static bool virtqueue_enable_cb_delayed_packed()

in virtio_ring.c [1556:1613]

• 35 lines of code
• 6 McCabe index (conditional complexity)

static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
{
	struct vring_virtqueue *vq = to_vvq(_vq);
	u16 used_idx, wrap_counter;
	u16 bufs;

	START_USE(vq);

	/*
	 * We optimistically turn back on interrupts, then check if there was
	 * more to do.
	 */

	if (vq->event) {
		/* TODO: tune this threshold */
		bufs = (vq->packed.vring.num - vq->vq.num_free) * 3 / 4;
		wrap_counter = vq->packed.used_wrap_counter;

		used_idx = vq->last_used_idx + bufs;
		if (used_idx >= vq->packed.vring.num) {
			used_idx -= vq->packed.vring.num;
			wrap_counter ^= 1;
		}

		vq->packed.vring.driver->off_wrap = cpu_to_le16(used_idx |
			(wrap_counter << VRING_PACKED_EVENT_F_WRAP_CTR));

		/*
		 * We need to update event offset and event wrap
		 * counter first before updating event flags.
		 */
		virtio_wmb(vq->weak_barriers);
	}

	if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DISABLE) {
		vq->packed.event_flags_shadow = vq->event ?
				VRING_PACKED_EVENT_FLAG_DESC :
				VRING_PACKED_EVENT_FLAG_ENABLE;
		vq->packed.vring.driver->flags =
				cpu_to_le16(vq->packed.event_flags_shadow);
	}

	/*
	 * We need to update event suppression structure first
	 * before re-checking for more used buffers.
	 */
	virtio_mb(vq->weak_barriers);

	if (is_used_desc_packed(vq,
				vq->last_used_idx,
				vq->packed.used_wrap_counter)) {
		END_USE(vq);
		return false;
	}

	END_USE(vq);
	return true;
}