um: add earlyprintk support
User Mode Linux can also benefit from earlyprintk. UML's earlyprintk
writes kernel messages directly to stdout.
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/Kconfig.debug b/arch/um/Kconfig.debug
index 8fce5e5..85c86edd 100644
--- a/arch/um/Kconfig.debug
+++ b/arch/um/Kconfig.debug
@@ -37,4 +37,14 @@
stack seen so far.
This option will slow down process creation and destruction somewhat.
+
+config EARLY_PRINTK
+ bool "Early printk"
+ default y
+ ---help---
+ Write kernel log output directly to stdout.
+
+ This is useful for kernel debugging when your machine crashes very
+ early before the console code is initialized.
+
endmenu
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index f06a5da..83c7c2e 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -244,6 +244,7 @@
extern void setup_machinename(char *machine_out);
extern void setup_hostinfo(char *buf, int len);
extern void os_dump_core(void) __attribute__ ((noreturn));
+extern void um_early_printk(const char *s, unsigned int n);
/* time.c */
extern void idle_sleep(unsigned long long nsecs);
diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
index 11192335..c4491c1 100644
--- a/arch/um/kernel/Makefile
+++ b/arch/um/kernel/Makefile
@@ -17,6 +17,7 @@
obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
obj-$(CONFIG_GPROF) += gprof_syms.o
obj-$(CONFIG_GCOV) += gmon_syms.o
+obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
USER_OBJS := config.o
diff --git a/arch/um/kernel/early_printk.c b/arch/um/kernel/early_printk.c
new file mode 100644
index 0000000..ec649bf
--- /dev/null
+++ b/arch/um/kernel/early_printk.c
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2011 Richard Weinberger <richrd@nod.at>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/console.h>
+#include <linux/init.h>
+#include "os.h"
+
+static void early_console_write(struct console *con, const char *s, unsigned int n)
+{
+ um_early_printk(s, n);
+}
+
+static struct console early_console = {
+ .name = "earlycon",
+ .write = early_console_write,
+ .flags = CON_BOOT,
+ .index = -1,
+};
+
+static int __init setup_early_printk(char *buf)
+{
+ register_console(&early_console);
+
+ return 0;
+}
+
+early_param("earlyprintk", setup_early_printk);
diff --git a/arch/um/os-Linux/util.c b/arch/um/os-Linux/util.c
index 42827ca..5803b18 100644
--- a/arch/um/os-Linux/util.c
+++ b/arch/um/os-Linux/util.c
@@ -139,3 +139,8 @@
uml_abort();
}
+
+void um_early_printk(const char *s, unsigned int n)
+{
+ printf("%.*s", n, s);
+}
