Re: [PATCH v2] Input: evdev - Add EVIOC mechanism to extract theMT slot state

[Chase Douglas]

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?

-- Chase
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