[uml-devel] [PATCH 2/2] um: add a kmsg_dumper

[Thomas M. <th...@m3...>]

Add a kmsg_dumper, that dumps the kmsg buffer to stderr, when no
console is available.
This an enables the printing of early panic() calls triggered in
uml_postsetup().

Signed-off-by: Thomas Meyer <th...@m3...>
---
 arch/um/drivers/ubd_kern.c  |  5 +++--
 arch/um/include/shared/os.h |  1 +
 arch/um/kernel/Makefile     |  2 +-
 arch/um/kernel/kmsg_dump.c  | 44 ++++++++++++++++++++++++++++++++++++++++++++
 arch/um/kernel/um_arch.c    |  2 ++
 arch/um/os-Linux/util.c     | 12 ++++++++++++
 6 files changed, 63 insertions(+), 3 deletions(-)
 create mode 100644 arch/um/kernel/kmsg_dump.c

diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index 08eec0b..36741f4 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -238,6 +238,7 @@ 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);
 extern void os_fix_helper_signals(void);
+extern int os_printf_stderr(const char *fmt, ...);
 
 /* time.c */
 extern void idle_sleep(unsigned long long nsecs);
diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
index d8b78a0..572e781 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 smp.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 0000000..8047ca5a3
--- /dev/null
+++ b/arch/um/kernel/kmsg_dump.c
@@ -0,0 +1,44 @@
+#include <linux/kmsg_dump.h>
+#include <linux/console.h>
+#include <shared/init.h>
+#include <shared/kern.h>
+#include <os.h>
+
+static struct kmsg_dumper kmsg_dumper;
+
+static void kmsg_dumper_stderr(struct kmsg_dumper *dumper,
+				enum kmsg_dump_reason reason)
+{
+	static char line[1024];
+
+	size_t len = 0;
+	int con_count = 0;
+	struct console *con = NULL;
+
+	/* only dump kmsg when no console is available */
+	if (!console_trylock()) {
+		return;
+	}
+	for_each_console(con) {
+		con_count++;
+	}
+	console_unlock();
+
+	if (con_count > 0) {
+		return;
+	}
+
+	os_printf_stderr("kmsg_dump:\n");
+	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+		line[len] = '\0';
+		os_printf_stderr("%s", line);
+	}
+}
+
+int __init kmsg_dumper_stderr_init(void)
+{
+	kmsg_dumper.dump = kmsg_dumper_stderr;
+	return kmsg_dump_register(&kmsg_dumper);
+}
+
+__uml_initcall(kmsg_dumper_stderr_init);
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index ab72560..4f6fc24 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>
@@ -234,6 +235,7 @@ 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;
diff --git a/arch/um/os-Linux/util.c b/arch/um/os-Linux/util.c
index faee55e..a4cc3a0 100644
--- a/arch/um/os-Linux/util.c
+++ b/arch/um/os-Linux/util.c
@@ -152,3 +152,15 @@ void um_early_printk(const char *s, unsigned int n)
 {
 	printf("%.*s", n, s);
 }
+
+int os_printf_stderr(const char *fmt, ...)
+{
+	va_list list;
+	int rc;
+
+	va_start(list, fmt);
+	rc = vfprintf(stderr, fmt, list);
+	va_end(list);
+
+	return rc;
+}
-- 
1.9.3