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Put in a long comment explaining what's confusing about this routine,

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and explaining that we leave the "unused argument" warning in place as a
reminder that we need to fix this routine someday, when we actually have
a capture against which to test it.
This commit is contained in:
guy 2003-11-19 01:09:48 +00:00
parent 988cd2bb0e
commit 5997b27eb6
1 changed files with 43 additions and 1 deletions
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44
print-vjc.c
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@ -25,7 +25,7 @@
#ifndef lint
static const char rcsid[] _U_ =
"@(#) $Header: /tcpdump/master/tcpdump/print-vjc.c,v 1.13 2003-11-16 09:36:41 guy Exp $ (LBL)";
"@(#) $Header: /tcpdump/master/tcpdump/print-vjc.c,v 1.14 2003-11-19 01:09:48 guy Exp $ (LBL)";
#endif
#include <tcpdump-stdinc.h>
@ -39,6 +39,48 @@ static const char rcsid[] _U_ =
#include "slcompress.h"
#include "ppp.h"
/*
* XXX - for BSD/OS PPP, what packets get supplied with a PPP header type
* of PPP_VJC and what packets get supplied with a PPP header type of
* PPP_VJNC? PPP_VJNC is for "UNCOMPRESSED_TCP" packets, and PPP_VJC
* is for COMPRESSED_TCP packets (PPP_IP is used for TYPE_IP packets).
*
* RFC 1144 implies that, on the wire, the packet type is *not* needed
* for PPP, as different PPP protocol types can be used; it only needs
* to be put on the wire for SLIP.
*
* It also indicates that, for compressed SLIP:
*
* If the COMPRESSED_TCP bit is set in the first byte, it's
* a COMPRESSED_TCP packet; that byte is the change byte, and
* the COMPRESSED_TCP bit, 0x80, isn't used in the change byte.
*
* If the upper 4 bits of the first byte are 7, it's an
* UNCOMPRESSED_TCP packet; that byte is the first byte of
* the UNCOMPRESSED_TCP modified IP header, with a connection
* number in the protocol field, and with the version field
* being 7, not 4.
*
* Otherwise, the packet is an IPv4 packet (where the upper 4 bits
* of the packet are 4).
*
* So this routine looks as if it's sort-of intended to handle
* compressed SLIP, although it doesn't handle UNCOMPRESSED_TCP
* correctly for that (it doesn't fix the version number and doesn't
* do anything to the protocol field), and doesn't check for COMPRESSED_TCP
* packets correctly for that (you only check the first bit - see
* B.1 in RFC 1144).
*
* But it's called for BSD/OS PPP, not SLIP - perhaps BSD/OS does weird
* things with the headers?
*
* Without a BSD/OS VJC-compressed PPP trace, or knowledge of what the
* BSD/OS VJC code does, we can't say what's the case.
*
* We therefore leave "proto" - which is the PPP protocol type - in place,
* *not* marked as unused, for now, so that GCC warnings about the
* unused argument remind us that we should fix this some day.
*/
int
vjc_print(register const char *bp, u_short proto)
{