From 04a418495e0852263d77c4fb82adf470feaafef3 Mon Sep 17 00:00:00 2001
From: Thomas Meyer <thomas@m3y3r.de>
Date: Sat, 28 Mar 2015 10:07:37 +0100
Subject: [PATCH] um: add a kmsg_dumper
Add a kmsg_dumper, that dumps the kmsg buffer to stdout, when no console
is available. This an enables the printing of early panic() calls
triggered in uml_postsetup().
When a panic() call happens so early in the UML kernel no
earlyprintk/console is available yet, but with a kmsg_dumper in place
the kernel message buffer will be outputted to the user, to give a
better hint, of what the failure was.
Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Richard Weinberger <richard@nod.at>
---
arch/um/kernel/Makefile | 2 +-
arch/um/kernel/kmsg_dump.c | 43 ++++++++++++++++++++++++++++++++++++++
arch/um/kernel/um_arch.c | 2 ++
3 files changed, 46 insertions(+), 1 deletion(-)
create mode 100644 arch/um/kernel/kmsg_dump.c
diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
index b7e31e5a8c0c..a6a5e42caaef 100644
--- a/arch/um/kernel/Makefile
+++ b/arch/um/kernel/Makefile
@@ -13,7 +13,7 @@ clean-files :=
obj-y = config.o exec.o exitcode.o irq.o ksyms.o mem.o \
physmem.o process.o ptrace.o reboot.o sigio.o \
signal.o syscall.o sysrq.o time.o tlb.o trap.o \
- um_arch.o umid.o maccess.o skas/
+ um_arch.o umid.o maccess.o kmsg_dump.o skas/
obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
obj-$(CONFIG_GPROF) += gprof_syms.o
diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
new file mode 100644
index 000000000000..407d49251d6f
--- /dev/null
+++ b/arch/um/kernel/kmsg_dump.c
@@ -0,0 +1,43 @@
+#include <linux/kmsg_dump.h>
+#include <linux/console.h>
+#include <shared/init.h>
+#include <shared/kern.h>
+#include <os.h>
+
+static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
+ enum kmsg_dump_reason reason)
+{
+ static char line[1024];
+
+ size_t len = 0;
+ bool con_available = false;
+
+ /* only dump kmsg when no console is available */
+ if (!console_trylock())
+ return;
+
+ if (console_drivers != NULL)
+ con_available = true;
+
+ console_unlock();
+
+ if (con_available == true)
+ return;
+
+ printf("kmsg_dump:\n");
+ while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+ line[len] = '\0';
+ printf("%s", line);
+ }
+}
+
+static struct kmsg_dumper kmsg_dumper = {
+ .dump = kmsg_dumper_stdout
+};
+
+int __init kmsg_dumper_stdout_init(void)
+{
+ return kmsg_dump_register(&kmsg_dumper);
+}
+
+__uml_postsetup(kmsg_dumper_stdout_init);
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 9b06957e98ce..926ecdceba86 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -11,6 +11,7 @@
#include <linux/string.h>
#include <linux/utsname.h>
#include <linux/sched.h>
+#include <linux/kmsg_dump.h>
#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/sections.h>
@@ -211,6 +212,7 @@ static void __init uml_postsetup(void)
static int panic_exit(struct notifier_block *self, unsigned long unused1,
void *unused2)
{
+ kmsg_dump(KMSG_DUMP_PANIC);
bust_spinlocks(1);
bust_spinlocks(0);
uml_exitcode = 1;