Date: Fri, 29 Aug 2008 18:28:53 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Sam Leffler <sam@freebsd.org> Cc: gnn@freebsd.org, net@freebsd.org, "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net> Subject: Re: Small patch to multicast code... Message-ID: <20080829162853.GB46693@onelab2.iet.unipi.it> In-Reply-To: <48B4A62D.3080300@freebsd.org> References: <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> <m2abezwojl.wl%gnn@neville-neil.com> <48B4A62D.3080300@freebsd.org>
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On Tue, Aug 26, 2008 at 05:56:13PM -0700, Sam Leffler wrote: > gnn@freebsd.org wrote: > >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. > > > > > pull the headers up. copy just the headers. no deep copy. 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). cheers luigihome | help
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