iomap: add public helpers for uptodate state manipulation

Add a new iomap_start_folio_write helper to abstract away the
write_bytes_pending handling, and export it and the existing
iomap_finish_folio_write for non-iomap writeback in fuse.

Signed-off-by: Joanne Koong <[email protected]>
[hch: split from a larger patch]
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Brian Foster <[email protected]>
Reviewed-by: "Darrick J. Wong" <[email protected]>

Author: joannekoong

fs/iomap/buffered-io.c

@@ -1527,7 +1527,18 @@ vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops,
 }
 EXPORT_SYMBOL_GPL(iomap_page_mkwrite);
 
-static void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
+void iomap_start_folio_write(struct inode *inode, struct folio *folio,
+		size_t len)
+{
+	struct iomap_folio_state *ifs = folio->private;
+
+	WARN_ON_ONCE(i_blocks_per_folio(inode, folio) > 1 && !ifs);
+	if (ifs)
+		atomic_add(len, &ifs->write_bytes_pending);
+}
+EXPORT_SYMBOL_GPL(iomap_start_folio_write);
+
+void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
 		size_t len)
 {
 	struct iomap_folio_state *ifs = folio->private;
@@ -1538,6 +1549,7 @@ static void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
 	if (!ifs || atomic_sub_and_test(len, &ifs->write_bytes_pending))
 		folio_end_writeback(folio);
 }
+EXPORT_SYMBOL_GPL(iomap_finish_folio_write);
 
 /*
  * We're now finished for good with this ioend structure.  Update the page
@@ -1660,7 +1672,6 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
 		loff_t pos, loff_t end_pos, unsigned int dirty_len)
 {
 	struct iomap_ioend *ioend = wpc->wb_ctx;
-	struct iomap_folio_state *ifs = folio->private;
 	size_t poff = offset_in_folio(folio, pos);
 	unsigned int ioend_flags = 0;
 	unsigned int map_len = min_t(u64, dirty_len,
@@ -1703,8 +1714,7 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
 	if (!bio_add_folio(&ioend->io_bio, folio, map_len, poff))
 		goto new_ioend;
 
-	if (ifs)
-		atomic_add(map_len, &ifs->write_bytes_pending);
+	iomap_start_folio_write(wpc->inode, folio, map_len);
 
 	/*
 	 * Clamp io_offset and io_size to the incore EOF so that ondisk
@@ -1877,7 +1887,7 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 		 * all blocks.
 		 */
 		WARN_ON_ONCE(atomic_read(&ifs->write_bytes_pending) != 0);
-		atomic_inc(&ifs->write_bytes_pending);
+		iomap_start_folio_write(inode, folio, 1);
 	}
 
 	/*

include/linux/iomap.h

@@ -461,6 +461,11 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
 		loff_t pos, loff_t end_pos, unsigned int dirty_len);
 int iomap_ioend_writeback_submit(struct iomap_writepage_ctx *wpc, int error);
 
+void iomap_start_folio_write(struct inode *inode, struct folio *folio,
+		size_t len);
+void iomap_finish_folio_write(struct inode *inode, struct folio *folio,
+		size_t len);
+
 int iomap_writepages(struct iomap_writepage_ctx *wpc);
 
 /*