linux-kernel - Re: input.c: start on release

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Message-Id: <200702241157.08228.dtor@insightbb.com>
Date:	Sat, 24 Feb 2007 11:57:07 -0500
From:	Dmitry Torokhov <dtor@...ightbb.com>
To:	Pete Zaitcev <zaitcev@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: input.c: start on release

On Friday 23 February 2007 19:44, Pete Zaitcev wrote:
> On Fri, 23 Feb 2007 10:06:14 -0500, "Dmitry Torokhov" <dmitry.torokhov@...il.com> wrote:
> > On 2/23/07, Pete Zaitcev <zaitcev@...hat.com> wrote:
> 
> > > void input_release_device(struct input_handle *handle)
> > > {
> > > ....
> > >        if (handle->handler->start)
> > >                handle->handler->start(handle);
> 
> > It should be ->start(). You are probably confused a little by the name
> > of the function. input_release_device() is called when userspace
> > issues ioctl(fd, EVIOCGRAB, 0) releasing (or ungrabbing) the device
> > (as opposed to xxx_release(file, inode) type functions that are called
> > when last user of a file drops off). In our case we want to give
> > handlers a chance to resume their control over device. Right now
> > standard keyboard driver uses start method do bring back in sync LED
> > state of a keyborad-like device after it was released (ungrabbed).
> 
> Thanks for the explanation. I suspect people asked you 100 times before.
> I can see why we would want to do this when a grab ends, but why do
> we do this on every close of /dev/input/mice? The call path is:
> 
>  mousedev_release ->
>  mixdev_release (optional for some majors)
>  input_close_device ->
>  input_release_device
>

The actual work withing input_release_device happens only when called
for handle that grabbed the device earlier. The reason why we call it
when closing a device so that device is not left in grabbed state if
userspace forgot to release it voluntarily.
 
> Same thing happens upon disconnect, though this is probably harmless,
> as the device is gone already anyway.
> 
> To tell you the truth, all I really want is to hold a static mutex
> across a call to input_close_device(). Can I do that?

Are you trying to fix locking in mousedev?

-- 
Dmitry
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