On Sun, 19 Nov 2006 20:57:11 +0000 Al Viro wrote:
> On Sun, Nov 19, 2006 at 11:04:33AM -0800, Randy Dunlap wrote:
> > Andi Kleen wrote:
> > >>>I would copy a relatively simple C implementation, like
> > >>>arch/h8300/lib/checksum.c
> > >>As long as the h8300 version has the same output as the x86 version.
> > >
> > >The trouble is that the different architecture have different output
> > >for csum_partial. So you already got a bug when someone wants to move
> > >file systems.
> > >
> > >-Andi
> >
> > That argues for having only one version of it (in a lib.; my preference)
> > -or- Every module having its own local copy/version of it. :(
>
> Wrong. csum_partial() result is defined modulo 0xffff and it's basically
> "whatever's convenient as intermediate for this architecture".
>
> reiserfs use of it is just plain broken. net/* is fine, since all
> final uses are via csum_fold() or equivalents.
>
> Note that reiserfs use is broken in another way: it takes fixed-endian value
> and feeds it to cpu_to_le32(). IOW, even if everything had literally the
> same csum_partial(), the value it shits on disk would be endian-dependent.
>
> As for net/*, with proper types it's pretty straightforward. See
> davem's net-2.6.20 for that...
OK. I guessed that there was some sanity in there somewhere (either
in the provider or consumer), but apparently there's none in either place.
:(
---
~Randy
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