semaphore: introduce a semaphore_reset helper

This simply clears the internal counter of a semaphore.

kernel-src/include/semaphore.h

@@ -27,6 +27,7 @@ typedef struct semaphore_t{
 int semaphore_wait(semaphore_t *sem, bool interruptible);
 int semaphore_timedwait(semaphore_t *sem, time_t timeoutusec, bool interruptible);
 void semaphore_signal(semaphore_t *sem);
+void semaphore_reset(semaphore_t *sem);
 bool semaphore_test(semaphore_t *sem);
 bool semaphore_haswaiters(semaphore_t *sem);
 

kernel-src/lib/semaphore.c

@@ -125,6 +125,13 @@ void semaphore_signal(semaphore_t *sem) {
 	interrupt_set(intstate);
 }
 
+void semaphore_reset(semaphore_t *sem) {
+	bool intstate = spinlock_acquireirqclear(&sem->lock);
+	__assert(sem->head == NULL);
+	sem->i = 0;
+	spinlock_releaseirqrestore(&sem->lock, intstate);
+}
+
 bool semaphore_haswaiters(semaphore_t *sem) {
 	bool intstate = interrupt_set(false);
 	spinlock_acquire(&sem->lock);