jbd2: add COW fields to struct jbd2_journal_handle

Add fields needed for the copy-on-write ext4 development work.

The h_cowing flag is used by ext4 snapshots code to mark the task in
COWING state.

The h_XXX_credits fields are used to track buffer credits usage
(accounted by COW and non-COW operations).

The h_cow_XXX fields are used as per task debugging counters.

Merging this commit into mainline will allow users to test ext4
snapshots as a standalone module, without the need to patch and
install a development kernel.

Signed-off-by: Amir Goldstein <[e-mail]>
Signed-off-by: "Theodore Ts'o" <[e-mail]>

include/linux/jbd2.h

···
 	int			h_err;
 
 	/* Flags [no locking] */
-	unsigned int	h_sync:		1;	/* sync-on-close */
-	unsigned int	h_jdata:	1;	/* force data journaling */
-	unsigned int	h_aborted:	1;	/* fatal error on handle */
+	unsigned int	h_sync:1;	/* sync-on-close */
+	unsigned int	h_jdata:1;	/* force data journaling */
+	unsigned int	h_aborted:1;	/* fatal error on handle */
+	unsigned int	h_cowing:1;	/* COWing block to snapshot */
+
+	/* Number of buffers requested by user:
+	 * (before adding the COW credits factor) */
+	unsigned int	h_base_credits:14;
+
+	/* Number of buffers the user is allowed to dirty:
+	 * (counts only buffers dirtied when !h_cowing) */
+	unsigned int	h_user_credits:14;
+
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	h_lockdep_map;
+#endif
+
+#ifdef CONFIG_JBD2_DEBUG
+	/* COW debugging counters: */
+	unsigned int h_cow_moved; /* blocks moved to snapshot */
+	unsigned int h_cow_copied; /* blocks copied to snapshot */
+	unsigned int h_cow_ok_jh; /* blocks already COWed during current
+				     transaction */
+	unsigned int h_cow_ok_bitmap; /* blocks not set in COW bitmap */
+	unsigned int h_cow_ok_mapped;/* blocks already mapped in snapshot */
+	unsigned int h_cow_bitmaps; /* COW bitmaps created */
+	unsigned int h_cow_excluded; /* blocks set in exclude bitmap */
 #endif
 };