From owner-freebsd-net  Wed Jan 24 10:30:25 2001
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To: Luigi Rizzo <rizzo@aciri.org>
Cc: net@FreeBSD.ORG
Subject: Re: dubious code in ip_output() ?
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Wed, 24 Jan 2001 10:21:14 -0800
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>the change attached at the end was applied to ip_output()
>long ago -- it checks for room in the interface queue early
>in the delivery process -- but does this before passing the packet
>to the firewall.
>
>To me this seems incorrect because the firewall can drop the packet,
>divert it to a socket, maybe (not sure) change the output interface,
>pass it to a dummynet pipe, etc.
>
>Maybe none of these things were there at the time this code
>was committed, but it sounds like we should remove it now.
>
>(btw -- we also need to report up errors from dummynet
>and divert whenever this is possible... I will also look
>into this.)
>
>Opinions ?

   The original problem that was being solved is that the code would start
queuing fragments of a large packet to the output queue and then notice that
it was full and discard the remaining fragments. This resulted in completely
useless packet fragments being output on the wire (fragments that would never
form a complete packet). You can imagine the various problems that this
causes.
   So the code can't be removed, but it could be moved a bit later, perhaps.
It was at the correct location at the time that I wrote it, however.

-DG

David Greenman
Co-founder, The FreeBSD Project - http://www.freebsd.org
President, TeraSolutions, Inc. - http://www.terasolutions.com
Pave the road of life with opportunities.


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