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Re: [RFC 11/32] xfs: convert to struct inode_time

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [RFC 11/32] xfs: convert to struct inode_time
From: "H. Peter Anvin" <hpa@xxxxxxxxx>
Date: Fri, 30 May 2014 18:22:55 -0700
Cc: Arnd Bergmann <arnd@xxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, joseph@xxxxxxxxxxxxxxxx, john.stultz@xxxxxxxxxx, hch@xxxxxxxxxxxxx, tglx@xxxxxxxxxxxxx, geert@xxxxxxxxxxxxxx, lftan@xxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
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No, not a strawman.  Replace with Jan 26, 2038 and you have the same situation.

On May 30, 2014 6:14:50 PM PDT, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>On Fri, May 30, 2014 at 05:41:14PM -0700, H. Peter Anvin wrote:
>> On 05/30/2014 05:37 PM, Dave Chinner wrote:
>> > 
>> > IOWs, the filesystem has to be able to reject any attempt to set a
>> > timestamp that is can't represent on disk otherwise Bad Stuff will
>> > happen,
>> 
>> Actually it is questionable if it is worse to reject a timestamp or
>just
>> let it wrap.  Rejecting a valid timestamp is a bit like "You don't
>> exist, go away."
>
>I think having the new systems calls being able to
>return EINVAL if the value cannot be stored permanently on disk
>correctly is the right thing to do. Having it silently mangled
>by the filesystem and returning "everything is just fine, trust me"
>is close to the worst solution I can think of. That's exactly what
>leads to overflow bugs occurring....
>
>> > and filesystems have to be able to specify in their on
>> > disk format what timestamp encoding is being used. The solution
>will
>> > be different for every filesystem that needs to support time beyond
>> > 2038.
>> 
>> Actually the cutoff can be really different for each filesystem, not
>> necessarily 2038.  However, I maintain the above still holds.
>
>Sure, but all filesystems are supposed to handle at least the
>current unix epoch.
>
>> Consider a filesystem that kept timestamps in YYMMDDHHMMSS format. 
>What
>> would you have expected such a filesystem to do on Jan 1, 2000?
>
>Strawman.
>
>We don't need to cater for fundamentally broken designs that can't
>even handle the current unix epoch correctly. If such filesystems
>exist, then they can simple say "original unix epoch support only"
>and do whatever crap they are doing right now.
>
>Cheers,
>
>Dave.

-- 
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