[PATCH evdev] Export device node as property.

[Dan Nicholson]

On Fri, Feb 4, 2011 at 5:17 AM, Peter Korsgaard <jacmet at sunsite.dk> wrote:
>>>>>> "Peter" == Peter Hutterer <peter.hutterer at who-t.net> writes:
>
> Hi,
>
>  >> I obviously like the concept, but this assumption basically breaks
>  >> remote X. What I think we really need is a unique identifier for XI
>  >> devices (to be able to reapply properties at next login), and with
>  >> hotplugging, the device node isn't really a good choice.
>  >>
>  >> For evdev I still think our best bet for a unique identifier is
>  >> EVIOCGPHYS, like I did back then:
>  >>
>  >> http://peter.korsgaard.com/patches/xorg/evdev-add-phys-property-EVIOCGPHYS-as-stable-identifer-v2.patch
>  >>
>  >> E.G. use something like usb-0000:00:1d.1-1/input0 rather than
>  >> /dev/input/event14.
>
>  Peter> the reasons why I chose the device node (after some feedback
>  Peter> from Lennart)
>
>  Peter> were:
>
>  Peter> - the device node is the only reliable identifier we have in the
>  Peter>   driver. on any system, irregardless of the platform, the device
>  Peter>   node will be avaible.
>
> Also on Windows / Cygwin?
>
>  Peter> - the device node can be tracked back to the configuration
>  Peter>   backend and the configuration. I configure devices in the
>  Peter>   xorg.conf with /dev/input/eventX, not through the phys.
>
> True. But most people presumably don't hand edit xorg.conf, but rather
> use gnome-mouse-preferences or whatever.
>
> The question is perhaps what the use case for this property is? To
> easily figure out what xinput id corresponds to a config entry in
> xorg.conf? The reason I wanted the property was slightly different. As
> the xinput ids are not stable, I wanted a stable identifier so I can
> reapply xinput settings at login time (E.G. for the coordinate
> transformation matrix for multihead touchscreens) through
> gnome-settings-daemon, similar to how it does for the xrandr setup.

Maybe another property is needed to satisfy that. What about "Device
UID", which is string setup by the driver. On evdev, it uses
EVIOCGPHYS, but it's up to the driver since it has the most details
about the device. I still think "Device Node" is useful, but I see
your point about needing a unique identifier. Then
gnome-settings-daemon can look at the combination of DISPLAY hostname
and "Device UID" to know which cached settings to grab.

--
Dan