Re: [Qemu-devel] [PATCH v13 15/17] iotests: add simple incremental backup case

[John Snow <jsnow@redhat.com>]

On 02/20/2015 05:02 AM, Stefan Hajnoczi wrote:
> On Fri, Feb 13, 2015 at 05:08:56PM -0500, John Snow wrote:
>> +    def check_incremental(self, target=None):
>> +        if target is None:
>> +            target = self.bitmaps[-1].last_target()
>> +        self.assertTrue(iotests.compare_images(self.test_img, target))
>> +        return True
>> +
>> +
>> +    def hmp_io_writes(self, drive, patterns):
>> +        for pattern in patterns:
>> +            self.vm.hmp_qemu_io(drive, 'write -P%s %s %s' % pattern)
>> +        self.vm.hmp_qemu_io(drive, 'flush')
>
> Please don't read image files while the guest is still running.  Image
> formats do not support concurrent readers and writers.
>
> Three options:
> 1. Stop the guest before accessing self.test_img
> 2. Use drive-backup to make a full copy of self.test_img that can be
>     accessed.
> 3. Test specific patterns in the backup file instead of using
>     compare_images (qemu-io -c 'read -P 0xff 0 512' img)
>

I'm not sure I understand the complication, here. There is no "running 
guest," so these HMP writes are emulating the guest writes. As Max says, 
we're using -qtest here.

If you really want, I can introduce emulated stop/resume commands just 
for the sake of demonstration (I had them in there before) but for 
iotests I don't see why it's strictly necessary.

--js