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SubjectRe: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter
On Thu, 28 Sep 2017 14:18:25 +0200
Peter Zijlstra <peterz@infradead.org> 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@infradead.org>
> ---
> 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)
> {
>

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