the host share them.
Before breaking out of the loop over descriptors in gem_rint(),
DMA-resynchronize the first Rx descriptor we found that does not
belong to the host. We must avoid a cached descriptor "covering"
a descriptor in RAM, because the cached descriptor may say that
the descriptor still belongs to the NIC, when that is not true,
and the driver will hang.
XXX I believe this driver only works by luck on hosts that both
XXX have a cacheline size greater than the size of a descriptor
XXX (16 bytes) and lack DMA/cache coherency. I need to add some
XXX trickery to make sure that we don't scribble over the NIC's
XXX changes to a descriptor when we flush a cached descriptor to
XXX RAM with bus_dmamap_sync(9).
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