simh-testsetgenerator/sim_ether.c

/* sim_ether.c: OS-dependent network routines
  ------------------------------------------------------------------------------
   Copyright (c) 2002-2003, David T. Hittner

   Permission is hereby granted, free of charge, to any person obtaining a
   copy of this software and associated documentation files (the "Software"),
   to deal in the Software without restriction, including without limitation
   the rights to use, copy, modify, merge, publish, distribute, sublicense,
   and/or sell copies of the Software, and to permit persons to whom the
   Software is furnished to do so, subject to the following conditions:

   The above copyright notice and this permission notice shall be included in
   all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
   THE AUTHOR BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
   IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

   Except as contained in this notice, the name of the author shall not be
   used in advertising or otherwise to promote the sale, use or other dealings
   in this Software without prior written authorization from the author.

  ------------------------------------------------------------------------------

  This ethernet simulation is based on the PCAP and WinPcap packages.

  PCAP/WinPcap was chosen as the basis for network code since it is the most
  "universal" of the various network packages available. Using this style has
  allowed rapid network development for the major SIMH platforms. Developing
  a network package specifically for SIMH was rejected due to the time required;
  the advantage would be a more easily compiled and integrated code set.

  There are various problems associated with use of ethernet networking, which
  would be true regardless of the network package used, since there are no
  universally accepted networking methods. The most serious of these is getting
  the proper networking package loaded onto the system, since most environments
  do not come with the network interface packages loaded.

  The second most serious network issue relates to security. The network
  simulation needs to simulate operating system level functionality (packet
  driving). However, the host network programming interfaces tend to operate at
  the user level of functionality, so getting to the full functionality of
  the network interface usually requires that the person executing the
  network code be a privileged user of the host system. See the PCAP/WinPcap
  documentation for the appropriate host platform if unprivileged use of
  networking is needed - there may be known workarounds.

  ------------------------------------------------------------------------------

  Modification history:

  15-Dec-03  MP   polished generic libpcap support.
  05-Dec-03  DTH  Genericized eth_devices() and #ifdefs
  03-Dec-03  MP   Added Solaris support
  02-Dec-03  DTH  Corrected decnet fix to use reflection counting
  01-Dec-03  DTH  Added BPF source filtering and reflection counting
  28-Nov-03  DTH  Rewrote eth_devices using universal pcap_findalldevs()
  25-Nov-03  DTH  Verified DECNET_FIX, reversed ifdef to mainstream code
  19-Nov-03  MP   Fixed BPF functionality on Linux/BSD.
  17-Nov-03  DTH  Added xBSD simplification
  14-Nov-03  DTH  Added #ifdef DECNET_FIX for problematic duplicate detection code
  13-Nov-03  DTH  Merged in __FreeBSD__ support
  21-Oct-03  MP   Added enriched packet dumping for debugging
  20-Oct-03  MP   Added support for multiple ethernet devices on VMS
  20-Sep-03  Ankan Add VMS support (Alpha only)
  29-Sep-03  MP   Changed separator character in eth_fmt_mac to be ":" to
                  format ethernet addresses the way the BPF compile engine
                  wants to see them.
                  Added BPF support to filter packets
                  Added missing printf in eth_close
  07-Jun-03  MP   Added WIN32 support for DECNET duplicate address detection.
  06-Jun-03  MP   Fixed formatting of Ethernet Protocol Type in eth_packet_trace
  30-May-03  DTH  Changed WIN32 to _WIN32 for consistency
  07-Mar-03  MP   Fixed Linux implementation of PacketGetAdapterNames to also
                  work on Red Hat 6.2-sparc and Debian 3.0r1-sparc.
  03-Mar-03  MP   Changed logging to be consistent on stdout and sim_log
  01-Feb-03  MP   Changed type of local variables in eth_packet_trace to
                  conform to the interface needs of eth_mac_fmt wich produces
                  char data instead of unsigned char data.  Suggested by the
                  DECC compiler.
  15-Jan-03  DTH  Corrected PacketGetAdapterNames parameter2 datatype
  26-Dec-02  DTH  Merged Mark Pizzolato's enhancements with main source
                  Added networking documentation
                  Changed _DEBUG to ETH_DEBUG
  20-Dec-02  MP   Added display of packet CRC to the eth_packet_trace.
                  This helps distinguish packets with identical lengths
                  and protocols.
  05-Dec-02  MP   With the goal of draining the input buffer more rapidly
                  changed eth_read to call pcap_dispatch repeatedly until
                  either a timeout returns nothing or a packet allowed by
                  the filter is seen.  This more closely reflects how the
                  pcap layer will work when the filtering is actually done
                  by a bpf filter.
  31-Oct-02  DTH  Added USE_NETWORK conditional
                  Reworked not attached test
                  Added OpenBSD support (from Federico Schwindt)
                  Added ethX detection simplification (from Megan Gentry)
                  Removed sections of temporary code
                  Added parameter validation
  23-Oct-02  DTH  Beta 5 released
  22-Oct-02  DTH  Added all_multicast and promiscuous support
                  Fixed not attached behavior
  21-Oct-02  DTH  Added NetBSD support (from Jason Thorpe)
                  Patched buffer size to make sure entire packet is read in
                  Made 'ethX' check characters passed as well as length
                  Corrected copyright again
  16-Oct-02  DTH  Beta 4 released
                  Corrected copyright
  09-Oct-02  DTH  Beta 3 released
                  Added pdp11 write acceleration (from Patrick Caulfield)
  08-Oct-02  DTH  Beta 2 released
                  Integrated with 2.10-0p4
                  Added variable vector and copyrights
  04-Oct-02  DTH  Added linux support (from Patrick Caulfield)
  03-Oct-02  DTH  Beta version of xq/sim_ether released for SIMH 2.09-11
  24-Sep-02  DTH  Finished eth_devices, eth_getname
  18-Sep-02  DTH  Callbacks implemented
  13-Sep-02  DTH  Basic packet read/write written
  20-Aug-02  DTH  Created Sim_Ether for O/S independant ethernet implementation

  ------------------------------------------------------------------------------
*/

#include <ctype.h>
#include "sim_ether.h"
#include "sim_sock.h"

extern FILE *sim_log;

/* make common BSD code a bit easier to read in this file */
/* OS/X seems to define and compile using one of these BSD types */
#if defined(__NetBSD__) || defined (__OpenBSD__) || defined (__FreeBSD__)
#define xBSD 1
#endif

/* make common winpcap code a bit easier to read in this file */
#if defined(_WIN32) || defined(VMS)
#define WIN_PCAP 1
#define HAS_PCAP_SENDPACKET 1
#define PCAP_READ_TIMEOUT -1
#else
#define PCAP_READ_TIMEOUT  1
#endif

/*============================================================================*/
/*                  OS-independant ethernet routines                          */
/*============================================================================*/

void eth_mac_fmt(ETH_MAC* mac, char* buff)
{
  uint8* m = (uint8*) mac;
  sprintf(buff, "%02X:%02X:%02X:%02X:%02X:%02X", m[0], m[1], m[2], m[3], m[4], m[5]);
  return;
}

static const uint32 crcTable[256] = {
  0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F,
  0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988,
  0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91, 0x1DB71064, 0x6AB020F2,
  0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
  0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9,
  0xFA0F3D63, 0x8D080DF5, 0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,
  0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B, 0x35B5A8FA, 0x42B2986C,
  0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
  0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423,
  0xCFBA9599, 0xB8BDA50F, 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
  0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D, 0x76DC4190, 0x01DB7106,
  0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
  0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D,
  0x91646C97, 0xE6635C01, 0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E,
  0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457, 0x65B0D9C6, 0x12B7E950,
  0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
  0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541, 0x3DD895D7,
  0xA4D1C46D, 0xD3D6F4FB, 0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0,
  0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA,
  0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
  0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81,
  0xB7BD5C3B, 0xC0BA6CAD, 0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,
  0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683, 0xE3630B12, 0x94643B84,
  0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
  0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB,
  0x196C3671, 0x6E6B06E7, 0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,
  0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5, 0xD6D6A3E8, 0xA1D1937E,
  0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
  0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55,
  0x316E8EEF, 0x4669BE79, 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
  0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F, 0xC5BA3BBE, 0xB2BD0B28,
  0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
  0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F,
  0x72076785, 0x05005713, 0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38,
  0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21, 0x86D3D2D4, 0xF1D4E242,
  0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
  0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69,
  0x616BFFD3, 0x166CCF45, 0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2,
  0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC,
  0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
  0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693,
  0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94,
  0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D
};

uint32 eth_crc32(uint32 crc, const void* vbuf, size_t len)
{
  const uint32 mask = 0xFFFFFFFF;
  const unsigned char* buf = (const unsigned char*)vbuf;

  crc ^= mask;
  while (0 != len--)
    crc = (crc >> 8) ^ crcTable[ (crc ^ (*buf++)) & 0xFF ];
  return(crc ^ mask);
}

void eth_packet_trace_ex(ETH_PACK* packet, char* msg, int dmp)
{
  char src[20];
  char dst[20];
  unsigned short* proto = (unsigned short*) &packet->msg[12];
  uint32 crc = eth_crc32(0, packet->msg, packet->len);
  eth_mac_fmt((ETH_MAC*)&packet->msg[0], dst);
  eth_mac_fmt((ETH_MAC*)&packet->msg[6], src);
  printf("Eth: %s  dst: %s  src: %s  proto: 0x%04X  len: %d  crc: %X\r\n",
         msg, dst, src, ntohs(*proto), packet->len, crc);
  if (dmp) {
    int i, same, group, sidx, oidx;
    char outbuf[80], strbuf[18];
    static char hex[] = "0123456789ABCDEF";
    for (i=same=0; i<packet->len; i += 16) {
      if ((i > 0) && (0 == memcmp(&packet->msg[i], &packet->msg[i-16], 16))) {
        ++same;
        continue;
      }
      if (same > 0) {
        printf("%04X thru %04X same as above\r\n", i-(16*same), i-1);
        same = 0;
      }
      group = (((packet->len - i) > 16) ? 16 : (packet->len - i));
      for (sidx=oidx=0; sidx<group; ++sidx) {
        outbuf[oidx++] = ' ';
        outbuf[oidx++] = hex[(packet->msg[i+sidx]>>4)&0xf];
        outbuf[oidx++] = hex[packet->msg[i+sidx]&0xf];
        if (isprint(packet->msg[i+sidx]))
          strbuf[sidx] = packet->msg[i+sidx];
        else
          strbuf[sidx] = '.';
      }
      outbuf[oidx] = '\0';
      strbuf[sidx] = '\0';
      printf("%04X%-48s %s\r\n", i, outbuf, strbuf);
    }
    if (same > 0)
      printf("%04X thru %04X same as above\r\n", i-(16*same), packet->len-1);
  }
}

void eth_packet_trace(ETH_PACK* packet, char* msg)
{
  eth_packet_trace_ex(packet, msg, packet->len > 1514);
}

char* eth_getname(int number, char* name)
{
#define ETH_SUPPORTED_DEVICES 10
  ETH_LIST  list[ETH_SUPPORTED_DEVICES];
  int count = eth_devices(ETH_SUPPORTED_DEVICES, list);

  if (count < number) return 0;
  strcpy(name, list[number].name);
  return name;
}

void eth_zero(ETH_DEV* dev)
{
  /* set all members to NULL OR 0 */
  memset(dev, 0, sizeof(ETH_DEV));
  dev->reflections = -1;                          /* not established yet */
}

/*============================================================================*/
/*                        Non-implemented versions                            */
/*============================================================================*/

#if !defined (USE_NETWORK)
t_stat eth_open (ETH_DEV* dev, char* name)
  {return SCPE_NOFNC;}
t_stat eth_close (ETH_DEV* dev)
  {return SCPE_NOFNC;}
t_stat eth_write (ETH_DEV* dev, ETH_PACK* packet, ETH_PCALLBACK routine)
  {return SCPE_NOFNC;}
t_stat eth_read (ETH_DEV* dev, ETH_PACK* packet, ETH_PCALLBACK routine)
  {return SCPE_NOFNC;}
t_stat eth_filter (ETH_DEV* dev, int addr_count, ETH_MAC* addresses,
                   ETH_BOOL all_multicast, ETH_BOOL promiscuous)
  {return SCPE_NOFNC;}
int eth_devices (int max, ETH_LIST* dev)
  {return 0;}
#else	 /* endif unimplemented */

/*============================================================================*/
/*      WIN32, Linux, and xBSD routines use WinPcap and libpcap packages      */
/*        OpenVMS Alpha uses a WinPcap port and an associated execlet         */
/*============================================================================*/

#include <pcap.h>
#include <string.h>
#ifdef xBSD
#include <sys/ioctl.h>
#endif /* xBSD */

#if !defined (HAS_PCAP_SENDPACKET)
/* libpcap has no function to write a packet, so we need to implement
   pcap_sendpacket() for compatibility with the WinPcap base code.
   Return value: 0=Success, -1=Failure */
int pcap_sendpacket(pcap_t* handle, u_char* msg, int len)
{
#if defined (linux)
  return (send(pcap_fileno(handle), msg, len, 0) == len)? 0 : -1;
#else
  return (write(pcap_fileno(handle), msg, len) == len)? 0 : -1;
#endif /* linux */
}
#endif /* !HAS_PCAP_SENDPACKET */

t_stat eth_open(ETH_DEV* dev, char* name)
{
  const int bufsz = (BUFSIZ < ETH_MAX_PACKET) ? ETH_MAX_PACKET : BUFSIZ;
  char errbuf[PCAP_ERRBUF_SIZE];
  char temp[1024];
  char* savname = name;
  int   num;
  char* msg;

  /* initialize device */
  eth_zero(dev);

  /* translate name of type "ethX" to real device name */
  if ((strlen(name) == 4)
      && (tolower(name[0]) == 'e')
      && (tolower(name[1]) == 't')
      && (tolower(name[2]) == 'h')
      && isdigit(name[3])
     ) {
    num = atoi(&name[3]);
    savname = eth_getname(num, temp);
  }

  /* attempt to connect device */
  memset(errbuf, 0, sizeof(errbuf));
  dev->handle = (void*) pcap_open_live(savname, bufsz, ETH_PROMISC, PCAP_READ_TIMEOUT, errbuf);
  if (!dev->handle) { /* can't open device */
    msg = "Eth: pcap_open_live error - %s\r\n";
    printf (msg, errbuf);
    if (sim_log) fprintf (sim_log, msg, errbuf);
    return SCPE_OPENERR;
  } else {
    msg = "Eth: opened %s\r\n";
    printf (msg, savname);
    if (sim_log) fprintf (sim_log, msg, savname);
  }

  /* save name of device */
  dev->name = malloc(strlen(savname)+1);
  strcpy(dev->name, savname);

#if defined (xBSD)
  /* Tell the kernel that the header is fully-formed when it gets it.
     This is required in order to fake the src address. */
  {
    int one = 1;
    ioctl(pcap_fileno(dev->handle), BIOCSHDRCMPLT, &one);
  }
#endif /* xBSD */

#if !defined (WIN_PCAP)
  /* set ethernet device non-blocking so pcap_dispatch() doesn't hang */
  if (pcap_setnonblock (dev->handle, 1, errbuf) == -1) {
    msg = "Eth: Failed to set non-blocking: %s\r\n";
    printf (msg, errbuf);
    if (sim_log) fprintf (sim_log, msg, errbuf);
  }
#endif
  return SCPE_OK;
}

t_stat eth_close(ETH_DEV* dev)
{
  char* msg = "Eth: closed %s\r\n";

  /* make sure device exists */
  if (!dev) return SCPE_UNATT;

  /* close the device */
  pcap_close(dev->handle);
  printf (msg, dev->name);
  if (sim_log) fprintf (sim_log, msg, dev->name);

  /* clean up the mess */
  free(dev->name);
  eth_zero(dev);

  return SCPE_OK;
}

t_stat eth_reflect(ETH_DEV* dev, ETH_MAC mac)
{
  ETH_PACK send, recv;
  t_stat status;
  int i;

  /* build a packet */
  memset (&send, 0, sizeof(ETH_PACK));
  send.len = ETH_MIN_PACKET;                              /* minimum packet size */
  memcpy(&send.msg[0], mac, sizeof(ETH_MAC));             /* target address */
  memcpy(&send.msg[6], mac, sizeof(ETH_MAC));             /* source address */
  send.msg[12] = 0x90;                                    /* loopback packet type */
  for (i=14; i<send.len; i++)
    send.msg[i] = 32 + i;                                 /* gibberish */

  /* send the packet */
  status = eth_write (dev, &send, NULL);

  /* empty the read queue and count the reflections */
  dev->reflections = 0;
  do {
    memset (&recv, 0, sizeof(ETH_PACK));
    status = eth_read (dev, &recv, NULL);
    if (memcmp(send.msg, recv.msg, ETH_MIN_PACKET)== 0)
      dev->reflections++;
  } while (recv.len > 0);

#ifdef ETH_DEBUG
  {
    char* msg = "Eth: reflections = %d\r\n";
    printf (msg, dev->reflections);
    if (sim_log) fprintf (sim_log, msg, dev->reflections);
  }
#endif
  return dev->reflections;
}

t_stat eth_write(ETH_DEV* dev, ETH_PACK* packet, ETH_PCALLBACK routine)
{
  int status = 1;   /* default to failure */

  /* make sure device exists */
  if (!dev) return SCPE_UNATT;

  /* make sure packet exists */
  if (!packet) return SCPE_ARG;

  /* make sure packet is acceptable length */
  if ((packet->len >= ETH_MIN_PACKET) && (packet->len <= ETH_MAX_PACKET)) {
    /* dispatch write request (synchronous; no need to save write info to dev) */
#ifdef ETH_DEBUG
    eth_packet_trace (packet, "writing");
#endif
    status = pcap_sendpacket((pcap_t*)dev->handle, (u_char*)packet->msg, packet->len);

    /* detect sending of decnet loopback packet */
    if ((status == 0) && DECNET_SELF_FRAME(dev->decnet_addr, packet->msg)) 
      dev->decnet_self_sent += dev->reflections;

  } /* if packet->len */

  /* call optional write callback function */
  if (routine)
    (routine)(status);

  return SCPE_OK;
}

void eth_callback(u_char* info, const struct pcap_pkthdr* header, const u_char* data)
{
  ETH_DEV*  dev = (ETH_DEV*) info;
  int to_me = 1;

  /* detect sending of decnet loopback packet */
  if (DECNET_SELF_FRAME(dev->decnet_addr, data)) {
    /* lower reflection count - if already zero, pass it on */
    if (dev->decnet_self_sent > 0) {
      dev->decnet_self_sent--;
      to_me = 0;
    }
  }

  if (to_me) {

    /* set data in passed read packet */
    dev->read_packet->len = header->len;
    memcpy(dev->read_packet->msg, data, header->len);

#ifdef ETH_DEBUG
    eth_packet_trace (dev->read_packet, "reading");
#endif

    /* call optional read callback function */
    if (dev->read_callback)
      (dev->read_callback)(0);
  }
}

t_stat eth_read(ETH_DEV* dev, ETH_PACK* packet, ETH_PCALLBACK routine)
{
  int status;

  /* make sure device exists */
  if (!dev) return SCPE_UNATT;

  /* make sure packet exists */
  if (!packet) return SCPE_ARG;

  /* set read packet */
  dev->read_packet = packet;
  packet->len = 0;

  /* set optional callback routine */
  dev->read_callback = routine;

  /* dispatch read request to either receive a filtered packet or timeout */
  do {
    status = pcap_dispatch((pcap_t*)dev->handle, 1, &eth_callback, (u_char*)dev);
  } while ((status) && (0 == packet->len));
  return SCPE_OK;
}

t_stat eth_filter(ETH_DEV* dev, int addr_count, ETH_MAC* addresses,
                  ETH_BOOL all_multicast, ETH_BOOL promiscuous)
{
  int i;
  bpf_u_int32  bpf_subnet, bpf_netmask;
  char buf[110+66*ETH_FILTER_MAX];
  char errbuf[PCAP_ERRBUF_SIZE];
  struct bpf_program bpf;
  char mac[20];
  char* buf2;
  char* msg;
  t_stat status;

  /* make sure device exists */
  if (!dev) return SCPE_UNATT;

  /* filter count OK? */
  if ((addr_count < 0) || (addr_count > ETH_FILTER_MAX))
    return SCPE_ARG;
  else
    if (!addresses) return SCPE_ARG;

  /* clear filter array */
  memset(dev->filter_address, 0, sizeof(dev->filter_address));

  /* set new filter addresses */
  for (i = 0; i < addr_count; i++)
    memcpy(dev->filter_address[i], addresses[i], sizeof(ETH_MAC));

  /* store other flags */
  dev->all_multicast = all_multicast;
  dev->promiscuous   = promiscuous;

#ifdef ETH_DEBUG
  printf("Eth: Filter Set\r\n");
  for (i = 0; i < addr_count; i++) {
    char mac[20];
    eth_mac_fmt(&dev->filter_address[i], mac);
    printf("  Addr[%d]: %s\r\n", i, mac);
  }
  printf("%s%s\r\n", dev->all_multicast ? "  All Multicast\r\n" : "", 
                     dev->promiscuous   ? "  Promiscuous\r\n"   : "");
#endif

  /* test reflections */
  if (dev->reflections == -1)
    status = eth_reflect(dev, dev->filter_address[0]);

  /* setup BPF filters and other fields to minimize packet delivery */
  strcpy(buf, "");

  /* construct destination filters - since the real ethernet interface was set
     into promiscuous mode by eth_open(), we need to filter out the packets that
     our simulated interface doesn't want. */
  if (!dev->promiscuous) {
    for (i = 0; i < addr_count; i++) {
      eth_mac_fmt(&dev->filter_address[i], mac);
      if (!strstr(buf, mac))    /* eliminate duplicates */
        sprintf(&buf[strlen(buf)], "%s(ether dst %s)", (*buf) ? " or " : "", mac);
    }
    if (dev->all_multicast)
      sprintf(&buf[strlen(buf)], "%s(ether multicast)", (*buf) ? " or " : "");
  }

  /* construct source filters - this prevents packets from being reflected back 
     by systems where WinPcap and libpcap cause packet reflections. Note that
     some systems do not reflect packets at all. This *assumes* that the 
     simulated NIC will not send out packets with multicast source fields. */
  if ((addr_count > 0) && (dev->reflections > 0)) {
    if (strlen(buf) > 0)
      sprintf(&buf[strlen(buf)], " and ");
    sprintf (&buf[strlen(buf)], "not (");
    buf2 = &buf[strlen(buf)];
    for (i = 0; i < addr_count; i++) {
      if (dev->filter_address[i][0] & 0x01) continue; /* skip multicast addresses */
      eth_mac_fmt(&dev->filter_address[i], mac);
      if (!strstr(buf2, mac))   /* eliminate duplicates */
        sprintf(&buf2[strlen(buf2)], "%s(ether src %s)", (*buf2) ? " or " : "", mac);
    }
    sprintf (&buf[strlen(buf)], ")");
  }
  /* When starting, DECnet sends out a packet with the source and destination
     addresses set to the same value as the DECnet MAC address. This packet is
     designed to find and help diagnose DECnet address conflicts. Normally, this
     packet would not be seen by the sender, only by the other machine that has
     the same DECnet address. If the ethernet subsystem is reflecting packets,
     DECnet will fail to start if it sees the reflected packet, since it thinks
     another system is using this DECnet address. We have to let these packets
     through, so that if another machine has the same DECnet address that we
     can detect it. Both eth_write() and eth_callback() help by checking the
     reflection count - eth_write() adds the reflection count to
     dev->decnet_self_sent, and eth_callback() check the value - if the
     dev->decnet_self_sent count is zero, then the packet has come from another
     machine with the same address, and needs to be passed on to the simulated
     machine. */
  memset(dev->decnet_addr, 0, sizeof(ETH_MAC));
  /* check for decnet address in filters */
  if ((addr_count) && (dev->reflections > 0)) {
    for (i = 0; i < addr_count; i++) {
      eth_mac_fmt(&dev->filter_address[i], mac);
      if (memcmp(mac, "AA:00:04", 8) == 0) {
        memcpy(dev->decnet_addr, &dev->filter_address[i], sizeof(ETH_MAC));
        /* let packets through where dst and src are the same as our decnet address */
        sprintf (&buf[strlen(buf)], " or ((ether dst %s) and (ether src %s))", mac, mac);
        break;
      }
    }
  }

#ifdef ETH_DEBUG
  msg = "Eth: BPF string is: |%s|\r\n";
  printf (msg, buf);
  if (sim_log) fprintf (sim_log, msg, buf);
#endif


  /* get netmask, which is required for compiling */
  if (pcap_lookupnet(dev->handle, &bpf_subnet, &bpf_netmask, errbuf)<0) {
      bpf_netmask = 0;
  }
  /* compile filter string */
  if ((status = pcap_compile(dev->handle, &bpf, buf, 1, bpf_netmask)) < 0) {
    sprintf(errbuf, "%s", pcap_geterr(dev->handle));
    msg = "Eth: pcap_compile error: %s\r\n";
    printf(msg, errbuf);
    if (sim_log) fprintf (sim_log, msg, errbuf);
    /* show erroneous BPF string */
    msg = "Eth: BPF string is: |%s|\r\n";
    printf (msg, buf);
    if (sim_log) fprintf (sim_log, msg, buf);
  } else {
    /* apply compiled filter string */
    if ((status = pcap_setfilter(dev->handle, &bpf)) < 0) {
      sprintf(errbuf, "%s", pcap_geterr(dev->handle));
      msg = "Eth: pcap_setfilter error: %s\r\n";
      printf(msg, errbuf);
      if (sim_log) fprintf (sim_log, msg, errbuf);
    } else {
#if !defined (WIN_PCAP)
      /* set file non-blocking */
      status = pcap_setnonblock (dev->handle, 1, errbuf);
#endif
    }
    pcap_freecode(&bpf);
  }

  return SCPE_OK;
}

/*
     The libpcap provided API pcap_findalldevs() on most platforms, will 
     leverage the getifaddrs() API if it is available in preference to 
     alternate platform specific methods of determining the interface list.

     A limitation of getifaddrs() is that it returns only interfaces which
     have associated addresses.  This may not include all of the interesting
     interfaces that we are interested in since a host may have dedicated
     interfaces for a simulator, which is otherwise unused by the host.

     One could hand craft the the build of libpcap to specifically use 
     alternate methods to implement pcap_findalldevs().  However, this can 
     get tricky, and would then result in a sort of deviant libpcap.

     Additionally, we're really only interested in Ethernet LAN type 
     interfaces here.  It would be nice if the flags provided by pcap_if_t
     actually told us if an interface was a Point to Point or a LAN interface 
     and if it was an ethernet.  This isn't implemented anywhere.

     This routine exists to allow platform specific code to validate and/or 
     extend the set of available interfaces to include any that are not
     returned by pcap_findalldevs.

*/
int eth_host_devices(int used, int max, ETH_LIST* list)
{
  return used;
}

int eth_devices(int max, ETH_LIST* list)
{
  pcap_if_t* alldevs;
  pcap_if_t* dev;
  int i;
  char errbuf[PCAP_ERRBUF_SIZE];

  /* retrieve the device list */
  if (pcap_findalldevs(&alldevs, errbuf) == -1) {
    char* msg = "Eth: error in pcap_findalldevs: %s\r\n";
    printf (msg, errbuf);
    if (sim_log) fprintf (sim_log, msg, errbuf);
  } else {
    /* copy device list into the passed structure */
    for (i=0, dev=alldevs; dev; dev=dev->next) {
      if ((dev->flags & PCAP_IF_LOOPBACK) || (!strcmp("any", dev->name))) continue;
      list[i].num = i;
      sprintf(list[i].name, "%s", dev->name);
      if (dev->description)
        sprintf(list[i].desc, "%s", dev->description);
      else
        sprintf(list[i].desc, "%s", "No description available");
      if (i++ >= max) break;
    }

    /* free device list */
    pcap_freealldevs(alldevs);
  }

  /* Add any host specific devices and/or validate those already found */
  i = eth_host_devices(i, max, list);

  /* return device count */
  return i;
}

#endif /* USE_NETWORK */