page-xfer: Handle partial splicing

In case if pipe buffers are full the splicing
may wakeup reader first with incomplete data
transfer. Thus splice data in cycle.
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/page-xfer.c

@@ -147,11 +147,19 @@ static inline int send_psi(int sk, struct page_server_iov *pi)
 static int write_pages_to_server(struct page_xfer *xfer,
 		int p, unsigned long len)
 {
+	ssize_t ret, left = len;
+
 	pr_debug("Splicing %lu bytes / %lu pages into socket\n", len, len / PAGE_SIZE);
 
-	if (splice(p, NULL, xfer->sk, NULL, len, SPLICE_F_MOVE) != len) {
-		pr_perror("Can't write pages to socket");
-		return -1;
+	while (left > 0) {
+		ret = splice(p, NULL, xfer->sk, NULL, left, SPLICE_F_MOVE);
+		if (ret < 0) {
+			pr_perror("Can't write pages to socket");
+			return -1;
+		}
+
+		pr_debug("\tSpliced: %lu bytes sent\n", (unsigned long)ret);
+		left -= ret;
 	}
 
 	return 0;