[PATCH] Provide console_device()

[This patch series has also been separately sent to the architecture
 maintainers]

Add console_device() to return the console tty driver structure and the
index.  Acquire the console lock while scanning the list of console drivers
to protect us against console driver list manipulations.
Signed-off-by: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/char/tty_io.c

@@ -1363,13 +1363,8 @@ static int tty_open(struct inode * inode, struct file * filp)
 	}
 #endif
 	if (device == MKDEV(TTYAUX_MAJOR,1)) {
-		struct console *c = console_drivers;
-		for (c = console_drivers; c; c = c->next) {
-			if (!c->device)
-				continue;
-			driver = c->device(c, &index);
-			if (!driver)
-				continue;
+		driver = console_device(&index);
+		if (driver) {
 			/* Don't let /dev/console block */
 			filp->f_flags |= O_NONBLOCK;
 			noctty = 1;

include/linux/console.h

@@ -104,6 +104,7 @@ extern void acquire_console_sem(void);
 extern void release_console_sem(void);
 extern void console_conditional_schedule(void);
 extern void console_unblank(void);
+extern struct tty_driver *console_device(int *);
 extern int is_console_locked(void);
 
 /* Some debug stub to catch some of the obvious races in the VT code */

kernel/printk.c

@@ -683,6 +683,26 @@ void console_unblank(void)
 }
 EXPORT_SYMBOL(console_unblank);
 
+/*
+ * Return the console tty driver structure and its associated index
+ */
+struct tty_driver *console_device(int *index)
+{
+	struct console *c;
+	struct tty_driver *driver = NULL;
+
+	acquire_console_sem();
+	for (c = console_drivers; c != NULL; c = c->next) {
+		if (!c->device)
+			continue;
+		driver = c->device(c, index);
+		if (driver)
+			break;
+	}
+	release_console_sem();
+	return driver;
+}
+
 /*
  * The console driver calls this routine during kernel initialization
  * to register the console printing procedure with printk() and to