xfs: kill the b_strat callback in xfs_buf

The b_strat callback is used by xfs_buf_iostrategy to perform additional
checks before submitting a buffer.  It is used in xfs_bwrite and when
writing out delayed buffers.  In xfs_bwrite it we can de-virtualize the
call easily as b_strat is set a few lines above the call to
xfs_buf_iostrategy.  For the delayed buffers the rationale is a bit
more complicated:

 - there are three callers of xfs_buf_delwri_queue, which places buffers
   on the delwri list:
    (1) xfs_bdwrite - this sets up b_strat, so it's fine
    (2) xfs_buf_iorequest.  None of the callers can have XBF_DELWRI set:
	- xlog_bdstrat is only used for log buffers, which are never delwri
	- _xfs_buf_read explicitly clears the delwri flag
	- xfs_buf_iodone_work retries log buffers only
	- xfsbdstrat - only used for reads, superblock writes without the
	  delwri flag, log I/O and file zeroing with explicitly allocated
	  buffers.
	- xfs_buf_iostrategy - only calls xfs_buf_iorequest if b_strat is
	  not set
    (3) xfs_buf_unlock
	- only puts the buffer on the delwri list if the DELWRI flag is
	  already set.  The DELWRI flag is only ever set in xfs_bwrite,
	  xfs_buf_iodone_callbacks, or xfs_trans_log_buf.  For
	  xfs_buf_iodone_callbacks and xfs_trans_log_buf we require
	  an initialized buf item, which means b_strat was set to
	  xfs_bdstrat_cb in xfs_buf_item_init.

Conclusion: we can just get rid of the callback and replace it with
explicit calls to xfs_bdstrat_cb.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 3 insertions, 7 deletions

diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index f4d4e708a8d6..ea79072f5210 100644
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -987,13 +987,12 @@ xfs_bwrite(
 {
         int                     error;
 
-        bp->b_strat = xfs_bdstrat_cb;
         bp->b_mount = mp;
         bp->b_flags |= XBF_WRITE;
         bp->b_flags &= ~(XBF_ASYNC | XBF_READ);
 
         xfs_buf_delwri_dequeue(bp);
-        xfs_buf_iostrategy(bp);
+        xfs_bdstrat_cb(bp);
 
         error = xfs_buf_iowait(bp);
         if (error)
@@ -1009,7 +1008,6 @@ xfs_bdwrite(
 {
         trace_xfs_buf_bdwrite(bp, _RET_IP_);
 
-        bp->b_strat = xfs_bdstrat_cb;
         bp->b_mount = mp;
 
         bp->b_flags &= ~XBF_READ;
@@ -1044,7 +1042,6 @@ xfs_bioerror(
         XFS_BUF_UNDONE(bp);
         XFS_BUF_STALE(bp);
 
-        XFS_BUF_CLR_BDSTRAT_FUNC(bp);
         xfs_biodone(bp);
 
         return EIO;
@@ -1074,7 +1071,6 @@ xfs_bioerror_relse(
         XFS_BUF_DONE(bp);
         XFS_BUF_STALE(bp);
         XFS_BUF_CLR_IODONE_FUNC(bp);
-        XFS_BUF_CLR_BDSTRAT_FUNC(bp);
         if (!(fl & XBF_ASYNC)) {
                 /*
                  * Mark b_error and B_ERROR _both_.
@@ -1869,7 +1865,7 @@ xfsbufd(
                         struct xfs_buf *bp;
                         bp = list_first_entry(&tmp, struct xfs_buf, b_list);
                         list_del_init(&bp->b_list);
-                        xfs_buf_iostrategy(bp);
+                        xfs_bdstrat_cb(bp);
                         count++;
                 }
                 if (count)
@@ -1916,7 +1912,7 @@ xfs_flush_buftarg(
                         bp->b_flags &= ~XBF_ASYNC;
                         list_add(&bp->b_list, &wait_list);
                 }
-                xfs_buf_iostrategy(bp);
+                xfs_bdstrat_cb(bp);
         }
 
         if (wait) {