Date: Fri, 09 Nov 2012 18:33:59 +0100 From: Andre Oppermann <andre@freebsd.org> To: Adrian Chadd <adrian@freebsd.org> Cc: pyunyh@gmail.com, FreeBSD Net <freebsd-net@freebsd.org>, Pyun YongHyeon <yongari@freebsd.org> Subject: Re: svn commit: r242739 - stable/9/sys/dev/ti Message-ID: <509D3E87.9020701@freebsd.org> In-Reply-To: <CAJ-Vmo=MeSEx3cSERnzaqCOhLdNxqCQV0yhpQMRcWFLP475zHA@mail.gmail.com> References: <201211080206.qA826RiN054539@svn.freebsd.org> <CAJ-VmomEOPGbLwmOmL0EdenZA7QKbV5P-hAYsTRcwLao2LbAqg@mail.gmail.com> <20121108023858.GA3127@michelle.cdnetworks.com> <CAJ-Vmoma1DJRT8_ezdEpVYrZXak%2B2B4mBHAPxhoUKr0nUrO6YQ@mail.gmail.com> <509BC2E2.4030907@freebsd.org> <CAJ-Vmo=QuP1s=ppnp2u%2BVpuJRbncaHLwi_0ku5=dr9%2BReYp79w@mail.gmail.com> <509C4684.2030102@freebsd.org> <CAJ-VmonUhcNgZojevpjNCZP41VKRZwFY7NM773NiZ9oM3PFOkg@mail.gmail.com> <509CBA0C.3070008@freebsd.org> <CAJ-Vmo=MeSEx3cSERnzaqCOhLdNxqCQV0yhpQMRcWFLP475zHA@mail.gmail.com>
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On 09.11.2012 17:51, Adrian Chadd wrote: > On 9 November 2012 00:08, Andre Oppermann <andre@freebsd.org> wrote: > >> Firewalling doesn't change the packet and no checksum is needed. >> NAT does change the packet and the pesky pseudo-header in the TCP/ >> UDP checksum. However here only the pseudo-header checksum is >> recalculated and reintegrated into the one-complement payload checksum. >> The payload itself is not being looked at, except for protocols that >> do contain IP addresses in their internal commands or such. There >> the payload is modified. The same reintegration trick can be used. >> In the majority of cases these packets are very small though and >> the entire checksum is simply recalculated. As the packets are very >> small no fragmentation is occuring. >> The IPv4 header checksum is never ever a problem and always works. >> >> Can we please put this to rest now. > > Andre, > > I'm assuming that Pyun fixed a real bug that he really did see. My day > job is dealing with these kinds of corner cases with embedded hardware > that does offload-y type stuff. > So yes, I'd really like to know what's going on under the hood and fix it. There isn't anything to fix other than removing a poorly supported and implemented feature. Nothings breaks if it goes away. > You may be able to make it all go away with a bunch of logical > reasoning but if it weren't a problem, Pyun would've never stumbled > across it and had to disable checksumming. I found the problem and wanted to remove this particular mis-feature from the stack. To do that he removed it from two drivers, one of them very old with no known users. -- Andre > I'll chase this up privately with him and see what was really going on. > > Thanks, > > > > Adrian > >
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