ocfs2: add cleancache support

This eighth patch of eight in this cleancache series "opts-in"
cleancache for ocfs2.  Clustered filesystems must explicitly enable
cleancache by calling cleancache_init_shared_fs anytime an instance
of the filesystem is mounted.  Ocfs2 is currently the only user of
the clustered filesystem interface but nevertheless, the cleancache
hooks in the VFS layer are sufficient for ocfs2 including the matching
cleancache_flush_fs hook which must be called on unmount.

Details and a FAQ can be found in Documentation/vm/cleancache.txt

[v8: trivial merge conflict update]
[v5: [email protected]: simplify init hook and any future fs init changes]
Signed-off-by: Dan Magenheimer <[email protected]>
Signed-off-by: Joel Becker <[email protected]>
Reviewed-by: Jeremy Fitzhardinge <[email protected]>
Reviewed-by: Konrad Rzeszutek Wilk <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Rik Van Riel <[email protected]>
Cc: Jan Beulich <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Ted Tso <[email protected]>
Cc: Nitin Gupta <[email protected]>

fs/ocfs2/super.c

@@ -41,6 +41,7 @@
 #include <linux/mount.h>
 #include <linux/seq_file.h>
 #include <linux/quotaops.h>
+#include <linux/cleancache.h>
 
 #define CREATE_TRACE_POINTS
 #include "ocfs2_trace.h"
@@ -2352,6 +2353,7 @@ static int ocfs2_initialize_super(struct super_block *sb,
 		mlog_errno(status);
 		goto bail;
 	}
+	cleancache_init_shared_fs((char *)&uuid_net_key, sb);
 
 bail:
 	return status;