On Tue, Apr 20, 2010 at 02:22:58PM +0100, Paul Brook wrote: > > Does this mean that virtio-blk supports all three combinations? > > > > 1. FLUSH that isn't a barrier > > 2. FLUSH that is also a barrier > > 3. Barrier that is not a flush > > > > 1 is good for fsync-like operations; > > 2 is good for journalling-like ordered operations. > > 3 sounds like it doesn't mean a lot as the host cache provides no > > guarantees and has no ordering facility that can be used. > > (3) allows the guest to queue overlapping transfers with well defined results. > I have no idea how useful this is in practice, but it's certainly plausible. > > Paul In theory, yes. At the moment, qemu only implements FLUSH and lguest only implements barrier without FLUSH. If you think it's useful, maybe start by using FLUSH+barrier in linux guest driver, that'd demonstrate how it's used. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
