Add wait_event_killable

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

include/linux/wait.h

@@ -346,6 +346,47 @@ do {									\
 	__ret;								\
 })
 
+#define __wait_event_killable(wq, condition, ret)			\
+do {									\
+	DEFINE_WAIT(__wait);						\
+									\
+	for (;;) {							\
+		prepare_to_wait(&wq, &__wait, TASK_KILLABLE);		\
+		if (condition)						\
+			break;						\
+		if (!fatal_signal_pending(current)) {			\
+			schedule();					\
+			continue;					\
+		}							\
+		ret = -ERESTARTSYS;					\
+		break;							\
+	}								\
+	finish_wait(&wq, &__wait);					\
+} while (0)
+
+/**
+ * wait_event_killable - sleep until a condition gets true
+ * @wq: the waitqueue to wait on
+ * @condition: a C expression for the event to wait for
+ *
+ * The process is put to sleep (TASK_KILLABLE) until the
+ * @condition evaluates to true or a signal is received.
+ * The @condition is checked each time the waitqueue @wq is woken up.
+ *
+ * wake_up() has to be called after changing any variable that could
+ * change the result of the wait condition.
+ *
+ * The function will return -ERESTARTSYS if it was interrupted by a
+ * signal and 0 if @condition evaluated to true.
+ */
+#define wait_event_killable(wq, condition)				\
+({									\
+	int __ret = 0;							\
+	if (!(condition))						\
+		__wait_event_killable(wq, condition, __ret);		\
+	__ret;								\
+})
+
 /*
  * Must be called with the spinlock in the wait_queue_head_t held.
  */