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Subject[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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