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    SubjectRe: [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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