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

From: Henrik Rydberg
Date: Fri Jun 25 2010 - 09:39:19 EST

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.


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