Re: [Qemu-devel] [Qemu-block] [PATCH v2 1/2] blockdev: release the AioContext at drive_backup_prepare

[Sergio Lopez <slp@redhat.com>]

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Kevin Wolf <kwolf@redhat.com> writes:

> Am 13.09.2019 um 21:54 hat John Snow geschrieben:
>> 
>> 
>> On 9/13/19 11:25 AM, Sergio Lopez wrote:
>> > do_drive_backup() already acquires the AioContext, so release it
>> > before the call.
>> > 
>> > Signed-off-by: Sergio Lopez <slp@redhat.com>
>> > ---
>> >  blockdev.c | 6 +-----
>> >  1 file changed, 1 insertion(+), 5 deletions(-)
>> > 
>> > diff --git a/blockdev.c b/blockdev.c
>> > index fbef6845c8..3927fdab80 100644
>> > --- a/blockdev.c
>> > +++ b/blockdev.c
>> > @@ -1783,20 +1783,16 @@ static void drive_backup_prepare(BlkActionState *common, Error **errp)
>> >  
>> >      aio_context = bdrv_get_aio_context(bs);
>> >      aio_context_acquire(aio_context);
>> > -
>
> Are you removing this unrelated empty line intentionally?

Yes. In the sense of that whole set of lines being a "open drained
section" block.

>> >      /* Paired with .clean() */
>> >      bdrv_drained_begin(bs);
>> 
>> Do we need to make this change to blockdev_backup_prepare as well?
>
> Actually, the whole structure feels a bit wrong. We get the bs here and
> take its lock, then release the lock again and forget the reference,
> only to do both things again inside do_drive_backup().
>
> The way snapshots work is that the "normal" snapshot commands are
> wrappers that turn it into a single-entry transaction. Then you have
> only one code path where you can resolve the ID and take the lock just
> once. So maybe backup should work like this, too?

I'm neither opposed nor in favor, but I think this is outside the scope
of this patch series.

Sergio.

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