ocfs2: Add the USERSPACE_STACK incompat bit.

The filesystem gains the USERSPACE_STACK incomat bit and the
s_cluster_info field on the superblock.  When a userspace stack is in
use, the name of the stack is stored on-disk for mount-time
verification.

The "cluster_stack" option is added to mount(2) processing.  The mount
process needs to pass the matching stack name.  If the passed name and
the on-disk name do not match, the mount is failed.

When using the classic o2cb stack, the incompat bit is *not* set and no
mount option is used other than the usual heartbeat=local.  Thus, the
filesystem is compatible with older tools.

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

fs/ocfs2/ocfs2.h

@@ -248,6 +248,7 @@ struct ocfs2_super
 	struct ocfs2_alloc_stats alloc_stats;
 	char dev_str[20];		/* "major,minor" of the device */
 
+	char osb_cluster_stack[OCFS2_STACK_LABEL_LEN + 1];
 	struct ocfs2_cluster_connection *cconn;
 	struct ocfs2_lock_res osb_super_lockres;
 	struct ocfs2_lock_res osb_rename_lockres;
@@ -368,6 +369,12 @@ static inline int ocfs2_is_soft_readonly(struct ocfs2_super *osb)
 	return ret;
 }
 
+static inline int ocfs2_userspace_stack(struct ocfs2_super *osb)
+{
+	return (osb->s_feature_incompat &
+		OCFS2_FEATURE_INCOMPAT_USERSPACE_STACK);
+}
+
 static inline int ocfs2_mount_local(struct ocfs2_super *osb)
 {
 	return (osb->s_feature_incompat & OCFS2_FEATURE_INCOMPAT_LOCAL_MOUNT);