Function eventfd_read

freebsd/kern/sys_eventfd.c:147–187

}

static int
eventfd_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{
	struct eventfd *efd;
	eventfd_t count;
	int error;

	if (uio->uio_resid < sizeof(eventfd_t))
		return (EINVAL);

	error = 0;
	efd = fp->f_data;
	mtx_lock(&efd->efd_lock);
	while (error == 0 && efd->efd_count == 0) {
		if ((fp->f_flag & FNONBLOCK) != 0) {
			mtx_unlock(&efd->efd_lock);
			return (EAGAIN);
		}
		error = mtx_sleep(&efd->efd_count, &efd->efd_lock, PCATCH,
		    "efdrd", 0);
	}
	if (error == 0) {
		MPASS(efd->efd_count > 0);
		if ((efd->efd_flags & EFD_SEMAPHORE) != 0) {
			count = 1;
			--efd->efd_count;
		} else {
			count = efd->efd_count;
			efd->efd_count = 0;
		}
		KNOTE_LOCKED(&efd->efd_sel.si_note, 0);
		selwakeup(&efd->efd_sel);
		wakeup(&efd->efd_count);
		mtx_unlock(&efd->efd_lock);
		error = uiomove(&count, sizeof(eventfd_t), uio);
	} else
		mtx_unlock(&efd->efd_lock);

	return (error);
}

static int
eventfd_write(struct file *fp, struct uio *uio, struct ucred *active_cred,