Re: [Qemu-devel] Multi-head support RFC

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> In QEMU 1.3, there was a DisplayState list. We used one DisplayState per 
> monitor. The DisplayChangeListener has a new hw_add_display vector, so 
> that when the UI requests a second monitor the new display gets attached 
> to the emulated hardware. (patch: add_display_ptr)

I don't think we want actually add/remove stuff here.  On real hardware
your gfx card has a fixed set of display connectors, and I think we are
best of mimic that.

Support for propagating connect/disconnect events and enabling/disabling
displays needs to be added properly.  Currently qxl/spice can handle
this, but it uses a private side channel.

> A new vector, hw_store_edid, was added to DisplayState so that UIs could 
> tell emulated hardware what the EDID for a given display should be. 
> (patch: edid-vector)

Note that multiple uis can be active at the same time.
What happened with the edids then?

> VRAM size was made configurable, so that more could be allocated to 
> handle multiple high-resolution displays. (patch: variable-vram-size)

upstream stdvga has this meanwhile.

> I don't think it makes sense to have a QemuConsole per display.

Why not?  That is exactly my plan.  Just have the virtual graphic card
call graphic_console_init() multiple times, once for each display
connector it has.

Do you see fundamental issues with that approach?

> I can use a model similar to what qxl does, and put the framebuffer for 
> each display inside a single DisplaySurface allocated to be a bounding 
> rectangle around all framebuffers. This has the advantage of looking 
> like something that already exists in the tree, but has several 
> disadvantages.

Indeed.  I don't recommend that.  It is that way for several historical
reasons (one being that the code predates the qemu console cleanup in
the 1.5 devel cycle).

> Are these features something that people would want to see in the tree? 

Sure.  One of the reasons for the console cleanup was to allow proper
multihead support.

cheers,
  Gerd