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Subject: Re: [virtio] [PATCH v2] initialization: add extra device status handshake
Il 25/09/2013 10:28, Michael S. Tsirkin ha scritto: > > Failure to start vhost (which is fatal for vhost-scsi, > > since there is no userspace fallback unlike vhost-net) could be reported > > by not acknowledging FEATURES_OK. > > I think what you are asking for really, is > DEVICE_OK flag that locks both features and rings > and enables device. Yes, you're right. Plus the fact that the device might not acknowledge DEVICE_OK, which renders the device unusable. There is a difference, though. What happens if a virtqueue is only enabled by a particular feature? FEATURES_OK would let the device disable discovery of that virtqueue. DEVICE_OK wouldn't. Paolo > It would have to be set from driver quite late in life.