start adding the tag to iov_iter

For now, just use the same thing we pass to ->direct_IO() - it's all
iovec-based at the moment.  Pass it explicitly to iov_iter_init() and
account for kvec vs. iovec in there, by the same kludge NFS ->direct_IO()
uses.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/pipe.c

@@ -287,7 +287,7 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
 	if (unlikely(total_len == 0))
 		return 0;
 
-	iov_iter_init(&iter, iov, nr_segs, total_len, 0);
+	iov_iter_init(&iter, READ, iov, nr_segs, total_len);
 
 	do_wakeup = 0;
 	ret = 0;