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Date: Tue, 28 May 2013 11:24:16 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] ide: Set BSY bit during FLUSH
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To: Kevin Wolf <kwolf@redhat.com>
Cc: stefano.stabellini@eu.citrix.com, Stefan Hajnoczi <stefanha@gmail.com>, Heiko Rommel <rommel@suse.com>, qemu-devel@nongnu.org, Bruce Rogers <brogers@suse.com>, "Gonglei (Arei)" <arei.gonglei@huawei.com>, qemu-stable <qemu-stable@nongnu.org>, =?ISO-8859-1?Q?Andreas_F=E4rber?= <afaerber@suse.de>

Il 28/05/2013 11:18, Kevin Wolf ha scritto:
>>> The other part why I haven't sent a fix yet is that I don't have a test
>>> case for it.
>>
>> Temporarily add a sleep(31) in qemu_fdatasync()?
>>
>> I was lazy in testing with -snapshot to not corrupt my disk image, which
>> would not trigger the same issue since qcow2-backed AFAIU.
>>
>>> I guess I need to extend blkdebug first before this can be
>>> reliably tested by qtest.
>>
>> It can't, since it's not a pure device emulation issue but depends on
>> the relative timing of filesystem operations and subsequent commands.
> 
> That's why you need to take influence on the timing. It's no excuse for
> merging without a test case. If we only ever tested devices that have no
> relation to the outside world, our testing would be pretty useless and
> always stay as bad as it is today in many areas.

I don't think the qtest would be timing dependent.  The Linux testcase
is timing dependent, but for the qtest all you need to check is "is BUSY
set during a flush?".  This can be done with blkdebug suspend/resume,
except that there is no way to call bdrv_debug_resume from QEMU.

Paolo