Re: [Qemu-devel] [PATCH v2 5/6] vhost-user: add slave-req-fd support

[Maxime Coquelin]

On 05/30/2017 08:17 PM, Michael S. Tsirkin wrote:
> On Fri, May 26, 2017 at 04:28:57PM +0200, Maxime Coquelin wrote:
> > From: Marc-André Lureau<address@hidden>
> >
> > Learn to give a socket to the slave to let him make requests to the
> > master.
> >
> > Signed-off-by: Marc-André Lureau<address@hidden>
> > Signed-off-by: Maxime Coquelin<address@hidden>
> > ---
> >   docs/specs/vhost-user.txt |  32 +++++++++++-
> >   hw/virtio/vhost-user.c    | 127 ++++++++++++++++++++++++++++++++++++++++++++++
> >   2 files changed, 157 insertions(+), 2 deletions(-)
> >
> > diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
> > index 036890f..5fa7016 100644
> > --- a/docs/specs/vhost-user.txt
> > +++ b/docs/specs/vhost-user.txt
> > @@ -139,6 +139,7 @@ in the ancillary data:
> >    * VHOST_USER_SET_VRING_KICK
> >    * VHOST_USER_SET_VRING_CALL
> >    * VHOST_USER_SET_VRING_ERR
> > + * VHOST_USER_SET_SLAVE_REQ_FD
> >   
> >   If Master is unable to send the full message or receives a wrong reply it will
> >   close the connection. An optional reconnection mechanism can be implemented.
> > @@ -252,6 +253,18 @@ Once the source has finished migration, rings will be 
> > stopped by
> >   the source. No further update must be done before rings are
> >   restarted.
> >   
> > +Slave communication
> > +-------------------
> > +
> > +An optional communication channel is provided if the slave declares
> > +VHOST_USER_PROTOCOL_F_SLAVE_REQ protocol feature, to allow the slave to make
> > +requests to the master.
> > +
> > +The fd is provided via VHOST_USER_SET_SLAVE_REQ_FD ancillary data.
> > +
> > +A slave may then send VHOST_USER_SLAVE_* messages to the master
> > +using this fd communication channel.
> > +
> >   Protocol features
> >   -----------------
> >   
> > @@ -260,9 +273,10 @@ Protocol features
> >   #define VHOST_USER_PROTOCOL_F_RARP           2
> >   #define VHOST_USER_PROTOCOL_F_REPLY_ACK      3
> >   #define VHOST_USER_PROTOCOL_F_MTU            4
> > +#define VHOST_USER_PROTOCOL_F_SLAVE_REQ      5
> >   
> > -Message types
> > --------------
> > +Master message types
> > +--------------------
> >   
> >    * VHOST_USER_GET_FEATURES
> >   
>
> So down the road, we should make sure a device without
> VHOST_USER_PROTOCOL_F_SLAVE_REQ does not advertise IOMMU
> since you don't handle these messages otherwise.

Right, I will add a check to ensure this, and make this clearer
in the IOMMU spec part.

Thanks,
Maxime