tty: Update tty verification procedure

We need to make sure that the only one external tty
is present, since otherwise we have no idea on which
pts index to connect them on restore.

This patch extends tty_verify_active_pairs procedure to
count how many external tty is present in the dump image.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

tty.c

@@ -152,15 +152,23 @@ static int tty_get_index(u32 id)
 /* Make sure the active pairs do exist */
 int tty_verify_active_pairs(void)
 {
-	int i;
+	int i, unpaired_slaves = 0;
 
 	for (i = 0; i < (MAX_TTYS << 1); i += 2) {
 		if (test_bit(i, tty_active_pairs) &&
 		    !test_bit(i + 1, tty_active_pairs)) {
-			pr_err("Found slave peer index %d without "
-				"correspond master peer\n",
-				tty_get_index(i));
-			return -1;
+			if (!opts.shell_job) {
+				pr_err("Found slave peer index %d without "
+				       "correspond master peer\n",
+				       tty_get_index(i));
+				return -1;
+			}
+
+			if (++unpaired_slaves > 1) {
+				pr_err("Only one slave external peer "
+				       "is allowed\n");
+				return -1;
+			}
 		}
 	}
 
@@ -844,6 +852,9 @@ int collect_tty(void)
 		ret = collect_image(CR_FD_TTY, PB_TTY,
 				sizeof(struct tty_info),
 				collect_one_tty);
+	if (!ret)
+		ret = tty_verify_active_pairs();
+
 	return ret;
 }