iomap: Add __iomap_get_folio helper

Add an __iomap_get_folio() helper as the counterpart of the existing
__iomap_put_folio() helper.  Use the new helper in iomap_write_begin().
Not a functional change.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/iomap/buffered-io.c

@@ -602,6 +602,17 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
 	return 0;
 }
 
+static struct folio *__iomap_get_folio(struct iomap_iter *iter, loff_t pos,
+		size_t len)
+{
+	const struct iomap_page_ops *page_ops = iter->iomap.page_ops;
+
+	if (page_ops && page_ops->page_prepare)
+		return page_ops->page_prepare(iter, pos, len);
+	else
+		return iomap_get_folio(iter, pos);
+}
+
 static void __iomap_put_folio(struct iomap_iter *iter, loff_t pos, size_t ret,
 		struct folio *folio)
 {
@@ -642,10 +653,7 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
 	if (!mapping_large_folio_support(iter->inode->i_mapping))
 		len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos));
 
-	if (page_ops && page_ops->page_prepare)
-		folio = page_ops->page_prepare(iter, pos, len);
-	else
-		folio = iomap_get_folio(iter, pos);
+	folio = __iomap_get_folio(iter, pos, len);
 	if (IS_ERR(folio))
 		return PTR_ERR(folio);