Date: Thu, 22 May 2003 17:33:33 -0700 (PDT) From: wpaul@FreeBSD.ORG (Bill Paul) To: hrs@eos.ocn.ne.jp (Hiroki Sato) Cc: current@freebsd.org Subject: Re: possible bug fix for 82550-based fxp packet truncation problem Message-ID: <20030523003333.E83B537B401@hub.freebsd.org> In-Reply-To: <20030523.043131.02305993.hrs@eos.ocn.ne.jp> from Hiroki Sato at "May 23, 2003 04:31:31 am"
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> Don Lewis <truckman@freebsd.org> wrote
> in <200305220823.h4M8N9M7075271@gw.catspoiler.org>:
>
> truckman> If you are using one of my previous patches which worked around the
> truckman> problem by disabling the IPCB mode, you may want to try the patch below.
>
> This works fine in my environment. My fxp has the following id:
>
> fxp0@pci7:2:0: class=0x020000 card=0x10508086 chip=0x12298086 rev=0x0d hdr=0x00
>
> Without any patches, packets whose size is 216+(N*1480) are dropped
> as I reported on -stable before. Similarly I tried "ping -s X" with
> various payload size from X=1 to X=6000 in the system using the
> patched kernel, but no error is reported.
>
Just to let people know, I have been trying to investigate this, but
my time has been somewhat limited lately. The original reason I turned
off the IP checksumming on transmit was that there was one test case
where the chip seemed to be generating improper checksums. That is,
if you did something like: ping -s 1473 <otherhost>. This would result
in a full sized frame, plus a small IP fragment containing just one
byte of data. On the machine I used for testing, the small fragment
was rejected by the host on the other side due to a bad header checksum.
The machine I was testing on was an old Gateway 2000 Pentium 166 system.
I have since tried re-enabling the IP checksumming on transmit and
re-run the test on an Athlon system, and everything works correctly.
(Coincidentally, I ran a similar test on a PowerPC 440GP board running
VxWorks and everything worked correctly there too.)
So my theory is that the original bug I found was not due to the chip
computing bad checksums, although I'm at a loss to say what the cause
really was. And I don't have that particular machine handy anymore. :/
As an experiment, you might try re-enabling the IP header checksumming to
see just what happens. If the ping -s 1473 tests succeeds, then maybe
I was smoking crack and we should turn IP checksumming back on.
-Bill
--
=============================================================================
-Bill Paul (510) 749-2329 | Senior Engineer, Master of Unix-Fu
wpaul@windriver.com | Wind River Systems
=============================================================================
"If stupidity were a handicap, you'd have the best parking spot."
=============================================================================
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