libpcap for DOS
---------------

This file contains some notes on building and using libpcap for MS-DOS.
Look in `README' and `pcap.man' for usage and details. These targets are
supported:

 - Borland C 4.0+ small or large model.
 - Metaware HighC 3.1+ with PharLap DOS-extender
 - GNU C 2.7+ with djgpp 2.01+ DOS extender
 - Watcom C 11.x with DOS4GW extender

Note: the files in the libpcap.zip contains short truncated filenames.
  So for djgpp to work with these, disable the use of long file names by
  setting "LFN=n" in the environment. On the other hand, if you get libpcap
  from Github or the official libpcap.tar.gz, some filenames are beyond 8+3.
  In this case set "LFN=y".

Files specific to DOS are pcap-dos.[ch] and the assembly and C files in
the MSDOS sub-directory. Remember to built the libpcap library from the top
install directory. And not from the MSDOS sub-directory.

Note for djgpp users:
  If you got the libpcap from the official site www.tcpdump, then that
  distribution does NOT contain any sources for building 32-bit drivers.
  Instead get the full version at
     https://www.watt-32.net/pcap/libpcap.zip

  and set "USE_32BIT_DRIVERS = 1" in msdos\common.dj.


Requirements
------------

DOS-libpcap currently only works reliably with a real-mode Ethernet packet-
driver. This driver must be installed prior to using any program (e.g.
tcpdump) compiled with libpcap. Work is underway to implement protected-
mode drivers for 32-bit targets (djgpp only). The 3Com 3c509 driver is
working almost perfectly. Due to lack of LAN-cards, I've not had the
opportunity to test other drivers. These 32-bit drivers are modified
Linux drivers.


Required packages
-----------------

The following packages and tools must be present for all targets.

1. Watt-32 tcp/ip library. This library is *not* used to send or
   receive network data. It's mostly used to access the 'hosts'
   file and other <netdb.h> features. Get 'watt32s*.zip' at:

     https://www.watt-32.net

2. Exception handler and disassember library (libexc.a) is needed if
   "USE_EXCEPT = 1" in common.dj. Available at:

     https://www.watt-32.net/misc/exc_dx07.zip

3. Flex & Bison is used to generate parser for the filter handler
   pcap_compile:
     ftp://ftp.delorie.com/pub/djgpp/current/v2gnu/flx254b.zip
     ftp://ftp.delorie.com/pub/djgpp/current/v2gnu/bsn241b.zip

4. NASM assembler v 0.98 or later is required when building djgpp and
   Watcom targets:
     https://www.nasm.us/

5. sed (Stream Editor) is required for doing `make depend'.
   It's available at:
     ftp://ftp.delorie.com/pub/djgpp/current/v2gnu/sed422b.zip

   A touch tool to update the time-stamp of a file. E.g.:
     ftp://ftp.delorie.com/pub/djgpp/current/v2gnu/grep29b.zip

6. For djgpp rm.exe and cp.exe are required. These should already be
   part of your djgpp installation. Also required (experimental at the
   time) for djgpp is DLX 2.91 or later. This tool is for the generation
   of dynamically loadable modules.


Compiling libpcap
-----------------

Follow these steps in building libpcap:

1. Make sure you've installed Watt-32 properly (see it's `INSTALL' file).
   During that installation a environment variable `WATT_ROOT' is set.
   This variable is used for building libpcap also (`WATT_INC' is
   deducted from `WATT_ROOT'). djgpp users should also define environment
   variables `C_INCLUDE_PATH' and `LIBRARY_PATH' to point to the include
   directory and library directory respectively.  E.g. put this in your
   AUTOEXEC.BAT:
     set C_INCLUDE_PATH=c:/net/watt/inc
     set LIBRARY_PATH=c:/net/watt/lib

2. Revise the msdos/common.dj file for your djgpp/gcc installation;
   - change the value of `GCCLIB' to match location of libgcc.a.
   - set `USE_32BIT_DRIVERS = 1' to build 32-bit driver objects.


3. Build pcap by using appropriate makefile. For djgpp, use:
     `make -f msdos/makefile.dj'  (i.e. GNU `make')

   For a Watcom target say:
     `wmake -f msdos\makefile.wc'

   For a Borland target say:
     `maker -f msdos\Makefile pcap_bc.lib'  (Borland's `maker.exe')

   And for a HighC/Pharlap target say:
     `maker -f msdos\Makefile pcap_hc.lib'  (Borland's `maker.exe')

   You might like to change some `CFLAGS' -- only `DEBUG' define currently
   have any effect. It shows a rotating "fan" in upper right corner of
   screen.  Remove `DEBUG' if you don't like it. You could add
   `-fomit-frame-pointer' to `CFLAGS' to speed up the generated code.
   But note, this makes debugging and crash-traceback difficult. Only
   add it if you're fully confident your application is 100% stable.

   Note: Code in `USE_NDIS2' does not work at the moment.

4. The resulting library is put in current directory. There's some
   test-program for `libpcap': `filtertest.exe', `findalldevstest.exe',
     `nonblocktest.exe' and `opentest.exe'.

   But linking the library with `tcpdump' is the ultimate test. DOS/djgpp
   should now hopefully be a supported target. Get the sources at:
     https://www.tcpdump.org/
   or
     https://github.com/the-tcpdump-group/tcpdump/

   (click on the 'Download ZIP' on the right side of that page.)


Extensions to libpcap
---------------------

I've included some extra functions to DOS-libpcap:

  `pcap_config_hook (const char *keyword, const char *value)' :

    Allows an application to set values of internal libpcap variables.
    `keyword' and an associated `value' should be present in the `debug_tab[]'
    array in pcap-dos.c (currently only used to set debug-levels and parameters
    for the 32-bit network drivers.) Thus an application using DOS-libpcap can
    override the default value during it's configure process (see tcpdump's
    msdos/config.c file for an extended example).

  `pcap_set_wait (pcap_t *, void (*)(void), int)' :

    Only effective when reading offline traffic from dump-files.
    Function `pcap_offline_read()' will wait (and optionally yield)
    before printing next packet. This will simulate the pace the packets
    where actually recorded.


Happy sniffing !


Gisle Vanem <gvanem@yahoo.no>

October 1999, 2004, 2006, 2013