On Thu, Oct 19, 2017 at 11:04:48PM +0200, Paolo Bonzini wrote: > On 19/10/2017 19:43, Michael S. Tsirkin wrote: > > On Thu, Oct 19, 2017 at 05:43:18PM +0200, Paolo Bonzini wrote: > >> On 19/10/2017 17:39, Michael S. Tsirkin wrote: > >>>> Add VHOST_USER_GET_CONFIG/VHOST_USER_SET_CONFIG messages which can be > >>>> used for live migration of vhost user devices, also vhost user devices > >>>> can benefit from the messages to get/set virtio config space from/to the > >>>> I/O target. For the purpose to support virtio config space change, > >>>> VHOST_USER_SET_CONFIG_FD message is added as the event notifier > >>>> in case virtio config space change in the I/O target. > >>>> > >>>> Signed-off-by: Changpeng Liu <changpeng....@intel.com> > >>> I don't much like it that config is getting passed through. > >>> > >>> IMO this makes managing things harder not easier. > >>> > >>> How about specific messages about specific parts of > >>> config space that you want to get from the backend? > >> > >> In the case of virtio-blk that would be all of it. Do you have a case > >> in mind where some part of the configuration space is owned by QEMU? > >> > >> Paolo > > > > Yes. seg_max > > The seg_max limit is established by whoever reads buffers from the vring > and passes them down to the lower layer. For vhost-blk that's the > device server, not QEMU. > > Paolo
Good point. How about num_queues though? Also why is there SET_CONFIG? Does not look like blk uses it. And I wonder how do we do it for other devices. E.g. for net there's a bit in the middle of the config field that deals with migration. -- MST
