xfs: consolidate superblock logging functions

We now have several superblock loggin functions that are identical
except for the transaction reservation and whether it shoul dbe a
synchronous transaction or not. Consolidate these all into a single
function, a single reserveration and a sync flag and call it
xfs_sync_sb().

Also, xfs_mod_sb() is not really a modification function - it's the
operation of logging the superblock buffer. hence change the name of
it to reflect this.

Note that we have to change the mp->m_update_flags that are passed
around at mount time to a boolean simply to indicate a superblock
update is needed.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/libxfs/xfs_sb.h b/fs/xfs/libxfs/xfs_sb.h
index e193caa..b25bb9a 100644
--- a/fs/xfs/libxfs/xfs_sb.h
+++ b/fs/xfs/libxfs/xfs_sb.h
@@ -28,7 +28,8 @@
 extern int	xfs_initialize_perag_data(struct xfs_mount *, xfs_agnumber_t);
 
 extern void	xfs_sb_calc_crc(struct xfs_buf *bp);
-extern void	xfs_mod_sb(struct xfs_trans *tp);
+extern void	xfs_log_sb(struct xfs_trans *tp);
+extern int	xfs_sync_sb(struct xfs_mount *mp, bool wait);
 extern void	xfs_sb_mount_common(struct xfs_mount *mp, struct xfs_sb *sbp);
 extern void	xfs_sb_from_disk(struct xfs_sb *to, struct xfs_dsb *from);
 extern void	xfs_sb_to_disk(struct xfs_dsb *to, struct xfs_sb *from);