block: rbd: update sysfs interface

The existing sysfs interface has been updated to be in the same format
as described in Documentation/ABI/README. This will be useful for
scripting and tracking changes in the ABI. Attributes have been grouped
by functionality and/or the date on which they were added.

There are a couple of more changes:
- The attributes have been annotated with file permissions RO/RW/WO.
- Added description of the bus attribute supported_features
Signed-off-by: NAishwarya Pant <aishpant@gmail.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/ABI/testing/sysfs-bus-rbd

-What:		/sys/bus/rbd/
-Date:		November 2010
-Contact:	Yehuda Sadeh <yehuda@newdream.net>,
-		Sage Weil <sage@newdream.net>
+What:		/sys/bus/rbd/add
+Date:		Oct, 2010
+KernelVersion:	v2.6.37
+Contact:	Sage Weil <sage@newdream.net>
 Description:
+		(WO) Add rbd block device.
 
-Being used for adding and removing rbd block devices.
+		Usage: <mon ip addr> <options> <pool name> <rbd image name> [<snap name>]
 
-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
 
- $ 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.
 
-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.
 
-Usage: <dev-id> [force]
+What:		/sys/bus/rbd/remove
+Date:		Oct, 2010
+KernelVersion:	v2.6.37
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		(WO) Remove rbd block device.
+
+		Usage: <dev-id> [force]
 
- $ echo 2 > /sys/bus/rbd/remove
+		 $ echo 2 > /sys/bus/rbd/remove
+
+		Optional "force" argument which when passed will wait for
+		running requests and then unmap the image. Requests sent to the
+		driver after initiating the removal will be failed. (August
+		2016, since 4.9.)
 
-Optional "force" argument which when passed will wait for running requests and
-then unmap the image. Requests sent to the driver after initiating the removal
-will be failed.  (August 2016, since 4.9.)
 
 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
+Date:		Dec, 2013
+KernelVersion:	v3.14
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		(WO) 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,
+
+		Usage is the same as for /sys/bus/rbd/add. If present, this
 		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.
+		/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
+Date:		Dec, 2013
+KernelVersion:	v3.14
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		(WO) 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,
+
+		Usage is the same as for /sys/bus/rbd/remove. If present, this
 		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_addr
-
-	The ceph unique client entity_addr_t (address + nonce).
-	The format is <address>:<port>/<nonce>: '1.2.3.4:1234/5678' or
-	'[1:2:3:4:5:6:7:8]:1234/5678'.  (August 2016, since 4.9.)
-
-client_id
-
-	The ceph unique client id that was assigned for this specific session.
-
-cluster_fsid
 
-	The ceph cluster UUID.  (August 2016, since 4.9.)
-
-config_info
-
-	The string written into /sys/bus/rbd/add{,_single_major}.  (August
-	2016, since 4.9.)
-
-features
-
-	A hexadecimal encoding of the feature bits for this image.
-
-major
-
-	The block device major number.
+What:		/sys/bus/rbd/supported_features
+Date:		Mar, 2017
+KernelVersion:	v4.11
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		(RO) Displays the features supported by the rbd module so that
+		userspace can generate meaningful error messages and spell out
+		unsupported features that need to be disabled.
+
+
+What:		/sys/bus/rbd/devices/<dev-id>/size
+What:		/sys/bus/rbd/devices/<dev-id>/major
+What:		/sys/bus/rbd/devices/<dev-id>/client_id
+What:		/sys/bus/rbd/devices/<dev-id>/pool
+What:		/sys/bus/rbd/devices/<dev-id>/name
+What:		/sys/bus/rbd/devices/<dev-id>/refresh
+What:		/sys/bus/rbd/devices/<dev-id>/current_snap
+Date:		Oct, 2010
+KernelVersion:	v2.6.37
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		size:		(RO) The size (in bytes) of the mapped block
+				device.
 
-minor
+		major:		(RO) The block device major number.
 
-	The block device minor number.  (December 2013, since 3.14.)
+		client_id:	(RO) The ceph unique client id that was assigned
+				for this specific session.
 
-name
+		pool:		(RO) The name of the storage pool where this rbd
+				image resides. An rbd image name is unique
+				within its pool.
 
-	The name of the rbd image.
+		name:		(RO) The name of the rbd image.
 
-image_id
+		refresh:	(WO) Writing to this file will reread the image
+				header data and set all relevant data structures
+				accordingly.
 
-	The unique id for the rbd image.  (For rbd image format 1
-	this is empty.)
+		current_snap:	(RO) The current snapshot for which the device
+				is mapped.
 
-pool
 
-	The name of the storage pool where this rbd image resides.
-	An rbd image name is unique within its pool.
+What:		/sys/bus/rbd/devices/<dev-id>/pool_id
+Date:		Jul, 2012
+KernelVersion:	v3.6
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		(RO) The unique identifier for the rbd image's pool. This is a
+		permanent attribute of the pool. A pool's id will never change.
 
-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.
+What:		/sys/bus/rbd/devices/<dev-id>/image_id
+What:		/sys/bus/rbd/devices/<dev-id>/features
+Date:		Oct, 2012
+KernelVersion:	v3.7
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		image_id:	(RO) The unique id for the rbd image. (For rbd
+				image format 1 this is empty.)
 
-size
+		features:	(RO) A hexadecimal encoding of the feature bits
+				for this image.
 
-	The size (in bytes) of the mapped block device.
 
-refresh
+What:		/sys/bus/rbd/devices/<dev-id>/parent
+Date:		Nov, 2012
+KernelVersion:	v3.8
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		(RO) Information identifying the chain of parent images in a
+		layered rbd image. Entries are separated by empty lines.
 
-	Writing to this file will reread the image header data and set
-	all relevant datastructures accordingly.
 
-current_snap
+What:		/sys/bus/rbd/devices/<dev-id>/minor
+Date:		Dec, 2013
+KernelVersion:	v3.14
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		(RO) The block device minor number.
 
-	The current snapshot for which the device is mapped.
 
-snap_id
+What:		/sys/bus/rbd/devices/<dev-id>/snap_id
+What:		/sys/bus/rbd/devices/<dev-id>/config_info
+What:		/sys/bus/rbd/devices/<dev-id>/cluster_fsid
+What:		/sys/bus/rbd/devices/<dev-id>/client_addr
+Date:		Aug, 2016
+KernelVersion:	v4.9
+Contact:	Sage Weil <sage@newdream.net>
+Description:
+		snap_id:	(RO) The current snapshot's id.
 
-	The current snapshot's id.  (August 2016, since 4.9.)
+		config_info:	(RO) The string written into
+				/sys/bus/rbd/add{,_single_major}.
 
-parent
+		cluster_fsid:	(RO) The ceph cluster UUID.
 
-	Information identifying the chain of parent images in a layered rbd
-	image.  Entries are separated by empty lines.
+		client_addr:	(RO) The ceph unique client
+				entity_addr_t (address + nonce). The format is
+				<address>:<port>/<nonce>: '1.2.3.4:1234/5678' or
+				'[1:2:3:4:5:6:7:8]:1234/5678'.