[libpcap] / pcap-usb-linux.c

/*
 * Copyright (c) 2006 Paolo Abeni (Italy)
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote 
 * products derived from this software without specific prior written 
 * permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * USB sniffing API implementation for Linux platform
 * By Paolo Abeni <paolo.abeni@email.it>
 * Modifications: Kris Katterjohn <katterjohn@gmail.com>
 *
 */
#ifndef lint
static const char rcsid[] _U_ =
    "@(#) $Header: /tcpdump/master/libpcap/pcap-usb-linux.c,v 1.33 2008-12-23 21:38:50 guy Exp $ (LBL)";
#endif
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "pcap-int.h"
#include "pcap-usb-linux.h"
#include "pcap/usb.h"

#ifdef NEED_STRERROR_H
#include "strerror.h"
#endif

#include <ctype.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <dirent.h>
#include <byteswap.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#ifdef HAVE_LINUX_USBDEVICE_FS_H
/*
 * We might need <linux/compiler.h> to define __user for
 * <linux/usbdevice_fs.h>.
 */
#ifdef HAVE_LINUX_COMPILER_H
#include <linux/compiler.h>
#endif /* HAVE_LINUX_COMPILER_H */
#include <linux/usbdevice_fs.h>
#endif /* HAVE_LINUX_USBDEVICE_FS_H */

#define USB_IFACE "usbmon"
#define USB_TEXT_DIR_OLD "/sys/kernel/debug/usbmon"
#define USB_TEXT_DIR "/sys/kernel/debug/usb/usbmon"
#define SYS_USB_BUS_DIR "/sys/bus/usb/devices"
#define PROC_USB_BUS_DIR "/proc/bus/usb"
#define USB_LINE_LEN 4096

#if __BYTE_ORDER == __LITTLE_ENDIAN
#define htols(s) s
#define htoll(l) l
#define htol64(ll) ll
#else
#define htols(s) bswap_16(s)
#define htoll(l) bswap_32(l)
#define htol64(ll) bswap_64(ll)
#endif

struct mon_bin_stats {
        u_int32_t queued;
        u_int32_t dropped;
};

struct mon_bin_get {
        pcap_usb_header *hdr;
        void *data;
        size_t data_len;   /* Length of data (can be zero) */
};

struct mon_bin_mfetch {
        int32_t *offvec;   /* Vector of events fetched */
        int32_t nfetch;    /* Number of events to fetch (out: fetched) */
        int32_t nflush;    /* Number of events to flush */
};

#define MON_IOC_MAGIC 0x92

#define MON_IOCQ_URB_LEN _IO(MON_IOC_MAGIC, 1)
#define MON_IOCX_URB  _IOWR(MON_IOC_MAGIC, 2, struct mon_bin_hdr)
#define MON_IOCG_STATS _IOR(MON_IOC_MAGIC, 3, struct mon_bin_stats)
#define MON_IOCT_RING_SIZE _IO(MON_IOC_MAGIC, 4)
#define MON_IOCQ_RING_SIZE _IO(MON_IOC_MAGIC, 5)
#define MON_IOCX_GET   _IOW(MON_IOC_MAGIC, 6, struct mon_bin_get)
#define MON_IOCX_MFETCH _IOWR(MON_IOC_MAGIC, 7, struct mon_bin_mfetch)
#define MON_IOCH_MFLUSH _IO(MON_IOC_MAGIC, 8)

#define MON_BIN_SETUP   0x1 /* setup hdr is present*/
#define MON_BIN_SETUP_ZERO      0x2 /* setup buffer is not available */
#define MON_BIN_DATA_ZERO       0x4 /* data buffer is not available */
#define MON_BIN_ERROR   0x8

/* forward declaration */
static int usb_activate(pcap_t *);
static int usb_stats_linux(pcap_t *, struct pcap_stat *);
static int usb_stats_linux_bin(pcap_t *, struct pcap_stat *);
static int usb_read_linux(pcap_t *, int , pcap_handler , u_char *);
static int usb_read_linux_bin(pcap_t *, int , pcap_handler , u_char *);
static int usb_read_linux_mmap(pcap_t *, int , pcap_handler , u_char *);
static int usb_inject_linux(pcap_t *, const void *, size_t);
static int usb_setdirection_linux(pcap_t *, pcap_direction_t);
static void usb_cleanup_linux_mmap(pcap_t *);

/* facility to add an USB device to the device list*/
static int 
usb_dev_add(pcap_if_t** alldevsp, int n, char *err_str)
{
        char dev_name[10];
        char dev_descr[30]; 
        snprintf(dev_name, 10, USB_IFACE"%d", n);
        snprintf(dev_descr, 30, "USB bus number %d", n);

        if (pcap_add_if(alldevsp, dev_name, 0, 
            dev_descr, err_str) < 0)
                return -1;
        return 0; 
}

int 
usb_findalldevs(pcap_if_t **alldevsp, char *err_str)
{
        struct dirent* data;
        int ret = 0;
        DIR* dir;
        int n;
        char* name;
        size_t len;

        /* try scanning sysfs usb bus directory */
        dir = opendir(SYS_USB_BUS_DIR);
        if (dir != NULL) {
                while ((ret == 0) && ((data = readdir(dir)) != 0)) {
                        name = data->d_name;

                        if (strncmp(name, "usb", 3) != 0)
                                continue;

                        if (sscanf(&name[3], "%d", &n) == 0) 
                                continue;

                        ret = usb_dev_add(alldevsp, n, err_str);
                }

                closedir(dir);
                return ret;
        }

        /* that didn't work; try scanning procfs usb bus directory */
        dir = opendir(PROC_USB_BUS_DIR);
        if (dir != NULL) {
                while ((ret == 0) && ((data = readdir(dir)) != 0)) {
                        name = data->d_name;
                        len = strlen(name);

                        /* if this file name does not end with a number it's not of our interest */
                        if ((len < 1) || !isdigit(name[--len]))
                                continue;
                        while (isdigit(name[--len]));
                        if (sscanf(&name[len+1], "%d", &n) != 1) 
                                continue;

                        ret = usb_dev_add(alldevsp, n, err_str);
                }

                closedir(dir);
                return ret;
        }

        /* neither of them worked */
        return 0;
}

static 
int usb_mmap(pcap_t* handle)
{
        int len = ioctl(handle->fd, MON_IOCQ_RING_SIZE);
        if (len < 0) 
                return 0;

        handle->md.mmapbuflen = len;
        handle->md.mmapbuf = mmap(0, handle->md.mmapbuflen, PROT_READ,
            MAP_SHARED, handle->fd, 0);
        return handle->md.mmapbuf != MAP_FAILED;
}

#define CTRL_TIMEOUT    (5*1000)        /* milliseconds */

#define USB_DIR_IN              0x80
#define USB_TYPE_STANDARD       0x00
#define USB_RECIP_DEVICE        0x00

#define USB_REQ_GET_DESCRIPTOR  6

#define USB_DT_DEVICE           1

/* probe the descriptors of the devices attached to the bus */
/* the descriptors will end up in the captured packet stream */
/* and be decoded by external apps like wireshark */
/* without these identifying probes packet data can't be fully decoded */
static void
probe_devices(int bus)
{
        struct usbdevfs_ctrltransfer ctrl;
        struct dirent* data;
        int ret = 0;
        char buf[40];
        DIR* dir;

        /* scan usb bus directories for device nodes */
        snprintf(buf, sizeof(buf), "/dev/bus/usb/%03d", bus);
        dir = opendir(buf);
        if (!dir)
                return;

        while ((ret >= 0) && ((data = readdir(dir)) != 0)) {
                int fd;
                char* name = data->d_name;

                if (name[0] == '.')
                        continue;

                snprintf(buf, sizeof(buf), "/dev/bus/usb/%03d/%s", bus, data->d_name);
                
                fd = open(buf, O_RDWR);
                if (fd == -1)
                        continue;

                /*
                 * Sigh.  Different kernels have different member names
                 * for this structure.
                 */
#ifdef HAVE_USBDEVFS_CTRLTRANSFER_BREQUESTTYPE
                ctrl.bRequestType = USB_DIR_IN | USB_TYPE_STANDARD | USB_RECIP_DEVICE;
                ctrl.bRequest = USB_REQ_GET_DESCRIPTOR;
                ctrl.wValue = USB_DT_DEVICE << 8;
                ctrl.wIndex = 0;
                ctrl.wLength = sizeof(buf);
#else
                ctrl.requesttype = USB_DIR_IN | USB_TYPE_STANDARD | USB_RECIP_DEVICE;
                ctrl.request = USB_REQ_GET_DESCRIPTOR;
                ctrl.value = USB_DT_DEVICE << 8;
                ctrl.index = 0;
                ctrl.length = sizeof(buf);
#endif
                ctrl.data = buf;
                ctrl.timeout = CTRL_TIMEOUT;

                ret = ioctl(fd, USBDEVFS_CONTROL, &ctrl);

                close(fd);
        }
        closedir(dir);
}

pcap_t *
usb_create(const char *device, char *ebuf, int *is_ours)
{
        const char *cp;
        char *cpend;
        long devnum;
        pcap_t *p;

        /* Does this look like a USB monitoring device? */
        cp = strrchr(device, '/');
        if (cp == NULL)
                cp = device;
        /* Does it begin with USB_IFACE? */
        if (strncmp(cp, USB_IFACE, sizeof USB_IFACE - 1) != 0) {
                /* Nope, doesn't begin with USB_IFACE */
                *is_ours = 0;
                return NULL;
        }
        /* Yes - is USB_IFACE followed by a number? */
        cp += sizeof USB_IFACE - 1;
        devnum = strtol(cp, &cpend, 10);
        if (cpend == cp || *cpend != '\0') {
                /* Not followed by a number. */
                *is_ours = 0;
                return NULL;
        }
        if (devnum < 0) {
                /* Followed by a non-valid number. */
                *is_ours = 0;
                return NULL;
        }

        /* OK, it's probably ours. */
        *is_ours = 1;

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

        p->activate_op = usb_activate;
        return (p);
}

static int
usb_activate(pcap_t* handle)
{
        char            full_path[USB_LINE_LEN];

        /* Initialize some components of the pcap structure. */
        handle->bufsize = handle->snapshot;
        handle->offset = 0;
        handle->linktype = DLT_USB_LINUX;

        handle->inject_op = usb_inject_linux;
        handle->setfilter_op = install_bpf_program; /* no kernel filtering */
        handle->setdirection_op = usb_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;

        /*get usb bus index from device name */
        if (sscanf(handle->opt.source, USB_IFACE"%d", &handle->md.ifindex) != 1)
        {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                        "Can't get USB bus index from %s", handle->opt.source);
                return PCAP_ERROR;
        }

        /*now select the read method: try to open binary interface */
        snprintf(full_path, USB_LINE_LEN, LINUX_USB_MON_DEV"%d", handle->md.ifindex);  
        handle->fd = open(full_path, O_RDONLY, 0);
        if (handle->fd >= 0)
        {
                if (handle->opt.rfmon) {
                        /*
                         * Monitor mode doesn't apply to USB devices.
                         */
                        close(handle->fd);
                        return PCAP_ERROR_RFMON_NOTSUP;
                }

                /* binary api is available, try to use fast mmap access */
                if (usb_mmap(handle)) {
                        handle->linktype = DLT_USB_LINUX_MMAPPED;
                        handle->stats_op = usb_stats_linux_bin;
                        handle->read_op = usb_read_linux_mmap;
                        handle->cleanup_op = usb_cleanup_linux_mmap;
                        probe_devices(handle->md.ifindex);

                        /*
                         * "handle->fd" is a real file, so "select()" and
                         * "poll()" work on it.
                         */
                        handle->selectable_fd = handle->fd;
                        return 0;
                }

                /* can't mmap, use plain binary interface access */
                handle->stats_op = usb_stats_linux_bin;
                handle->read_op = usb_read_linux_bin;
                probe_devices(handle->md.ifindex);
        }
        else {
                /*Binary interface not available, try open text interface */
                snprintf(full_path, USB_LINE_LEN, USB_TEXT_DIR"/%dt", handle->md.ifindex);  
                handle->fd = open(full_path, O_RDONLY, 0);
                if (handle->fd < 0)
                {
                        if (errno == ENOENT)
                        {
                                /*
                                 * Not found at the new location; try
                                 * the old location.
                                 */
                                snprintf(full_path, USB_LINE_LEN, USB_TEXT_DIR_OLD"/%dt", handle->md.ifindex);  
                                handle->fd = open(full_path, O_RDONLY, 0);
                        }
                        if (handle->fd < 0) {
                                /* no more fallback, give it up*/
                                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                        "Can't open USB bus file %s: %s", full_path, strerror(errno));
                                return PCAP_ERROR;
                        }
                }

                if (handle->opt.rfmon) {
                        /*
                         * Monitor mode doesn't apply to USB devices.
                         */
                        close(handle->fd);
                        return PCAP_ERROR_RFMON_NOTSUP;
                }

                handle->stats_op = usb_stats_linux;
                handle->read_op = usb_read_linux;
        }

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

        /* for plain binary access and text access we need to allocate the read
         * buffer */
        handle->buffer = malloc(handle->bufsize);
        if (!handle->buffer) {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                         "malloc: %s", pcap_strerror(errno));
                close(handle->fd);
                return PCAP_ERROR;
        }
        return 0;
}

static inline int 
ascii_to_int(char c)
{
        return c < 'A' ? c- '0': ((c<'a') ? c - 'A' + 10: c-'a'+10);
}

/*
 * see <linux-kernel-source>/Documentation/usb/usbmon.txt and 
 * <linux-kernel-source>/drivers/usb/mon/mon_text.c for urb string 
 * format description
 */
static int
usb_read_linux(pcap_t *handle, int max_packets, pcap_handler callback, u_char *user)
{
        /* see:
        * /usr/src/linux/Documentation/usb/usbmon.txt 
        * for message format
        */
        unsigned timestamp;
        int tag, cnt, ep_num, dev_addr, dummy, ret, urb_len, data_len;
        char etype, pipeid1, pipeid2, status[16], urb_tag, line[USB_LINE_LEN];
        char *string = line;
        u_char * rawdata = handle->buffer;
        struct pcap_pkthdr pkth;
        pcap_usb_header* uhdr = (pcap_usb_header*)handle->buffer;
        u_char urb_transfer=0;
        int incoming=0;

        /* ignore interrupt system call errors */
        do {
                ret = read(handle->fd, line, USB_LINE_LEN - 1);
                if (handle->break_loop)
                {
                        handle->break_loop = 0;
                        return -2;
                }
        } while ((ret == -1) && (errno == EINTR));
        if (ret < 0)
        {
                if (errno == EAGAIN)
                        return 0;       /* no data there */

                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "Can't read from fd %d: %s", handle->fd, strerror(errno));
                return -1;
        }

        /* read urb header; %n argument may increment return value, but it's 
        * not mandatory, so does not count on it*/
        string[ret] = 0;
        ret = sscanf(string, "%x %d %c %c%c:%d:%d %s%n", &tag, &timestamp, &etype, 
                &pipeid1, &pipeid2, &dev_addr, &ep_num, status, 
                &cnt);
        if (ret < 8)
        {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "Can't parse USB bus message '%s', too few tokens (expected 8 got %d)",
                    string, ret);
                return -1;
        }
        uhdr->id = tag;
        uhdr->device_address = dev_addr;
        uhdr->bus_id = handle->md.ifindex;
        uhdr->status = 0;
        string += cnt;

        /* don't use usbmon provided timestamp, since it have low precision*/
        if (gettimeofday(&pkth.ts, NULL) < 0) 
        {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                        "Can't get timestamp for message '%s' %d:%s", 
                        string, errno, strerror(errno));
                return -1;
        }
        uhdr->ts_sec = pkth.ts.tv_sec;
        uhdr->ts_usec = pkth.ts.tv_usec;

        /* parse endpoint information */
        if (pipeid1 == 'C')
                urb_transfer = URB_CONTROL;
        else if (pipeid1 == 'Z')
                urb_transfer = URB_ISOCHRONOUS;
        else if (pipeid1 == 'I')
                urb_transfer = URB_INTERRUPT;
        else if (pipeid1 == 'B')
                urb_transfer = URB_BULK;
        if (pipeid2 == 'i') {
                ep_num |= URB_TRANSFER_IN;
                incoming = 1;
        }
        if (etype == 'C')
                incoming = !incoming;

        /* direction check*/
        if (incoming)
        {
                if (handle->direction == PCAP_D_OUT)
                        return 0;
        }
        else
                if (handle->direction == PCAP_D_IN)
                        return 0;
        uhdr->event_type = etype;
        uhdr->transfer_type = urb_transfer;
        uhdr->endpoint_number = ep_num;
        pkth.caplen = sizeof(pcap_usb_header);
        rawdata += sizeof(pcap_usb_header);

        /* check if this is a setup packet */
        ret = sscanf(status, "%d", &dummy);
        if (ret != 1)
        {
                /* this a setup packet, setup data can be filled with underscore if
                * usbmon has not been able to read them, so we must parse this fields as 
                * strings */
                pcap_usb_setup* shdr;
                char str1[3], str2[3], str3[5], str4[5], str5[5];
                ret = sscanf(string, "%s %s %s %s %s%n", str1, str2, str3, str4, 
                str5, &cnt);
                if (ret < 5)
                {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                "Can't parse USB bus message '%s', too few tokens (expected 5 got %d)",
                                string, ret);
                        return -1;
                }
                string += cnt;

                /* try to convert to corresponding integer */
                shdr = &uhdr->setup;
                shdr->bmRequestType = strtoul(str1, 0, 16);
                shdr->bRequest = strtoul(str2, 0, 16);
                shdr->wValue = htols(strtoul(str3, 0, 16));
                shdr->wIndex = htols(strtoul(str4, 0, 16));
                shdr->wLength = htols(strtoul(str5, 0, 16));

                uhdr->setup_flag = 0;
        }
        else 
                uhdr->setup_flag = 1;

        /* read urb data */
        ret = sscanf(string, " %d%n", &urb_len, &cnt);
        if (ret < 1)
        {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                  "Can't parse urb length from '%s'", string);
                return -1;
        }
        string += cnt;

        /* urb tag is not present if urb length is 0, so we can stop here 
         * text parsing */
        pkth.len = urb_len+pkth.caplen;
        uhdr->urb_len = urb_len;
        uhdr->data_flag = 1;
        data_len = 0;
        if (uhdr->urb_len == 0)
                goto got;

        /* check for data presence; data is present if and only if urb tag is '=' */
        if (sscanf(string, " %c", &urb_tag) != 1)
        {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                        "Can't parse urb tag from '%s'", string);
                return -1;
        }

        if (urb_tag != '=') 
                goto got;

        /* skip urb tag and following space */
        string += 3;

        /* if we reach this point we got some urb data*/
        uhdr->data_flag = 0;

        /* read all urb data; if urb length is greater then the usbmon internal 
         * buffer length used by the kernel to spool the URB, we get only
         * a partial information.
         * At least until linux 2.6.17 there is no way to set usbmon intenal buffer
         * length and default value is 130. */
        while ((string[0] != 0) && (string[1] != 0) && (pkth.caplen < handle->snapshot))
        {
                rawdata[0] = ascii_to_int(string[0]) * 16 + ascii_to_int(string[1]);
                rawdata++;
                string+=2;
                if (string[0] == ' ')
                        string++;
                pkth.caplen++;
                data_len++;
        }

got:
        uhdr->data_len = data_len;
        if (pkth.caplen > handle->snapshot)
                pkth.caplen = handle->snapshot;

        if (handle->fcode.bf_insns == NULL ||
            bpf_filter(handle->fcode.bf_insns, handle->buffer,
              pkth.len, pkth.caplen)) {
                handle->md.packets_read++;
                callback(user, &pkth, handle->buffer);
                return 1;
        }
        return 0;       /* didn't pass filter */
}

static int
usb_inject_linux(pcap_t *handle, const void *buf, size_t size)
{
        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, "inject not supported on "
                "USB devices");
        return (-1);
}

static int 
usb_stats_linux(pcap_t *handle, struct pcap_stat *stats)
{
        int dummy, ret, consumed, cnt;
        char string[USB_LINE_LEN];
        char token[USB_LINE_LEN];
        char * ptr = string;
        int fd;

        snprintf(string, USB_LINE_LEN, USB_TEXT_DIR"/%ds", handle->md.ifindex);
        fd = open(string, O_RDONLY, 0);
        if (fd < 0)
        {
                if (errno == ENOENT)
                {
                        /*
                         * Not found at the new location; try the old
                         * location.
                         */
                        snprintf(string, USB_LINE_LEN, USB_TEXT_DIR_OLD"/%ds", handle->md.ifindex);
                        fd = open(string, O_RDONLY, 0);
                }
                if (fd < 0) {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                                "Can't open USB stats file %s: %s", 
                                string, strerror(errno));
                        return -1;
                }
        }

        /* read stats line */
        do {
                ret = read(fd, string, USB_LINE_LEN-1);
        } while ((ret == -1) && (errno == EINTR));
        close(fd);

        if (ret < 0)
        {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                        "Can't read stats from fd %d ", fd);
                return -1;
        }
        string[ret] = 0;

        /* extract info on dropped urbs */
        for (consumed=0; consumed < ret; ) {
                /* from the sscanf man page: 
                 * The C standard says: "Execution of a %n directive does 
                 * not increment the assignment count returned at the completion
                 * of  execution" but the Corrigendum seems to contradict this.
                 * Do not make any assumptions on the effect of %n conversions 
                 * on the return value and explicitly check for cnt assignmet*/
                int ntok;

                cnt = -1;
                ntok = sscanf(ptr, "%s%n", token, &cnt);
                if ((ntok < 1) || (cnt < 0))
                        break;
                consumed += cnt;
                ptr += cnt;
                if (strcmp(token, "nreaders") == 0)
                        ret = sscanf(ptr, "%d", &stats->ps_drop);
                else 
                        ret = sscanf(ptr, "%d", &dummy);
                if (ntok != 1)
                        break;
                consumed += cnt;
                ptr += cnt;
        }

        stats->ps_recv = handle->md.packets_read;
        stats->ps_ifdrop = 0;
        return 0;
}

static int 
usb_setdirection_linux(pcap_t *p, pcap_direction_t d)
{
        p->direction = d;
        return 0;
}


static int 
usb_stats_linux_bin(pcap_t *handle, struct pcap_stat *stats)
{
        int ret;
        struct mon_bin_stats st;
        ret = ioctl(handle->fd, MON_IOCG_STATS, &st);
        if (ret < 0)
        {
                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                        "Can't read stats from fd %d:%s ", handle->fd, strerror(errno));
                return -1;
        }

        stats->ps_recv = handle->md.packets_read + st.queued;
        stats->ps_drop = st.dropped;
        stats->ps_ifdrop = 0;
        return 0;
}

/*
 * see <linux-kernel-source>/Documentation/usb/usbmon.txt and 
 * <linux-kernel-source>/drivers/usb/mon/mon_bin.c binary ABI
 */
static int
usb_read_linux_bin(pcap_t *handle, int max_packets, pcap_handler callback, u_char *user)
{
        struct mon_bin_get info;
        int ret;
        struct pcap_pkthdr pkth;
        int clen = handle->snapshot - sizeof(pcap_usb_header);

        /* the usb header is going to be part of 'packet' data*/
        info.hdr = (pcap_usb_header*) handle->buffer;
        info.data = handle->buffer + sizeof(pcap_usb_header);
        info.data_len = clen;

        /* ignore interrupt system call errors */
        do {
                ret = ioctl(handle->fd, MON_IOCX_GET, &info);
                if (handle->break_loop)
                {
                        handle->break_loop = 0;
                        return -2;
                }
        } while ((ret == -1) && (errno == EINTR));
        if (ret < 0)
        {
                if (errno == EAGAIN)
                        return 0;       /* no data there */

                snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                    "Can't read from fd %d: %s", handle->fd, strerror(errno));
                return -1;
        }

        /* we can get less that than really captured from kernel, depending on
         * snaplen, so adjust header accordingly */
        if (info.hdr->data_len < clen)
                clen = info.hdr->data_len;
        info.hdr->data_len = clen;
        pkth.caplen = clen + sizeof(pcap_usb_header);
        pkth.len = info.hdr->data_len + sizeof(pcap_usb_header);
        pkth.ts.tv_sec = info.hdr->ts_sec;
        pkth.ts.tv_usec = info.hdr->ts_usec;

        if (handle->fcode.bf_insns == NULL ||
            bpf_filter(handle->fcode.bf_insns, handle->buffer,
              pkth.len, pkth.caplen)) {
                handle->md.packets_read++;
                callback(user, &pkth, handle->buffer);
                return 1;
        }

        return 0;       /* didn't pass filter */
}

/*
 * see <linux-kernel-source>/Documentation/usb/usbmon.txt and 
 * <linux-kernel-source>/drivers/usb/mon/mon_bin.c binary ABI
 */
#define VEC_SIZE 32
static int
usb_read_linux_mmap(pcap_t *handle, int max_packets, pcap_handler callback, u_char *user)
{
        struct mon_bin_mfetch fetch;
        int32_t vec[VEC_SIZE];
        struct pcap_pkthdr pkth;
        pcap_usb_header* hdr;
        int nflush = 0;
        int packets = 0;
        int clen, max_clen;

        max_clen = handle->snapshot - sizeof(pcap_usb_header);

        for (;;) {
                int i, ret;
                int limit = max_packets - packets;
                if (limit <= 0)
                        limit = VEC_SIZE;
                if (limit > VEC_SIZE)
                        limit = VEC_SIZE;

                /* try to fetch as many events as possible*/
                fetch.offvec = vec;
                fetch.nfetch = limit;
                fetch.nflush = nflush;
                /* ignore interrupt system call errors */
                do {
                        ret = ioctl(handle->fd, MON_IOCX_MFETCH, &fetch);
                        if (handle->break_loop)
                        {
                                handle->break_loop = 0;
                                return -2;
                        }
                } while ((ret == -1) && (errno == EINTR));
                if (ret < 0)
                {
                        if (errno == EAGAIN)
                                return 0;       /* no data there */

                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                            "Can't mfetch fd %d: %s", handle->fd, strerror(errno));
                        return -1;
                }

                /* keep track of processed events, we will flush them later */
                nflush = fetch.nfetch;
                for (i=0; i<fetch.nfetch; ++i) {
                        /* discard filler */
                        hdr = (pcap_usb_header*) &handle->md.mmapbuf[vec[i]];
                        if (hdr->event_type == '@') 
                                continue;

                        /* we can get less that than really captured from kernel, depending on
                        * snaplen, so adjust header accordingly */
                        clen = max_clen;
                        if (hdr->data_len < clen)
                                clen = hdr->data_len;

                        /* get packet info from header*/
                        pkth.caplen = clen + sizeof(pcap_usb_header_mmapped);
                        pkth.len = hdr->data_len + sizeof(pcap_usb_header_mmapped);
                        pkth.ts.tv_sec = hdr->ts_sec;
                        pkth.ts.tv_usec = hdr->ts_usec;

                        if (handle->fcode.bf_insns == NULL ||
                            bpf_filter(handle->fcode.bf_insns, (u_char*) hdr,
                              pkth.len, pkth.caplen)) {
                                handle->md.packets_read++;
                                callback(user, &pkth, (u_char*) hdr);
                                packets++;
                        }
                }

                /* with max_packets <= 0 we stop afer the first chunk*/
                if ((max_packets <= 0) || (packets == max_packets))
                        break;
        }

        /* flush pending events*/
        ioctl(handle->fd, MON_IOCH_MFLUSH, nflush);
        return packets;
}

static void
usb_cleanup_linux_mmap(pcap_t* handle)
{
        /* if we have a memory-mapped buffer, unmap it */
        if (handle->md.mmapbuf != NULL) {
                munmap(handle->md.mmapbuf, handle->md.mmapbuflen);
                handle->md.mmapbuf = NULL;
        }
        pcap_cleanup_live_common(handle);
}