From d634f194d4e2e58d57927c812aca097e67a2287d Mon Sep 17 00:00:00 2001
From: Richard Weinberger <richard@nod.at>
Date: Tue, 24 May 2011 17:13:01 -0700
Subject: [PATCH] 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>
---
arch/um/Kconfig.debug | 10 ++++++++++
arch/um/include/shared/os.h | 1 +
arch/um/kernel/Makefile | 1 +
arch/um/kernel/early_printk.c | 33 +++++++++++++++++++++++++++++++++
arch/um/os-Linux/util.c | 5 +++++
5 files changed, 50 insertions(+)
create mode 100644 arch/um/kernel/early_printk.c
diff --git a/arch/um/Kconfig.debug b/arch/um/Kconfig.debug
index 8fce5e536b0f..85c86edd1e67 100644
--- a/arch/um/Kconfig.debug
+++ b/arch/um/Kconfig.debug
@@ -37,4 +37,14 @@ config DEBUG_STACK_USAGE
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 f06a5da71a8f..83c7c2ecd614 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -244,6 +244,7 @@ extern int raw(int fd);
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 1119233597a1..c4491c15afb2 100644
--- a/arch/um/kernel/Makefile
+++ b/arch/um/kernel/Makefile
@@ -17,6 +17,7 @@ obj-y = config.o exec.o exitcode.o init_task.o irq.o ksyms.o mem.o \
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 000000000000..ec649bf72f68
--- /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 42827cafa6af..5803b1887672 100644
--- a/arch/um/os-Linux/util.c
+++ b/arch/um/os-Linux/util.c
@@ -139,3 +139,8 @@ void os_dump_core(void)
uml_abort();
}
+
+void um_early_printk(const char *s, unsigned int n)
+{
+ printf("%.*s", n, s);
+}
--
GitLab