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Date: Fri, 20 Feb 2015 09:22:40 -0500
From: Max Reitz <mreitz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v13 15/17] iotests: add simple incremental
	backup case
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To: Stefan Hajnoczi <stefanha@redhat.com>, John Snow <jsnow@redhat.com>
Cc: kwolf@redhat.com, famz@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, vsementsov@parallels.com

On 2015-02-20 at 05:02, 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.

If I'm not mistaken, there is no guest. VMs started using iotests.py 
have -machine accel=qtest set.

Max

>
> 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)