linux-kernel - Re: [PATCH] ufs: Fix build errors on 32 bit machines

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Date:   Sun, 18 Jun 2017 02:30:44 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Evgeniy Dushistov <dushistov@...l.ru>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] ufs: Fix build errors on 32 bit machines

On 06/17/2017 11:23 AM, Al Viro wrote:
> On Sat, Jun 17, 2017 at 10:35:13AM -0700, Guenter Roeck wrote:
>> Various 32 builds fail with error messages such as
>>
>> ERROR: "__udivdi3" [fs/ufs/ufs.ko] undefined!
>>
>> due to a variable type change from 32 bit to 64 bit.
> 
> Actually, that's not the only problem in that place.  The breakage
> came in 2.4.14.7; the critical part was this:
>              default:
> -               usb1->fs_optim = SWAB32(UFS_OPTTIME);
> +               usb1->fs_optim = cpu_to_fs32(sb, UFS_OPTTIME);
>          
>              case UFS_OPTTIME:
>                  request = uspi->s_fpb;
> -               if (SWAB32(usb1->fs_cstotal.cs_nffree) < uspi->s_dsize *
> +               if (fs32_to_cpu(sb, usb1->fs_cstotal.cs_nffree) < uspi->s_dsize *
>                      (uspi->s_minfree - 2) / 100)
>                          break;
> -               usb1->fs_optim = SWAB32(UFS_OPTSPACE);
> +               usb1->fs_optim = cpu_to_fs32(sb, UFS_OPTTIME);
>                  break;
> 
> See the problem?  Instead of hysteresis loop flipping between optspace and opttime
> allocation policies, it *never* switches out of opttime.
> 
Yes. Nice catch.

> That came in
> 
> commit 6293d56ca18db9ed322b2a5550ac7b27bd538cff
> Author: Linus Torvalds <torvalds@...lon.transmeta.com>
> Date:   Mon Feb 4 20:33:51 2002 -0800
> 
>      v2.4.14.6 -> v2.4.14.7
>      
>        - Jeff Garzik: network driver updates
>        - Christoph Hellwig: UFS filesystem byteorder cleanups
>        - me: modified Andrea VM page allocator tuning
> 
> so probably a typo in Christoph's patches, missed by everyone at the time.
> 
> And I would prefer to have the nffree levels at which we switch back and
> forth precalculated at mount time.  I'll send a fix (along with those
> for the last remaining xfstests failures) later today.
> 

Agreed, but wouldn't it be more important to get the code to compile for now ?
After all, optimizing the calculation is an enhancement, not a bug fix.

Thanks,
Guenter