Am 12.04.2013 um 14:06 hat Stefan Hajnoczi geschrieben: > On Fri, Apr 12, 2013 at 12:27 PM, Paolo Bonzini <pbonz...@redhat.com> wrote: > > Il 12/04/2013 12:04, Kevin Wolf ha scritto: > >> Or actually, if you want to avoid .bdrv_drain for now, the patch that I > >> started when I thought a bit about this, had a default .bdrv_drain > >> implementation that just forwarded the request to bs->file if it wasn't > >> implemented by a block driver. For the QED case, this would work. > > > > It's similar to bdrv_co_flush. Drain bs first, then bs->backing_hd > > (this is not needed in bdrv_co_flush), then bs->file, then the driver > > can do it on other files. > > Thanks for explaining Kevin. I didn't check whether bdrv_states > included all BlockDriverStates. > > The simplest solution is to put all BlockDriverStates on a global list. > > A .bdrv_drain() interface is more flexible but I don't see a need for it yet.
We don't need the .bdrv_drain() callback yet, but please implement it without a global list and with a function that forwards requests to bs->file and bs->backing_hd like Paolo suggested. This will be the obvious place to add the .bdrv_drain() callback later. The reason why I prefer this approach is that it allows draining a single BlockDriverState. After your patches we're really close to enabling this and converting some bdrv_drain_all() to more specific bdrv_drain(bs) calls. Kevin
