iomap: Refactor iomap_write_delalloc_punch() function out

This patch factors iomap_write_delalloc_punch() function out. This function
is resposible for actual punch out operation.
The reason for doing this is, to avoid deep indentation when we bring
punch-out of individual non-dirty blocks within a dirty folio in a later
patch (which adds per-block dirty status handling to iomap) to avoid
delalloc block leak.
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/iomap/buffered-io.c

@@ -883,6 +883,33 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
 }
 EXPORT_SYMBOL_GPL(iomap_file_buffered_write);
 
+static int iomap_write_delalloc_punch(struct inode *inode, struct folio *folio,
+		loff_t *punch_start_byte, loff_t start_byte, loff_t end_byte,
+		iomap_punch_t punch)
+{
+	int ret = 0;
+
+	if (!folio_test_dirty(folio))
+		return ret;
+
+	/* if dirty, punch up to offset */
+	if (start_byte > *punch_start_byte) {
+		ret = punch(inode, *punch_start_byte,
+				start_byte - *punch_start_byte);
+		if (ret)
+			return ret;
+	}
+
+	/*
+	 * Make sure the next punch start is correctly bound to
+	 * the end of this data range, not the end of the folio.
+	 */
+	*punch_start_byte = min_t(loff_t, end_byte,
+				folio_pos(folio) + folio_size(folio));
+
+	return ret;
+}
+
 /*
  * Scan the data range passed to us for dirty page cache folios. If we find a
  * dirty folio, punch out the preceeding range and update the offset from which
@@ -906,6 +933,7 @@ static int iomap_write_delalloc_scan(struct inode *inode,
 {
 	while (start_byte < end_byte) {
 		struct folio	*folio;
+		int ret;
 
 		/* grab locked page */
 		folio = filemap_lock_folio(inode->i_mapping,
@@ -916,26 +944,12 @@ static int iomap_write_delalloc_scan(struct inode *inode,
 			continue;
 		}
 
-		/* if dirty, punch up to offset */
-		if (folio_test_dirty(folio)) {
-			if (start_byte > *punch_start_byte) {
-				int	error;
-
-				error = punch(inode, *punch_start_byte,
-						start_byte - *punch_start_byte);
-				if (error) {
-					folio_unlock(folio);
-					folio_put(folio);
-					return error;
-				}
-			}
-
-			/*
-			 * Make sure the next punch start is correctly bound to
-			 * the end of this data range, not the end of the folio.
-			 */
-			*punch_start_byte = min_t(loff_t, end_byte,
-					folio_pos(folio) + folio_size(folio));
+		ret = iomap_write_delalloc_punch(inode, folio, punch_start_byte,
+						 start_byte, end_byte, punch);
+		if (ret) {
+			folio_unlock(folio);
+			folio_put(folio);
+			return ret;
 		}
 
 		/* move offset to start of next folio in range */