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, 16 insertions, 12 deletions

diff --git a/fs/zonefs/file.c b/fs/zonefs/file.c
index edca4bbe4b72..c88e2c851753 100644
--- a/fs/zonefs/file.c
+++ b/fs/zonefs/file.c
@@ -124,29 +124,33 @@ static void zonefs_readahead(struct readahead_control *rac)
  * Map blocks for page writeback. This is used only on conventional zone files,
  * which implies that the page range can only be within the fixed inode size.
  */
-static int zonefs_write_map_blocks(struct iomap_writepage_ctx *wpc,
-				   struct inode *inode, loff_t offset,
-				   unsigned int len)
+static ssize_t zonefs_writeback_range(struct iomap_writepage_ctx *wpc,
+		struct folio *folio, u64 offset, unsigned len, u64 end_pos)
 {
-	struct zonefs_zone *z = zonefs_inode_zone(inode);
+	struct zonefs_zone *z = zonefs_inode_zone(wpc->inode);
 
 	if (WARN_ON_ONCE(zonefs_zone_is_seq(z)))
 		return -EIO;
-	if (WARN_ON_ONCE(offset >= i_size_read(inode)))
+	if (WARN_ON_ONCE(offset >= i_size_read(wpc->inode)))
 		return -EIO;
 
 	/* If the mapping is already OK, nothing needs to be done */
-	if (offset >= wpc->iomap.offset &&
-	    offset < wpc->iomap.offset + wpc->iomap.length)
-		return 0;
+	if (offset < wpc->iomap.offset ||
+	    offset >= wpc->iomap.offset + wpc->iomap.length) {
+		int error;
+
+		error = zonefs_write_iomap_begin(wpc->inode, offset,
+				z->z_capacity - offset, IOMAP_WRITE,
+				&wpc->iomap, NULL);
+		if (error)
+			return error;
+	}
 
-	return zonefs_write_iomap_begin(inode, offset,
-					z->z_capacity - offset,
-					IOMAP_WRITE, &wpc->iomap, NULL);
+	return iomap_add_to_ioend(wpc, folio, offset, end_pos, len);
 }
 
 static const struct iomap_writeback_ops zonefs_writeback_ops = {
-	.map_blocks		= zonefs_write_map_blocks,
+	.writeback_range	= zonefs_writeback_range,
 };
 
 static int zonefs_writepages(struct address_space *mapping,