fuse: use iomap for folio laundering

Use iomap for folio laundering, which will do granular dirty
writeback when laundering a large folio.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Link: https://lore.kernel.org/20250715202122.2282532-4-joannelkoong@gmail.com
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: joannekoong

fs/fuse/file.c

@@ -2058,45 +2058,6 @@ static struct fuse_writepage_args *fuse_writepage_args_setup(struct folio *folio
 	return wpa;
 }
 
-static int fuse_writepage_locked(struct folio *folio)
-{
-	struct address_space *mapping = folio->mapping;
-	struct inode *inode = mapping->host;
-	struct fuse_inode *fi = get_fuse_inode(inode);
-	struct fuse_writepage_args *wpa;
-	struct fuse_args_pages *ap;
-	struct fuse_file *ff;
-	int error = -EIO;
-
-	ff = fuse_write_file_get(fi);
-	if (!ff)
-		goto err;
-
-	wpa = fuse_writepage_args_setup(folio, 0, ff);
-	error = -ENOMEM;
-	if (!wpa)
-		goto err_writepage_args;
-
-	ap = &wpa->ia.ap;
-	ap->num_folios = 1;
-
-	folio_start_writeback(folio);
-	fuse_writepage_args_page_fill(wpa, folio, 0, 0, folio_size(folio));
-
-	spin_lock(&fi->lock);
-	list_add_tail(&wpa->queue_entry, &fi->queued_writes);
-	fuse_flush_writepages(inode);
-	spin_unlock(&fi->lock);
-
-	return 0;
-
-err_writepage_args:
-	fuse_file_put(ff, false);
-err:
-	mapping_set_error(folio->mapping, error);
-	return error;
-}
-
 struct fuse_fill_wb_data {
 	struct fuse_writepage_args *wpa;
 	struct fuse_file *ff;
@@ -2282,8 +2243,19 @@ static int fuse_writepages(struct address_space *mapping,
 static int fuse_launder_folio(struct folio *folio)
 {
 	int err = 0;
+	struct fuse_fill_wb_data data = {
+		.inode = folio->mapping->host,
+	};
+	struct iomap_writepage_ctx wpc = {
+		.inode = folio->mapping->host,
+		.iomap.type = IOMAP_MAPPED,
+		.ops = &fuse_writeback_ops,
+		.wb_ctx	= &data,
+	};
+
 	if (folio_clear_dirty_for_io(folio)) {
-		err = fuse_writepage_locked(folio);
+		err = iomap_writeback_folio(&wpc, folio);
+		err = fuse_iomap_writeback_submit(&wpc, err);
 		if (!err)
 			folio_wait_writeback(folio);
 	}