linux-kernel - Re: reiserfs NET=n build error

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Date:	Mon, 4 Dec 2006 16:19:06 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	Jeff Mahoney <jeffm@...e.com>, Al Viro <viro@....linux.org.uk>,
	Andi Kleen <ak@...e.de>, reiserfs-dev@...esys.com,
	sam@...nborg.org
Subject: Re: reiserfs NET=n build error

On Tue, 28 Nov 2006 11:47:57 -0800 Randy Dunlap wrote:

> On Sun, 19 Nov 2006 17:32:11 -0500 Jeff Mahoney wrote:
> 
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > 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.
> > 
> > Oh great. Even better. :(
> 
> Even more:  MD/raid (=m) is broken in this way also.
> It uses csum_partial(), which isn't present (CONFIG_NET=n).
> 
> Kernel: arch/x86_64/boot/bzImage is ready  (#9)
>   Building modules, stage 2.
>   MODPOST 101 modules
> WARNING: "csum_partial" [drivers/md/md-mod.ko] undefined!
> make[1]: *** [__modpost] Error 1
> make: *** [modules] Error 2
> 
> CONFIG_MD=y
> CONFIG_BLK_DEV_MD=m
> CONFIG_MD_LINEAR=m
> # CONFIG_MD_RAID0 is not set
> CONFIG_MD_RAID1=m
> # CONFIG_MD_RAID10 is not set
> # CONFIG_MD_RAID456 is not set
> CONFIG_MD_MULTIPATH=m
> # CONFIG_MD_FAULTY is not set
> CONFIG_BLK_DEV_DM=y
> CONFIG_DM_DEBUG=y
> CONFIG_DM_CRYPT=m
> CONFIG_DM_SNAPSHOT=y
> CONFIG_DM_MIRROR=y
> CONFIG_DM_ZERO=m
> CONFIG_DM_MULTIPATH=y
> CONFIG_DM_MULTIPATH_EMC=m
> 
> ---
> ~Randy
> full broken config for MD:
> http://oss.oracle.com/~rdunlap/configs/config-md-csum

Ingo, Neil:

Al has summarized that csum_partial() is arch-specific.
However, drivers/md/md.c uses it.

Does that mean that RAID volumes are not portable across
(some) architectures?

Should md.c use a specific, known, fixed (as in static,
arch-independent) version of csum_partial()?

Will changing now possibly make some existing volumes
non-portable?

Thanks,
---
~Randy
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