Re: [Qemu-devel] [RFC 2/5] vhost-user: Introduce new request to send virtio device status

[Maxime Coquelin]

On 02/27/2018 04:01 PM, Michael S. Tsirkin wrote:
> On Fri, Feb 16, 2018 at 06:29:07PM +0100, Maxime Coquelin wrote:
> > diff --git a/docs/interop/vhost-user.txt b/docs/interop/vhost-user.txt
> > index 9fcf48d611..daa452bd36 100644
> > --- a/docs/interop/vhost-user.txt
> > +++ b/docs/interop/vhost-user.txt
> > @@ -368,6 +368,7 @@ Protocol features
> >   #define VHOST_USER_PROTOCOL_F_MTU            4
> >   #define VHOST_USER_PROTOCOL_F_SLAVE_REQ      5
> >   #define VHOST_USER_PROTOCOL_F_CROSS_ENDIAN   6
> > +#define VHOST_USER_PROTOCOL_F_VIRTIO_STATUS  7
> >   
> >   Master message types
> >   --------------------
> > @@ -663,6 +664,19 @@ Master message types
> >         field, and slaves MUST NOT accept SET_CONFIG for read-only
> >         configuration space fields unless the live migration bit is set.
> >   
> > +* VHOST_USER_SET_VIRTIO_STATUS
> > +
> > +      Id: 26
> > +      Equivalent ioctl: N/A
> > +      Master payload: u64
> > +      Slave payload: N/A
> > +
> > +      Sent by the vhost-user master to notify of virtio device status change.
> > +      The payload is a u64 representing the virtio device status as defined in
> > +      the virtio specification.
> > +      The request should be sent only when VHOST_USER_PROTOCOL_F_VIRTIO_STATUS
> > +      protocol feature has been negotiated.
> > +
> >   Slave message types
> >   -------------------
> >   
>
> So for now backend was only activated after DRIVER_OK. Does this message
> mean that we must send updates such as _DRIVER as well?

Yes, even if I don't see a use for _ACKNOWLEDGE and _DRIVER today.

> Further, this is kind of one-way, but there are several cases where device
> modifies the status.  One is NEEDS_RESET. Another is clearing
> of FEATURES_OK.

Do you mean we should also notify the backend in case of NEEDS_RESET, or
clearing of FEATURES_OK?

Or you mean we should provide a way for the backend to update the device
status, e.g. by having a slave-initiated VHOST_USER_SET_VIRTIO_STATUS
request?

Thanks,
Maxime