linux-kernel - Re: [PATCH] input: evdev: Use multi-reader buffer to save space (rev5)

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Date:	Fri, 25 Jun 2010 01:14:45 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Henrik Rydberg <rydberg@...omail.se>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jiri Kosina <jkosina@...e.cz>,
	Mika Kuoppala <mika.kuoppala@...ia.com>,
	Benjamin Tissoires <tissoire@...a.fr>,
	Rafi Rubin <rafi@...s.upenn.edu>
Subject: Re: [PATCH] input: evdev: Use multi-reader buffer to save space
 (rev5)

On Wed, Jun 23, 2010 at 10:11:47AM +0200, Henrik Rydberg wrote:
> Dmitry Torokhov wrote:
> 
> > Overall I am starting getting concerned about proper isolation between
> > clients. Right now, if one client stops reading events and another one
> > issues grab then the first client will only get events that were
> > accumulated before grab tookm place. With the new shared buffer the
> > first client may get "grabbed" events if it stop for long enough for
> > buffer to wrap around.
> 
> Doing some research, the semantics of ioctl have obviously been discussed
> before, and I believe this points to another such issue. When grabbing a device,
> are we guaranteeing that the device no longer sends events to other clients, or
> are we guaranteeing that other clients can no longer read the device? If the
> latter, clearing all client buffers in conjunction with a grab would be
> appropriate, and would solve this issue.


Yes, I think it would be acceptable approach.

> 
> > Do we really same that much memory here? We normally do not have that
> > many users connected to event devices at once...
> 
> Ok, let's scratch this. Although I think the idea of multi-reader buffers is
> sound, it is obviously sufficiently incompatible with the current approach to
> produce distastefully complex patches. I will return with a new set which only
> fixes the buffer resize problem, and leaves the rest for later.
> 

Right, let's merge this and also MT slots and revisit this issue at some
later point.

Thanks.

-- 
Dmitry
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