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Date: Fri, 29 Aug 2008 18:41:45 +0200
From: Luigi Rizzo <rizzo@iet.unipi.it>
To: Sam Leffler <sam@freebsd.org>
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Cc: "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net>, gnn@freebsd.org,
	net@freebsd.org
Subject: Re: Small patch to multicast code...
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On Fri, Aug 29, 2008 at 09:32:10AM -0700, Sam Leffler wrote:
> Luigi Rizzo wrote:
...
> >and to be more explicit - the result of m_pullup is that
> >the number of bytes specified as m_pullup argument are in
> >a private piece of memory -- the 'data' region within the mbuf -- so
> >you can freely play with them without trouble.
> >
> >That is why i suggested to just increase the argument to m_pullup
> >by the size of the udp header so one can overwrite the checksum
> >within the mbuf without touching the shared part in the cluster
> >(if any).
> >  
> 
> Hmm, never considered the m_pullup guaranteed a private copy (but I see 
> it in the code).  The original semantics were just that the data was 
> contiguous.

funny, i thought the guarantee of a writable copy was also part
of the original semantics :)

	cheers
	luigi