Messages in this thread | | | From | Magnus Vigerlöf <> | Subject | input: evdev.c EVIOCGRAB semantics question | Date | Sat, 12 Aug 2006 17:24:16 +0200 |
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Hi,
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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