linux-ext4 - Re: [PATCH] fstests: generic: Check if cycle mount and sleep can affect fiemap result

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Date:   Thu, 6 Apr 2017 11:28:01 -0500
From:   Eric Sandeen <sandeen@...deen.net>
To:     Theodore Ts'o <tytso@....edu>, Eryu Guan <eguan@...hat.com>
Cc:     Qu Wenruo <quwenruo@...fujitsu.com>, linux-btrfs@...r.kernel.org,
        fstests@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] fstests: generic: Check if cycle mount and sleep can
 affect fiemap result

On 4/6/17 11:26 AM, Theodore Ts'o wrote:
> On Wed, Apr 05, 2017 at 10:35:26AM +0800, Eryu Guan wrote:
>>
>> Test fails with ext3/2 when driving with ext4 driver, fiemap changed
>> after umount/mount cycle, then changed back to original result after
>> sleeping some time. An ext4 bug? (cc'ed linux-ext4 list.)
> 
> I haven't had time to look at this, but I'm not sure this test is a
> reasonable one on the face of it.
> 
> A file system may choose to optimize a file's extent tree for whatever
> reason it wants, whenever it wants, including on an unmount --- and
> that would not be an invalid thing to do.  So to have an xfstests that
> causes a test failure if a file system were to, say, do some cleanup
> at mount or unmount time, or when the file is next opened, to merge
> adjacent extents together (and hence change what is returned by
> FIEMAP) might be strange, or even weird --- but is this any of user
> space's business?  Or anything we want to enforce as wrong wrong wrong
> by xfstests?

I had the same question.  If the exact behavior isn't defined anywhere,
I don't know what we can be testing, TBH.

-Eric

> 		       		   	   - Ted