Re: [Qemu-devel] [PATCH v2 3/7] block: implement reference count for BlockDriverState

[Stefan Hajnoczi <stefanha@redhat.com>]

On Tue, Jul 30, 2013 at 02:16:08PM +0200, Andreas Färber wrote:
> Am 30.07.2013 09:52, schrieb Fam Zheng:
> > Introduce bdrv_ref/bdrv_unref to manage the lifecycle of
> > BlockDriverState. They are unused for now but will used to replace
> > bdrv_delete() later.
> > 
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > ---
> >  block.c                   | 22 ++++++++++++++++++++++
> >  include/block/block.h     |  2 ++
> >  include/block/block_int.h |  1 +
> >  3 files changed, 25 insertions(+)
> 
> Didn't Kevin and Markus look into turning BlockDriverState into QOM
> objects a while back? That would give you reference counting for free,
> even atomic unlike this patch.

Splitting BlockDriverState into QOM objects has proven hard because
there is more than one class in today's BlockDriverState struct.  I
think handling refcounts separate is actually a good idea.

It tackles the lifecycle work without getting caught up in all the other
considerations (which QOM objects to have, -drive -> -blockdev
transition, etc).

So I guess the answer is that the QOM work is not ready.  This series
may actually help clean things up for the QOM work, which can then
switch to the objects' own refcount.

Stefan