Re: [linux-usb-devel] detecting when keys are being pressed on a keyboard

["Dmitry Torokhov" <dmitry.torokhov@gmail.com>]

Hi Oliver,

On 9/24/07, Oliver Neukum <oliver@neukum.org> wrote:
> Am Freitag 21 September 2007 schrieb Jiri Kosina:
> > On Fri, 21 Sep 2007, Oliver Neukum wrote:
> >
> > > I got the strange case of a keyboard going into autosuspend while a key
> > > was being pressed. The key release never arrived and I had to unplug the
> > > keyboard to get the key unstuck. Is there a clean way to learn from
> > > hid-core.c if a keyboard has keys pressed?
> >
> > Hi Oliver,
> >
> > HID doesn't keep any permanent state by itself. If you want to know
> > whether a given key is currently pressed or not, you'd have to inspect the
> > bitfields inside input_dev*, I am afraid.
>
> I see no way to do this without a race condition. The field isn't locked
> as far as I can tell.

You can take input_dev->event_lock to stop event from propagating
through input core while you are evaluating the bits. Input lcoking
changes are im -mm and will be merged into 2.6.24.

> Secondly, what is to happen in case of a system wide suspend? Will
> the system wake up thinking that the key is still pressed?
>

For now it will but it is about to change. Input device will send
'release' events for all pressed keys from their suspend method.

-- 
Dmitry