[ofa-general] Re: socket buffer accounting with UDP/ipoib

[Roland Dreier]

 > > +		ib_dma_sync_single_for_cpu(priv->ca, addr, IPOIB_BUF_SIZE,
 > > +					   DMA_FROM_DEVICE);
 > > +		skb_copy_from_linear_data_offset(skb, IB_GRH_BYTES, new_skb->data,
 > > +						 wc->byte_len - IB_GRH_BYTES);
 > > +		ib_dma_sync_single_for_device(priv->ca, addr, IPOIB_BUF_SIZE,
 > > +					      DMA_FROM_DEVICE);
 > 
 > BTW, why is ib_dma_sync_single_for_device necessary here?

Not sure what you're asking exactly.  The sync for device is needed to
match the previous sync for the cpu obviously.  We need both syncs for
the same reason we need the unmap when we don't copy -- we're copying
data out of the skb we gave to the device earlier, so we need to make
sure the cpu sees the right data.