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From: John Snow <jsnow@redhat.com>
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Date: Fri, 8 Dec 2017 14:13:48 -0500
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH] iotests: Tweak 030 in order
 to trigger a race condition with parallel jobs
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To: Alberto Garcia <berto@igalia.com>, Eric Blake <eblake@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, Max Reitz <mreitz@redhat.com>



On 12/07/2017 02:34 PM, Alberto Garcia wrote:
> On Thu 07 Dec 2017 08:16:41 PM CET, Eric Blake wrote:
>>>              qemu_io('-f', iotests.imgfmt,
>>> -                    '-c', 'write -P %d %d %d' % (i, i*1024*1024, num_kb * 1024),
>>> +                    '-c', 'write -P 0xFF %dk %dk' % (i * 512, num_kb),
>>
>> I guess changing from a variable to a fixed 0xff pattern doesn't make
>> a difference?
> 
> I noticed that with the previous code we would write zeroes to the first
> image (i == 0), and with that I can't reproduce the bug. I assume that
> block-stream doesn't copy the data in that case. Changing it to anything
> != 0 solves the problem.
> 

I think I ran into a similar problem with an AHCI test once.

Reviewed-by: John Snow <jsnow@redhat.com>

> And answering your question, it doesn't really matter if we write the
> same value in all places, we only check the output of 'qemu-io -c map'.
> Plus the areas don't even overlap.
> 
> Berto
>