On Wed 2021-01-06 13:04:57, Sergey Senozhatsky wrote:
On (21/01/05 17:49), Petr Mladek wrote:
The following change solved the problem for me as well. It causes that ttynull is initialized after stdiocons console.
diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c index eced70ec54e1..602af4d30bd4 100644 --- a/drivers/tty/ttynull.c +++ b/drivers/tty/ttynull.c @@ -121,7 +121,6 @@ static void __exit ttynull_exit(void) tty_port_destroy(&ttynull_port); } -module_init(ttynull_init); -module_exit(ttynull_exit); +late_initcall_sync(ttynull_init); MODULE_LICENSE("GPL v2");
But I am not completely sure that it is the right solution.
Wow, hmm, puzzled. Why does it help?
I have been as well. But it seems that I got it, see below.
It is strange. Console should get registered only when it was added by add_preferred_console(). It means that ttynull_init() should not register by default.
[..]
Some clue might be in stderr_console. It has to be explicitly unregistered to avoid staying as the default console, see unregister_stderr() in arch/um/drivers/stderr_console.c
Hmm... Some random thoughts:
Looking at arch/um/drivers/stderr_console.c - it doesn't have tty driver and it doesn't register one.
stderr_console.c is used only during early boot.
stdio_console.c is the console that is supposed to print kunit test results. And it has tty driver.
But I still don't understand why the initcall patch helped. Can you shed some light on it?
The trick is that both stdio_init() and ttynull_init():
+ call register_console() + the console has tty driver
The first one is registered as a fallback when there is no preferred console (has_preferred_console()).
It means that late_initcall_sync(ttynull_init) makes sense. We need to call register_console() from ttynull_init() so that it is registered when defined on the command line. But it should be the last chance to register a fallback console with tty binding.
Alternative solution is to ignore ttynull as the fallback console in register_console(). I mean the following:
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index ffdd0dc7ec6d..cdb77903b0af 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2816,8 +2816,12 @@ void register_console(struct console *newcon) * See if we want to use this console driver. If we * didn't select a console we take the first one * that registers here. + * + * Ignore ttynull console. It should be used only + * when explicitly configured or as an ultimate + * fallback when no better console gets registered at all. */ - if (!has_preferred_console) { + if (!has_preferred_console && strcmp(newcon->name, "ttynull") != 0) { if (newcon->index < 0) newcon->index = 0; if (newcon->setup == NULL ||
Best Regards, Petr