-extern unsigned long copy_user_generic(void *to, const void *from, unsigned len);
-
-extern unsigned long copy_to_user(void __user *to, const void *from, unsigned len);
-extern unsigned long copy_from_user(void *to, const void __user *from, unsigned len);
-extern unsigned long copy_in_user(void __user *to, const void __user *from, unsigned len);
-
-static __always_inline int __copy_from_user(void *dst, const void __user *src, unsigned size)
+__must_check unsigned long
+copy_user_generic(void *to, const void *from, unsigned len);
+
+__must_check unsigned long
+copy_to_user(void __user *to, const void *from, unsigned len);
+__must_check unsigned long
+copy_from_user(void *to, const void __user *from, unsigned len);
+__must_check unsigned long
+copy_in_user(void __user *to, const void __user *from, unsigned len);
+
+static __always_inline __must_check
+int __copy_from_user(void *dst, const void __user *src, unsigned size)