Is Mutex Ceiling Priority Supported?

I’m using QNX 6.2.1.

In pthread.h…

extern int pthread_mutex_getprioceiling(const pthread_mutex_t *__mutex, int
*__prioceiling);
extern int pthread_mutex_setprioceiling(pthread_mutex_t *__mutex, int
__prioceiling, int *__old_ceiling);

A call to either of these returns 22 (EINVAL) - the mutex doesn’t currently
exist.

But a lock or unlock of the same mutex returns 0 (EOK).