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

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Date:	Fri, 25 Jun 2010 15:19:30 +0200
From:	Henrik Rydberg <rydberg@...omail.se>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
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)

Dmitry Torokhov wrote:
> 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.

Sounds good. I just resent the main MT patches, adding some more Cc:s, and to
make sure we both have the same version. :-) Regarding the ioctl stuff for MT
slots, I did not send those again, I am not sure what to do with them.

Thanks,
Henrik

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