printk: Introduce kmsg_dump_reason_str()

The pstore subsystem already had a private version of this function.
With the coming addition of the pstore/zone driver, this needs to be
shared. As it really should live with printk, move it there instead.

Link: https://lore.kernel.org/lkml/20200515184434.8470-4-keescook@chromium.org/
Acked-by: Petr Mladek <pmladek@suse.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 9826014..3378bcb 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -70,6 +70,8 @@ void kmsg_dump_rewind(struct kmsg_dumper *dumper);
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
 int kmsg_dump_unregister(struct kmsg_dumper *dumper);
+
+const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason);
 #else
 static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
@@ -111,6 +113,11 @@ static inline int kmsg_dump_unregister(struct kmsg_dumper *dumper)
 {
 	return -EINVAL;
 }
+
+static inline const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
+{
+	return "Disabled";
+}
 #endif
 
 #endif /* _LINUX_KMSG_DUMP_H */