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.

---
 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

index 2d840a0..3345e71 100644
@@ -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

index ea92aa1..f1efeee 100644
@@ -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;

2.1.0





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