tty: add serial driver & popular serial majors

Fixes restoring on AMBA serial line. That is /dev/ttyAMA0,
which is the default serial port to use on qemu-system-aarch64.
(at least in those articles, which I meet it's in boot cmdline)
Also should add support for C/R /dev/ttyUSB*

One may check major numbers on
https://www.kernel.org/doc/Documentation/devices.txt
Also by grepping on kernel repository.

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/include/tty.h

@@ -9,6 +9,10 @@
 /* Kernel's limit */
 #define TERMIOS_NCC	19
 
+/* Popular serial console's majors, which not defined in <linux/major.h> */
+#define USB_SERIAL_MAJOR	188
+#define LOW_DENSE_SERIAL_MAJOR	204
+
 extern const struct fdtype_ops tty_dump_ops;
 
 struct tty_driver;

criu/tty.c

@@ -210,6 +210,12 @@ static struct tty_driver ext_driver = {
 	.open			= open_ext_tty,
 };
 
+static struct tty_driver serial_driver = {
+	.type			= TTY_TYPE__SERIAL,
+	.name			= "serial",
+	.open			= open_simple_tty,
+};
+
 static int pts_fd_get_index(int fd, const struct fd_parms *p)
 {
 	int index;
@@ -268,6 +274,10 @@ struct tty_driver *get_tty_driver(dev_t rdev, dev_t dev)
 			 * of kernel).
 			 */
 			return &vt_driver;
+		/* Other minors points to UART serial ports */
+	case USB_SERIAL_MAJOR:
+	case LOW_DENSE_SERIAL_MAJOR:
+		return &serial_driver;
 	case UNIX98_PTY_MASTER_MAJOR ... (UNIX98_PTY_MASTER_MAJOR + UNIX98_PTY_MAJOR_COUNT - 1):
 		return &ptm_driver;
 	case UNIX98_PTY_SLAVE_MAJOR:
@@ -668,6 +678,7 @@ static bool tty_is_master(struct tty_info *info)
 	case TTY_TYPE__CONSOLE:
 	case TTY_TYPE__CTTY:
 		return true;
+	case TTY_TYPE__SERIAL:
 	case TTY_TYPE__VT:
 		if (!opts.shell_job)
 			return true;
@@ -1368,6 +1379,7 @@ static int collect_one_tty_info_entry(void *obj, ProtobufCMessage *msg, struct c
 		break;
 	case TTY_TYPE__CTTY:
 	case TTY_TYPE__CONSOLE:
+	case TTY_TYPE__SERIAL:
 	case TTY_TYPE__VT:
 	case TTY_TYPE__EXT_TTY:
 		if (info->tie->pty) {

images/tty.proto

@@ -31,6 +31,7 @@ enum TtyType {
 	VT		= 3;
 	CTTY		= 4;
 	EXT_TTY		= 5;
+	SERIAL		= 6;
 }
 
 message tty_info_entry {