cifs: stop using generic_writepages

generic_writepages is just a wrapper that calls ->writepages on a range,
and thus in the way of eventually removing ->writepage.  Switch cifs
to just open code it in preparation of removing ->writepage.

[note: I suspect just integrating the small wsize case with the rest
 of the writeback code might be a better idea here, but that needs
 someone more familiar with the code]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/file.c

@@ -2646,6 +2646,21 @@ wdata_send_pages(struct cifs_writedata *wdata, unsigned int nr_pages,
 	return rc;
 }
 
+static int
+cifs_writepage_locked(struct page *page, struct writeback_control *wbc);
+
+static int cifs_write_one_page(struct page *page, struct writeback_control *wbc,
+		void *data)
+{
+	struct address_space *mapping = data;
+	int ret;
+
+	ret = cifs_writepage_locked(page, wbc);
+	unlock_page(page);
+	mapping_set_error(mapping, ret);
+	return ret;
+}
+
 static int cifs_writepages(struct address_space *mapping,
 			   struct writeback_control *wbc)
 {
@@ -2662,10 +2677,11 @@ static int cifs_writepages(struct address_space *mapping,
 
 	/*
 	 * If wsize is smaller than the page cache size, default to writing
-	 * one page at a time via cifs_writepage
+	 * one page at a time.
 	 */
 	if (cifs_sb->ctx->wsize < PAGE_SIZE)
-		return generic_writepages(mapping, wbc);
+		return write_cache_pages(mapping, wbc, cifs_write_one_page,
+				mapping);
 
 	xid = get_xid();
 	if (wbc->range_cyclic) {