iomap: export iomap_writeback_folio

JIRA: https://issues.redhat.com/browse/RHEL-121230

commit 8b217cf
Author: Christoph Hellwig <hch@lst.de>
Date:   Thu Jul 10 15:33:34 2025 +0200

    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 <hch@lst.de>
    Link: https://lore.kernel.org/20250710133343.399917-11-hch@lst.de
    Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
    Reviewed-by: Darrick J. Wong <djwong@kernel.org>
    Signed-off-by: Christian Brauner <brauner@kernel.org>

Signed-off-by: Brian Foster <bfoster@redhat.com>

Author: Brian Foster

fs/iomap/buffered-io.c

@@ -1633,8 +1633,7 @@ static bool iomap_writeback_handle_eof(struct folio *folio, struct inode *inode,
 	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;
@@ -1716,6 +1715,7 @@ static int iomap_writeback_folio(struct iomap_writepage_ctx *wpc,
 	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

@@ -462,6 +462,7 @@ void iomap_start_folio_write(struct inode *inode, struct folio *folio,
 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);
 
 /*