Re: [Qemu-devel] [PATCH 4/6] vhost-user: support registering external host notifiers

[Michael S. Tsirkin]

On Fri, May 25, 2018 at 12:05:50AM +0800, Tiwei Bie wrote:
> On Thu, May 24, 2018 at 06:49:47PM +0300, Michael S. Tsirkin wrote:
> > On Thu, May 24, 2018 at 06:33:34PM +0800, Tiwei Bie wrote:
> > > This patch introduces VHOST_USER_PROTOCOL_F_HOST_NOTIFIER.
> > > With this feature negotiated, vhost-user backend can register
> > > memory region based host notifiers. And it will allow the guest
> > > driver in the VM to notify the hardware accelerator at the
> > > vhost-user backend directly.
> > > 
> > > Signed-off-by: Tiwei Bie <address@hidden>
> > 
> > So maybe we don't need a new VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD?
> > Let's check VHOST_USER_PROTOCOL_F_HOST_NOTIFIER instead?
> 
> Yeah. I think it would be the best choice!
> 
> If this feature (HOST NOTIFIER) is negotiated, it means
> the QEMU is able to safely receive (the expected number
> of) file descriptors.
> 
> > 
> > > ---
> [...]
> > > +typedef struct VhostUserHostNotifier {
> > > +    MemoryRegion mr;
> > > +    void *addr;
> > > +    bool set;
> > > +} VhostUserHostNotifier;
> > >  
> > >  typedef struct VhostUserState {
> > >      CharBackend *chr;
> > > +    VhostUserHostNotifier notifier[VIRTIO_QUEUE_MAX];
> > >  } VhostUserState;
> > 
> > So this notifier is per-queue. Can't we maintain it in
> > NetVhostUserState then?
> 
> This notifier is per virtio-queue. But NetVhostUserState
> is per net-queue-pair.
> 
> And ideally, I think this structure shouldn't be visible
> to net/vhost-user, vhost-user-scsi, vhost-user-crypto, etc.
> 
> Best regards,
> Tiwei Bie

I wonder whether we can create a new per vq structure.

-- 
MST