shm_copyin_path
error = shm_copyin_path(td, userpath, &path);
static int shm_copyin_path(struct thread *td, const char *userpath_in,
error = shm_copyin_path(td, uap->path, &path);
error = shm_copyin_path(td, uap->path_from, &path_from);
error = shm_copyin_path(td, uap->path_to, &path_to);