Date: Mon, 31 Jul 2006 11:43:54 +0900 From: Pyun YongHyeon <pyunyh@gmail.com> To: Yar Tikhiy <yar@comp.chem.msu.su> Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org, Pyun YongHyeon <yongari@FreeBSD.org> Subject: Re: cvs commit: src/sys/dev/em if_em.c Message-ID: <20060731024354.GA35573@cdnetworks.co.kr> In-Reply-To: <20060730095054.GA36267@comp.chem.msu.su> References: <200607270043.k6R0hY8g088353@repoman.freebsd.org> <20060729205009.GA37970@freefall.freebsd.org> <20060730064807.GA32731@cdnetworks.co.kr> <20060730095054.GA36267@comp.chem.msu.su>
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On Sun, Jul 30, 2006 at 01:50:55PM +0400, Yar Tikhiy wrote: > On Sun, Jul 30, 2006 at 03:48:07PM +0900, Pyun YongHyeon wrote: > > On Sat, Jul 29, 2006 at 08:50:09PM +0000, Yar Tikhiy wrote: > > > On Thu, Jul 27, 2006 at 12:43:34AM +0000, Pyun YongHyeon wrote: > > > > yongari 2006-07-27 00:43:34 UTC > > > > > > > > FreeBSD src repository > > > > > > > > Modified files: > > > > sys/dev/em if_em.c > > > > Log: > > > > Prepending an mbuf after loading a DMA map results in unexpected > > > > result. So, modify mbuf chains before loading a DMA map. > > > > > > > > Revision Changes Path > > > > 1.122 +28 -31 src/sys/dev/em/if_em.c > > > > > > Thanks a lot! Do you think this can fix kern/72933? > > > > > > > I can't sure it helps as the submitter reported the same issue > > on bge(4). > > Sorry, my question wasn't accurate. I believe that the original > PR in fact described a different issue with similar symptoms; it > was fixed quite a while ago. Then Lev Shamardin posted a follow-up > that he was still seeing the symptoms with em(4), which we (Gleb > Smirnoff and yours truly) couldn't fully understand because we were > missing the peculiarities of the interaction between DMA and mbufs > you're so well aware of. > > > Btw, I think the VLAN fixup code should use m_prepend(9) > > insatead of M_PREEND(9) because we don't know whether a new mbuf > > is allocated or not after M_PREPEND(9) call. > > If a new mbuf should be allocated to satisfy DMA, m_prepend(9) is No, prepending a new mbuf with m_prepend(9) is not necessary for DMA to work. > the function to use. M_PREPEND(9) can use the free space at the > beginning of the mbuf's data area if there is enough of it. I'm > unsure though whether we really need a new mbuf there. em_encap() > gets just a mbuf chain, which can be tweaked a little before starting > the DMA magic on it. > Sorry, I'm confused. I've misread VLAN fixup code. From my limited testing, it seems that it works as expected. Previously em(4) may have failed VLAN tag insertion if M_PREPEND(9) added a new mbuf into existing mbuf chains. > -- > Yar -- Regards, Pyun YongHyeon
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