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Re: [Qemu-devel] [PATCH] ide: Set BSY bit during FLUSH

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] ide: Set BSY bit during FLUSH
Date: Tue, 28 May 2013 11:48:26 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6

Il 28/05/2013 11:36, Kevin Wolf ha scritto:
> Am 28.05.2013 um 11:24 hat Paolo Bonzini geschrieben:
>> 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.
> That's exactly what I was talking about, suspending a request is taking
> influence on its timing. I'm looking into this right now. (And it's not
> just resume, bdrv_debug_suspend can't be called from QEMU either)

It can be called from the rules file though, can't it?

> In fact, I'm checking whether we can have a monitor command to issue
> qemu-io commands, which will be more generally useful for test cases. We
> just need to make obvious that it doesn't become an ABI. Maybe prefix it
> with "__org.qemu.debug-" or something like that.

Makes sense.  I'm not sure why you'd want to read or write from
testcases, but bdrv_drain(_all) can also be useful from testcases.


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