linux-ext4 - Re: [PATCH V2] xfstests: make 275 pass

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Message-ID: <4F15A2D0.2090900@sandeen.net>
Date:	Tue, 17 Jan 2012 10:33:20 -0600
From:	Eric Sandeen <sandeen@...deen.net>
To:	Dave Chinner <david@...morbit.com>
CC:	Eric Sandeen <sandeen@...hat.com>,
	ext4 development <linux-ext4@...r.kernel.org>,
	Eryu Guan <eguan@...hat.com>, xfs-oss <xfs@....sgi.com>
Subject: Re: [PATCH V2] xfstests: make 275 pass

On 1/4/12 6:39 PM, Dave Chinner wrote:
> On Wed, Jan 04, 2012 at 05:21:00PM -0600, Eric Sandeen wrote:
>> On 1/4/12 5:17 PM, Dave Chinner wrote:
>>> On Wed, Jan 04, 2012 at 02:54:25PM -0600, Eric Sandeen wrote:
>>>> Ok, this is a significant rework of 275, which made too many
>>>> assumptions about details of space usage and failed on several
>>>> filesystems (it passed on xfs, but only by accident).
>>>>
>>>> This new version tries to leave about 256k free, then tries
>>>> a single 1M IO, and fails only if 0 bytes are written.
>>>>
>>>> It also sends a lot more to $seq.full for debugging on failure
>>>> and fixes a few other stylistic things.
>>>>
>>>> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
>>>
>>> I just had another thought about this, Eric....
>>>
>>>> +# And at least some of it should succeed.
>>>> +_filesize=`du $SCRATCH_MNT/tmp1 | awk '{print $1}'`
>>>> +[ $_filesize -eq 0 ] && _fail "write file err: Partial write until enospc failed; wrote 0 bytes."
>>>
>>> The question that just came to mind was this assumes that allocation
>>> succeeded so therefore the partial write succeeded. But that's not
>>> necessary the case. The partial write might not succeed leaving the
>>> file size as zero, but the underlying FS might not remove all the
>>> blocks it allocated (nothing says that it has to). Hence to
>>> determine if a partial write succeeded, we also need to check that
>>> the file size itself is greater than zero....
>>
>> Probably need to read up on what posix says it should do.  I think
>> what you're saying is that it might leave blocks allocated past EOF?
>> That'd be surprising to me, but maybe I misunderstand?
> 
> There's no guarantee that du is even reporting blocks on disk. e.g
> for XFS du will also report reserved (in-memory) delalloc space on
> the inode and that includes speculative allocation beyond EOF. We
> don't have to remove specultive delalloc ranges when a partial write
> occurs, so effectively checking du output to see if a partial write
> succeeded is not a sufficient test to determine if the partial write
> succeeded or not.
> 
> However, if the partial write did succeed then the file size *must*
> change to reflect what was written. Hence I suspect all we actually
> need here is a file size check...

Ok; so would you be happy with just this?

# And at least some of it should succeed.
_filesize=`ls -l $SCRATCH_MNT/tmp1 | awk '{print $5}'`
[ $_filesize -eq 0 ] && _fail "write file err: Partial write until enospc failed; wrote 0 bytes."

If so I'll put your reviewed-by on it and get this pushed, ok?

-Eric

> Cheers,
> 
> Dave.

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