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

[Tiwei Bie <tiwei.bie@intel.com>]

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 <tiwei.bie@intel.com>
> 
> 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