Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

[Steven Rostedt]

On Thu, 28 Sep 2017 14:18:25 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> Add add the 'force_early_printk' kernel parameter to override printk()
> and force it into early_printk(). This bypasses all the cruft and fail
> from printk() and makes things work again.

Probably break this up into two patches. One for creation of
early_vprintk(), and the other to add the force_early_printk parameter.

-- Steve

> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  kernel/printk/printk.c |   68 +++++++++++++++++++++++++++++++++----------------
>  1 file changed, 47 insertions(+), 21 deletions(-)
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -365,6 +365,42 @@ __packed __aligned(4)
>  #endif
>  ;
>  
> +#ifdef CONFIG_EARLY_PRINTK
> +struct console *early_console;
> +
> +static bool __read_mostly force_early_printk;
> +
> +static int __init force_early_printk_setup(char *str)
> +{
> +	force_early_printk = true;
> +	return 0;
> +}
> +early_param("force_early_printk", force_early_printk_setup);
> +
> +static int early_vprintk(const char *fmt, va_list args)
> +{
> +	char buf[512];
> +	int n;
> +
> +	n = vscnprintf(buf, sizeof(buf), fmt, args);
> +	early_console->write(early_console, buf, n);
> +
> +	return n;
> +}
> +
> +asmlinkage __visible void early_printk(const char *fmt, ...)
> +{
> +	va_list ap;
> +
> +	if (!early_console)
> +		return;
> +
> +	va_start(ap, fmt);
> +	early_vprintk(fmt, ap);
> +	va_end(ap);
> +}
> +#endif
> +
>  /*
>   * The logbuf_lock protects kmsg buffer, indices, counters.  This can be taken
>   * within the scheduler's rq lock. It must be released before calling
> @@ -1816,6 +1852,11 @@ asmlinkage int vprintk_emit(int facility
>  		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
>  #endif
>  
> +#ifdef CONFIG_EARLY_PRINTK
> +	if (force_early_printk && early_console)
> +		return early_vprintk(fmt, args);
> +#endif
> +
>  	if (level == LOGLEVEL_SCHED) {
>  		level = LOGLEVEL_DEFAULT;
>  		in_sched = true;
> @@ -1939,7 +1980,12 @@ asmlinkage __visible int printk(const ch
>  	int r;
>  
>  	va_start(args, fmt);
> -	r = vprintk_func(fmt, args);
> +#ifdef CONFIG_EARLY_PRINTK
> +	if (force_early_printk && early_console)
> +		r = vprintk_default(fmt, args);
> +	else
> +#endif
> +		r = vprintk_func(fmt, args);
>  	va_end(args);
>  
>  	return r;
> @@ -1975,26 +2021,6 @@ static size_t msg_print_text(const struc
>  static bool suppress_message_printing(int level) { return false; }
>  #endif /* CONFIG_PRINTK */
>  
> -#ifdef CONFIG_EARLY_PRINTK
> -struct console *early_console;
> -
> -asmlinkage __visible void early_printk(const char *fmt, ...)
> -{
> -	va_list ap;
> -	char buf[512];
> -	int n;
> -
> -	if (!early_console)
> -		return;
> -
> -	va_start(ap, fmt);
> -	n = vscnprintf(buf, sizeof(buf), fmt, ap);
> -	va_end(ap);
> -
> -	early_console->write(early_console, buf, n);
> -}
> -#endif
> -
>  static int __add_preferred_console(char *name, int idx, char *options,
>  				   char *brl_options)
>  {
>