tty: Set correct tty name in 'active' sysfs attribute

The 'active' sysfs attribute should refer to the currently active tty
devices the console is running on, not the currently active console.

The console structure doesn't refer to any device in sysfs, only the tty
the console is running on has.  So we need to print out the tty names in
'active', not the console names.

This resolves an issue on s390 platforms in determining the correct
console device to use.

Cc: Lennart Poettering <lennart@poettering.net>
Cc: Kay Sievers <kay@vrfy.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: NWerner Fink <werner@suse.de>
Signed-off-by: NHannes Reinecke <hare@suse.de>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-tty

@@ -3,7 +3,8 @@ Date:		Nov 2010
 Contact:	Kay Sievers <kay.sievers@vrfy.org>
 Description:
 		 Shows the list of currently configured
-		 console devices, like 'tty1 ttyS0'.
+		 tty devices used for the console,
+		 like 'tty1 ttyS0'.
 		 The last entry in the file is the active
 		 device connected to /dev/console.
 		 The file supports poll() to detect virtual

drivers/tty/tty_io.c

@@ -1267,16 +1267,17 @@ static void pty_line_name(struct tty_driver *driver, int index, char *p)
  *	@p: output buffer of at least 7 bytes
  *
  *	Generate a name from a driver reference and write it to the output
- *	buffer.
+ *	buffer. Return the number of bytes written.
  *
  *	Locking: None
  */
-static void tty_line_name(struct tty_driver *driver, int index, char *p)
+static ssize_t tty_line_name(struct tty_driver *driver, int index, char *p)
 {
 	if (driver->flags & TTY_DRIVER_UNNUMBERED_NODE)
-		strcpy(p, driver->name);
+		return sprintf(p, "%s", driver->name);
 	else
-		sprintf(p, "%s%d", driver->name, index + driver->name_base);
+		return sprintf(p, "%s%d", driver->name,
+			       index + driver->name_base);
 }
 
 /**
@@ -3545,9 +3546,19 @@ static ssize_t show_cons_active(struct device *dev,
 		if (i >= ARRAY_SIZE(cs))
 			break;
 	}
-	while (i--)
-		count += sprintf(buf + count, "%s%d%c",
-				 cs[i]->name, cs[i]->index, i ? ' ':'\n');
+	while (i--) {
+		struct tty_driver *driver;
+		const char *name = cs[i]->name;
+		int index = cs[i]->index;
+
+		driver = cs[i]->device(cs[i], &index);
+		if (driver) {
+			count += tty_line_name(driver, index, buf + count);
+			count += sprintf(buf + count, "%c", i ? ' ':'\n');
+		} else
+			count += sprintf(buf + count, "%s%d%c",
+					 name, index, i ? ' ':'\n');
+	}
 	console_unlock();
 
 	return count;