[Linuxwacom-devel] Support for changing tablet models in a running X-server?

[Magnus <wi...@bi...>]

Hi,

For people who'd like the point to be made in the first five lines: I don't 
think (anymore) that support for changing the tablet model is a good idea for 
a driver to Xorg 7.0 (and maybe other X-servers).

Why not? Read on...

During the last weeks I've been looking through the source code of both 
linuxwacom and Xorg, and also the documentation to Xorg. I've come to realize 
the change that my module (wacomproxy) requires (the ability to change the 
properties of the defined XInput devices at runtime) might not be suitable 
for the current Xorg implementation (7.0, is this true for XFree86 as well?). 
This 'problem' would be the same as when you would switch between two 
different tablets.

The problem as I can see it is the change in the connected HW and the need to 
propagate these changes to the X-applications. As I understood it, neither 
Xorg nor the applications are prepared that something like this should happen 
and therefore can't deal with this in a good manner (if at all).

Upcoming releases of Xorg are addressing the addition/removal of XInput 
devices but they are talking of a new version of the XInputSpec (new 
functions; addition, removal, etc) (and there's a very, very small note that 
a change of the module ABI might be of interest). They also mention problems 
with the GTK-framwork regarding removal of XInput devices. See also 
http://wiki.x.org/wiki/XInputHotplug

So considering this, is it really a good idea to support changes of the tablet 
properties in the driver that I started with and that has been included in 
the -dev-branch? I'd hate myself if I managed to push Ping into a corner of 
sticky goo that I'm afraid that the changing tablet properties is...

Having true hotplugging of the XInput devices are of course the way we all 
want it, but trying to make something like that today with an X-server that 
does not support it...


I'm thinking of making changes in my module to lock it to only one tablet 
model (the first model connected or a specific tablet defined as a module 
param) due to this realization.

Comments are appreciated.

Thanks for listening to random thoughts written in the night
 Magnus