Re: [Qemu-devel] [RFC] libvhost-user: implement VHOST_USER_PROTOCOL_F_KICK_CALL_MSGS

[Johannes Berg]

On Sun, 2019-09-08 at 09:13 -0400, Michael S. Tsirkin wrote:

> > I think the only use for this extension would be for simulation
> > purposes, and even then only combined with the REPLY_ACK and SLAVE_REQ
> > extensions, i.e. you explicitly *want* your virtual machine to lock up /
> > wait for a response to the KICK command (and respectively, the device to
> > wait for a response to the CALL command).
> 
> OK so when combined with these, it's OK I think.

OK.

> Do we want to force this restriction in code maybe then?

Unlike in this patch, I was planning to not actually advertise
VHOST_USER_PROTOCOL_F_KICK_CALL_MSGS, and do that only if the user of
the library wants to advertise it, since devices used for simulation
also have to be careful about how they use this.

However, if I understand correctly we cannot enforce that all of them
are used at the same time - we're the device side, so we only advertise
our features and the master actually sets the ones it wants to use, no?

The only thing we could do is crash if it wants to use this feature
without the others, but would that really be helpful?

I'm starting to actually get this working, so I'll post new patches in a
few days or so.

johannes