[Spice-devel] how can i trace monitor change (etc) events

[Marc-André Lureau]

Hi

Thanks a lot for your analysis so far!

Adding David Airlie in CC

----- Original Message -----
> I have an explanation for this, but not a fix.  The fix needs to be made
> by the owner of this code (Alon or Dave according to the header!)
> 
> The bug lies in qxl_display.c:qxl_crtc_mode_set.  In this method, there
> is a conditional termed "recreate_primary".  The logic for this is based
> on qcrtc->index.  In other words, the "recreate_primary" branch is taken
> only on the first head.  In this case, the surface_id is FORCED to 0,
> and for all other heads, the actual surface_id is used.
> 
> However, no _actual_ surface_id's are 0.  See above.  All surfaces
> (valid for this context) have surface_id >0.  So it is IMPOSSIBLE for
> the monitor_config for the second monitor to have surface_id = 0.

Ok

> So you may be asking yourself (or me) - so how is it working (in
> gnome3)?  Well, that is funny.  It's just "working by coincidence" for
> gnome3, but broken by design.
> 
> Here's how that works.  When the bo is created, it _initially_ gets
> surface_id = 0.  The actual surface id (assigned by qxl_bo_check_id)
> isn't assigned until the qxl_update_area_ioctl is called (by userspace).

(there seems to be other paths to get surface checked/allocated,
with the qxl_release stuff. But I have no idea how this works)
 
>   In gnome3, this ioctl is called AFTER setting the mode on the 2nd
> monitor, so the second branch above which returns the "actual"
> surface_id still returns 0 because the surface hasn't been "checked"
> (whatever that means).  In MATE and other xrandr environments, the ioctl
> is called right BEFORE setting the mode, so the actual surface_id is
> assigned and we get the trap in spice-widget.c (which I have worked around).
> 
> Thoughts?
> 

How come gnome3 (and mate) draw correctly all the monitors on the surface 0  (that's the only things spice-gtk shows, even with your patch), since the crtc seems to be associated with a different surface?..

Hopefully Alon or Dave can shed some light here.