xfs: refactor xfs_trans_roll

Split xfs_trans_roll into a low-level helper that just rolls the
actual transaction and a new higher level xfs_trans_roll_inode
that takes care of logging and rejoining the inode.  This gets
rid of the NULL inode case, and allows to simplify the special
cases in the deferred operation code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index 7d62772..b25d3d2 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -228,7 +228,8 @@
 				      struct xfs_efd_log_item *, xfs_fsblock_t,
 				      xfs_extlen_t, struct xfs_owner_info *);
 int		xfs_trans_commit(struct xfs_trans *);
-int		xfs_trans_roll(struct xfs_trans **, struct xfs_inode *);
+int		xfs_trans_roll(struct xfs_trans **);
+int		xfs_trans_roll_inode(struct xfs_trans **, struct xfs_inode *);
 void		xfs_trans_cancel(xfs_trans_t *);
 int		xfs_trans_ail_init(struct xfs_mount *);
 void		xfs_trans_ail_destroy(struct xfs_mount *);