[PATCH 10/12] writeback: Add for_each_writeback_folio()

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

Wrap up the iterator with a nice bit of syntactic sugar.  Now the
caller doesn't need to know about wbc->err and can just return error,
not knowing that the iterator took care of storing errors correctly.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 include/linux/writeback.h | 14 +++++++++++---
 mm/page-writeback.c       | 11 ++++-------
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 7dd050b40e4b..84d5306ef045 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -369,14 +369,22 @@ int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
 
 bool wb_over_bg_thresh(struct bdi_writeback *wb);
 
+struct folio *writeback_iter_init(struct address_space *mapping,
+		struct writeback_control *wbc);
+struct folio *writeback_iter_next(struct address_space *mapping,
+		struct writeback_control *wbc, struct folio *folio, int error);
+
+#define for_each_writeback_folio(mapping, wbc, folio, error)		\
+	for (folio = writeback_iter_init(mapping, wbc);			\
+	     folio || ((error = wbc->err), false);			\
+	     folio = writeback_iter_next(mapping, wbc, folio, error))
+
 typedef int (*writepage_t)(struct folio *folio, struct writeback_control *wbc,
 				void *data);
-
-void tag_pages_for_writeback(struct address_space *mapping,
-			     pgoff_t start, pgoff_t end);
 int write_cache_pages(struct address_space *mapping,
 		      struct writeback_control *wbc, writepage_t writepage,
 		      void *data);
+
 int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
 void writeback_set_ratelimit(void);
 void tag_pages_for_writeback(struct address_space *mapping,
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index ef61d7006c5e..245d6318dfb2 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2451,7 +2451,7 @@ static struct folio *writeback_get_folio(struct address_space *mapping,
 	return folio;
 }
 
-static struct folio *writeback_iter_init(struct address_space *mapping,
+struct folio *writeback_iter_init(struct address_space *mapping,
 		struct writeback_control *wbc)
 {
 	if (wbc->range_cyclic) {
@@ -2473,7 +2473,7 @@ static struct folio *writeback_iter_init(struct address_space *mapping,
 	return writeback_get_folio(mapping, wbc);
 }
 
-static struct folio *writeback_iter_next(struct address_space *mapping,
+struct folio *writeback_iter_next(struct address_space *mapping,
 		struct writeback_control *wbc, struct folio *folio, int error)
 {
 	if (unlikely(error)) {
@@ -2550,13 +2550,10 @@ int write_cache_pages(struct address_space *mapping,
 	struct folio *folio;
 	int error;
 
-	for (folio = writeback_iter_init(mapping, wbc);
-	     folio;
-	     folio = writeback_iter_next(mapping, wbc, folio, error)) {
+	for_each_writeback_folio(mapping, wbc, folio, error)
 		error = writepage(folio, wbc, data);
-	}
 
-	return wbc->err;
+	return error;
 }
 EXPORT_SYMBOL(write_cache_pages);
 
-- 
2.39.2