Re: [Qemu-devel] [PATCH v2 2/2] iotests: New test 223 for exporting dirty bitmap over NBD

[Eric Blake <eblake@redhat.com>]

On 07/03/2018 05:09 AM, Vladimir Sementsov-Ogievskiy wrote:
> 02.07.2018 22:14, Eric Blake wrote:
>> Although this test is NOT a full test of image fleecing (as it
>> intentionally uses just a single block device directly exported
>> over NBD, rather than trying to set up a blockdev-backup job with
>> multiple BDS involved), it DOES prove that qemu as a server is
>> able to properly expose a dirty bitmap over NBD.
>>
>> When coupled with image fleecing, it is then possible for a
>> third-party client to do an incremental backup by using
>> qemu-img map with the x-dirty-bitmap option to learn which parts
>> of the file are dirty (perhaps confusingly, they are the portions
>> mapped as "data":false - which is part of the reason this is
>> still in the x- experimental namespace), along with another
>> normal client (perhaps 'qemu-nbd -c' to expose the server over
>> /dev/nbd0 and then just use normal I/O on that block device) to
>> read the dirty sections.
>>

>> +
>> +echo
>> +echo "=== End NBD server ==="
>> +echo
>> +
>> +_send_qemu_cmd $QEMU_HANDLE '{"execute":"nbd-server-remove",
>> +  "arguments":{"name":"n"}}' "return"
>> +_send_qemu_cmd $QEMU_HANDLE '{"execute":"nbd-server-stop"}' "return"
> 
> blockdev-del is not necessary?

I guess it's symmetric in that since we hotplugged the disk, we would 
also make sure hotunplug works after everything else has quit using it. 
But even the nbd-server-stop is not strictly necessary, since quitting 
qemu should have the same effect.  At this point, I'm not too worried 
about changing the test.

> 
> with or without:
> 
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Thanks for the review; the pull request went through without your 
notation being appended, but it never hurts to have additional review 
(and we still have time even after 3.0 soft freeze to fix any important 
bugs in what went in).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org