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    Subjectinput: evdev.c EVIOCGRAB semantics question

    What is the purpose of the EVIOCGRAB ioctl in evdev.c? Is it to prevent the
    device driver from sending events to other event handlers? Is it to prevent
    other applications from receiving events that has the device handler open?
    First, last, or both?

    I discovered the following behavior when I fired up a second X-server on my
    machine with my Wacom tablet connected: The second X-server opened the tablet
    as well and everything worked as it should. However when I switched back to
    the first X-server the tablet didn't work at all. Only when I stopped the
    second X-server did the tablet start working in the first X-server again. If
    I changed the code in evdev to ignore the EVIOCGRAB-ioctl the tablet works in
    both X-servers, but that caused other problems.

    Now, having two X-servers might not be the most common thing to have, but
    having other applications that depends on the movement from the tablet might
    be more common.

    As is it now, it's useless (more or less) to run wacdump to display the tablet
    specific events in a understandable manner. An application that generates
    events through uinput based on tablet events and some other qualifiers
    (mouseemu, simulating mouse scroll wheel) will not work either.

    And yes, the X-server must grab the tablet. Otherwise events will go
    through /dev/input/mice as well and mess up applications that depend on the
    tablet-specific absolute events.

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      Last update: 2006-08-12 17:27    [W:0.019 / U:7.188 seconds]
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