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From: Alberto Garcia <berto@igalia.com>
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Date: Thu, 07 Dec 2017 20:34:12 +0100
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Subject: Re: [Qemu-devel] [PATCH] iotests: Tweak 030 in order to trigger a
 race condition with parallel jobs
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To: 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 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.

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