kmsg_dump: fix build for CONFIG_PRINTK=n

kmsg_dump() fails to build when CONFIG_PRINTK=n; provide stubs
for the kmsg_dump*() functions when CONFIG_PRINTK=n.

kernel/printk.c: In function 'kmsg_dump':
kernel/printk.c:1501: error: 'log_buf_len' undeclared (first use in this function)
kernel/printk.c:1502: error: 'logged_chars' undeclared (first use in this function)
kernel/printk.c:1506: error: 'log_buf' undeclared (first use in this function)
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Simon Kagstrom <simon.kagstrom@netinsight.net>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

include/linux/kmsg_dump.h

@@ -35,10 +35,26 @@ struct kmsg_dumper {
 	int registered;
 };
 
+#ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
 int kmsg_dump_unregister(struct kmsg_dumper *dumper);
+#else
+static inline void kmsg_dump(enum kmsg_dump_reason reason)
+{
+}
+
+static inline int kmsg_dump_register(struct kmsg_dumper *dumper)
+{
+	return -EINVAL;
+}
+
+static inline int kmsg_dump_unregister(struct kmsg_dumper *dumper)
+{
+	return -EINVAL;
+}
+#endif
 
 #endif /* _LINUX_KMSG_DUMP_H */

kernel/printk.c

@@ -1405,7 +1405,6 @@ bool printk_timed_ratelimit(unsigned long *caller_jiffies,
 	return false;
 }
 EXPORT_SYMBOL(printk_timed_ratelimit);
-#endif
 
 static DEFINE_SPINLOCK(dump_list_lock);
 static LIST_HEAD(dump_list);
@@ -1524,3 +1523,4 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 		dumper->dump(dumper, reason, s1, l1, s2, l2);
 	spin_unlock_irqrestore(&dump_list_lock, flags);
 }
+#endif