udev_volume_id - partition, filesystem, disklabel reader

This program is normally called from a udev rule, to provide udev with the
name, uuid or the filesystem type of a partition to name a device node.
udev_volume_id opens the blockdevice specified by the environment variable
DEVPATH and searches for a filesystem superblock to read the label. The
following commandline switches are supported to specify what udev_volume_id
should print to stdout:

       no option prints all values
  -h   prints help text
  -l   prints the label of the partition
  -u   prints the uuid of the partition
  -d   read disk instead of partition

If -d is specified udev_volume_id tries to read the label from the main
block device where the partition belongs to. For now this is only useful
for s390 dasd labels.

udev_volume_id will only return successful if the string asked for, is not
empty. All trailing whitespace will be removed, spaces replaced by underscore
and slashes ignored.

The following rule will create a symlink named with the label string:
  KERNEL="[hs]d*", PROGRAM="/sbin/udev_volume_id -l", SYMLINK="%c"

If no label is found udev_volume_id exits with nonzero and the rule will be
ignored.

To give it a try, you may call it on the commandline:

  [root@pim udev.kay]# DEVPATH=/block/hda/hda3 extras/volume_id/udev_volume_id
  T:ext3
  L:Music Store
  N:Music_Store
  U:d2da42b5-bbd9-44eb-a72c-cc4542fcb71e

  [root@pim udev.kay]# DEVPATH=/block/hda/hda3 extras/volume_id/udev_volume_id -l
  Music_Store

  [root@pim udev.kay]# DEVPATH=/block/hda/hda1 extras/volume_id/udev_volume_id -t
  swap


Please send any comment/questions/concerns to me or:
	linux-hotplug-devel@lists.sourceforge.net

Kay Sievers <kay.sievers@vrfy.org>