On Sat, 2009-07-04 at 13:52 -0400, Andy Walls wrote: > Hans, > > The inline source file at the end of this post is a small program I used > to play with libudev to see if it would complement the media controller > concept (as you suspected it would). > > Documentation on the libudev calls is here: > > http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/ > > The test program I wrote takes a (type,major,minor) tuple and lists the > device node and device symlinks as fetched by libudev. > > My test setup was a little strange since libudev is no longer maintained > separately but is bundled in with udev. On my Fedora 9 system I have > udev v124 (Fedora 9 stock) and libudev v143 (custom built from the udev > 143 source). > > Here's some output: > > $ ./finddev -c -M 81 -m 9 > Requested device: type 'c', major 81, minor 9 > Device directory path: '/dev' > Device node: '/dev/video0' > Device link: '/dev/video' > > $ ls -alR /dev/* | grep '[ /]video0' > lrwxrwxrwx 1 root root 6 2009-07-04 08:34 /dev/video -> video0 > crw-rw----+ 1 root root 81, 9 2009-07-04 08:34 /dev/video0 > > (OK for video nodes) > > > $ ./finddev -c -M 116 -m 6 > Requested device: type 'c', major 116, minor 6 > Device directory path: '/dev' > Device node: '/dev/snd/pcmC0D0p' > > $ ls -alR /dev/* | grep '[ /]pcmC0D0p' > crw-rw----+ 1 root root 116, 6 2009-07-04 13:43 pcmC0D0p > > (OK for ALSA PCM stream nodes). > > > Do you have any other particular questions about libudev's capabilities? OK, so more tests. Two Major groups: with udev still running and with udev not running (killed after I log in). Case 1: - udev running: - Adding a manual symlink # cd /dev # ln -s video0 mpeg0 Result: finddev using libudev doesn't find the manual symlink Case 2: - udev running - A manual mknod # cd /dev # mknod mpeg0 c 81 9 Result: finddev doesn't find the manually created device node Case 3: - same as case 2, but manually delete /dev/video0 Result: finddev reports /dev/video0 ! :( Case 4: - same as case 3 - add to 50-udev-default.rules: KERNEL=="video[0-9]*", SYMLINK+="mpeg%n" - Reload udev rules udevadm control --reload_rules udevadm trigger --subsystem-match=video4linux Result: findddev reports the new '/dev/mpeg0' symlink for /dev/video0 as well as the the '/dev/video' synmlink and the '/dev/video0' device node. :) Case 5: - same as case 3 - add to 50-udev-default.rules: KERNEL=="video[0-9]*", NAME="mpeg%n" - Reload udev rules udevadm control --reload_rules udevadm trigger --subsystem-match=video4linux Result: SELinux gripes at me because HAL is allowed to acces the attributes of /dev/mpeg*. :) finddev reports the new /dev/mpeg0 and the /dev/video symlink to it and they both exist in the filesystem. :) Case 6: - after case 5 - kill udevd. :) Result: finddev finds /dev/mpeg0 and the /dev/video symlink Case 7: - after case 6: - manually remove /dev/mpeg0 and /dev/video Result: finddev reports /dev/mpeg0 and the /dev/video symlink. :? Apparently libudev uses what's in the udev database and /sys but doesn't look in the /dev directory for manual actions, even when udevd is dead. Regards, Andy > Regards, > Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
