Re: [Qemu-devel] [RFC v2 1/2] docs: vhost-user: add in-band kick/call messages

[Johannes Berg]

Hi Michael,

I had just wanted to prepare a resend, but

> > Hmm I don't like this. I propose that with 
> > VHOST_USER_PROTOCOL_F_IN_BAND_NOTIFICATIONS
> > we just don't allow VHOST_USER_SET_VRING_CALL (if you think it's
> > important to allow them, we can say that we do not require them).
> 
> You can't actually skip SET_VRING_CALL, it's necessary to start a vring,
> so libvhost-user for example calls dev->iface->queue_set_started() only
> in this case. The docs in the "Starting and stopping rings" section also
> explain this.

[...]

> See above. But I guess we could put a flag into bit 9 indicating that
> you want to use messages instead of polling or a file descriptor, if you
> prefer.

Personally, I don't think it matters since right now I can see the in-
band notification as being really necessary/useful only for simulation
work, and in that case no polling will be doable.

If you do think it's important to not make the two mutually exclusive,
how would you prefer to have this handled? With a new flag, e.g. in bit
9, indicating "use inband signalling instead of polling or eventfd"?

Thanks,
johannes