commit 24bcc89c upstream.

There are three case of updating journal superblock. In the first case, we want
to mark journal as empty (setting s_sequence to 0), in the second case we want
to update log tail, in the third case we want to update s_errno. Split these
cases into separate functions. It makes the code slightly more straightforward
and later patches will make the distinction even more important.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
[bwh: Prerequisite for "jbd2: fix ocfs2 corrupt when updating journal
 superblock fails".
 Backported to 3.2: drop changes to trace events.]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>