F9: udev gives wrong permissions to vivi

Andrea mariofutire at googlemail.com
Sun Jul 13 11:45:06 UTC 2008


I am trying to load the module "vivi" which is a virtual video driver (very useful to test applications)

Anybody can do it like "modprobe vivi"

It creates an additional /dev/videoXX device.

The problem is that the permissions of this device are "wrong".

If I attach a real USB webcam, the /dev/videoX created has the right permissions.

This is what the permissions look like

crw-rw----  1 root root 81, 0 2008-07-12 20:41 /dev/video0
crw-rw----  1 root root 81, 1 2008-07-12 20:41 /dev/video1
crw-rw----  1 root root 81, 2 2008-07-12 20:41 /dev/video2
crw-rw----+ 1 root root 81, 3 2008-07-12 20:42 /dev/video3

In this case I did

modprobe vivi n_devs=3  (for video0-2)
then I plugged in a USB webcam. (for video3)

The order does not matter.

The difference is the "+" that the real webcam gets.
This way a normal user is not allowed to read /dev/video0.
I can manually change the permission, but I'd like to avoid the step each time I use it.

In udev rules I can only find this rule about videoX (in 50-udev-default.rules)
KERNEL=="video0",               SYMLINK+="video"

Anybody know exactly how it works?
How can I debug it?


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