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My test setup was a little strange since libudev is no longer maintained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 1 -m 3
Requested device: type 'c', major 1, minor 3
Device directory path: '/dev'
Device node: '/dev/null'
Device link: '/dev/XOR'
$ ls -al /dev/ | grep '[ /]null'
crw-rw-rw- 1 root root 1, 3 2009-07-04 08:34 null
lrwxrwxrwx 1 root root 4 2009-07-04 08:34 X0R -> null
lrwxrwxrwx 1 root root 4 2009-07-04 08:34 XOR -> null
(Hmmm, not perfect for /dev/null)
$ ./finddev -b -M 11 -m 0
Requested device: type 'b', major 11, minor 0
Device directory path: '/dev'
Device node: '/dev/sr0'
Device link: '/dev/scd0'
Device link: '/dev/disk/by-path/pci-0000:00:14.1-scsi-1:0:0:0'
Device link: '/dev/cdrom'
Device link: '/dev/cdrw'
$ ls -alR /dev/* | grep '[ /]sr0'
lrwxrwxrwx 1 root root 3 2009-07-04 08:34 /dev/cdrom -> sr0
lrwxrwxrwx 1 root root 3 2009-07-04 08:34 /dev/cdrw -> sr0
lrwxrwxrwx 1 root root 3 2009-07-04 08:34 /dev/scd0 -> sr0
brw-rw----+ 1 root disk 11, 0 2009-07-04 08:34 /dev/sr0
lrwxrwxrwx 1 root root 9 2009-07-04 08:34 pci-0000:00:14.1-scsi-1:0:0:0 ->
../../sr0
(OK for the CDROM drive.)
$ ./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?
Regards,
Andy
/*
* finddev.c - Find a device node given (type,major,minor) using libudev
* Copyright (C) 2009 Andy Walls <awa...@radix.net>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Compilation:
* gcc -o finddev finddev.c -Wall -ludev
*
* Example invocation (/dev/null on my system):
* ./finddev -c -M 1 -m 3
*/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <libudev.h>
struct parsed_args {
int major;
int minor;
char type;
};
int parse_args(int argc, char *argv[], struct parsed_args *args)
{
int c, ret;
ret = 0;
args->major = args->minor = -1;
args->type = 'c';
while ((c = getopt(argc, argv, "bcM:m:")) != -1) {
switch (c) {
case 'b': args->type = 'b'; break;
case 'c': args->type = 'c'; break;
case 'M': args->major = atoi(optarg); break;
case 'm': args->minor = atoi(optarg); break;
default: ret = -1; break;
}
}
if (ret || args->major == -1 || args->minor == -1) {
fprintf(stderr, "Usage: %s [-b|-c] -M major -m minor\n",
argv[0]);
ret = -1;
}
return ret;
}
int main(int argc, char *argv[])
{
struct parsed_args args;
dev_t devnum;
struct udev *udev;
struct udev_device *udev_device;
const char *s;
struct udev_list_entry *udev_list_entry;
if (parse_args(argc,argv, &args))
exit(1);
printf("Requested device: type '%c', major %d, minor %d\n",
args.type, args.major, args.minor);
devnum = makedev(args.major, args.minor);
udev = udev_new();
if (udev == NULL) {
fprintf(stderr, "udev_new() failed\n");
exit(2);
}
printf("Device directory path: '%s'\n", udev_get_dev_path(udev));
udev_device = udev_device_new_from_devnum(udev, args.type, devnum);
if (udev_device == NULL) {
fprintf(stderr, "udev_device_new_from_devnum() failed\n");
udev_unref(udev);
exit(3);
}
s = udev_device_get_devnode(udev_device);
if (s) {
printf("Device node: '%s'\n", s);
} else {
fprintf(stderr, "udev_device_get_devnode() failed\n");
udev_device_unref(udev_device);
udev_unref(udev);
exit(4);
}
udev_list_entry_foreach(udev_list_entry,
udev_device_get_devlinks_list_entry(udev_device)) {
s = udev_list_entry_get_name(udev_list_entry);
printf("Device link: '%s'\n", s);
}
udev_device_unref(udev_device);
udev_unref(udev);
exit(0);
}
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