On Thu, May 14, 2020 at 05:19:40PM +0900, David Stevens wrote: > Sorry for the duplicate reply, didn't notice this until now. > > > Just storing > > the uuid should be doable (assuming this doesn't change during the > > lifetime of the buffer), so no need for a callback. > > Directly storing the uuid doesn't work that well because of > synchronization issues. The uuid needs to be shared between multiple > virtio devices with independent command streams, so to prevent races > between importing and exporting, the exporting driver can't share the > uuid with other drivers until it knows that the device has finished > registering the uuid. That requires a round trip to and then back from > the device. Using a callback allows the latency from that round trip > registration to be hidden. Uh, that means you actually do something and there's locking involved. Makes stuff more complicated, invariant attributes are a lot easier generally. Registering that uuid just always doesn't work, and blocking when you're exporting? -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
