linux-kernel - Re: [PATCH v2] Input: evdev - Add EVIOC mechanism to extract the MT slot state

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Message-ID: <20120106200332.GC23619@core.coreip.homeip.net>
Date:	Fri, 6 Jan 2012 12:03:33 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Chase Douglas <chase.douglas@...onical.com>
Cc:	Henrik Rydberg <rydberg@...omail.se>,
	Benjamin Tissoires <benjamin.tissoires@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Input: evdev - Add EVIOC mechanism to extract the MT
 slot state

On Fri, Jan 06, 2012 at 11:34:06AM -0800, Chase Douglas wrote:
> On 01/06/2012 11:18 AM, Henrik Rydberg wrote:
> > On Fri, Jan 06, 2012 at 07:55:44PM +0100, Henrik Rydberg wrote:
> >>> 2 different processes should be fine; the problem would be if 2 threads
> >>> of the same process share the same file descriptor. So far the rest of
> >>> evdev copes just fine with multiple threads using the same fd (all
> >>> operations are atomic in this regard), setting ABS_MT_SLOT before
> >>> fetching the state break this property.
> >>
> >> Are we talking about the need for a per-client mutex, or something
> >> more subtle, like introducing indirect coupling between threads
> >> through per-client states? The former ought to be easily remedied.
> > 
> > Ok, maybe not to so easy after all, which probably answers my own
> > question. Looks like a EVIOCGMTSLOT, taking both slot and event code
> > as argument, would be the cleaner route to take. Another ioctl, how do we
> > feel about that?
> 
> What's the problem with userspace locking?

It relies on userspace? ;)

-- 
Dmitry
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