Re: Move vhost-user SET_STATUS 0 after get vring base?

[Michael S. Tsirkin]

On Tue, Apr 18, 2023 at 11:18:11AM -0400, Stefan Hajnoczi wrote:
> Hi,
> Cindy's commit ca71db438bdc ("vhost: implement vhost_dev_start method")
> added SET_STATUS calls to vhost_dev_start() and vhost_dev_stop() for all
> vhost backends.
> 
> Eugenio's commit c3716f260bff ("vdpa: move vhost reset after get vring
> base") deferred the SET_STATUS 0 call in vhost_dev_stop() until after
> GET_VRING_BASE for vDPA only. In that commit Eugenio said, "A patch to
> make vhost_user_dev_start more similar to vdpa is desirable, but it can
> be added on top".
> 
> I agree and think it's a good idea to keep the vhost backends in sync
> where possible.
> 
> vhost-user still has the old behavior where QEMU sends SET_STATUS 0
> before GET_VRING_BASE. Most existing vhost-user backends don't implement
> the SET_STATUS message, so I think no one has tripped over this yet.
> 
> Any thoughts on making vhost-user behave like vDPA here?
> 
> Stefan

Wow. Well  SET_STATUS 0 resets the device so yes, I think doing that
before GET_VRING_BASE will lose a state. Donnu how it does not trip
up people, indeed the only idea is if people ignore SET_STATUS.


-- 
MST