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, 14 insertions, 12 deletions

diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index 7703d0471139..0cc41de54aba 100644
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -2469,23 +2469,25 @@ out:
 	return error;
 }
 
-static int gfs2_map_blocks(struct iomap_writepage_ctx *wpc, struct inode *inode,
-		loff_t offset, unsigned int len)
+static ssize_t gfs2_writeback_range(struct iomap_writepage_ctx *wpc,
+		struct folio *folio, u64 offset, unsigned int len, u64 end_pos)
 {
-	int ret;
-
-	if (WARN_ON_ONCE(gfs2_is_stuffed(GFS2_I(inode))))
+	if (WARN_ON_ONCE(gfs2_is_stuffed(GFS2_I(wpc->inode))))
 		return -EIO;
 
-	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 ret;
 
-	memset(&wpc->iomap, 0, sizeof(wpc->iomap));
-	ret = gfs2_iomap_get(inode, offset, INT_MAX, &wpc->iomap);
-	return ret;
+		memset(&wpc->iomap, 0, sizeof(wpc->iomap));
+		ret = gfs2_iomap_get(wpc->inode, offset, INT_MAX, &wpc->iomap);
+		if (ret)
+			return ret;
+	}
+
+	return iomap_add_to_ioend(wpc, folio, offset, end_pos, len);
 }
 
 const struct iomap_writeback_ops gfs2_writeback_ops = {
-	.map_blocks		= gfs2_map_blocks,
+	.writeback_range	= gfs2_writeback_range,
 };