[PATCH v6 06/16] printk: Prefer the console either via name or devname exclusively

[Petr Mladek]

The commit 7640f1a44eba ("printk: Add
match_devname_and_update_preferred_console()") added the possibility
to prefer a console driver via device name. The name of the console driver
gets assigned when the device gets initialized and it tries whether
it is eligible for a console.

The above mentioned commit ensures that __add_preferred_console() is called
at least with name or devname value. But it does not check whether
both are defined which is a nonsense.

Add the check and do not fail quietly. Also shuffle the code a bit
to make it ready for adding more checks.

Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
Reviewed-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Acked-by: Chris Down <chris@xxxxxxxxxxxxxx>
---
 kernel/printk/printk.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 6bba67e142e1..d082169a8615 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2561,6 +2561,12 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
  * in register_console(). Finally, it enforces some rules:
  *
  *   1. Do not accept empty @name or @devname.
+ *
+ *   2. Either @name OR @devname are allowed. [*]
+ *
+ *  [*] 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().
  */
 static int add_or_update_preferred_console(unsigned int i,
 					   const char *name, const short idx,
@@ -2595,11 +2601,23 @@ static int add_or_update_preferred_console(unsigned int i,
 	if (!pc->name[0] && !pc->devname[0])
 		is_new_entry = true;
 
-	if (is_new_entry) {
-		if (devname)
-			strscpy(pc->devname, devname);
-		if (name)
-			strscpy(pc->name, name);
+	if (is_new_entry && 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;
+		}
+
+		strscpy(pc->devname, devname);
+		pc->index = idx;
+	}
+
+	if (is_new_entry && name) {
+		strscpy(pc->name, name);
 		pc->index = idx;
 	}
 
-- 
2.56.0