[openib-general] ipoib: question

[Michael S. Tsirkin]

Roland, where exactly does the following math come from?

static inline struct ipoib_neigh **to_ipoib_neigh(struct neighbour *neigh)
{
        return (struct ipoib_neigh **) (neigh->ha + 24 -
                                        (offsetof(struct neighbour, ha) & 4));
}

1. What does & 4 do here?
2. Why are we subsrctucting a function of ha offset?
4. What is 24? Is it related to INFINIBAND_ALEN?

Thanks,

-- 
MST