iomap: Simplify iomap_writepage_map()

Rename end_offset to end_pos and file_offset to pos to match the rest
of the file.  Simplify the loop by calculating nblocks up front instead
of each time around the loop.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

fs/iomap/buffered-io.c

@@ -1307,37 +1307,36 @@ iomap_add_to_ioend(struct inode *inode, loff_t offset, struct page *page,
 static int
 iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 		struct writeback_control *wbc, struct inode *inode,
-		struct page *page, u64 end_offset)
+		struct page *page, u64 end_pos)
 {
 	struct folio *folio = page_folio(page);
 	struct iomap_page *iop = iomap_page_create(inode, folio);
 	struct iomap_ioend *ioend, *next;
 	unsigned len = i_blocksize(inode);
-	u64 file_offset; /* file offset of page */
+	unsigned nblocks = i_blocks_per_folio(inode, folio);
+	u64 pos = folio_pos(folio);
 	int error = 0, count = 0, i;
 	LIST_HEAD(submit_list);
 
 	WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) != 0);
 
 	/*
-	 * Walk through the page to find areas to write back. If we run off the
-	 * end of the current map or find the current map invalid, grab a new
-	 * one.
+	 * Walk through the folio to find areas to write back. If we
+	 * run off the end of the current map or find the current map
+	 * invalid, grab a new one.
 	 */
-	for (i = 0, file_offset = page_offset(page);
-	     i < (PAGE_SIZE >> inode->i_blkbits) && file_offset < end_offset;
-	     i++, file_offset += len) {
+	for (i = 0; i < nblocks && pos < end_pos; i++, pos += len) {
 		if (iop && !test_bit(i, iop->uptodate))
 			continue;
 
-		error = wpc->ops->map_blocks(wpc, inode, file_offset);
+		error = wpc->ops->map_blocks(wpc, inode, pos);
 		if (error)
 			break;
 		if (WARN_ON_ONCE(wpc->iomap.type == IOMAP_INLINE))
 			continue;
 		if (wpc->iomap.type == IOMAP_HOLE)
 			continue;
-		iomap_add_to_ioend(inode, file_offset, page, iop, wpc, wbc,
+		iomap_add_to_ioend(inode, pos, page, iop, wpc, wbc,
 				 &submit_list);
 		count++;
 	}
@@ -1361,7 +1360,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 		 * now.
 		 */
 		if (wpc->ops->discard_folio)
-			wpc->ops->discard_folio(folio, file_offset);
+			wpc->ops->discard_folio(folio, pos);
 		if (!count) {
 			ClearPageUptodate(page);
 			unlock_page(page);