static bool virtqueue_kick_prepare_packed()

in virtio_ring.c [1318:1365]

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

static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
{
	struct vring_virtqueue *vq = to_vvq(_vq);
	u16 new, old, off_wrap, flags, wrap_counter, event_idx;
	bool needs_kick;
	union {
		struct {
			__le16 off_wrap;
			__le16 flags;
		};
		u32 u32;
	} snapshot;

	START_USE(vq);

	/*
	 * We need to expose the new flags value before checking notification
	 * suppressions.
	 */
	virtio_mb(vq->weak_barriers);

	old = vq->packed.next_avail_idx - vq->num_added;
	new = vq->packed.next_avail_idx;
	vq->num_added = 0;

	snapshot.u32 = *(u32 *)vq->packed.vring.device;
	flags = le16_to_cpu(snapshot.flags);

	LAST_ADD_TIME_CHECK(vq);
	LAST_ADD_TIME_INVALID(vq);

	if (flags != VRING_PACKED_EVENT_FLAG_DESC) {
		needs_kick = (flags != VRING_PACKED_EVENT_FLAG_DISABLE);
		goto out;
	}

	off_wrap = le16_to_cpu(snapshot.off_wrap);

	wrap_counter = off_wrap >> VRING_PACKED_EVENT_F_WRAP_CTR;
	event_idx = off_wrap & ~(1 << VRING_PACKED_EVENT_F_WRAP_CTR);
	if (wrap_counter != vq->packed.avail_wrap_counter)
		event_idx -= vq->packed.vring.num;

	needs_kick = vring_need_event(event_idx, new, old);
out:
	END_USE(vq);
	return needs_kick;
}