vhost: actually track log eventfd file

While reviewing vhost log code, I found out that log_file is never
set. Note: I haven't tested the change (QEMU doesn't use LOG_FD yet).

Cc: stable@vger.kernel.org
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
	__u16 old, new;
	__virtio16 event;
	bool v;
	/* Flush out used index updates. This is paired
	 * with the barrier that the Guest executes when enabling
	 * interrupts. */
	smp_mb();

	if (vhost_has_feature(vq, VIRTIO_F_NOTIFY_ON_EMPTY) &&
	    unlikely(vq->avail_idx == vq->last_avail_idx))
		return true;

	if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
		__virtio16 flags;
		if (__get_user(flags, &vq->avail->flags)) {
			vq_err(vq, "Failed to get flags");
			return true;
		}
		return !(flags & cpu_to_vhost16(vq, VRING_AVAIL_F_NO_INTERRUPT));
	}
	old = vq->signalled_used;
	v = vq->signalled_used_valid;
	new = vq->signalled_used = vq->last_used_idx;
	vq->signalled_used_valid = true;

	if (unlikely(!v))
		return true;

	if (__get_user(event, vhost_used_event(vq))) {
		vq_err(vq, "Failed to get used event idx");
		return true;
	}
	return vring_need_event(vhost16_to_cpu(vq, event), new, old);
}

static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
	__u16 old, new;
	__virtio16 event;
	bool v;
	/* Flush out used index updates. This is paired
	 * with the barrier that the Guest executes when enabling
	 * interrupts. */
	smp_mb();

	if (vhost_has_feature(vq, VIRTIO_F_NOTIFY_ON_EMPTY) &&
	    unlikely(vq->avail_idx == vq->last_avail_idx))
		return true;

	if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
		__virtio16 flags;
		if (__get_user(flags, &vq->avail->flags)) {
			vq_err(vq, "Failed to get flags");
			return true;
		}
		return !(flags & cpu_to_vhost16(vq, VRING_AVAIL_F_NO_INTERRUPT));
	}
	old = vq->signalled_used;
	v = vq->signalled_used_valid;
	new = vq->signalled_used = vq->last_used_idx;
	vq->signalled_used_valid = true;

	if (unlikely(!v))
		return true;

	if (__get_user(event, vhost_used_event(vq))) {
		vq_err(vq, "Failed to get used event idx");
		return true;
	}
	return vring_need_event(vhost16_to_cpu(vq, event), new, old);
}
