Re: a question about lid input device

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

On Wed, Jul 07, 2010 at 11:08:05AM +0800, Zhang Rui wrote:
> On Tue, 2010-07-06 at 04:27 +0800, Dmitry Torokhov wrote:
> > On Mon, Jul 05, 2010 at 04:49:45PM -0300, Henrique de Moraes Holschuh wrote:
> > > On Mon, 05 Jul 2010, Zhang Rui wrote:
> > > > > I think if you can listen to uevents you can just as easily open /dev/ 
> > > > > input/eventX and listen to proper input events.
> > > > > 
> > > > the question is users may want to get the lid switch STATUS,
> > > > asynchronously.
> > > 
> > > More often than not, you need to know the current state when dealing
> > > with EV_SW, to be able to do anything sensbile with it in GUIs, etc.
> > > 
> > 
> > I understand the need of getting the current state of a lid
> > switch/key/etc (and for that someone just need to write a utility
> > useable from shell scripts). But I do not understand how adding switch
> > state to uevents (that are emitted normally only when a new device is
> > created) will help here.
> > 
> driver core creates a sysfs attribute for uevent. and users may query
> this file to get the lid state, say:
> $ cat /sys/class/input/input1/uevent 
> PRODUCT=19/0/5/0
> NAME="Lid Switch"
> PHYS="PNP0C0D/button/input0"
> EV==21
> SW==1
> MODALIAS=input:b0019v0000p0005e0000-e0,5,kramlsfw0,
> 
> I'm not quite familiar with the uevent stuff, so please correct me if
> I'm wrong. :)
> IMO, for input switch device, it's reasonable to report the switch state
> in uevent, in which HAL may also be interested. And users may get the
> switch status by running "cat /sys/class/input/inputX/uevent" as well.
> 

No, I am sorry, you are inventing a new interface. Uevents normally
signal device creation and removal and carry capabilities, not the
state; there can be more than one switch/button per device, and so on.

Just write an utility that queries state via ioctl.

Thanks,

-- 
Dmitry