jbd2: If a journal checksum error is detected, propagate the error to ext4

If a journal checksum error is detected, the ext4 filesystem will call
ext4_error(), and the mount will either continue, become a read-only
mount, or cause a kernel panic based on the superblock flags
indicating the user's preference of what to do in case of filesystem
corruption being detected.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 05e2b30..d147f0f 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -919,6 +919,9 @@
 	struct proc_dir_entry	*j_proc_entry;
 	struct transaction_stats_s j_stats;
 
+	/* Failed journal commit ID */
+	unsigned int		j_failed_commit;
+
 	/*
 	 * An opaque pointer to fs-private information.  ext3 puts its
 	 * superblock pointer here