int sched_setscheduler (
  pid_t pid,
  int policy,
  const struct sched_param *param);
int sched_getscheduler (pid_t pid);

int sched_setparam (pid_t pid, const struct sched_param *param);
int sched_getparam (pid_t pid, struct sched_param *param);

struct sched_param
{
  ...
  int sched_priority;
  ...
};

int sched_yield (void);