rfkill: add __must_check annotations

rfkill is not a small, mere detail in wireless support.  Once it starts
supporting rfkill and users start counting on that support, a wireless
device is at risk of operating in dangerous conditions should rfkill
support fail to properly activate.

Therefore, add the required __must_check annotations on some key functions
of the rfkill API, for which the wireless drivers absolutely MUST handle
the failure mode safely in order to avoid a potentially dangerous situation
where the wireless transmitter is left enabled when the user don't want it
to.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Cc: Matthew Garrett <mjg@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/linux/rfkill.h

@@ -110,9 +110,10 @@ struct rfkill {
 };
 #define to_rfkill(d)	container_of(d, struct rfkill, dev)
 
-struct rfkill *rfkill_allocate(struct device *parent, enum rfkill_type type);
+struct rfkill * __must_check rfkill_allocate(struct device *parent,
+					     enum rfkill_type type);
 void rfkill_free(struct rfkill *rfkill);
-int rfkill_register(struct rfkill *rfkill);
+int __must_check rfkill_register(struct rfkill *rfkill);
 void rfkill_unregister(struct rfkill *rfkill);
 
 int rfkill_force_state(struct rfkill *rfkill, enum rfkill_state state);

net/rfkill/rfkill.c

@@ -645,7 +645,8 @@ static void rfkill_remove_switch(struct rfkill *rfkill)
  * NOTE: If registration fails the structure shoudl be freed by calling
  * rfkill_free() otherwise rfkill_unregister() should be used.
  */
-struct rfkill *rfkill_allocate(struct device *parent, enum rfkill_type type)
+struct rfkill * __must_check rfkill_allocate(struct device *parent,
+					     enum rfkill_type type)
 {
 	struct rfkill *rfkill;
 	struct device *dev;
@@ -716,7 +717,7 @@ static void rfkill_led_trigger_unregister(struct rfkill *rfkill)
  * structure needs to be registered. Immediately from registration the
  * switch driver should be able to service calls to toggle_radio.
  */
-int rfkill_register(struct rfkill *rfkill)
+int __must_check rfkill_register(struct rfkill *rfkill)
 {
 	static atomic_t rfkill_no = ATOMIC_INIT(0);
 	struct device *dev = &rfkill->dev;