[Xorg] Input device hotplug
krh at bitplanet.net
Tue Jun 29 04:36:53 PDT 2004
Egbert Eich wrote:
> Kristian Høgsberg writes:
> > Hi all,
> > I've been working on making the X.org server hotplug aware with respect
> > to input devices. The current situation is that all devices must be
> > setup in the config file and adding new devices requires config file
> > editing and server restart. What I've been trying to implement is that
> > you can plug in an input device while the X server is running and it
> > will show up as a new XInput device.
> > The overall design I'm thinking of is to keep the device discovery
> > mechanism out of the X server. By adding requests to add and remove
> > devices a client program can monitor hotplug events and tell the server
> > to add or remove devices accordingly.
> Having the discover mechanism live outside of the X server is only useful if
> it is generic to the system and not specific to X. Any program interested
> in input devices should be able to take advantage of its services.
> While currently it is not possible to run multiple X servers on the
> same system (multi seat) it might well be in the future. In this
> case it must be made sure that only one of these servers connects to
> the device and that after a replug the same server gets the device
Yeah, that's a good point. The discovery mechanism should remember
which server to add the device to.
> > One thing I'ld like to discuss is where to add the add and remove device
> > interface -- I dont think XFree86-Misc is the right place. My first
> > approach to this was that the new functionality should be an Xorg
> > private interface, but I'm thinking that maybe it would be better if it
> > was a standardized extension to XInput. In that case, is the proposed
> > interface too Xorg specific?
> No, adding this to an extension would only make sense if a functionality
> is to be network transparent. This doesn't seem to be the case for input
> devices. Input devices pysically live on the machine the server exists
> on. Therefore a local interface should suffice.
> I basically had the same idea like you when I implemented the interface
> for APM years ago. My first implementation used an extension however it
> didn't seem to make much sense in using an X client which would communicate
> with the server just to send information across that could be obtained
> by the Xserver itself.
> Therefore I decided to add an interface to the DDX splitting it into
> a OS independent and OS dependent part.
Even if you only need local access, I think it makes sense to implement
it as an X request. This avoids adding another ad-hoc IPC mechanism;
you could create a unix socket and make a protocol for sending these
requests back and forth, but I'ld rather just sidestep possible security
implications and use what is already in place.
But I think there might be a case for remote access, e.g. if you run a
remote X session and the client wants to add/remove devices...
> The XInput extension may have to be extended to be able to send events
> to notify clients about the new device. Also it may be useful to provide
> more information about the device to the clients (for example some ID
> or serial number) so the client is able to (re)identify devices.
> > Comments are welcome. I'm currently trying to get my prototype cleaned
> > up, and then I'll attach it to a bugzilla entry
> I hope my comments have been helpful. This is certainly an importand issue
> which should be discussed.
More information about the xorg