Re: [Qemu-devel] [PATCH] cpus: Fix event order on resume of stopped guest

[Markus Armbruster <armbru@redhat.com>]

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?