xfs: make xfs_bmapi_convert_delalloc() to allocate the target offset

Since xfs_bmapi_convert_delalloc() only attempts to allocate the entire
delalloc extent and require multiple invocations to allocate the target
offset. So xfs_convert_blocks() add a loop to do this job and we call it
in the write back path, but xfs_convert_blocks() isn't a common helper.
Let's do it in xfs_bmapi_convert_delalloc() and drop
xfs_convert_blocks(), preparing for the post EOF delalloc blocks
converting in the buffered write begin path.
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

fs/xfs/libxfs/xfs_bmap.c

@@ -4590,8 +4590,8 @@ xfs_bmapi_write(
  * invocations to allocate the target offset if a large enough physical extent
  * is not available.
  */
-int
-xfs_bmapi_convert_delalloc(
+static int
+xfs_bmapi_convert_one_delalloc(
 	struct xfs_inode	*ip,
 	int			whichfork,
 	xfs_off_t		offset,
@@ -4724,6 +4724,36 @@ xfs_bmapi_convert_delalloc(
 	return error;
 }
 
+/*
+ * Pass in a dellalloc extent and convert it to real extents, return the real
+ * extent that maps offset_fsb in iomap.
+ */
+int
+xfs_bmapi_convert_delalloc(
+	struct xfs_inode	*ip,
+	int			whichfork,
+	loff_t			offset,
+	struct iomap		*iomap,
+	unsigned int		*seq)
+{
+	int			error;
+
+	/*
+	 * Attempt to allocate whatever delalloc extent currently backs offset
+	 * and put the result into iomap.  Allocate in a loop because it may
+	 * take several attempts to allocate real blocks for a contiguous
+	 * delalloc extent if free space is sufficiently fragmented.
+	 */
+	do {
+		error = xfs_bmapi_convert_one_delalloc(ip, whichfork, offset,
+					iomap, seq);
+		if (error)
+			return error;
+	} while (iomap->offset + iomap->length <= offset);
+
+	return 0;
+}
+
 int
 xfs_bmapi_remap(
 	struct xfs_trans	*tp,

fs/xfs/xfs_aops.c

@@ -233,45 +233,6 @@ xfs_imap_valid(
 	return true;
 }
 
-/*
- * Pass in a dellalloc extent and convert it to real extents, return the real
- * extent that maps offset_fsb in wpc->iomap.
- *
- * The current page is held locked so nothing could have removed the block
- * backing offset_fsb, although it could have moved from the COW to the data
- * fork by another thread.
- */
-static int
-xfs_convert_blocks(
-	struct iomap_writepage_ctx *wpc,
-	struct xfs_inode	*ip,
-	int			whichfork,
-	loff_t			offset)
-{
-	int			error;
-	unsigned		*seq;
-
-	if (whichfork == XFS_COW_FORK)
-		seq = &XFS_WPC(wpc)->cow_seq;
-	else
-		seq = &XFS_WPC(wpc)->data_seq;
-
-	/*
-	 * Attempt to allocate whatever delalloc extent currently backs offset
-	 * and put the result into wpc->iomap.  Allocate in a loop because it
-	 * may take several attempts to allocate real blocks for a contiguous
-	 * delalloc extent if free space is sufficiently fragmented.
-	 */
-	do {
-		error = xfs_bmapi_convert_delalloc(ip, whichfork, offset,
-				&wpc->iomap, seq);
-		if (error)
-			return error;
-	} while (wpc->iomap.offset + wpc->iomap.length <= offset);
-
-	return 0;
-}
-
 static int
 xfs_map_blocks(
 	struct iomap_writepage_ctx *wpc,
@@ -290,6 +251,7 @@ xfs_map_blocks(
 	struct xfs_iext_cursor	icur;
 	int			retries = 0;
 	int			error = 0;
+	unsigned int		*seq;
 
 	if (xfs_is_shutdown(mp))
 		return -EIO;
@@ -387,7 +349,19 @@ xfs_map_blocks(
 	trace_xfs_map_blocks_found(ip, offset, count, whichfork, &imap);
 	return 0;
 allocate_blocks:
-	error = xfs_convert_blocks(wpc, ip, whichfork, offset);
+	/*
+	 * Convert a dellalloc extent to a real one. The current page is held
+	 * locked so nothing could have removed the block backing offset_fsb,
+	 * although it could have moved from the COW to the data fork by another
+	 * thread.
+	 */
+	if (whichfork == XFS_COW_FORK)
+		seq = &XFS_WPC(wpc)->cow_seq;
+	else
+		seq = &XFS_WPC(wpc)->data_seq;
+
+	error = xfs_bmapi_convert_delalloc(ip, whichfork, offset,
+				&wpc->iomap, seq);
 	if (error) {
 		/*
 		 * If we failed to find the extent in the COW fork we might have