Date: Fri, 29 Aug 2008 15:35:46 -0700 From: Andrew Thompson <thompsa@FreeBSD.org> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net>, Sam Leffler <sam@freebsd.org>, net@freebsd.org, gnn@freebsd.org Subject: Re: Small patch to multicast code... Message-ID: <20080829223546.GG98483@citylink.fud.org.nz> In-Reply-To: <20080829164145.GA47030@onelab2.iet.unipi.it> References: <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> <20080829162853.GB46693@onelab2.iet.unipi.it> <48B8248A.3060103@freebsd.org> <20080829164145.GA47030@onelab2.iet.unipi.it>
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On Fri, Aug 29, 2008 at 06:41:45PM +0200, Luigi Rizzo wrote: > 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 :) The bridge code does a deep copy of the packet for each interface it broadcasts on due the firewall code modifying the headers. It sounds like this should just be a copy+pullup instead. Andrew
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