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/xfs_qm_syscalls.c b/fs/xfs/xfs_qm_syscalls.c
index 8d7e5f0..b8a565e 100644
--- a/fs/xfs/xfs_qm_syscalls.c
+++ b/fs/xfs/xfs_qm_syscalls.c
@@ -92,7 +92,7 @@
 		mutex_unlock(&q->qi_quotaofflock);
 
 		/* XXX what to do if error ? Revert back to old vals incore ? */
-		return xfs_qm_write_sb_changes(mp);
+		return xfs_sync_sb(mp, false);
 	}
 
 	dqtype = 0;
@@ -369,7 +369,8 @@
 	if ((qf & flags) == flags)
 		return -EEXIST;
 
-	if ((error = xfs_qm_write_sb_changes(mp)))
+	error = xfs_sync_sb(mp, false);
+	if (error)
 		return error;
 	/*
 	 * If we aren't trying to switch on quota enforcement, we are done.
@@ -796,7 +797,7 @@
 	mp->m_sb.sb_qflags = (mp->m_qflags & ~(flags)) & XFS_MOUNT_QUOTA_ALL;
 	spin_unlock(&mp->m_sb_lock);
 
-	xfs_mod_sb(tp);
+	xfs_log_sb(tp);
 
 	/*
 	 * We have to make sure that the transaction is secure on disk before we