[Spice-devel] [RFC PATCH spice-common v2 02/20] A version 2 of the MousePosition message

[Frediano Ziglio]

> 
> Hi
> 
> On Wed, Aug 22, 2018 at 11:11 PM Jonathon Jongsma <jjongsma at redhat.com>
> wrote:
> >
> > On Thu, 2018-08-16 at 18:26 +0200, Lukáš Hrázký wrote:
> > > The version 2 is using a (channel_id, monitor_id) pair to uniquely
> > > identify the display on which the event occured, instead of the
> > > ambiguous display_id.
> > >
> > > Signed-off-by: Lukáš Hrázký <lhrazky at redhat.com>
> > > ---
> > >  common/messages.h | 8 ++++++++
> > >  spice.proto       | 8 ++++++++
> > >  2 files changed, 16 insertions(+)
> > >
> > > diff --git a/common/messages.h b/common/messages.h
> > > index 942ba07..9b05cee 100644
> > > --- a/common/messages.h
> > > +++ b/common/messages.h
> > > @@ -460,6 +460,14 @@ typedef struct SpiceMsgcMousePosition {
> > >      uint8_t display_id;
> > >  } SpiceMsgcMousePosition;
> > >
> > > +typedef struct SpiceMsgcMousePositionV2 {
> > > +    uint32_t x;
> > > +    uint32_t y;
> > > +    uint32_t buttons_state;
> > > +    uint32_t channel_id;
> > > +    uint32_t monitor_id;
> > > +} SpiceMsgcMousePositionV2;
> > > +
> > >  typedef struct SpiceMsgcMousePress {
> > >      int32_t button;
> > >      int32_t buttons_state;
> > > diff --git a/spice.proto b/spice.proto
> > > index 80976d4..14475fc 100644
> > > --- a/spice.proto
> > > +++ b/spice.proto
> > > @@ -1092,6 +1092,14 @@ channel InputsChannel : BaseChannel {
> > >          uint8 display_id;
> > >      } @ctype(SpiceMsgcMousePosition) mouse_position;
> > >
> > > +    message {
> > > +        uint32 x;
> > > +        uint32 y;
> > > +        mouse_button_mask buttons_state;
> > > +        uint32 channel_id;
> > > +        uint32 monitor_id;

uint8 for both channel_id and monitor_id.

> > > +    } @ctype(SpiceMsgcMousePositionV2) mouse_position_v2;
> > > +
> > >      message {
> > >          mouse_button button;
> > >          mouse_button_mask buttons_state;
> >
> >
> > This protocol change is clearly necessary if we're going to support any
> > configurations other than those that we've supported in the past.
> 
> It's not clear to me that it's necessary if we still have the same
> constrains, that allow us to use the "displayid = channeld_id ||
> monitor_id" formula.

The formula is not "channel_id || monitor_id", this is just confusing, is
more "channel_id + monitor_id" or using GCC extension "channel_id ?: monitor_id".
Note that this formula is present in spice-gtk, virt-viewer (as Lukash mentioned),
and in SPICE protocol as index in agent MonitorsConfig (structure that is
used also by the server) and agent MouseState (as display_id field).
One of the main reason of these patches is that before (as use cases were limited)
the agent understand what the display_id was, now this is no more true.

Note also that under Linux currently all these protocol limitations allows
to support only a single device with multiple output, which is a problem for
vGPU. Under Windows we support multiple devices but all devices are limited
to one monitor. Extending Linux using the same limitation requires currently
that all monitor output would be mapped to a single DisplayChannel surface
(as currently only surface 0 can be primary) with all monitor sub-area of
the single surface. The complexity of this just for the above formula is not
worth. Extending the Windows idea (also in Linux) would require to have single
monitor for each DisplayChannel (so QXL devices has to be limited to one output)
so potentially we need to map a single device (like vGPU) to multiple
DisplayChannels (each with one monitor). This I think would be the only option
to carry on the above formula (which I state again is part of the protocol).
Potentially is possible to allocate in advance enough DisplayChannels (on the
server) to make possible to bind/unbind the outputs dynamically. This last
however won't solve the agent not knowing what a given display_id is and
would require some protocol updates (but not between client and server).
I think Jonathon, whom is mainly working on multi monitor support, was
thinking on not using these mappings but instead using a single DisplayChannel
for a single vGPU device even with multiple outputs.
Personally I would remove the restriction (mainly implementation, not
protocol) of having the primary surface only with surface_id == 0, this
was discussed also with Gerd when atomic settings were implemented in Linux
driver.

> 
> So do we have to support both multiple display channel & multiple
> monitors per display channels? Could you give some details on how this
> is going to operate?
> 

See above

> Iff it's the case, we will need to modify the protocol.
> 

Yes, this is what these patches are also about.

> 
> > One thing I just realized is that a channel id is not enough by itself
> > to uniquely identify a channel. You need a channel type and a channel
> > id. You could argue that I'm being pedantic and that it's obvious that
> > we're talking about display channels here. And maybe you'd be right.
> > But maybe it would be better to be more explicit? You could do that
> > either by using the existing SpiceChannelId type (which is a pair of
> > (type, id)), or by simply using a more descriptive name (e.g.
> > display_channel, or display_channel_id).
> >
> > Or if nobody else cares, we could leave it like this.
> >
> > Reviewed-by: Jonathon Jongsma <jjongsma at redhat.com>

Frediano