ocfs2: Document /sys/fs/ocfs2

Add ABI documentation for these files:

/sys/fs/ocfs2/max_locking_protocol
/sys/fs/ocfs2/loaded_cluster_plugins
/sys/fs/ocfs2/active_cluster_plugin
/sys/fs/ocfs2/cluster_stack

Signed-off-by: Joel Becker <[e-mail]>
Signed-off-by: Mark Fasheh <[e-mail]>

Documentation/ABI/testing/sysfs-ocfs2

···
+What:		/sys/fs/ocfs2/
+Date:		April 2008
+Contact:	[e-mail]
+Description:
+		The /sys/fs/ocfs2 directory contains knobs used by the
+		ocfs2-tools to interact with the filesystem.
+
+What:		/sys/fs/ocfs2/max_locking_protocol
+Date:		April 2008
+Contact:	[e-mail]
+Description:
+		The /sys/fs/ocfs2/max_locking_protocol file displays version
+		of ocfs2 locking supported by the filesystem.  This version
+		covers how ocfs2 uses distributed locking between cluster
+		nodes.
+
+		The protocol version has a major and minor number.  Two
+		cluster nodes can interoperate if they have an identical
+		major number and an overlapping minor number - thus,
+		a node with version 1.10 can interoperate with a node
+		sporting version 1.8, as long as both use the 1.8 protocol.
+
+		Reading from this file returns a single line, the major
+		number and minor number joined by a period, eg "1.10".
+
+		This file is read-only.  The value is compiled into the
+		driver.
+
+What:		/sys/fs/ocfs2/loaded_cluster_plugins
+Date:		April 2008
+Contact:	[e-mail]
+Description:
+		The /sys/fs/ocfs2/loaded_cluster_plugins file describes
+		the available plugins to support ocfs2 cluster operation.
+		A cluster plugin is required to use ocfs2 in a cluster.
+		There are currently two available plugins:
+
+		* 'o2cb' - The classic o2cb cluster stack that ocfs2 has
+			used since its inception.
+		* 'user' - A plugin supporting userspace cluster software
+			in conjunction with fs/dlm.
+
+		Reading from this file returns the names of all loaded
+		plugins, one per line.
+
+		This file is read-only.  Its contents may change as
+		plugins are loaded or removed.
+
+What:		/sys/fs/ocfs2/active_cluster_plugin
+Date:		April 2008
+Contact:	[e-mail]
+Description:
+		The /sys/fs/ocfs2/active_cluster_plugin displays which
+		cluster plugin is currently in use by the filesystem.
+		The active plugin will appear in the loaded_cluster_plugins
+		file as well.  Only one plugin can be used at a time.
+
+		Reading from this file returns the name of the active plugin
+		on a single line.
+
+		This file is read-only.  Which plugin is active depends on
+		the cluster stack in use.  The contents may change
+		when all filesystems are unmounted and the cluster stack
+		is changed.
+
+What:		/sys/fs/ocfs2/cluster_stack
+Date:		April 2008
+Contact:	[e-mail]
+Description:
+		The /sys/fs/ocfs2/cluster_stack file contains the name
+		of current ocfs2 cluster stack.  This value is set by
+		userspace tools when bringing the cluster stack online.
+
+		Cluster stack names are 4 characters in length.
+
+		When the 'o2cb' cluster stack is used, the 'o2cb' cluster
+		plugin is active.  All other cluster stacks use the 'user'
+		cluster plugin.
+
+		Reading from this file returns the name of the current
+		cluster stack on a single line.
+
+		Writing a new stack name to this file changes the current
+		cluster stack unless there are mounted ocfs2 filesystems.
+		If there are mounted filesystems, attempts to change the
+		stack return an error.
+
+Users:
+	ocfs2-tools <[e-mail]>