Re: [PATCH 6/6] generic: various atomic write tests with scsi_debug

[John Garry <john.g.garry@oracle.com>]

On 14/05/2025 17:01, Darrick J. Wong wrote:
>> It seems many sub-tests are same as 1222
>>
>> It is difficult to factor them out?
> Yes.  g/1222 will _notrun itself if the scsi_debug module isn't present
> or the fake device cannot be created.  Apparently many of the people who
> run fstests also have test infrastructure that cannot handle modules, so
> they don't run anything involving scsi_debug.

ok...

> 
> That's why g/1223 only requires that the scratch fs advertises some sort
> of atomic write capability, it doesn't care how it provides that.
> 
> <snip>
> 
>>> diff --git a/tests/generic/1224 b/tests/generic/1224
>>> new file mode 100644
>>> index 00000000..fb178be4
>>> --- /dev/null
>>> +++ b/tests/generic/1224

> <snip>

>>
>> But we also test RWF_NOWAIT at some stage?
>>
>> RWF_NOWAIT should fail always for filesystem-based atomic write
> It's hard to test NOWAIT because the selected io path might not actually
> encounter contention, and there are various things that NOWAIT will wait
> on anyway (like memory allocation and metadata reads).

The filesystem-based atomic write will always try to allocate blocks, 
and this will fail for NOWAIT.

But, come to think of it, this is not even a useful test - so forget the 
suggestion. I was just testing this as a sanity check to prove that we 
are getting expected behavior.

> 
> <snip>
> 
> 
>>> diff --git a/tests/xfs/1217 b/tests/xfs/1217
>>> new file mode 100755
>>> index 00000000..012a1f46
>>> --- /dev/null
>>> +++ b/tests/xfs/1217
>>> @@ -0,0 +1,70 @@
>>> +#! /bin/bash
>>> +# SPDX-License-Identifier: GPL-2.0
>>> +# Copyright (c) 2025 Oracle.  All Rights Reserved.
>>> +#
>>> +# FS QA Test 1217
>>> +#
>>> +# Check that software atomic writes can complete an operation after a crash.
>>> +#
>> Could we prove that we get a torn write for a regular non-atomic write also?
> Perhaps?  But I don't see the point -- non-atomic write completions
> could be done atomically.

oh, from my reading of the test, I thought that we were ensuring that we 
are writing over many extents, and so could not be completed atomically 
for a non-atomic write.

BTW, there is a typo in a comment for that test, please see "ssecond block"

Thanks,
John