[PATCH] dm linear: support ioctls

When an ioctl is performed on a device with a linear target, simply pass it on
to the underlying block device.

Note that the ioctl will pass through the filtering in blkdev_ioctl() twice.

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>