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From: "Eggert, Lars" <lars@netapp.com>
To: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>
Subject: enable tcpdump GUESS_TSO flag?
Thread-Topic: enable tcpdump GUESS_TSO flag?
Thread-Index: AQHOMSbyh8pfApUoREqP7JnSG2Yuog==
Date: Thu, 4 Apr 2013 11:24:18 +0000
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Hi,

I wonder whether it'd be a good idea to enable tcpdump's GUESS_TSO flag by =
default? It enables a heuristic that lets tcpdump understand pcaps that inc=
lude segments generated by TCP TSO (which otherwise show up as "IP bad-len =
0".)

See the dicussion at http://www.mail-archive.com/tcpdump-workers@lists.tcpd=
ump.org/msg01051.html for details.

Lars

diff --git a/usr.sbin/tcpdump/tcpdump/Makefile b/usr.sbin/tcpdump/tcpdump/M=
akefile
index ca8ec4c..5fd73a1 100644
--- a/usr.sbin/tcpdump/tcpdump/Makefile
+++ b/usr.sbin/tcpdump/tcpdump/Makefile
@@ -45,6 +45,10 @@ CFLAGS+=3D -I${.CURDIR} -I${TCPDUMP_DISTDIR}
 CFLAGS+=3D -DHAVE_CONFIG_H
 CFLAGS+=3D -D_U_=3D"__attribute__((unused))"
=20
+# Enable tcpdump heuristic to identify TSO-generated packets; see
+# http://www.mail-archive.com/tcpdump-workers@lists.tcpdump.org/msg01051.h=
tml
+CFLAGS+=3D -DGUESS_TSO
+
 .if ${MK_INET6_SUPPORT} !=3D "no"
 SRCS+=3D	print-ip6.c print-ip6opts.c print-mobility.c print-ripng.c \
 	print-icmp6.c print-babel.c print-frag6.c print-rt6.c print-ospf6.c \