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

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  [PATCH 2/3] early_printk: Add force_early_printk kernel parameter Peter Zijlstra <peterz@infradead.org> - 2017-09-28 14:30 +0200
    Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter Randy Dunlap <rdunlap@infradead.org> - 2017-09-28 17:50 +0200
      Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter Peter Zijlstra <peterz@infradead.org> - 2017-09-28 18:10 +0200
        Re: [PATCH 2/3] early_printk: Add force_early_printk kernel parameter Randy Dunlap <rdunlap@infradead.org> - 2017-09-28 19:10 +0200

#1741490 — [PATCH 2/3] early_printk: Add force_early_printk kernel parameter

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.

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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#1741657

On 09/28/17 05:18, Peter Zijlstra wrote:

<attachment not shown>

Hi Peter,

Please add that kernel parameter to Documentation/admin-guide/kernel-parameters.txt.

thanks,
-- 
~Randy

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#1741673

On Thu, Sep 28, 2017 at 08:41:37AM -0700, Randy Dunlap wrote:

> Please add that kernel parameter to Documentation/admin-guide/kernel-parameters.txt.

Something like so?

--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1165,6 +1165,11 @@
 			parameter will force ia64_sal_cache_flush to call
 			ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
 
+	force_early_printk
+			Forcefully uses early_console (as per earlyprintk=)
+			usage for regular printk, bypassing everything,
+			including the syslog (dmesg will be empty).
+
 	forcepae [X86-32]
 			Forcefully enable Physical Address Extension (PAE).
 			Many Pentium M systems disable PAE but may have a

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#1741712

On 09/28/17 09:07, Peter Zijlstra wrote:
> On Thu, Sep 28, 2017 at 08:41:37AM -0700, Randy Dunlap wrote:
> 
>> Please add that kernel parameter to Documentation/admin-guide/kernel-parameters.txt.
> 
> Something like so?

Yes, thanks. Ack.

> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1165,6 +1165,11 @@
>  			parameter will force ia64_sal_cache_flush to call
>  			ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
>  
> +	force_early_printk
> +			Forcefully uses early_console (as per earlyprintk=)
> +			usage for regular printk, bypassing everything,
> +			including the syslog (dmesg will be empty).
> +
>  	forcepae [X86-32]
>  			Forcefully enable Physical Address Extension (PAE).
>  			Many Pentium M systems disable PAE but may have a
> 


-- 
~Randy

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