What:		/sys/bus/rbd/
Date:		November 2010
Contact:	Yehuda Sadeh <yehuda@newdream.net>,
		Sage Weil <sage@newdream.net>
Description:

Being used for adding and removing rbd block devices.

Usage: <mon ip addr> <options> <pool name> <rbd image name> [snap name]

 $ echo "192.168.0.1 name=admin rbd foo" > /sys/bus/rbd/add

The snapshot name can be "-" or omitted to map the image read/write. A <dev-id>
will be assigned for any registered block device. If snapshot is used, it will
be mapped read-only.

Removal of a device:

  $ echo <dev-id> > /sys/bus/rbd/remove

Entries under /sys/bus/rbd/devices/<dev-id>/
--------------------------------------------

client_id

	The ceph unique client id that was assigned for this specific session.

major

	The block device major number.

name

	The name of the rbd image.

pool

	The name of the storage pool where this rbd image resides.
	An rbd image name is unique within its pool.

pool_id

	The unique identifier for the rbd image's pool.  This is
	a permanent attribute of the pool.  A pool's id will never
	change.

size

	The size (in bytes) of the mapped block device.

refresh

	Writing to this file will reread the image header data and set
	all relevant datastructures accordingly.

current_snap

	The current snapshot for which the device is mapped.

create_snap

	Create a snapshot:

	 $ echo <snap-name> > /sys/bus/rbd/devices/<dev-id>/snap_create

snap_*

	A directory per each snapshot


Entries under /sys/bus/rbd/devices/<dev-id>/snap_<snap-name>
-------------------------------------------------------------

snap_id

	The rados internal snapshot id assigned for this snapshot

snap_size

	The size of the image when this snapshot was taken.