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 <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

diff --git a/Documentation/ABI/testing/sysfs-ocfs2 b/Documentation/ABI/testing/sysfs-ocfs2
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+What:          /sys/fs/ocfs2/
+Date:          April 2008
+Contact:       ocfs2-devel@oss.oracle.com
+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:       ocfs2-devel@oss.oracle.com
+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:       ocfs2-devel@oss.oracle.com
+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:       ocfs2-devel@oss.oracle.com
+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:       ocfs2-devel@oss.oracle.com
+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 <ocfs2-tools-devel@oss.oracle.com>