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Date: Fri, 22 Aug 2008 03:27:11 +0100
From: "Bruce M. Simpson" <bms@FreeBSD.org>
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Cc: Luigi Rizzo <rizzo@iet.unipi.it>, net@freebsd.org
Subject: Re: Small patch to multicast code...
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gnn@freebsd.org wrote:
>> The only thing i can think of is that it's the UDP checksum,
>> residing beyond hlen, which is overwritten somewhere in the
>> call to if_simloop -- in which case perhaps a better fix is
>> to m_pullup() the udp header as well ?
>>     
>
> It is the checksum that gets trashed, yes.
> ...
> The m_*() routines actually have reasonable comments, it just seems
> the wrong one was used here.
>   

Actually, m_copy() has been legacy for some time now -- see comments.

I'd be concerned that the change to m_dup() (which makes a full mbuf 
chain copy) rather than m_copym() (which bumps refcounts) is going to 
eat into the mbuf clusters on fast links, though it's an easy band-aid 
for the problem.

I agree with Luigi that some of the API contract for mbuf(9) doesn't 
hold any more now that we have TSO and other offload.

cheers
BMS