[PATCH v4 04/11] printk: Separate code for adding/updating preferred console metadata

[Petr Mladek <pmladek@suse.com>]

The logic for adding or updating a preferred console is currently
duplicated within __add_preferred_console(), making the code difficult
to follow and prone to consistency issues.

Introduce update_preferred_console() to centralize the initialization
and updating of struct preferred_console entries. This refactoring
explicitly defines and enforces the following rules:

1. Console names and/or indexes are not set when a console is preferred
   via devname; these are resolved later during device matching.
2. Console names are only added alongside a valid index.
3. Only matching entries are updated.
4. Console and Braille options are never cleared. They are updated
   only via the command line.
5. The global 'preferred_dev_console' index and 'console_set_on_cmdline'
   flag are updated consistently.

Additionally, rename braille_set_options() to braille_update_options()
to better reflect its conditional behavior.

Behavior change:

The original code never updated the preferred console options
when it was preferred more times, e.g. via the command line
and/or some platform specific code, e.g. SPCR or device tree.

The new code explicitly allows to update the console options
when they are preferred over the command line.

It mostly worked even before but only because the command line was
processed early enough before handling SPCR, device tree, or other
platform specific init code.

The main behavior change is when the same console is preferred more
times on the command line. Newly, the later or Braille variant
wins. It is a more common and expected behavior.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/braille.h |   7 +-
 kernel/printk/printk.c  | 153 +++++++++++++++++++++++++++++++---------
 2 files changed, 122 insertions(+), 38 deletions(-)

diff --git a/kernel/printk/braille.h b/kernel/printk/braille.h
index 55cd3178a17a..0bdac303f8b1 100644
--- a/kernel/printk/braille.h
+++ b/kernel/printk/braille.h
@@ -5,9 +5,10 @@
 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 
 static inline void
-braille_set_options(struct preferred_console *pc, char *brl_options)
+braille_update_options(struct preferred_console *pc, char *brl_options)
 {
-	pc->brl_options = brl_options;
+	if (brl_options)
+		pc->brl_options = brl_options;
 }
 
 /*
@@ -29,7 +30,7 @@ _braille_unregister_console(struct console *console);
 #else
 
 static inline void
-braille_set_options(struct preferred_console *pc, char *brl_options)
+braille_update_options(struct preferred_console *pc, char *brl_options)
 {
 }
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e162e8836683..b7dbbc1baeb1 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2544,18 +2544,123 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
 }
 #endif
 
-static void set_user_specified(struct preferred_console *pc, bool user_specified)
+/** add_or_update_preferred_console - Add or update a given entry in
+ *	the preferred_consoles[] table.
+ * @i: index of the entry in @preferred_consoles table which should get updated.
+ * @name: The name of the preferred console driver.
+ * @idx: Preferred console index, e.g. port number.
+ * @devname: The name of the preferred physical device.
+ * @options: Options used when setting up the console driver.
+ * @brl_options: Options used when setting up the console driver
+ *	as a braille console.
+ * @user_specified: True if preferred via the kernel command line.
+ *
+ * The function ensures that the given values are consistent. Also
+ * it updates some global variables which are used to make the right
+ * decisions in register_console().
+ *
+ * Rules:
+ *
+ *   1. Either @name and valid @idx OR @devname and @idx=-1 are allowed.
+ *	Note that a valid @name and @idx will get assigned later when
+ *	@devname matches during the device initialization.
+ *   2. Specify @brl_options if the console should be enabled as
+ *	a Braille console [*]
+ *   3. Only matching entries can be updated.
+ *   4. @options passed via the command line are used when the same
+ *	console is preferred also by some platform-specific code.
+ *
+ * [*] 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,
+					   const char *devname, char *options,
+					   char *brl_options, bool user_specified)
 {
-	if (!user_specified)
-		return;
+	struct preferred_console *pc;
+
+	if (i >= MAX_PREFERRED_CONSOLES) {
+		pr_err_once("Reached maximal number of preferred consoles.\n");
+		return -E2BIG;
+	}
+
+	pc = &preferred_consoles[i];
+
+	if (WARN_ON(!name && !devname))
+		return -EINVAL;
+
+	if (devname) {
+		/*
+		 * A valid console name and index will get assigned when
+		 * a matching device gets registered.
+		 */
+		if (name) {
+			pr_err("Adding a preferred console devname with a hard-coded console name: %s, %s\n",
+			       devname, name);
+			return -EINVAL;
+		}
+		if (pc->name[0]) {
+			pr_err("Updating a preferred console entry with an already assigned console name via devname: %s, %s\n",
+			       devname, pc->name);
+			return -EINVAL;
+		}
+		if (idx != -1) {
+			pr_err("Adding a preferred console devname with a hard-coded index: %s, %d\n",
+			       devname, idx);
+			return -EINVAL;
+		}
+
+		if (!pc->devname[0]) {
+			/* This is a new entry. */
+			strscpy(pc->devname, devname);
+			pc->index = idx;
+		} else if (strcmp(pc->devname, devname) != 0) {
+			pr_err("Updating a preferred console with an invalid devname: %s vs. %s\n",
+			       pc->devname, devname);
+			return -EINVAL;
+		}
+	}
+
+	if (name) {
+		/* A console name must be defined with a valid index. */
+		if (idx < 0) {
+			pr_err("Adding a preferred console with an invalid index: %s, %d\n",
+			       name, idx);
+			return -EINVAL;
+		}
+
+		if (!pc->name[0]) {
+			/* This is a new entry. */
+			strscpy(pc->name, name);
+			pc->index = idx;
+		} else if (strcmp(pc->name, name) != 0 || pc->index != idx) {
+			pr_err("Updating a preferred console with an invalid name or index: %s%d vs. %s%d\n",
+			       pc->name, pc->index, name, idx);
+			return -EINVAL;
+		}
+	}
+
+	if (!pc->options || (user_specified && options))
+		pc->options = options;
+
+	braille_update_options(pc, brl_options);
+
+	if (!brl_options)
+		preferred_dev_console = i;
 
 	/*
 	 * @pc console was defined by the user on the command line.
 	 * Do not clear when added twice also by SPCR or the device tree.
 	 */
-	pc->user_specified = true;
-	/* At least one console defined by the user on the command line. */
-	console_set_on_cmdline = 1;
+	if (user_specified) {
+		pc->user_specified = true;
+		console_set_on_cmdline = 1;
+	}
+
+	return 0;
 }
 
 static int __add_preferred_console(const char *name, const short idx,
@@ -2563,19 +2668,11 @@ static int __add_preferred_console(const char *name, const short idx,
 				   char *brl_options, bool user_specified)
 {
 	struct preferred_console *pc;
-	int i;
+	unsigned int i;
 
 	if (!name && !devname)
 		return -EINVAL;
 
-	/*
-	 * We use a signed short index for struct console for device drivers to
-	 * indicate a not yet assigned index or port. However, a negative index
-	 * value is not valid when the console name and index are defined on
-	 * the command line.
-	 */
-	if (name && idx < 0)
-		return -EINVAL;
 
 	/*
 	 *	See if this tty is not yet registered, and
@@ -2584,28 +2681,14 @@ static int __add_preferred_console(const char *name, const short idx,
 	for (i = 0, pc = preferred_consoles;
 	     i < MAX_PREFERRED_CONSOLES && (pc->name[0] || pc->devname[0]);
 	     i++, pc++) {
-		if ((name && strcmp(pc->name, name) == 0 && pc->index == idx) ||
-		    (devname && strcmp(pc->devname, devname) == 0)) {
-			if (!brl_options)
-				preferred_dev_console = i;
-			set_user_specified(pc, user_specified);
-			return 0;
-		}
+		if (name && strcmp(pc->name, name) == 0 && pc->index == idx)
+			break;
+		if (devname && strcmp(pc->devname, devname) == 0)
+			break;
 	}
-	if (i == MAX_PREFERRED_CONSOLES)
-		return -E2BIG;
-	if (!brl_options)
-		preferred_dev_console = i;
-	if (name)
-		strscpy(pc->name, name);
-	if (devname)
-		strscpy(pc->devname, devname);
-	pc->options = options;
-	set_user_specified(pc, user_specified);
-	braille_set_options(pc, brl_options);
 
-	pc->index = idx;
-	return 0;
+	return add_or_update_preferred_console(i, name, idx, devname, options,
+					       brl_options, user_specified);
 }
 
 static int __init console_msg_format_setup(char *str)
-- 
2.54.0