Sorry if my remarks were confusing, it was just missing from the previous patch and it needs to be:

desc->len = mbuf->pkt_len;

We need to keep this the same as the original code. This is a scenario where we need to copy the data from an mbuf that isn't in from the pool of buffers allocated for the umem. So the desc->len needs to be set to that of the (non umem) mbuf. 

The other changes look good. Nearly there,

Thanks again

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