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Date:      Tue, 26 Aug 2008 15:42:54 -0400
From:      gnn@FreeBSD.org
To:        "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net>
Cc:        net@FreeBSD.org
Subject:   Re: Small patch to multicast code...
Message-ID:  <m2abezwojl.wl%gnn@neville-neil.com>
In-Reply-To: <20080826144130.S66593@maildrop.int.zabbadoz.net>
References:  <m27iaa6v43.wl%gnn@neville-neil.com> <20080821203519.GA51534@onelab2.iet.unipi.it> <m23aky6ncl.wl%gnn@neville-neil.com> <48AE23FF.9070009@FreeBSD.org> <m2tzdd6j36.wl%gnn@neville-neil.com> <48AF08B7.4090804@FreeBSD.org> <m2fxowhgq8.wl%gnn@neville-neil.com> <48AF330B.4010802@FreeBSD.org> <m28wuohfm5.wl%gnn@neville-neil.com> <20080825190207.GA73478@zibbi.meraka.csir.co.za> <20080825194038.GA75840@zibbi.meraka.csir.co.za> <m2y72jx33z.wl%gnn@neville-neil.com> <20080826144130.S66593@maildrop.int.zabbadoz.net>

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At Tue, 26 Aug 2008 14:50:33 +0000 (UTC),
Bjoern A. Zeeb wrote:
> 
> On Tue, 26 Aug 2008, George V. Neville-Neil wrote:
> 
> Hi,
> 
> > At Mon, 25 Aug 2008 21:40:38 +0200,
> > John Hay wrote:
> >>
> >> I have tried it and it does fix my problem. RIP2 over multicast works
> >> again. :-)
> >
> > Good to hear.  I'm waiting on a bit more feedback but I think I'll be
> > checking this in soon, with a big comment talking about the
> > performance implications etc.
> 
> So wait a second; what was the m_pullup vs. m_dup thing? Has anyone
> actually tried that? I mean using a sledgehammer if a mitten would be
> enough is kind of .. uhm. You get it.

Perhaps I'm confused, I've been off dealing with other issues for a
few days, but m_pullup doesn't make a copy of the packet or its
fields, only makes sure that it's contiguous in memory.  Am I wrong in that?

Since the bug is that two pieces of code modify the same data, in ways
that interfere, I'm not sure how we can avoid making a copy.  It might
be nice to limit the copy, but we'd still need two copies, one for the
loopback device and one for the real device.

Best,
George



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