplen = packet_len;
        if (caplen > handle->snapshot)
                caplen = handle->snapshot;

        /* Run the packet filter if not using kernel filter */
        if (!handle->md.use_bpf && handle->fcode.bf_insns) {
                if (bpf_filter(handle->fcode.bf_insns, bp,
                                packet_len, caplen) == 0)
                {
                        /* rejected by filter */
                        return 0;
                }
        }

        /* Fill in our own header data */

        if (ioctl(handle->fd, SIOCGSTAMP, &pcap_header.ts) == -1) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                         "SIOCGSTAMP: %s", pcap_strerror(errno));
                return -1;
        }
        pcap_header.caplen      = caplen;
        pcap_header.len         = packet_len;

        /*
         * Count the packet.
         *
         * Arguably, we should count them before we check the filter,
         * as on many other platforms "ps_recv" counts packets
         * handed to the filter rather than packets that passed
         * the filter, but if filtering is done in the kernel, we
         * can't get a count of packets that passed the filter,
         * and that would mean the meaning of "ps_recv" wouldn't
         * be the same on all Linux systems.
         *
         * XXX - it's not the same on all systems in any case;
         * ideally, we should have a "get the statistics" call
         * that supplies more counts and indicates which of them
         * it supplies, so that we supply a count of packets
         * handed to the filter only on platforms where that
         * information is available.
         *
         * We count them here even if we can get the packet count
         * from the kernel, as we can only determine at run time
         * whether we'll be able to get it from the kernel (if
         * HAVE_TPACKET_STATS isn't defined, we can't get it from
         * the kernel, but if it is defined, the library might
         * have been built with a 2.4 or later kernel, but we
         * might be running on a 2.2[.x] kernel without Alexey
         * Kuznetzov's turbopacket patches, and thus the kernel
         * might not be able to supply those statistics).  We
         * could, I guess, try, when opening the socket, to get
         * the statistics, and if we can not increment the count
         * here, but it's not clear that always incrementing
         * the count is more expensive than always testing a flag
         * in memory.
         *
         * We keep the count in "md.packets_read", and use that for
         * "ps_recv" if we can't get the statistics from the kernel.
         * We do that because, if we *can* get the statistics from
         * the kernel, we use "md.stat.ps_recv" and "md.stat.ps_drop"
         * as running counts, as reading the statistics from the
         * kernel resets the kernel statistics, and if we directly
         * increment "md.stat.ps_recv" here, that means it will
         * count packets *twice* on systems where we can get kernel
         * statistics - once here, and once in pcap_stats_linux().
         */
        handle->md.packets_read++;

        /* Call the user supplied callback function */
        callback(userdata, &pcap_header, bp);

        return 1;
}

static int
pcap_inject_linux(pcap_t *handle, const void *buf, size_t size)
{
        int ret;

#ifdef HAVE_PF_PACKET_SOCKETS
        if (!handle->md.sock_packet) {
                /* PF_PACKET socket */
                if (handle->md.ifindex == -1) {
                        /*
                         * We don't support sending on the "any" device.
                         */
                        strlcpy(handle->errbuf,
                            "Sending packets isn't supported on the \"any\" device",
                            PCAP_ERRBUF_SIZE);
                        return (-1);
                }

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

        ret = send(handle->fd, buf, size, 0);
        if (ret == -1) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, "send: %s",
                    pcap_strerror(errno));
                return (-1);
        }
        return (ret);
}                           

/*
 *  Get the statistics for the given packet capture handle.
 *  Reports the number of dropped packets iff the kernel supports
 *  the PACKET_STATISTICS "getsockopt()" argument (2.4 and later
 *  kernels, and 2.2[.x] kernels with Alexey Kuznetzov's turbopacket
 *  patches); otherwise, that information isn't available, and we lie
 *  and report 0 as the count of dropped packets.
 */
static int
pcap_stats_linux(pcap_t *handle, struct pcap_stat *stats)
{
#ifdef HAVE_TPACKET_STATS
        struct tpacket_stats kstats;
        socklen_t len = sizeof (struct tpacket_stats);
#endif

#ifdef HAVE_TPACKET_STATS
        /*
         * Try to get the packet counts from the kernel.
         */
        if (getsockopt(handle->fd, SOL_PACKET, PACKET_STATISTICS,
                        &kstats, &len) > -1) {
                /*
                 * On systems where the PACKET_STATISTICS "getsockopt()"
                 * argument is supported on PF_PACKET sockets:
                 *
                 *      "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.
                 *
                 *      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 the
                 * 2.4.9 kernel, "tp_packets" is incremented for every
                 * packet that passes the packet filter *and* is
                 * successfully queued on the socket; "tp_drops" is
                 * incremented for every packet dropped because there's
                 * not enough free space in the socket 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.
                 */
                handle->md.stat.ps_recv += kstats.tp_packets;
                handle->md.stat.ps_drop += kstats.tp_drops;
                *stats = handle->md.stat;
                return 0;
        }
        else
        {
                /*
                 * If the error was EOPNOTSUPP, fall through, so that
                 * if you build the library on a system with
                 * "struct tpacket_stats" and run it on a system
                 * that doesn't, it works as it does if the library
                 * is built on a system without "struct tpacket_stats".
                 */
                if (errno != EOPNOTSUPP) {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                            "pcap_stats: %s", pcap_strerror(errno));
                        return -1;
                }
        }
#endif
        /*
         * On systems where the PACKET_STATISTICS "getsockopt()" argument
         * is not supported on PF_PACKET sockets:
         *
         *      "ps_recv" counts only packets that *passed* the filter,
         *      not packets that didn't pass the filter.  It does not
         *      count packets dropped because we ran out of buffer
         *      space.
         *
         *      "ps_drop" is not supported.
         *
         *      "ps_recv" doesn't include packets not yet read from
         *      the kernel by libpcap.
         *
         * We maintain the count of packets processed by libpcap in
         * "md.packets_read", for reasons described in the comment
         * at the end of pcap_read_packet().  We have no idea how many
         * packets were dropped.
         */
        stats->ps_recv = handle->md.packets_read;
        stats->ps_drop = 0;
        return 0;
}

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

int
pcap_platform_finddevs(pcap_if_t **alldevsp, char *errbuf)
{
        if (pcap_add_if(alldevsp, "any", 0, any_descr, errbuf) < 0)
                return (-1);

#ifdef HAVE_DAG_API
        if (dag_platform_finddevs(alldevsp, errbuf) < 0)
                return (-1);
#endif /* HAVE_DAG_API */

#ifdef HAVE_SEPTEL_API
        if (septel_platform_finddevs(alldevsp, errbuf) < 0)
                return (-1);
#endif /* HAVE_SEPTEL_API */

#ifdef PCAP_SUPPORT_BT
        if (bt_platform_finddevs(alldevsp, errbuf) < 0)
                return (-1);
#endif

#ifdef PCAP_SUPPORT_USB
        if (usb_platform_finddevs(alldevsp, errbuf) < 0)
                return (-1);
#endif

        return (0);
}

/*
 *  Attach the given BPF code to the packet capture device.
 */
static int
pcap_setfilter_linux(pcap_t *handle, struct bpf_program *filter)
{
#ifdef SO_ATTACH_FILTER
        struct sock_fprog       fcode;
        int                     can_filter_in_kernel;
        int                     err = 0;
#endif

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

        /* 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 overriden if
         * installing a kernel filter succeeds.
         */
        handle->md.use_bpf = 0;

        /* Install kernel level filter if possible */

#ifdef SO_ATTACH_FILTER
#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 65535 as the
                 * operand, 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;
                }
        }

        if (can_filter_in_kernel) {
                if ((err = set_kernel_filter(handle, &fcode)) == 0)
                {
                        /* Installation succeded - using kernel filter. */
                        handle->md.use_bpf = 1;
                }
                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 != 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 (!handle->md.use_bpf)
                reset_kernel_filter(handle);

        /*
         * 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;
#endif /* SO_ATTACH_FILTER */

        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)
{
#ifdef HAVE_PF_PACKET_SOCKETS
        if (!handle->md.sock_packet) {
                handle->direction = d;
                return 0;
        }
#endif
        /*
         * We're not using PF_PACKET sockets, so we can't determine
         * the direction of the packet.
         */
        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
            "Setting direction is not supported on SOCK_PACKET sockets");
        return -1;
}


#ifdef HAVE_PF_PACKET_SOCKETS
/*
 * Map the PACKET_ value to a LINUX_SLL_ value; we
 * want the same numerical value to be used in
 * the link-layer header even if the numerical values
 * for the PACKET_ #defines change, so that programs
 * that look at the packet type field will always be
 * able to handle DLT_LINUX_SLL captures.
 */
static short int
map_packet_type_to_sll_type(short int sll_pkttype)
{
        switch (sll_pkttype) {

        case PACKET_HOST:
                return htons(LINUX_SLL_HOST);

        case PACKET_BROADCAST:
                return htons(LINUX_SLL_BROADCAST);

        case PACKET_MULTICAST:
                return  htons(LINUX_SLL_MULTICAST);

        case PACKET_OTHERHOST:
                return htons(LINUX_SLL_OTHERHOST);

        case PACKET_OUTGOING:
                return htons(LINUX_SLL_OUTGOING);

        default:
                return -1;
        }
}
#endif

/*
 *  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, int cooked_ok)
{
        switch (arptype) {

        case ARPHRD_ETHER:
                /*
                 * This is (presumably) a real Ethernet capture; 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 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 "activate_new()",
                 * as we fall back on cooked mode there; are there any
                 * others?
                 */
                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_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;

#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:
                /*
                 * We assume that those all mean RFC 2625 IP-over-
                 * Fibre Channel, with the RFC 2625 header at
                 * the beginning of the packet.
                 */
                handle->linktype = DLT_IP_OVER_FC;
                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 */
                //handle->md.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;

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

/* ===== Functions to interface to the newer kernels ================== */

/*
 * Try to open a packet socket using the new kernel PF_PACKET interface.
 * Returns 1 on success, 0 on an error that means the new interface isn't
 * present (so the old SOCK_PACKET interface should be tried), and a
 * PCAP_ERROR_ value on an error that means that the old mechanism won't
 * work either (so it shouldn't be tried).
 */
static int
activate_new(pcap_t *handle)
{
#ifdef HAVE_PF_PACKET_SOCKETS
        int                     sock_fd = -1, arptype;
        int                     err = 0;
        struct packet_mreq      mr;
        const char* device = handle->opt.source;

        /*
         * Open a socket with protocol family packet. If a device is
         * given we try to open it in raw mode otherwise we use
         * the cooked interface.
         */
        sock_fd = device ?
                socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))
              : socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL));

        if (sock_fd == -1) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, "socket: %s",
                         pcap_strerror(errno) );
                return 0;       /* try old mechanism */
        }

        /* It seems the kernel supports the new interface. */
        handle->md.sock_packet = 0;

        /*
         * Get the interface index of the loopback device.
         * If the attempt fails, don't fail, just set the
         * "md.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()".
         */
        handle->md.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 (device) {
                /* Assume for now we don't need cooked mode. */
                handle->md.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_wext(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;
                        }
                }
                arptype = iface_get_arptype(sock_fd, device, handle->errbuf);
                if (arptype < 0) {
                        close(sock_fd);
                        return arptype;
                }
                map_arphrd_to_dlt(handle, arptype, 1);
                if (handle->linktype == -1 ||
                    handle->linktype == DLT_LINUX_SLL ||
                    handle->linktype == DLT_LINUX_IRDA ||
                    handle->linktype == DLT_LINUX_LAPD ||
                    (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 (close(sock_fd) == -1) {
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                         "close: %s", pcap_strerror(errno));
                                return PCAP_ERROR;
                        }
                        sock_fd = socket(PF_PACKET, SOCK_DGRAM,
                            htons(ETH_P_ALL));
                        if (sock_fd == -1) {
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                    "socket: %s", pcap_strerror(errno));
                                return PCAP_ERROR;
                        }
                        handle->md.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;
                        }

                        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_LINUX_SLL;
                }

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

                if ((err = iface_bind(sock_fd, handle->md.ifindex,
                    handle->errbuf)) < 0) {
                        close(sock_fd);
                        if (err == -2)
                                return PCAP_ERROR;
                        else
                                return 0;       /* try old mechanism */
                }
        } else {
                /*
                 * This is cooked mode.
                 */
                handle->md.cooked = 1;
                handle->linktype = DLT_LINUX_SLL;

                /*
                 * We're not bound to a device.
                 * XXX - true?  Or true only if we're using
                 * the "any" 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.
                 */
                handle->md.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.
         */

        if (device && handle->opt.promisc) {
                memset(&mr, 0, sizeof(mr));
                mr.mr_ifindex = handle->md.ifindex;
                mr.mr_type    = PACKET_MR_PROMISC;
                if (setsockopt(sock_fd, SOL_PACKET, PACKET_ADD_MEMBERSHIP,
                    &mr, sizeof(mr)) == -1) {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                "setsockopt: %s", pcap_strerror(errno));
                        close(sock_fd);
                        return PCAP_ERROR;
                }
        }

        /*
         * This is a 2.2[.x] or later kernel (we know that
         * because we're not using a SOCK_PACKET socket -
         * PF_PACKET is supported only in 2.2 and later
         * kernels).
         *
         * We can safely pass "recvfrom()" a byte count
         * based on the snapshot length.
         *
         * 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()").
         */
        if (handle->md.cooked) {
                if (handle->snapshot < SLL_HDR_LEN + 1)
                        handle->snapshot = SLL_HDR_LEN + 1;
        }
        handle->bufsize = handle->snapshot;

        /* Save the socket FD in the pcap structure */
        handle->fd       = sock_fd;

        return 1;
#else
        strncpy(ebuf,
                "New packet capturing interface not supported by build "
                "environment", PCAP_ERRBUF_SIZE);
        return 0;
#endif
}

static int 
activate_mmap(pcap_t *handle)
{
#ifdef HAVE_PACKET_RING
        int ret;

        if (handle->opt.buffer_size == 0) {
                /* by default request 2M for the ring buffer */
                handle->opt.buffer_size = 2*1024*1024;
        }
        ret = create_ring(handle);
        if (ret == 0)
                return ret;

        /* override some defaults and inherit the other fields from
         * activate_new
         * handle->offset is used to get the current position into the rx ring 
         * handle->cc is used to store the ring size */
        handle->read_op = pcap_read_linux_mmap;
        handle->close_op = pcap_close_linux_mmap;
        handle->setfilter_op = pcap_setfilter_linux_mmap;
        handle->setnonblock_op = pcap_setnonblock_mmap;
        handle->getnonblock_op = pcap_getnonblock_mmap;
        handle->selectable_fd = handle->fd;
        return 1;
#else /* HAVE_PACKET_RING */
        return 0;
#endif /* HAVE_PACKET_RING */
}

#ifdef HAVE_PACKET_RING

static void
compute_ring_block(int frame_size, unsigned *block_size, unsigned *frames_per_block)
{
        /* compute the minumum 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. */
        *block_size = getpagesize();
        while (*block_size < frame_size) 
                *block_size <<= 1;

        *frames_per_block = *block_size/frame_size;
}

static int
create_ring(pcap_t *handle)
{
        unsigned i, j, ringsize, frames_per_block;
        struct tpacket_req req;

        /* Note that with large snapshot (say 64K) only a few frames 
         * will be available in the ring even with pretty large ring size
         * (and a lot of memory will be unused). 
         * The snap len should be carefully chosen to achive best
         * performance */
        req.tp_frame_size = TPACKET_ALIGN(handle->snapshot+TPACKET_HDRLEN);
        req.tp_frame_nr = handle->opt.buffer_size/req.tp_frame_size;
        compute_ring_block(req.tp_frame_size, &req.tp_block_size, &frames_per_block);
        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;

        /* ask the kernel to create the ring */
retry:
        if (setsockopt(handle->fd, SOL_PACKET, PACKET_RX_RING,
                                        (void *) &req, sizeof(req))) {
                /* try to reduce requested ring size to prevent memory failure */
                if ((errno == ENOMEM) && (req.tp_block_nr > 1)) {
                        req.tp_frame_nr >>= 1;
                        req.tp_block_nr = req.tp_frame_nr/frames_per_block;
                        goto retry;
                }
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, "can't create rx ring on "
                                "packet socket %d: %d-%s", handle->fd, errno, 
                                pcap_strerror(errno));
                return 0;
        }

        /* memory map the rx ring */
        ringsize = req.tp_block_nr * req.tp_block_size;
        handle->bp = mmap(0, ringsize, PROT_READ| PROT_WRITE, MAP_SHARED, 
                                        handle->fd, 0);
        if (handle->bp == MAP_FAILED) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, "can't mmap rx ring: %d-%s",
                        errno, pcap_strerror(errno));

                /* clear the allocated ring on error*/
                destroy_ring(handle);
                return 0;
        }

        /* allocate a ring for each frame header pointer*/
        handle->cc = req.tp_frame_nr;
        handle->buffer = malloc(handle->cc * sizeof(struct tpacket_hdr*));
        if (!handle->buffer) {
                destroy_ring(handle);
                return 0;
        }

        /* fill the header ring with proper frame ptr*/
        handle->offset = 0;
        for (i=0; i<req.tp_block_nr; ++i) {
                u_char *base = &handle->bp[i*req.tp_block_size];
                for (j=0; j<frames_per_block; ++j, ++handle->offset) {
                        RING_GET_FRAME(handle) = (struct tpacket_hdr*) 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)
{
        /* tell the kernel to destroy the ring*/
        struct tpacket_req req;
        memset(&req, 0, sizeof(req));
        setsockopt(handle->fd, SOL_PACKET, PACKET_RX_RING,
                                (void *) &req, sizeof(req));

        /* if ring is mapped, unmap it*/
        if (handle->bp) {
                /* need to re-compute the ring size */
                unsigned frames_per_block, block_size;
                compute_ring_block(handle->bufsize, &block_size, &frames_per_block);

                /* do not perform sanity check here: we can't recover any error */
                munmap(handle->bp, block_size * handle->cc / frames_per_block);
                handle->bp = 0;
        }

        /* if the header ring is allocated, clear it*/
        if (handle->buffer) {
                free(handle->buffer);
                handle->buffer = 0;
        }
}

static void
pcap_close_linux_mmap( pcap_t *handle )
{
        destroy_ring(handle);
        pcap_close_linux(handle);
}


static int
pcap_getnonblock_mmap(pcap_t *p, char *errbuf)
{
        /* use negative value of timeout to indicate non blocking ops */
        return (p->md.timeout<0);
}

static int
pcap_setnonblock_mmap(pcap_t *p, int nonblock, char *errbuf)
{
        /* map each value to the corresponding 2's complement, to 
         * preserve the timeout value provided with pcap_set_timeout */
        if (nonblock) {
                if (p->md.timeout > 0)
                        p->md.timeout = p->md.timeout*-1 - 1;
        } else 
                if (p->md.timeout < 0)
                        p->md.timeout = (p->md.timeout+1)*-1;
        return 0;
}

static int
pcap_read_linux_mmap(pcap_t *handle, int max_packets, pcap_handler callback, 
                u_char *user)
{
        int pkts = 0;

        /* wait for frames availability.*/
        if ((handle->md.timeout >= 0) && !(RING_GET_FRAME(handle)->tp_status)) {
                struct pollfd pollinfo;
                int ret;

                pollinfo.fd = handle->fd;
                pollinfo.events = POLLIN;

                do {
                        /* poll() requires a negative timeout to wait forever */
                        ret = poll(&pollinfo, 1, (handle->md.timeout > 0)?
                                                handle->md.timeout: -1);
                        if ((ret < 0) && (errno != EINTR)) {
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, 
                                         "can't poll on packet socket fd %d: %d-%s",
                                        handle->fd, errno, pcap_strerror(errno));
                                return -1;
                        }
                        /* check for break loop condition on interrupted syscall*/
                        if (handle->break_loop) {
                                handle->break_loop = 0;
                                return -2;
                        }
                } while (ret < 0);
        }

        /* non-positive values of max_packets are used to require all 
         * packets currently available in the ring */
        while ((pkts < max_packets) || (max_packets <= 0)) {
                int run_bpf;
                struct sockaddr_ll *sll;
                struct pcap_pkthdr pcaphdr;
                unsigned char *bp;
                struct tpacket_hdr* thdr = RING_GET_FRAME(handle);
                if (thdr->tp_status == TP_STATUS_KERNEL)
                        break;

                /* perform sanity check on internal offset. */
                if (thdr->tp_mac+thdr->tp_snaplen > handle->bufsize) {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, 
                                "corrupted frame on kernel ring mac "
                                "offset %d + caplen %d > frame len %d", 
                                thdr->tp_mac, thdr->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 such case md.use_bpf 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 = (unsigned char*)thdr + thdr->tp_mac;
                run_bpf = (!handle->md.use_bpf) || 
                        ((handle->md.use_bpf>1) && handle->md.use_bpf--);
                if (run_bpf && handle->fcode.bf_insns && 
                                (bpf_filter(handle->fcode.bf_insns, bp,
                                        thdr->tp_len, thdr->tp_snaplen) == 0))
                        goto skip;

                /* check direction and interface index */
                sll = (void*)thdr + TPACKET_ALIGN(sizeof(*thdr));
                if ((sll->sll_ifindex == handle->md.lo_ifindex) &&
                                        (sll->sll_pkttype == PACKET_OUTGOING))
                        goto skip;

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

                /* if required build in place the sll header*/
                if (handle->md.cooked) {
                        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 *)thdr + TPACKET_HDRLEN) {
                                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 = map_packet_type_to_sll_type(
                                                        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;

                        /* update packet len */
                        pcaphdr.caplen += SLL_HDR_LEN;
                        pcaphdr.len += SLL_HDR_LEN;
                }

                /* pass the packet to the user */
                pkts++;
                callback(user, &pcaphdr, bp);
                handle->md.packets_read++;

skip:
                /* next packet */
                thdr->tp_status = TP_STATUS_KERNEL;
                if (++handle->offset >= handle->cc)
                        handle->offset = 0;

                /* check for break loop condition*/
                if (handle->break_loop) {
                        handle->break_loop = 0;
                        return -2;
                }
        }
        return pkts;
}

static int 
pcap_setfilter_linux_mmap(pcap_t *handle, struct bpf_program *filter)
{
        int n, offset;
        int ret = pcap_setfilter_linux(handle, filter);
        if (ret < 0)
                return ret;

        /* if the kernel filter is enabled, we need to apply the filter on
         * all packets present into the ring. Get an upper bound of their number
         */
        if (!handle->md.use_bpf)
                return ret;

        /* walk the ring backward and count the free slot */
        offset = handle->offset;
        if (--handle->offset < 0)
                handle->offset = handle->cc - 1;
        for (n=0; n < handle->cc; ++n) {
                if (--handle->offset < 0)
                        handle->offset = handle->cc - 1;
                if (RING_GET_FRAME(handle)->tp_status != TP_STATUS_KERNEL)
                        break;
        }

        /* be careful to not change current ring position */
        handle->offset = offset;

        /* store the number of packets currently present in the ring */
        handle->md.use_bpf = 1 + (handle->cc - n);
        return ret;
}

#endif /* HAVE_PACKET_RING */


#ifdef HAVE_PF_PACKET_SOCKETS
/*
 *  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));
        strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

        if (ioctl(fd, SIOCGIFINDEX, &ifr) == -1) {
                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                         "SIOCGIFINDEX: %s", pcap_strerror(errno));
                return -1;
        }

        return ifr.ifr_ifindex;
}

/*
 *  Bind the socket associated with FD to the given device.
 */
static int
iface_bind(int fd, int ifindex, char *ebuf)
{
        struct sockaddr_ll      sll;
        int                     err;
        socklen_t               errlen = sizeof(err);

        memset(&sll, 0, sizeof(sll));
        sll.sll_family          = AF_PACKET;
        sll.sll_ifindex         = ifindex;
        sll.sll_protocol        = htons(ETH_P_ALL);

        if (bind(fd, (struct sockaddr *) &sll, sizeof(sll)) == -1) {
                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                         "bind: %s", pcap_strerror(errno));
                return -1;
        }

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

        if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) {
                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                        "getsockopt: %s", pcap_strerror(errno));
                return -2;
        }

        if (err > 0) {
                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                        "bind: %s", pcap_strerror(err));
                return -2;
        }

        return 0;
}

/*
 * Check whether the device supports the Wireless Extensions.
 * Returns 1 if it does, 0 if it doesn't, PCAP_ERROR_NO_SUCH_DEVICE
 * if the device doesn't even exist.
 */
static int
has_wext(int sock_fd, const char *device)
{
#ifdef IW_MODE_MONITOR
        struct iwreq ireq;

        strncpy(ireq.ifr_ifrn.ifrn_name, device,
            sizeof ireq.ifr_ifrn.ifrn_name);
        ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
        if (ioctl(sock_fd, SIOCGIWNAME, &ireq) >= 0)
                return 1;       /* yes */
        if (errno == ENODEV)
                return PCAP_ERROR_NO_SUCH_DEVICE;
#endif
        return 0;
}

/*
 * Per me si va ne la citta dolente,
 * Per me si va ne l'etterno dolore,
 *      ...
 * Lasciate ogne speranza, voi ch'intrate.
 */
typedef enum {
        MONITOR_WEXT,
        MONITOR_HOSTAP,
        MONITOR_PRISM,
        MONITOR_PRISM54,
        MONITOR_ACX100,
        MONITOR_RT2500,
        MONITOR_RT2570,
        MONITOR_RT73,
        MONITOR_RTL8XXX
} monitor_type;

/*
 * Use the Wireless Extensions, if we have them, to try to turn monitor mode
 * on if it's not already on.
 *
 * Returns 1 on success, 0 if we don't support the Wireless Extensions
 * on this device, or a PCAP_ERROR_ value if we do support them but
 * we weren't able to turn monitor mode on.
 */
static int
enter_rfmon_mode_wext(pcap_t *handle, int sock_fd, const char *device)
{
#ifdef IW_MODE_MONITOR
        /*
         * XXX - at least some adapters require non-Wireless Extensions
         * mechanisms to turn monitor mode on.
         *
         * Atheros cards might require that a separate "monitor virtual access
         * point" be created, with later versions of the madwifi driver.
         *
         * Some Intel Centrino adapters might require private ioctls to get
         * radio headers; the ipw2200 and ipw3945 drivers allow you to
         * configure a separate "rtapN" interface to capture in monitor
         * mode without preventing the adapter from operating normally.
         *
         * It would be Truly Wonderful if mac80211 and nl80211 cleaned this
         * up, and if all drivers were converted to mac80211 drivers.
         */
        int err;
        struct iwreq ireq;
        struct iw_priv_args *priv;
        monitor_type montype;
        int i;
        __u32 cmd;
        int args[2];
        int channel;

        /*
         * Does this device *support* the Wireless Extensions?
         */
        err = has_wext(sock_fd, device);
        if (err <= 0)
                return err;     /* either it doesn't or the device doesn't even exist */
        /*
         * Try to get all the Wireless Extensions private ioctls
         * supported by this device.
         *
         * First, get the size of the buffer we need, by supplying no
         * buffer and a length of 0.  If the device supports private
         * ioctls, it should return E2BIG, with ireq.u.data.length set
         * to the length we need.  If it doesn't support them, it should
         * return EOPNOTSUPP.
         */
        memset(&ireq, 0, sizeof ireq);
        strncpy(ireq.ifr_ifrn.ifrn_name, device,
            sizeof ireq.ifr_ifrn.ifrn_name);
        ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
        ireq.u.data.pointer = args;
        ireq.u.data.length = 0;
        ireq.u.data.flags = 0;
        if (ioctl(sock_fd, SIOCGIWPRIV, &ireq) != -1) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: SIOCGIWPRIV with a zero-length buffer didn't fail!",
                    device);
                return PCAP_ERROR;
        }
        if (errno == EOPNOTSUPP) {
                /*
                 * No private ioctls, so we assume that there's only one
                 * DLT_ for monitor mode.
                 */
                return 0;
        }
        if (errno != E2BIG) {
                /*
                 * Failed.
                 */
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: SIOCGIWPRIV: %s", device, pcap_strerror(errno));
                return PCAP_ERROR;
        }
        priv = malloc(ireq.u.data.length);
        if (priv == NULL) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                         "malloc: %s", pcap_strerror(errno));
                return PCAP_ERROR;
        }
        ireq.u.data.pointer = priv;
        if (ioctl(sock_fd, SIOCGIWPRIV, &ireq) == -1) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "%s: SIOCGIWPRIV: %s", device, pcap_strerror(errno));
                return PCAP_ERROR;
        }

        /*
         * Look for private ioctls to turn monitor mode on or, if
         * monitor mode is on, to set the header type.
         */
        montype = MONITOR_WEXT;
        cmd = 0;
        for (i = 0; i < ireq.u.data.length; i++) {
                if (strcmp(priv[i].name, "monitor_type") == 0) {
                        /*
                         * Hostap driver, use this one.
                         * Set monitor mode first.
                         * You can set it to 0 to get DLT_IEEE80211,
                         * 1 to get DLT_PRISM, or 2 to get
                         * DLT_IEEE80211_RADIO_AVS.
                         */
                        if ((priv[i].set_args & IW_PRIV_TYPE_MASK) != IW_PRIV_TYPE_INT)
                                break;
                        if (!(priv[i].set_args & IW_PRIV_SIZE_FIXED))
                                break;
                        if ((priv[i].set_args & IW_PRIV_SIZE_MASK) != 1)
                                break;
                        montype = MONITOR_HOSTAP;
                        cmd = priv[i].cmd;
                        break;
                }
                if (strcmp(priv[i].name, "set_prismhdr") == 0) {
                        /*
                         * Prism54 driver, use this one.
                         * Set monitor mode first.
                         * You can set it to 2 to get DLT_IEEE80211
                         * or 3 or get DLT_PRISM.
                         */
                        if ((priv[i].set_args & IW_PRIV_TYPE_MASK) != IW_PRIV_TYPE_INT)
                                break;
                        if (!(priv[i].set_args & IW_PRIV_SIZE_FIXED))
                                break;
                        if ((priv[i].set_args & IW_PRIV_SIZE_MASK) != 1)
                                break;
                        montype = MONITOR_PRISM54;
                        cmd = priv[i].cmd;
                        break;
                }
                if (strcmp(priv[i].name, "forceprismheader") == 0) {
                        /*
                         * RT2570 driver, use this one.
                         * Do this after turning monitor mode on.
                         * You can set it to 1 to get DLT_PRISM or 2
                         * to get DLT_IEEE80211.
                         */
                        if ((priv[i].set_args & IW_PRIV_TYPE_MASK) != IW_PRIV_TYPE_INT)
                                break;
                        if (!(priv[i].set_args & IW_PRIV_SIZE_FIXED))
                                break;
                        if ((priv[i].set_args & IW_PRIV_SIZE_MASK) != 1)
                                break;
                        montype = MONITOR_RT2570;
                        cmd = priv[i].cmd;
                        break;
                }
                if (strcmp(priv[i].name, "forceprism") == 0) {
                        /*
                         * RT73 driver, use this one.
                         * Do this after turning monitor mode on.
                         * Its argument is a *string*; you can
                         * set it to "1" to get DLT_PRISM or "2"
                         * to get DLT_IEEE80211.
                         */
                        if ((priv[i].set_args & IW_PRIV_TYPE_MASK) != IW_PRIV_TYPE_CHAR)
                                break;
                        if (priv[i].set_args & IW_PRIV_SIZE_FIXED)
                                break;
                        montype = MONITOR_RT73;
                        cmd = priv[i].cmd;
                        break;
                }
                if (strcmp(priv[i].name, "prismhdr") == 0) {
                        /*
                         * One of the RTL8xxx drivers, use this one.
                         * It can only be done after monitor mode
                         * has been turned on.  You can set it to 1
                         * to get DLT_PRISM or 0 to get DLT_IEEE80211.
                         */
                        if ((priv[i].set_args & IW_PRIV_TYPE_MASK) != IW_PRIV_TYPE_INT)
                                break;
                        if (!(priv[i].set_args & IW_PRIV_SIZE_FIXED))
                                break;
                        if ((priv[i].set_args & IW_PRIV_SIZE_MASK) != 1)
                                break;
                        montype = MONITOR_RTL8XXX;
                        cmd = priv[i].cmd;
                        break;
                }
                if (strcmp(priv[i].name, "rfmontx") == 0) {
                        /*
                         * RT2500 or RT61 driver, use this one.
                         * It has one one-byte parameter; set
                         * u.data.length to 1 and u.data.pointer to
                         * point to the parameter.
                         * It doesn't itself turn monitor mode on.
                         * You can set it to 1 to allow transmitting
                         * in monitor mode(?) and get DLT_IEEE80211,
                         * or set it to 0 to disallow transmitting in
                         * monitor mode(?) and get DLT_PRISM.
                         */
                        if ((priv[i].set_args & IW_PRIV_TYPE_MASK) != IW_PRIV_TYPE_INT)
                                break;
                        if ((priv[i].set_args & IW_PRIV_SIZE_MASK) != 2)
                                break;
                        montype = MONITOR_RT2500;
                        cmd = priv[i].cmd;
                        break;
                }
                if (strcmp(priv[i].name, "monitor") == 0) {
                        /*
                         * Either ACX100 or hostap, use this one.
                         * It turns monitor mode on.
                         * If it takes two arguments, it's ACX100;
                         * the first argument is 1 for DLT_PRISM
                         * or 2 for DLT_IEEE80211, and the second
                         * argument is the channel on which to
                         * run.  If it takes one argument, it's
                         * HostAP, and the argument is 2 for
                         * DLT_IEEE80211 and 3 for DLT_PRISM.
                         *
                         * If we see this, we don't quit, as this
                         * might be a version of the hostap driver
                         * that also supports "monitor_type".
                         */
                        if ((priv[i].set_args & IW_PRIV_TYPE_MASK) != IW_PRIV_TYPE_INT)
                                break;
                        if (!(priv[i].set_args & IW_PRIV_SIZE_FIXED))
                                break;
                        switch (priv[i].set_args & IW_PRIV_SIZE_MASK) {

                        case 1:
                                montype = MONITOR_PRISM;
                                cmd = priv[i].cmd;
                                break;

                        case 2:
                                montype = MONITOR_ACX100;
                                cmd = priv[i].cmd;
                                break;

                        default:
                                break;
                        }
                }
        }

        /*
         * XXX - ipw3945?  islism?
         */

        /*
         * Get the old mode.
         */
        strncpy(ireq.ifr_ifrn.ifrn_name, device,
            sizeof ireq.ifr_ifrn.ifrn_name);
        ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
        if (ioctl(sock_fd, SIOCGIWMODE, &ireq) == -1) {
                /*
                 * We probably won't be able to set the mode, either.
                 */
                return PCAP_ERROR_RFMON_NOTSUP;
        }

        /*
         * Is it currently in monitor mode?
         */
        if (ireq.u.mode == IW_MODE_MONITOR) {
                /*
                 * Yes.  Just leave things as they are.
                 * We don't offer multiple link-layer types, as
                 * changing the link-layer type out from under
                 * somebody else capturing in monitor mode would
                 * be considered rude.
                 */
                return 1;
        }
        /*
         * No.  We have to put the adapter into rfmon mode.
         */

        /*
         * 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.
                 */
                return PCAP_ERROR_RFMON_NOTSUP;
        }

        /*
         * Save the old mode.
         */
        handle->md.oldmode = ireq.u.mode;

        /*
         * Put the adapter in rfmon mode.  How we do this depends
         * on whether we have a special private ioctl or not.
         */
        if (montype == MONITOR_PRISM) {
                /*
                 * We have the "monitor" private ioctl, but none of
                 * the other private ioctls.  Use this, and select
                 * the Prism header.
                 *
                 * If it fails, just fall back on SIOCSIWMODE.
                 */
                memset(&ireq, 0, sizeof ireq);
                strncpy(ireq.ifr_ifrn.ifrn_name, device,
                    sizeof ireq.ifr_ifrn.ifrn_name);
                ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                ireq.u.data.length = 1; /* 1 argument */
                args[0] = 3;    /* request Prism header */
                memcpy(ireq.u.name, args, IFNAMSIZ);
                if (ioctl(sock_fd, cmd, &ireq) != -1) {
                        /*
                         * Success.
                         * Note that we have to put the old mode back
                         * when we close the device.
                         */
                        handle->md.must_clear |= MUST_CLEAR_RFMON;

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

                        return 1;
                }

                /*
                 * Failure.  Fall back on SIOCSIWMODE.
                 */
        }

        /*
         * First, turn monitor mode on.
         */
        strncpy(ireq.ifr_ifrn.ifrn_name, device,
            sizeof ireq.ifr_ifrn.ifrn_name);
        ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
        ireq.u.mode = IW_MODE_MONITOR;
        if (ioctl(sock_fd, SIOCSIWMODE, &ireq) == -1) {
                /*
                 * Scientist, you've failed.
                 */
                return PCAP_ERROR_RFMON_NOTSUP;
        }

        /*
         * Now select the appropriate radio header.
         */
        switch (montype) {

        case MONITOR_WEXT:
                /*
                 * We don't have any private ioctl to set the header.
                 */
                break;

        case MONITOR_HOSTAP:
                /*
                 * Select the AVS header if we can, otherwise
                 * select the Prism header.
                 */
                memset(&ireq, 0, sizeof ireq);
                strncpy(ireq.ifr_ifrn.ifrn_name, device,
                    sizeof ireq.ifr_ifrn.ifrn_name);
                ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                args[0] = 2;    /* request AVS header */
                memcpy(ireq.u.name, args, sizeof (int));
                if (ioctl(sock_fd, cmd, &ireq) == -1) {
                        /*
                         * Failure - try the Prism header.
                         */
                        memset(&ireq, 0, sizeof ireq);
                        strncpy(ireq.ifr_ifrn.ifrn_name, device,
                            sizeof ireq.ifr_ifrn.ifrn_name);
                        ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                        args[0] = 1;    /* request Prism header */
                        memcpy(ireq.u.name, args, sizeof (int));
                        ioctl(sock_fd, cmd, &ireq);
                }
                break;

        case MONITOR_PRISM:
                /*
                 * The private ioctl failed.
                 */
                break;

        case MONITOR_PRISM54:
                /*
                 * Select the Prism header.
                 */
                memset(&ireq, 0, sizeof ireq);
                strncpy(ireq.ifr_ifrn.ifrn_name, device,
                    sizeof ireq.ifr_ifrn.ifrn_name);
                ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                args[0] = 3;    /* request Prism header */
                memcpy(ireq.u.name, args, sizeof (int));
                ioctl(sock_fd, cmd, &ireq);
                break;

        case MONITOR_ACX100:
                /*
                 * Get the current channel.
                 */
                memset(&ireq, 0, sizeof ireq);
                strncpy(ireq.ifr_ifrn.ifrn_name, device,
                    sizeof ireq.ifr_ifrn.ifrn_name);
                ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                if (ioctl(sock_fd, SIOCGIWFREQ, &ireq) == -1) {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                            "%s: SIOCGIWFREQ: %s", device,
                            pcap_strerror(errno));
                        return PCAP_ERROR;
                }
                channel = ireq.u.freq.m;

                /*
                 * Select the Prism header, and set the channel to the
                 * current value.
                 */
                memset(&ireq, 0, sizeof ireq);
                strncpy(ireq.ifr_ifrn.ifrn_name, device,
                    sizeof ireq.ifr_ifrn.ifrn_name);
                ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                args[0] = 1;            /* request Prism header */
                args[1] = channel;      /* set channel */
                memcpy(ireq.u.name, args, 2*sizeof (int));
                ioctl(sock_fd, cmd, &ireq);
                break;

        case MONITOR_RT2500:
                /*
                 * Disallow transmission - that turns on the
                 * Prism header.
                 */
                memset(&ireq, 0, sizeof ireq);
                strncpy(ireq.ifr_ifrn.ifrn_name, device,
                    sizeof ireq.ifr_ifrn.ifrn_name);
                ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                args[0] = 0;    /* disallow transmitting */
                memcpy(ireq.u.name, args, sizeof (int));
                ioctl(sock_fd, cmd, &ireq);
                break;

        case MONITOR_RT2570:
                /*
                 * Force the Prism header.
                 */
                memset(&ireq, 0, sizeof ireq);
                strncpy(ireq.ifr_ifrn.ifrn_name, device,
                    sizeof ireq.ifr_ifrn.ifrn_name);
                ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                args[0] = 1;    /* request Prism header */
                memcpy(ireq.u.name, args, sizeof (int));
                ioctl(sock_fd, cmd, &ireq);
                break;

        case MONITOR_RT73:
                /*
                 * Force the Prism header.
                 */
                memset(&ireq, 0, sizeof ireq);
                strncpy(ireq.ifr_ifrn.ifrn_name, device,
                    sizeof ireq.ifr_ifrn.ifrn_name);
                ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                ireq.u.data.length = 1; /* 1 argument */
                ireq.u.data.pointer = "1";
                ireq.u.data.flags = 0;
                ioctl(sock_fd, cmd, &ireq);
                break;

        case MONITOR_RTL8XXX:
                /*
                 * Force the Prism header.
                 */
                memset(&ireq, 0, sizeof ireq);
                strncpy(ireq.ifr_ifrn.ifrn_name, device,
                    sizeof ireq.ifr_ifrn.ifrn_name);
                ireq.ifr_ifrn.ifrn_name[sizeof ireq.ifr_ifrn.ifrn_name - 1] = 0;
                args[0] = 1;    /* request Prism header */
                memcpy(ireq.u.name, args, sizeof (int));
                ioctl(sock_fd, cmd, &ireq);
                break;
        }

        /*
         * Note that we have to put the old mode back when we
         * close the device.
         */
        handle->md.must_clear |= MUST_CLEAR_RFMON;

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

        return 1;
#else
        /*
         * We don't have the Wireless Extensions available, so we can't
         * do monitor mode.
         */
        return 0;
#endif
}

#endif /* HAVE_PF_PACKET_SOCKETS */

/* ===== Functions to interface to the older kernels ================== */

/*
 * Try to open a packet socket using the old kernel interface.
 * Returns 1 on success and a PCAP_ERROR_ value on an error.
 */
static int
activate_old(pcap_t *handle)
{
        int             arptype;
        struct ifreq    ifr;
        const char      *device = handle->opt.source;
        struct utsname  utsname;
        int             mtu;

        /* Open the socket */

        handle->fd = socket(PF_INET, SOCK_PACKET, htons(ETH_P_ALL));
        if (handle->fd == -1) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                         "socket: %s", pcap_strerror(errno));
                return PCAP_ERROR;
        }

        /* It worked - we are using the old interface */
        handle->md.sock_packet = 1;

        /* ...which means we get the link-layer header. */
        handle->md.cooked = 0;

        /* Bind to the given device */

        if (!device) {
                strncpy(handle->errbuf, "pcap_activate: The \"any\" device isn't supported on 2.0[.x]-kernel systems",
                        PCAP_ERRBUF_SIZE);
                return PCAP_ERROR;
        }
        if (iface_bind_old(handle->fd, device, handle->errbuf) == -1)
                return PCAP_ERROR;

        /*
         * Try to get the link-layer type.
         */
        arptype = iface_get_arptype(handle->fd, device, handle->errbuf);
        if (arptype < 0)
                return PCAP_ERROR;

        /*
         * Try to find the DLT_ type corresponding to that
         * link-layer type.
         */
        map_arphrd_to_dlt(handle, arptype, 0);
        if (handle->linktype == -1) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                         "unknown arptype %d", arptype);
                return PCAP_ERROR;
        }

        /* Go to promisc mode if requested */

        if (handle->opt.promisc) {
                memset(&ifr, 0, sizeof(ifr));
                strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
                if (ioctl(handle->fd, SIOCGIFFLAGS, &ifr) == -1) {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                 "SIOCGIFFLAGS: %s", pcap_strerror(errno));
                        return PCAP_ERROR;
                }
                if ((ifr.ifr_flags & IFF_PROMISC) == 0) {
                        /*
                         * Promiscuous mode isn't currently on,
                         * so turn it on, and remember that
                         * we should turn it off when the
                         * pcap_t is closed.
                         */

                        /*
                         * 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 promiscuous
                                 * mode, just give up.
                                 */
                                return PCAP_ERROR;
                        }

                        ifr.ifr_flags |= IFF_PROMISC;
                        if (ioctl(handle->fd, SIOCSIFFLAGS, &ifr) == -1) {
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                         "SIOCSIFFLAGS: %s",
                                         pcap_strerror(errno));
                                return PCAP_ERROR;
                        }
                        handle->md.must_clear |= MUST_CLEAR_PROMISC;

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

        /*
         * Compute the buffer size.
         *
         * We're using SOCK_PACKET, so this might be a 2.0[.x]
         * kernel, and might require special handling - check.
         */
        if (uname(&utsname) < 0 ||
            strncmp(utsname.release, "2.0", 3) == 0) {
                /*
                 * Either we couldn't find out what kernel release
                 * this is, or it's a 2.0[.x] kernel.
                 *
                 * In the 2.0[.x] kernel, a "recvfrom()" on
                 * a SOCK_PACKET socket, with MSG_TRUNC set, will
                 * return the number of bytes read, so if we pass
                 * a length based on the snapshot length, it'll
                 * return the number of bytes from the packet
                 * copied to userland, not the actual length
                 * of the packet.
                 *
                 * This means that, for example, the IP dissector
                 * in tcpdump will get handed a packet length less
                 * than the length in the IP header, and will
                 * complain about "truncated-ip".
                 *
                 * So we don't bother trying to copy from the
                 * kernel only the bytes in which we're interested,
                 * but instead copy them all, just as the older
                 * versions of libpcap for Linux did.
                 *
                 * The buffer therefore needs to be big enough to
                 * hold the largest packet we can get from this
                 * device.  Unfortunately, we can't get the MRU
                 * of the network; we can only get the MTU.  The
                 * MTU may be too small, in which case a packet larger
                 * than the buffer size will be truncated *and* we
                 * won't get the actual packet size.
                 *
                 * However, if the snapshot length is larger than
                 * the buffer size based on the MTU, we use the
                 * snapshot length as the buffer size, instead;
                 * this means that with a sufficiently large snapshot
                 * length we won't artificially truncate packets
                 * to the MTU-based size.
                 *
                 * This mess just one of many problems with packet
                 * capture on 2.0[.x] kernels; you really want a
                 * 2.2[.x] or later kernel if you want packet capture
                 * to work well.
                 */
                mtu = iface_get_mtu(handle->fd, device, handle->errbuf);
                if (mtu == -1)
                        return PCAP_ERROR;
                handle->bufsize = MAX_LINKHEADER_SIZE + mtu;
                if (handle->bufsize < handle->snapshot)
                        handle->bufsize = handle->snapshot;
        } else {
                /*
                 * This is a 2.2[.x] or later kernel.
                 *
                 * We can safely pass "recvfrom()" a byte count
                 * based on the snapshot length.
                 */
                handle->bufsize = handle->snapshot;
        }

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

        return 1;
}

/*
 *  Bind the socket associated with FD to the given device using the
 *  interface of the old kernels.
 */
static int
iface_bind_old(int fd, const char *device, char *ebuf)
{
        struct sockaddr saddr;
        int             err;
        socklen_t       errlen = sizeof(err);

        memset(&saddr, 0, sizeof(saddr));
        strncpy(saddr.sa_data, device, sizeof(saddr.sa_data));
        if (bind(fd, &saddr, sizeof(saddr)) == -1) {
                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                         "bind: %s", pcap_strerror(errno));
                return -1;
        }

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

        if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) {
                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                        "getsockopt: %s", pcap_strerror(errno));
                return -1;
        }

        if (err > 0) {
                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                        "bind: %s", pcap_strerror(err));
                return -1;
        }

        return 0;
}


/* ===== System calls available on all supported kernels ============== */

/*
 *  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));
        strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

        if (ioctl(fd, SIOCGIFMTU, &ifr) == -1) {
                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                         "SIOCGIFMTU: %s", pcap_strerror(errno));
                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;

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

        if (ioctl(fd, SIOCGIFHWADDR, &ifr) == -1) {
                if (errno == ENODEV) {
                        /*
                         * No such device.
                         */
                        return PCAP_ERROR_NO_SUCH_DEVICE;
                }
                snprintf(ebuf, PCAP_ERRBUF_SIZE,
                         "SIOCGIFHWADDR: %s", pcap_strerror(errno));
                return PCAP_ERROR;
        }

        return ifr.ifr_hwaddr.sa_family;
}

#ifdef SO_ATTACH_FILTER
static int
fix_program(pcap_t *handle, struct sock_fprog *fcode)
{
        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) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                         "malloc: %s", pcap_strerror(errno));
                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_RET:
                        /*
                         * It's a return instruction; is the snapshot
                         * length a constant, rather than the contents
                         * of the accumulator?
                         */
                        if (BPF_MODE(p->code) == BPF_K) {
                                /*
                                 * Yes - if the value to be returned,
                                 * i.e. the snapshot length, is anything
                                 * other than 0, make it 65535, so that
                                 * the packet is truncated by "recvfrom()",
                                 * not by the filter.
                                 *
                                 * XXX - there's nothing we can easily do
                                 * if it's getting the value from the
                                 * accumulator; we'd have to insert
                                 * code to force non-zero values to be
                                 * 65535.
                                 */
                                if (p->k != 0)
                                        p->k = 65535;
                        }
                        break;

                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 (handle->md.cooked) {
                                        /*
                                         * Yes, so we need to fix this
                                         * instruction.
                                         */
                                        if (fix_offset(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(struct bpf_insn *p)
{
        /*
         * 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 == 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 {
                /*
                 * 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 &&
                    fcntl(handle->fd, F_SETFL, save_mode | O_NONBLOCK) >= 0) {
                        while (recv(handle->fd, &drain, sizeof drain,
                               MSG_TRUNC) >= 0)
                                ;
                        save_errno = errno;
                        fcntl(handle->fd, F_SETFL, save_mode);
                        if (save_errno != EAGAIN) {
                                /* Fatal error */
                                reset_kernel_filter(handle);
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                 "recv: %s", pcap_strerror(save_errno));
                                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;

                /*
                 * XXX - if this fails, we're really screwed;
                 * we have the total filter on the socket,
                 * and it won't come off.  What do we do then?
                 */
                reset_kernel_filter(handle);

                errno = save_errno;
        }
        return ret;
}

static int
reset_kernel_filter(pcap_t *handle)
{
        /*
         * 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;

        return setsockopt(handle->fd, SOL_SOCKET, SO_DETACH_FILTER,
                                   &dummy, sizeof(dummy));
}
#endif