Anthony Liguori <anth...@codemonkey.ws> writes: > On 02/05/2010 07:09 AM, Christoph Hellwig wrote: >> On Wed, Feb 03, 2010 at 01:00:47PM -0600, Anthony Liguori wrote: >> >>> But I don't think this is the wrong place to do it. The >>> BlockDriverState reflects that backing device, not the emulated device >>> itself. In this case, you're trying to set a property of the emulated >>> device. >>> >> I think that's very borderline. While the emulated device exposes these >> properties, they are in fact a property of the backing storage, the >> right sector and min/max I/O sizes are determined by the backing storage >> device. >> > > It's guest visible state that should be configured based on the > properties of the backing store. > > However, as you said, live migration complicates things. > > drive is not an optimal interface because it mixes host and guest > state.
Qdev separates guest and host stuff. -device does guest, -netdev, -chardev, -drive if=none do host. Unfortunately, -drive can also do host, with other values for parameter if. A clean, host-only -blockdev for use with -device would be nice to have. > But the subset of -drive that you normally use should be > independent of the guest. To be precise: those properties that make sense with if=none. > For instance, with: > > -drive file=/home/anthony/foo.img,cache=off,aio=native,id=foo -device > virtio-blk-pci,drive=foo There's an implied if=ide, which means it's mixed host and guest stuff. > file, cache, and aio are all host properties. They have no visible > impact to the guest and if I change those properties during live > migration, they take affect without the guest noticing > > These topology options still can be specified via -drive, but the > proper way of splitting things would have them as part of the -device > option. During live migration, things on the -device side inherited > as part of the live migration process. If it's guest-visible, it should live in guest state (qdev device state), and be configured with -device. Else, it should live in host state (block driver state), and be configured via -drive if=none (or -blockdev once we have it). [...]
