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

What:		/sys/bus/rbd/add_single_major
Date:		December 2013
KernelVersion:	3.14
Contact:	Sage Weil <sage@inktank.com>
Description:	Available only if rbd module is inserted with single_major
		parameter set to true.
		Usage is the same as for /sys/bus/rbd/add.  If present,
		should be used instead of the latter: any attempts to use
		/sys/bus/rbd/add if /sys/bus/rbd/add_single_major is
		available will fail for backwards compatibility reasons.

What:		/sys/bus/rbd/remove_single_major
Date:		December 2013
KernelVersion:	3.14
Contact:	Sage Weil <sage@inktank.com>
Description:	Available only if rbd module is inserted with single_major
		parameter set to true.
		Usage is the same as for /sys/bus/rbd/remove.  If present,
		should be used instead of the latter: any attempts to use
		/sys/bus/rbd/remove if /sys/bus/rbd/remove_single_major is
		available will fail for backwards compatibility reasons.

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.

minor

	The block device minor number.  (December 2013, since 3.14.)

name

	The name of the rbd image.

pool

	The pool where this rbd image resides. The pool-name pair is unique
	per rados system.

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.


