[Spice-devel] [PATCH spice-server 2/2] QXL devices must be registered before Stream Devices

[Frediano Ziglio]

> On Wed, 2019-02-13 at 09:19 -0500, Frediano Ziglio wrote:
> > > 
> > > Stream devices assume that all QXL devices are registered with the
> > > server before we receive any communications from the stream device.
> > > This
> > > is due to the fact that QXL display channel IDs are assigned
> > > directly
> > > from the QXL device ID, whereas Stream display channels are
> > > assigned
> > > channel IDs based on the next free ID. If the stream channel is
> > > created first, it will find that 0 is the first available display
> > > ID and
> > > use that for its channel ID. Then when QXL device #0 is registered,
> > > it
> > > will also create a display channel with channel ID 0, and they will
> > > conflict.
> > 
> > Interesting, should not be checked somewhere and detected as API
> > violation?
> > 
> > Frediano
> 
> 
> Maybe. Right now qemu always registers QXL devices immediately after
> qemu starts. And obviously we can't communicate via the stream device
> until the guest is fully up and running. So I think there's essentially
> no way for the bug to happen with current code. I think QXL channels
> will always get created before stream channels. But for completeness it
> probably would be good to add a check somewhere.
> 

It sounds a good option.

> The alternative is to disconnect the QXL ID from the channel ID. In
> other words, QXL display channels would use the next available channel
> ID (just like the stream channels do) instead of using the qxl->id as
> the channel_id. But I don't know if such a change would violate any
> other assumptions in the code.
> 

I'm not sure Qemu would be that happy about it.

> Jonathon
> 
> 

I'll post a patch.

Frediano