[PATCH v2 13/16] iomap: add iomap_writeback_dirty_folio()

[Joanne Koong <joannelkoong@xxxxxxxxx>]

Add iomap_writeback_dirty_folio() for writing back a dirty folio.
One use case of this is for laundering a folio.

Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
---
 fs/iomap/buffered-io.c | 27 +++++++++++++++++++--------
 include/linux/iomap.h  |  3 +++
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 25ae1d53eccb..d47abeefe92b 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1518,7 +1518,7 @@ static bool iomap_writepage_handle_eof(struct folio *folio, struct inode *inode,
 	return true;
 }
 
-static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
+static int iomap_writeback(struct iomap_writepage_ctx *wpc,
 		struct writeback_control *wbc, struct folio *folio)
 {
 	struct iomap_folio_state *ifs = folio->private;
@@ -1541,10 +1541,8 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 
 	trace_iomap_writepage(inode, pos, folio_size(folio));
 
-	if (!iomap_writepage_handle_eof(folio, inode, &end_pos)) {
-		folio_unlock(folio);
+	if (!iomap_writepage_handle_eof(folio, inode, &end_pos))
 		return 0;
-	}
 	WARN_ON_ONCE(end_pos <= pos);
 
 	if (i_blocks_per_folio(inode, folio) > 1) {
@@ -1602,9 +1600,8 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 	 * But we may end up either not actually writing any blocks, or (when
 	 * there are multiple blocks in a folio) all I/O might have finished
 	 * already at this point.  In that case we need to clear the writeback
-	 * bit ourselves right after unlocking the page.
+	 * bit ourselves.
 	 */
-	folio_unlock(folio);
 	if (ifs) {
 		if (atomic_dec_and_test(&ifs->write_bytes_pending))
 			folio_end_writeback(folio);
@@ -1633,12 +1630,26 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
 		return -EIO;
 
 	wpc->ops = ops;
-	while ((folio = writeback_iter(mapping, wbc, folio, &error)))
-		error = iomap_writepage_map(wpc, wbc, folio);
+	while ((folio = writeback_iter(mapping, wbc, folio, &error))) {
+		error = iomap_writeback(wpc, wbc, folio);
+		folio_unlock(folio);
+	}
 	return iomap_writeback_complete(wpc, error);
 }
 EXPORT_SYMBOL_GPL(iomap_writepages);
 
+int iomap_writeback_dirty_folio(struct folio *folio,
+		struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
+		const struct iomap_writeback_ops *ops)
+{
+	int error;
+
+	wpc->ops = ops;
+	error = iomap_writeback(wpc, wbc, folio);
+	return iomap_writeback_complete(wpc, error);
+}
+EXPORT_SYMBOL_GPL(iomap_writeback_dirty_folio);
+
 void iomap_start_folio_write(struct inode *inode, struct folio *folio,
 		size_t len)
 {
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 3115b00ff410..95646346dff5 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -478,6 +478,9 @@ void iomap_sort_ioends(struct list_head *ioend_list);
 int iomap_writepages(struct address_space *mapping,
 		struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
 		const struct iomap_writeback_ops *ops);
+int iomap_writeback_dirty_folio(struct folio *folio,
+		struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
+		const struct iomap_writeback_ops *ops);
 
 /*
  * Flags for direct I/O ->end_io:
-- 
2.47.1