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

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH] ide: Set BSY bit during FLUSH
Date: Tue, 28 May 2013 11:36:02 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

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)

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.


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