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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 1.129.2.29 2008-10-28 00:50:39 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"
#include "pcap/vlan.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
#  ifdef PACKET_AUXDATA
#   define HAVE_PACKET_AUXDATA
#  endif /* PACKET_AUXDATA */
# 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
#  ifdef TPACKET2_HDRLEN
#   define HAVE_TPACKET2
#  else
#   define TPACKET_V1   0
#  endif /* TPACKET2_HDRLEN */
# 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_cleanup_linux(pcap_t *);

00248 union thdr {
      struct tpacket_hdr      *h1;
      struct tpacket2_hdr     *h2;
      void              *raw;
};

#ifdef HAVE_PACKET_RING
#define RING_GET_FRAME(h) (((union thdr **)h->buffer)[h->offset])

static void destroy_ring(pcap_t *handle);
static int create_ring(pcap_t *handle);
static int prepare_tpacket_socket(pcap_t *handle);
static void pcap_cleanup_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, char *ebuf);
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_cleanup_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_cleanup_live_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         status = 0;
      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->cleanup_op = pcap_cleanup_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");
                  status = PCAP_WARNING_PROMISC_NOTSUP;
            }

      } 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 ((status = 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 (status == 0) {
            /* Non-fatal error; try old way */
            if ((status = 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).
             */
            goto fail;
      }

      if (handle->opt.buffer_size != 0) {
            /*
             * Set the socket buffer size to the specified value.
             */
            if (setsockopt(handle->fd, SOL_SOCKET, SO_RCVBUF,
                &handle->opt.buffer_size,
                sizeof(handle->opt.buffer_size)) == -1) {
                  snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                         "SO_RCVBUF: %s", pcap_strerror(errno));
                  status = PCAP_ERROR;
                  goto fail;
            }
      }

      /* Allocate the buffer */

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

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

      return status;

fail:
      pcap_cleanup_linux(handle);
      return status;
}

/*
 *  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
#if defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI)
      struct iovec            iov;
      struct msghdr           msg;
      struct cmsghdr          *cmsg;
      union {
            struct cmsghdr    cmsg;
            char        buf[CMSG_SPACE(sizeof(struct tpacket_auxdata))];
      } cmsg_buf;
#else /* defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI) */
      socklen_t         fromlen;
#endif /* defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI) */
      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.
       * We ignore EINTR, as that might just be due to a signal
       * being delivered - if the signal should interrupt the
       * loop, the signal handler should call pcap_breakloop()
       * to set handle->break_loop (we ignore it on other
       * platforms as well).
       * We also ignore ENETDOWN, so that we can continue to
       * capture traffic if the interface goes down and comes
       * back up again; comments in the kernel indicate that
       * we'll just block waiting for packets if we try to
       * receive from a socket that delivered ENETDOWN, and,
       * if we're using a memory-mapped buffer, we won't even
       * get notified of "network down" events.
       */
      bp = handle->buffer + handle->offset;

#if defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI)
      msg.msg_name            = &from;
      msg.msg_namelen         = sizeof(from);
      msg.msg_iov       = &iov;
      msg.msg_iovlen          = 1;
      msg.msg_control         = &cmsg_buf;
      msg.msg_controllen      = sizeof(cmsg_buf);
      msg.msg_flags           = 0;

      iov.iov_len       = handle->bufsize - offset;
      iov.iov_base            = bp + offset;
#endif /* defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI) */

      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;
            }

#if defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI)
            packet_len = recvmsg(handle->fd, &msg, MSG_TRUNC);
#else /* defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI) */
            fromlen = sizeof(from);
            packet_len = recvfrom(
                  handle->fd, bp + offset,
                  handle->bufsize - offset, MSG_TRUNC,
                  (struct sockaddr *) &from, &fromlen);
#endif /* defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI) */
      } while (packet_len == -1 && (errno == EINTR || errno == ENETDOWN));

      /* 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;
      }

#if defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI)
      for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
            struct tpacket_auxdata *aux;
            unsigned int len;
            struct vlan_tag *tag;

            if (cmsg->cmsg_len < CMSG_LEN(sizeof(struct tpacket_auxdata)) ||
                cmsg->cmsg_level != SOL_PACKET ||
                cmsg->cmsg_type != PACKET_AUXDATA)
                  continue;

            aux = (struct tpacket_auxdata *)CMSG_DATA(cmsg);
            if (aux->tp_vlan_tci == 0)
                  continue;

            len = packet_len > iov.iov_len ? iov.iov_len : packet_len;
            if (len < 2 * ETH_ALEN)
                  break;

            bp -= VLAN_TAG_LEN;
            memmove(bp, bp + VLAN_TAG_LEN, 2 * ETH_ALEN);

            tag = (struct vlan_tag *)(bp + 2 * ETH_ALEN);
            tag->vlan_tpid = htons(ETH_P_8021Q);
            tag->vlan_tci = htons(aux->tp_vlan_tci);

            packet_len += VLAN_TAG_LEN;
      }
#endif /* defined(HAVE_PACKET_AUXDATA) && defined(HAVE_LINUX_TPACKET_AUXDATA_TP_VLAN_TCI) */
#endif /* HAVE_PF_PACKET_SOCKETS */

      /*
       * 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;

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

      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, val;
      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)) != 1) {
                  close(sock_fd);
                  if (err < 0)
                        return err;
                  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;
            }
      }

      /* Enable auxillary data if supported and reserve room for
       * reconstructing VLAN headers. */
#ifdef HAVE_PACKET_AUXDATA
      val = 1;
      if (setsockopt(sock_fd, SOL_PACKET, PACKET_AUXDATA, &val,
                   sizeof(val)) == -1 && errno != ENOPROTOOPT) {
            snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                   "setsockopt: %s", pcap_strerror(errno));
            close(sock_fd);
            return PCAP_ERROR;
      }
      handle->offset += VLAN_TAG_LEN;
#endif /* HAVE_PACKET_AUXDATA */

      /*
       * 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 = prepare_tpacket_socket(handle);
      if (ret == 0)
            return ret;
      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->cleanup_op = pcap_cleanup_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 int
prepare_tpacket_socket(pcap_t *handle)
{
#ifdef HAVE_TPACKET2
      socklen_t len;
      int val;
#endif

      handle->md.tp_version = TPACKET_V1;
      handle->md.tp_hdrlen = sizeof(struct tpacket_hdr);

#ifdef HAVE_TPACKET2
      /* Probe whether kernel supports TPACKET_V2 */
      val = TPACKET_V2;
      len = sizeof(val);
      if (getsockopt(handle->fd, SOL_PACKET, PACKET_HDRLEN, &val, &len) < 0) {
            if (errno == ENOPROTOOPT)
                  return 1;
            snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                   "can't get TPACKET_V2 header len on socket %d: %d-%s",
                   handle->fd, errno, pcap_strerror(errno));
            return 0;
      }
      handle->md.tp_hdrlen = val;

      val = TPACKET_V2;
      if (setsockopt(handle->fd, SOL_PACKET, PACKET_VERSION, &val,
                   sizeof(val)) < 0) {
            snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                   "can't activate TPACKET_V2 on socket %d: %d-%s",
                   handle->fd, errno, pcap_strerror(errno));
            return 0;
      }
      handle->md.tp_version = TPACKET_V2;

      /* Reserve space for VLAN tag reconstruction */
      val = VLAN_TAG_LEN;
      if (setsockopt(handle->fd, SOL_PACKET, PACKET_RESERVE, &val,
                   sizeof(val)) < 0) {
            snprintf(handle->errbuf, PCAP_ERRBUF_SIZE,
                   "can't set up reserve on socket %d: %d-%s",
                   handle->fd, errno, pcap_strerror(errno));
            return 0;
      }

#endif /* HAVE_TPACKET2 */
      return 1;
}

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_ALIGN(handle->md.tp_hdrlen) +
                                sizeof(struct sockaddr_ll));
      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(union thdr *));
      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) {
            void *base = &handle->bp[i*req.tp_block_size];
            for (j=0; j<frames_per_block; ++j, ++handle->offset) {
                  RING_GET_FRAME(handle) = base;
                  base += req.tp_frame_size;
            }
      }

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

/* free all ring related resources*/
static void
destroy_ring(pcap_t *handle)
{
      /* 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;
      }
}

static void
pcap_cleanup_linux_mmap( pcap_t *handle )
{
      destroy_ring(handle);
      pcap_cleanup_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 inline union thdr *
pcap_get_ring_frame(pcap_t *handle, int status)
{
      union thdr h;

      h.raw = RING_GET_FRAME(handle);
      switch (handle->md.tp_version) {
      case TPACKET_V1:
            if (status != (h.h1->tp_status ? TP_STATUS_USER :
                                    TP_STATUS_KERNEL))
                  return NULL;
            break;
#ifdef HAVE_TPACKET2
      case TPACKET_V2:
            if (status != (h.h2->tp_status ? TP_STATUS_USER :
                                    TP_STATUS_KERNEL))
                  return NULL;
            break;
#endif
      }
      return h.raw;
}

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) &&
          !pcap_get_ring_frame(handle, TP_STATUS_USER)) {
            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;
            union thdr h;
            unsigned int tp_len;
            unsigned int tp_mac;
            unsigned int tp_snaplen;
            unsigned int tp_sec;
            unsigned int tp_usec;

            h.raw = pcap_get_ring_frame(handle, TP_STATUS_USER);
            if (!h.raw)
                  break;

            switch (handle->md.tp_version) {
            case TPACKET_V1:
                  tp_len         = h.h1->tp_len;
                  tp_mac         = h.h1->tp_mac;
                  tp_snaplen = h.h1->tp_snaplen;
                  tp_sec         = h.h1->tp_sec;
                  tp_usec        = h.h1->tp_usec;
                  break;
#ifdef HAVE_TPACKET2
            case TPACKET_V2:
                  tp_len         = h.h2->tp_len;
                  tp_mac         = h.h2->tp_mac;
                  tp_snaplen = h.h2->tp_snaplen;
                  tp_sec         = h.h2->tp_sec;
                  tp_usec        = h.h2->tp_nsec / 1000;
                  break;
#endif
            default:
                  snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, 
                        "unsupported tpacket version %d",
                        handle->md.tp_version);
                  return -1;
            }
            /* perform sanity check on internal offset. */
            if (tp_mac + tp_snaplen > handle->bufsize) {
                  snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, 
                        "corrupted frame on kernel ring mac "
                        "offset %d + caplen %d > frame len %d", 
                        tp_mac, tp_snaplen, handle->bufsize);
                  return -1;
            }

            /* run filter on received packet
             * If the kernel filtering is enabled we need to run the
             * filter until all the frames present into the ring 
             * at filter creation time are processed. 
             * In 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*)h.raw + 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,
                              tp_len, tp_snaplen) == 0))
                  goto skip;

            /* check direction and interface index */
            sll = (void *)h.raw + TPACKET_ALIGN(handle->md.tp_hdrlen);
            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 = tp_sec;
            pcaphdr.ts.tv_usec = tp_usec;
            pcaphdr.caplen = tp_snaplen;
            pcaphdr.len = tp_len;

            /* if required build in place the sll header*/
            if (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 *)h.raw +
                                 TPACKET_ALIGN(handle->md.tp_hdrlen) +
                                 sizeof(struct sockaddr_ll)) {
                        snprintf(handle->errbuf, PCAP_ERRBUF_SIZE, 
                              "cooked-mode frame doesn't have room for sll header");
                        return -1;
                  }

                  /*
                   * OK, that worked; construct the sll header.
                   */
                  hdrp = (struct sll_header *)bp;
                  hdrp->sll_pkttype = 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;
            }

#ifdef HAVE_TPACKET2
            if (handle->md.tp_version == TPACKET_V2 && h.h2->tp_vlan_tci &&
                tp_snaplen >= 2 * ETH_ALEN) {
                  struct vlan_tag *tag;

                  bp -= VLAN_TAG_LEN;
                  memmove(bp, bp + VLAN_TAG_LEN, 2 * ETH_ALEN);

                  tag = (struct vlan_tag *)(bp + 2 * ETH_ALEN);
                  tag->vlan_tpid = htons(ETH_P_8021Q);
                  tag->vlan_tci = htons(h.h2->tp_vlan_tci);

                  pcaphdr.caplen += VLAN_TAG_LEN;
                  pcaphdr.len += VLAN_TAG_LEN;
            }
#endif

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

skip:
            /* next packet */
            switch (handle->md.tp_version) {
            case TPACKET_V1:
                  h.h1->tp_status = TP_STATUS_KERNEL;
                  break;
#ifdef HAVE_TPACKET2
            case TPACKET_V2:
                  h.h2->tp_status = TP_STATUS_KERNEL;
                  break;
#endif
            }
            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 (!pcap_get_ring_frame(handle, 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.
 *  Return 1 on success, 0 if we should try a SOCK_PACKET socket,
 *  or a PCAP_ERROR_ value on a hard error.
 */
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) {
            if (errno == ENETDOWN) {
                  /*
                   * Return a "network down" indication, so that
                   * the application can report that rather than
                   * saying we had a mysterious failure and
                   * suggest that they report a problem to the
                   * libpcap developers.
                   */
                  return PCAP_ERROR_IFACE_NOT_UP;
            } else {
                  snprintf(ebuf, PCAP_ERRBUF_SIZE,
                         "bind: %s", pcap_strerror(errno));
                  return PCAP_ERROR;
            }
      }

      /* 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 0;
      }

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

      return 1;
}

/*
 * 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, char *ebuf)
{
#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 */
      snprintf(ebuf, PCAP_ERRBUF_SIZE,
          "%s: SIOCGIWPRIV: %s", device, pcap_strerror(errno));
      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.
 *
 * XXX - airmon-ng does special stuff with the Orinoco driver and the
 * wlan-ng driver.
 */
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.
       * airmon-ng does "wlanconfig ath create wlandev {if} wlanmode
       * monitor -bssid", which apparently spits out a line "athN"
       * where "athN" is the monitor mode device.  To leave monitor
       * mode, it destroys the monitor mode device.
       *
       * 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.
       * (airmon-ng doesn't appear to use that, though.)
       *
       * It would be Truly Wonderful if mac80211 and nl80211 cleaned this
       * up, and if all drivers were converted to mac80211 drivers.
       *
       * If interface {if} is a mac80211 driver, the file
       * /sys/class/net/{if}/phy80211 is a symlink to
       * /sys/class/ieee80211/{phydev}, for some {phydev}.
       *
       * On Fedora 9, with a 2.6.26.3-29 kernel, my Zydas stick, at
       * least, has a "wmaster0" device and a "wlan0" device; the
       * latter is the one with the IP address.  Both show up in
       * "tcpdump -D" output.  Capturing on the wmaster0 device
       * captures with 802.11 headers.
       *
       * airmon-ng searches through /sys/class/net for devices named
       * monN, starting with mon0; as soon as one *doesn't* exist,
       * it chooses that as the monitor device name.  If the "iw"
       * command exists, it does "iw dev {if} interface add {monif}
       * type monitor", where {monif} is the monitor device.  It
       * then (sigh) sleeps .1 second, and then configures the
       * device up.  Otherwise, if /sys/class/ieee80211/{phydev}/add_iface
       * is a file, it writes {mondev}, without a newline, to that file,
       * and again (sigh) sleeps .1 second, and then iwconfig's that
       * device into monitor mode and configures it up.  Otherwise,
       * you can't do monitor mode.
       *
       * All these devices are "glued" together by having the
       * /sys/class/net/{device}/phy80211 links pointing to the same
       * place, so, given a wmaster, wlan, or mon device, you can
       * find the other devices by looking for devices with
       * the same phy80211 link.
       *
       * To turn monitor mode off, delete the monitor interface,
       * either with "iw dev {monif} interface del" or by sending
       * {monif}, with no NL, down /sys/class/ieee80211/{phydev}/remove_iface
       *
       * Note: if you try to create a monitor device named "monN", and
       * there's already a "monN" device, it fails, as least with
       * the netlink interface (which is what iw uses), with a return
       * value of -ENFILE.  (Return values are negative errnos.)  We
       * could probably use that to find an unused device.
       */
      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, handle->errbuf);
      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 * sizeof (struct iw_priv_args));
      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));
            free(priv);
            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;
                  }
            }
      }
      free(priv);

      /*
       * 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;
      }

      /*
       * XXX - airmon-ng does "iwconfig {if} key off" after setting
       * monitor mode and setting the channel, and then does
       * "iwconfig up".
       */

      /*
       * 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_PERM_DENIED;
      }

      /* 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) {
            snprintf(ebuf, PCAP_ERRBUF_SIZE,
                   "SIOCGIFHWADDR: %s", pcap_strerror(errno));
            if (errno == ENODEV) {
                  /*
                   * No such device.
                   */
                  return PCAP_ERROR_NO_SUCH_DEVICE;
            }
            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

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