Re: [PATCH v3] input/uinput: add UI_GET_SYSNAME ioctl to retrieve the sysfs path

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

On Tue, Jan 21, 2014 at 08:56:51AM +1000, Peter Hutterer wrote:
> On Mon, Jan 20, 2014 at 05:17:08PM -0500, Benjamin Tissoires wrote:
> > On Mon, Jan 20, 2014 at 4:53 PM, Dmitry Torokhov
> > <dmitry.torokhov@gmail.com> wrote:
> > > Hi Benjamin,
> > >
> > > On Fri, Jan 17, 2014 at 02:12:51PM -0500, Benjamin Tissoires wrote:
> > >> Evemu [1] uses uinput to replay devices traces it has recorded. However,
> > >> the way evemu uses uinput is slightly different from how uinput is
> > >> supposed to be used.
> > >> Evemu relies on libevdev, which creates the device node through uinput.
> > >> It then injects events through the input device node directly (and it
> > >> completely skips the uinput node).
> > >>
> > >> Currently, libevdev relies on an heuristic to guess which input node was
> > >> created. The problem is that is heuristic is subjected to races between
> > >> different uinput devices or even with physical devices. Having a way
> > >> to retrieve the sysfs path allows us to find the event node without
> > >> having to rely on this heuristic.
> > >
> > > I have been thinking about it and I think that providing tight coupling
> > > between uinput and resulting event device is wrong thing to do. We do
> > > allow sending input events through uinput interface and I think evemu
> > > should be using it, instead of going halfway through uinput and halfway
> > > though evdev. Replaying though uinput would actually be more correct as
> > > it would involve the same code paths throgugh input core as with using
> > > real devices (see input_event() vs. input_inject_event() that is used by
> > > input handlers).
> > >
> > 
> > Yes, I am perfectly aware of the fact that evemu is not using uinput
> > in the way it is intended to be.
> > I agree that it should be using the uinput node to inject events but
> > this means that only the process which has created the virtual device
> > can access it. It seems weird, I know, but the typical use of evemu is
> > the following:
> > - in a first terminal: $> sudo evemu-device mydevice.desc
> > - In a second: $> sudo evemu-play /dev/input/event12 < mydevice.events
> > 
> > It looks weird here, but it allows to inject different events
> > recording for the same virtual device node. 
> 
> it also allows replaying an event through the device it was recorded on.
> it's not always necessary or desirable to create a uinput device, sometimes
> replaying it through the actual device is better to reproduce a certain bug.

I was not saying that we should remove ability to inject events through
evdev nodes, so I am not sure why you are bringing your last point, but
form your and Benjamin's other mails I can see why going through evdev
(that has a separate device node) might be beneficial.

Benjamin, please clean up the issues brought up by David and I should be
able to apply the patch.

Thanks.

-- 
Dmitry