jbd2: clean up how the journal device name is printed

Calculate the journal device name once and stash it away in the
journal_s structure.  This avoids needing to call bdevname()
everywhere and reduces stack usage by not needing to allocate an
on-stack buffer.  In addition, we eliminate the '/' that can appear in
device names (e.g. "cciss/c0d0p9" --- see kernel bugzilla #11321) that
can cause problems when creating proc directory names, and include the
inode number to support ocfs2 which creates multiple journals with
different inode numbers.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 3dd2090..66c3499 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -850,7 +850,8 @@
 	 */
 	struct block_device	*j_dev;
 	int			j_blocksize;
-	unsigned long long		j_blk_offset;
+	unsigned long long	j_blk_offset;
+	char			j_devname[BDEVNAME_SIZE+24];
 
 	/*
 	 * Device which holds the client fs.  For internal journal this will be