iomap: export iomap_writeback_folio

Allow fuse to use iomap_writeback_folio for folio laundering. Note
that the caller needs to manually submit the pending writeback context.

Signed-off-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Reviewed-by: Joanne Koong <[e-mail]>
Reviewed-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

fs/iomap/buffered-io.c

···
 	return true;
 }
 
-static int iomap_writeback_folio(struct iomap_writepage_ctx *wpc,
-		struct folio *folio)
+int iomap_writeback_folio(struct iomap_writepage_ctx *wpc, struct folio *folio)
 {
 	struct iomap_folio_state *ifs = folio->private;
 	struct inode *inode = wpc->inode;
···
 	mapping_set_error(inode->i_mapping, error);
 	return error;
 }
+EXPORT_SYMBOL_GPL(iomap_writeback_folio);
 
 int
 iomap_writepages(struct iomap_writepage_ctx *wpc)

include/linux/iomap.h

···
 void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
 		size_t len);
 
+int iomap_writeback_folio(struct iomap_writepage_ctx *wpc, struct folio *folio);
 int iomap_writepages(struct iomap_writepage_ctx *wpc);
 
 /*