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

[Johannes Berg]

On Mon, 2019-09-09 at 08:41 -0400, Michael S. Tsirkin wrote:

> > The only thing we could do is crash if it wants to use this feature
> > without the others, but would that really be helpful?
> 
> We can return failure from SET_PROTOCOL_FEATURES.
> We can also fail all following messages.

Only if we have F_REPLY_ACK, I think?

I suppose we could fail a later command that already needs a reply
without REPLY_ACK, but that seems difficult to debug?

Anyway, if you feel that we should have this as some sort of safeguard I
can try to do that; to me it feels rather pointless as libvhost-user is
more of a sample implementation than anything else.

Unless you also wanted to write into the spec that F_KICK_CALL_MSGS
absolutely *requires* F_REPLY_ACK, and add some text that tells a device
how to behave when F_KICK_CALL_MSGS is negotiated without F_REPLY_ACK?

johannes