unix: Add fake queuer for standalone dgram sockets

Similar to previous patch, this makes the second end
of dgram socketpair to be open till post open. This
allows to delay restore of message queue.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/sk-unix.c

@@ -1464,7 +1464,7 @@ static int open_unixsk_standalone(struct unix_sk_info *ui, int *new_fd)
 			return -1;
 
 		sk = sks[0];
-	} else if (ui->ue->type == SOCK_DGRAM && !ui->queuer) {
+	} else if (ui->ue->type == SOCK_DGRAM && queuer && queuer->ue->ino == FAKE_INO) {
 		struct sockaddr_un addr;
 		int sks[2];
 
@@ -1483,21 +1483,18 @@ static int open_unixsk_standalone(struct unix_sk_info *ui, int *new_fd)
 		 * to sks[0] (see unix_dgram_connect()->unix_may_send()).
 		 * The below is hack: we use that connect with AF_UNSPEC
 		 * clears socket's peer.
+		 * Note, that connect hack flushes receive queue,
+		 * so restore_unix_queue() must be after it.
 		 */
 		if (connect(sk, (struct sockaddr *)&addr, sizeof(addr.sun_family))) {
 			pr_perror("Can't clear socket's peer");
 			return -1;
 		}
 
-		/*
-		 * This must be after the connect() hack, because
-		 * connect() flushes receive queue.
-		 */
-		if (restore_unix_queue(sks[1], ui)) {
-			pr_perror("Can't restore socket queue");
+		if (setup_second_end(sks, file_master(&queuer->d)))
 			return -1;
-		}
-		close(sks[1]);
+
+		sk = sks[0];
 	} else {
 		if (ui->ue->uflags & USK_CALLBACK) {
 			sk = run_plugins(RESTORE_UNIX_SK, ui->ue->ino);
@@ -1786,7 +1783,8 @@ int add_fake_unix_queuers(void)
 	list_for_each_entry(ui, &unix_sockets, list) {
 		if ((ui->ue->uflags & USK_EXTERN) || ui->queuer)
 			continue;
-		if (!(ui->ue->state == TCP_ESTABLISHED && !ui->peer))
+		if (!(ui->ue->state == TCP_ESTABLISHED && !ui->peer) &&
+		     ui->ue->type != SOCK_DGRAM)
 			continue;
 		if (add_fake_queuer(ui))
 			return -1;