jbd2: add the b_cow_tid field to journal_head struct

The b_cow_tid field will be used by the ext4 snapshots code to store the transaction id when the buffer was last cowed. Merging this patch to mainline will allow users to test ext4 snapshots as a standalone module, without the need to patch and install a development kernel. On 64bit machines this field uses fills in a padding "hole" and does not increase the size of the struct. On a 32bit machine this patch increases the size of the struct from 60 to 64 bytes. Signed-off-by: Amir Goldstein <amir73il@users.sf.net> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

jbd2: add the b_cow_tid field to journal_head struct
The b_cow_tid field will be used by the ext4 snapshots code to store the transaction id when the buffer was last cowed. Merging this patch to mainline will allow users to test ext4 snapshots as a standalone module, without the need to patch and install a development kernel. On 64bit machines this field uses fills in a padding "hole" and does not increase the size of the struct. On a 32bit machine this patch increases the size of the struct from 60 to 64 bytes. Signed-off-by: Amir Goldstein <amir73il@users.sf.net> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Amir Goldstein · Theodore Ts'o
1 parent 688f869ce3
Showing 1 changed file with 7 additions and 0 deletions Side-by-side Diff
include/linux/journal-head.h
@@ -41,6 +41,13 @@
 	unsigned b_modified;
  
 	/*
+	 * This feild tracks the last transaction id in which this buffer
+	 * has been cowed
+	 * [jbd_lock_bh_state()]
+	 */
+	unsigned b_cow_tid;
+
+	/*
 	 * Copy of the buffer data frozen for writing to the log.
 	 * [jbd_lock_bh_state()]
 	 */
...	...	@@ -41,6 +41,13 @@
41	41	unsigned b_modified;
42	42
43	43	/*
	44	+ * This feild tracks the last transaction id in which this buffer
	45	+ * has been cowed
	46	+ * [jbd_lock_bh_state()]
	47	+ */
	48	+ unsigned b_cow_tid;
	49	+
	50	+ /*
44	51	* Copy of the buffer data frozen for writing to the log.
45	52	* [jbd_lock_bh_state()]
46	53	*/