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Date: Thu, 3 May 2018 14:26:42 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] cpus: Fix event order on resume of stopped
 guest
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To: Markus Armbruster <armbru@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com

Am 03.05.2018 um 14:17 hat Markus Armbruster geschrieben:
> Kevin Wolf <kwolf@redhat.com> writes:
> 
> > Am 23.04.2018 um 10:45 hat Markus Armbruster geschrieben:
> >> When resume of a stopped guest immediately runs into block device
> >> errors, the BLOCK_IO_ERROR event is sent before the RESUME event.
> >> 
> >> Reproducer:
> >> 
> >> 1. Create a scratch image
> >>    $ dd if=/dev/zero of=scratch.img bs=1M count=100
> >> 
> >>    Size doesn't actually matter.
> >> 
> >> 2. Prepare blkdebug configuration:
> >> 
> >>    $ cat >blkdebug.conf <<EOF
> >>    [inject-error]
> >>    event = "write_aio"
> >>    errno = "5"
> >>    EOF
> >> 
> >>    Note that errno 5 is EIO.
> >> 
> >> 3. Run a guest with an additional scratch disk, i.e. with additional
> >>    arguments
> >>    -drive if=none,id=scratch-drive,format=raw,werror=stop,file=blkdebug:blkdebug.conf:scratch.img
> >>    -device virtio-blk-pci,id=scratch,drive=scratch-drive
> >> 
> >>    The blkdebug part makes all writes to the scratch drive fail with
> >>    EIO.  The werror=stop pauses the guest on write errors.
> >> 
> >> 4. Connect to the QMP socket e.g. like this:
> >>    $ socat UNIX:/your/qmp/socket READLINE,history=$HOME/.qmp_history,prompt='QMP> '
> >> 
> >>    Issue QMP command 'qmp_capabilities':
> >>    QMP> { "execute": "qmp_capabilities" }
> >> 
> >> 5. Boot the guest.
> >> 
> >> 6. In the guest, write to the scratch disk, e.g. like this:
> >> 
> >>    # dd if=/dev/zero of=/dev/vdb count=1
> >> 
> >>    Do double-check the device specified with of= is actually the
> >>    scratch device!
> >> 
> >> 7. Issue QMP command 'cont':
> >>    QMP> { "execute": "cont" }
> >> 
> >> After step 6, I get a BLOCK_IO_ERROR event followed by a STOP event.  Good.
> >> 
> >> After step 7, I get BLOCK_IO_ERROR, then RESUME, then STOP.  Not so
> >> good; I'd expect RESUME, then BLOCK_IO_ERROR, then STOP.
> >
> > Do you want to rephrase this in the form of a script for qemu-iotests?
> >
> > I suppose the 'dd' line can be replaced by a 'qemu-io' monitor command.
> 
> Uh, can it?  With qemu-io, the write doesn't stop the guest, because it
> bypasses the device model, and thus blk_error_action().  I'm not aware
> of ways to make qemu-iotests write via a device model.  I'm afraid we
> need a full-fledged qtest.  Better ideas?

I'm afraid you're right. :-(

Did I ever mention that I don't really like having the werror logic in
the devices?

Kevin