Consistent handling of USB device buttons

Alex Dubov oakad at
Mon Aug 20 22:54:18 PDT 2012

Peter Hutterer <peter.hutterer <at>> writes:

> > 
> > 1. Buttons have session global effect and there's no easy, nor stable way
> > to limit their effect to a particular device.
> I don't understand this bit. can you paraphrase?

For example, if I press a button on a headset and say it maps to
"XF86VolumeUp", how does the mixer application is supposed to know
which channel to adjust? I would expect it to only affect the headset, not
the "master" channel which is normally set to built-in audio card.

> evdev will set up BTN_0...BTN_TASK as buttons on a device. anything else
> should be a keyboard. especially KEY_CAMERA should be a key. what specific
> device has the camera button set up as mouse button?

My most recent problem was with Plantronics Audio 648 USB headset (works on
XP out of the box). It's got 4 buttons ["call", "volume up", "volume down"
and "mic mute"], which for some reason are mapped by evdev to mouse buttons
[8, 3, 2, 1].

As per point 1 above, mouse button presses generated by headset seem
indistinguishable from normal mouse key presses when applications are
concerned (with expected funny results).


> Cheers,
>    Peter

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