On Wed, Mar 03, 2021 at 05:01:05PM -0500, Michael S. Tsirkin wrote: > On Wed, Mar 03, 2021 at 02:50:11PM +0000, Alex Bennée wrote: > Also, are we sure it's ok to send the messages and then send > VHOST_USER_SET_FEATURES with VHOST_USER_F_PROTOCOL_FEATURES clear? > Looks more like a violation to me ...
Looking again I agree it would be a violation to omit VHOST_USER_F_PROTOCOL_FEATURES in VHOST_USER_SET_FEATURES. Previously I only looked at VHOST_USER_SET_PROTOCOL_FEATURES where the spec says: Only legal if feature bit ``VHOST_USER_F_PROTOCOL_FEATURES`` is present in ``VHOST_USER_GET_FEATURES``. So negotiation is *not* necessary for sending VHOST_USER_SET_PROTOCOL_FEATURES. However, I missed that other features *do* require negotiation of VHOST_USER_F_PROTOCOL_FEATURES according to the spec. For example: If ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been negotiated, the ring is initialized in an enabled state. Now I think: 1. VHOST_USER_F_PROTOCOL_FEATURES *must* be included VHOST_USER_SET_FEATURES if the master supports it. 2. VHOST_USER_SET_PROTOCOL_FEATURES does not require negotiation, instead the master just needs to check that VHOST_USER_F_PROTOCOL_FEATURES is included in the VHOST_USER_GET_FEATURES reply. It's an exception. Stefan
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