[PATCH v6 14/16] printk: Do not set Braille console as preferred_console

[Petr Mladek <pmladek@suse.com>]

The Braille console reuses the framework for handling consoles preferred
via the command line. However, it is a special-purpose interface that
neither receives standard printk messages nor associates with
/dev/console.

Currently, the "preferred_dev_console" variable can point to a Braille
console entry in the "preferred_consoles[]" array. This occurs if an
entry was first created for a non-Braille console, but a later 'console='
parameter redefined it as a Braille console.

Since a Braille console will only ever be enabled as such, it should not
be tracked as the primary system console. Adjust the logic to ensure
"preferred_dev_console" continues to point to the previously designated
normal console instead.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Chris Down <chris@chrisdown.name>
---
 kernel/printk/console_register.h |  3 +++
 kernel/printk/printk.c           | 31 ++++++++++++++++++++++++-------
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/kernel/printk/console_register.h b/kernel/printk/console_register.h
index 9ab3e1cc749b..64cf12fd6ea5 100644
--- a/kernel/printk/console_register.h
+++ b/kernel/printk/console_register.h
@@ -2,6 +2,8 @@
 #ifndef _CONSOLE_REGISTER_H
 #define _CONSOLE_REGISTER_H
 
+#include <linux/list.h>
+
 struct preferred_console
 {
 	char	name[16];			/* Name of the driver	    */
@@ -12,6 +14,7 @@ struct preferred_console
 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 	char	*brl_options;			/* Options for braille driver */
 #endif
+	struct list_head preferred_dev_node;
 };
 
 #endif
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2bcf82b2c4e3..5ec34dc2d168 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -365,7 +365,7 @@ static int console_locked;
 #define MAX_PREFERRED_CONSOLES 8
 static struct preferred_console preferred_consoles[MAX_PREFERRED_CONSOLES];
 
-static int preferred_dev_console = -1;
+static LIST_HEAD(preferred_dev_console);
 static bool want_braille_console;
 /* Set when there is at least one console preferred via the command line. */
 int console_set_on_cmdline;
@@ -2567,9 +2567,16 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
  *
  *   3. Only matching entries can be updated.
  *
+ *   4. Braille console is never associated with /dev/console.[**]
+ *
  *  [*] A valid @name and @idx will get assigned for a devname later when
  *	@devname matches during the device initialization, see
  *	match_devname_and_update_preferred_console().
+ *
+ * [**] Braille console is using the mechanism for registering consoles
+ *	but it is very special. It is primarily used for user interaction
+ *	with the system. It neither gets printk() messages nor is
+ *	associated with /dev/console.
  */
 static int add_or_update_preferred_console(unsigned int i,
 					   const char *name, const short idx,
@@ -2649,10 +2656,20 @@ static int add_or_update_preferred_console(unsigned int i,
 		braille_set_options(pc, brl_options);
 	}
 
-	if (brl_options)
+	if (is_new_entry)
+		INIT_LIST_HEAD(&pc->preferred_dev_node);
+
+	/*
+	 * The last preferred console should get associated with /dev/console.
+	 * Except for the Braille console which can't get associated with
+	 * /dev/console.
+	 */
+	if (brl_options) {
 		want_braille_console = true;
-	else
-		preferred_dev_console = i;
+		list_del_init(&pc->preferred_dev_node);
+	} else if (!is_braille_console_preferred(pc)) {
+		list_move(&pc->preferred_dev_node, &preferred_dev_console);
+	}
 
 	if (user_specified) {
 		/*
@@ -4035,7 +4052,7 @@ static int __try_enable_preferred_console(struct console *newcon,
 				return err;
 		}
 		newcon->flags |= CON_ENABLED;
-		if (i == preferred_dev_console)
+		if (list_is_first(&pc->preferred_dev_node, &preferred_dev_console))
 			newcon->flags |= CON_CONSDEV;
 		return 0;
 	}
@@ -4079,7 +4096,7 @@ static int try_enable_console(struct console *newcon)
 	/*
 	 * First, try to enable the console driver as a Braille console.
 	 * It would have metadata in the preferred_consoles[] array.
-	 * But it won't be counted as preferred_dev_console because
+	 * But it won't be listed as preferred_dev_console because
 	 * it does not get printk() messages and is not associated
 	 * with /dev/console.
 	 *
@@ -4106,7 +4123,7 @@ static int try_enable_console(struct console *newcon)
 	 * Note that a console with tty binding will have CON_CONSDEV
 	 * flag set and will be first in the list.
 	 */
-	if (preferred_dev_console < 0) {
+	if (list_empty(&preferred_dev_console)) {
 		if (hlist_empty(&console_list) || !console_first()->device ||
 		    console_first()->flags & CON_BOOT) {
 			try_enable_default_console(newcon);
-- 
2.56.0