ocfs2: Move /sys/o2cb to /sys/fs/o2cb

/sys/fs is where we really want file system specific sysfs objects.

Ocfs2-tools has been updated to look in /sys/fs/o2cb. We can maintain
backwards compatibility with old ocfs2-tools by using a sysfs symlink. After
some time (2 years), the symlink can be safely removed. This patch also adds
documentation to make it easier for people to figure out what /sys/fs/o2cb
is used for.
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

Documentation/ABI/obsolete/o2cb

+What:		/sys/o2cb symlink
+Date:		Dec 2005
+KernelVersion:	2.6.16
+Contact:	ocfs2-devel@oss.oracle.com
+Description:	This is a symlink: /sys/o2cb to /sys/fs/o2cb. The symlink will
+		be removed when new versions of ocfs2-tools which know to look
+		in /sys/fs/o2cb are sufficiently prevalent. Don't code new
+		software to look here, it should try /sys/fs/o2cb instead.
+		See Documentation/ABI/stable/o2cb for more information on usage.
+Users:		ocfs2-tools. It's sufficient to mail proposed changes to
+		ocfs2-devel@oss.oracle.com.

Documentation/ABI/stable/o2cb

+What:		/sys/fs/o2cb/ (was /sys/o2cb)
+Date:		Dec 2005
+KernelVersion:	2.6.16
+Contact:	ocfs2-devel@oss.oracle.com
+Description:	Ocfs2-tools looks at 'interface-revision' for versioning
+		information. Each logmask/ file controls a set of debug prints
+		and can be written into with the strings "allow", "deny", or
+		"off". Reading the file returns the current state.
+Users:		ocfs2-tools. It's sufficient to mail proposed changes to
+		ocfs2-devel@oss.oracle.com.

Documentation/feature-removal-schedule.txt

@@ -318,3 +318,13 @@ Why:	Not used in-tree. The current out-of-tree users used it to
 	code / infrastructure should be in the kernel and not in some
 	out-of-tree driver.
 Who:	Thomas Gleixner <tglx@linutronix.de>
+
+---------------------------
+
+What:	/sys/o2cb symlink
+When:	January 2010
+Why:	/sys/fs/o2cb is the proper location for this information - /sys/o2cb
+	exists as a symlink for backwards compatibility for old versions of
+	ocfs2-tools. 2 years should be sufficient time to phase in new versions
+	which know to look in /sys/fs/o2cb.
+Who:	ocfs2-devel@oss.oracle.com

fs/ocfs2/cluster/sys.c

@@ -57,6 +57,7 @@ static struct kset *o2cb_kset;
 void o2cb_sys_shutdown(void)
 {
 	mlog_sys_shutdown();
+	sysfs_remove_link(NULL, "o2cb");
 	kset_unregister(o2cb_kset);
 }
 
@@ -68,6 +69,14 @@ int o2cb_sys_init(void)
 	if (!o2cb_kset)
 		return -ENOMEM;
 
+	/*
+	 * Create this symlink for backwards compatibility with old
+	 * versions of ocfs2-tools which look for things in /sys/o2cb.
+	 */
+	ret = sysfs_create_link(NULL, &o2cb_kset->kobj, "o2cb");
+	if (ret)
+		goto error;
+
 	ret = sysfs_create_group(&o2cb_kset->kobj, &o2cb_attr_group);
 	if (ret)
 		goto error;