iomap: refactor the writeback interface

Replace ->map_blocks with a new ->writeback_range, which differs in the
following ways:

 - it must also queue up the I/O for writeback, that is called into the
   slightly refactored and extended in scope iomap_add_to_ioend for
   each region
 - can handle only a part of the requested region, that is the retry
   loop for partial mappings moves to the caller
 - handles cleanup on failures as well, and thus also replaces the
   discard_folio method only implemented by XFS.

This will allow to use the iomap writeback code also for file systems
that are not block based like fuse.

Co-developed-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/20250710133343.399917-5-hch@lst.de
Acked-by: Damien Le Moal <dlemoal@kernel.org>	# zonefs
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 10 insertions, 11 deletions

diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 00179c9387c5..625d7911a2b5 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -416,18 +416,20 @@ static inline struct iomap_ioend *iomap_ioend_from_bio(struct bio *bio)
 
 struct iomap_writeback_ops {
 	/*
-	 * Required, maps the blocks so that writeback can be performed on
-	 * the range starting at offset.
+	 * Required, performs writeback on the passed in range
 	 *
-	 * Can return arbitrarily large regions, but we need to call into it at
+	 * Can map arbitrarily large regions, but we need to call into it at
 	 * least once per folio to allow the file systems to synchronize with
 	 * the write path that could be invalidating mappings.
 	 *
 	 * An existing mapping from a previous call to this method can be reused
 	 * by the file system if it is still valid.
+	 *
+	 * Returns the number of bytes processed or a negative errno.
 	 */
-	int (*map_blocks)(struct iomap_writepage_ctx *wpc, struct inode *inode,
-			  loff_t offset, unsigned len);
+	ssize_t (*writeback_range)(struct iomap_writepage_ctx *wpc,
+			struct folio *folio, u64 pos, unsigned int len,
+			u64 end_pos);
 
 	/*
 	 * Optional, allows the file systems to hook into bio submission,
@@ -438,12 +440,6 @@ struct iomap_writeback_ops {
 	 * the bio could not be submitted.
 	 */
 	int (*submit_ioend)(struct iomap_writepage_ctx *wpc, int status);
-
-	/*
-	 * Optional, allows the file system to discard state on a page where
-	 * we failed to submit any I/O.
-	 */
-	void (*discard_folio)(struct folio *folio, loff_t pos);
 };
 
 struct iomap_writepage_ctx {
@@ -463,6 +459,9 @@ void iomap_finish_ioends(struct iomap_ioend *ioend, int error);
 void iomap_ioend_try_merge(struct iomap_ioend *ioend,
 		struct list_head *more_ioends);
 void iomap_sort_ioends(struct list_head *ioend_list);
+ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
+		loff_t pos, loff_t end_pos, unsigned int dirty_len);
+
 int iomap_writepages(struct iomap_writepage_ctx *wpc);
 
 /*