[systemd-devel] [PATCH udev v5] udev: Add builtin/rule to export evdev information as udev properties

Zbigniew Jędrzejewski-Szmek zbyszek at in.waw.pl
Sun Jan 11 20:52:16 PST 2015

On Sun, Jan 11, 2015 at 08:47:19PM +0100, Carlos Garnacho wrote:
> This rule is only run on tablet/touchscreen devices, and extracts their size
> in millimeters, as it can be found out through their struct input_absinfo.
> The first usecase is exporting device size from tablets/touchscreens. This
> may be useful to separate policy and application at the time of mapping
> these devices to the available outputs in windowing environments that don't
> offer that information as readily (eg. Wayland). This way the compositor can
> stay deterministic, and the mix-and-match heuristics are performed outside.
> Conceivably, size/resolution information can be changed through EVIOCSABS
> anywhere else, but we're only interested in values prior to any calibration,
> this rule is thus only run on "add", and no tracking of changes is performed.
> This should only remain a problem if calibration were automatically applied
> by an earlier udev rule (read: don't).
>   v2: Folded rationale into commit log, made a builtin, set properties
>       on device nodes themselves
>   v3: Use inline function instead of macro for mm. size calculation,
>       use DECIMAL_STR_MAX, other code style issues
>   v4: Made rule more selective
>   v5: Minor style issues, renamed to a more generic builtin, refined
>       rule further.


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