Absolutely nothing, as long as the interface guarantees I don't see a larger scatterlist. With the current implementation it looks to me like this is always true, but if we were to stick to using a scatterlist, it would make sense to allow the user to specify a max sg length supported. This value could be different for in vs. out buffers.

Agreed. However, this one is a huge issue for ibmveth. ibmveth must write a tag to the first 8 bytes of each rx buffer before passing the buffer to the pSeries hypervisor. The hypervisor then writes this tag to the rx queue when the buffer is used. This first 8 bytes of the rx buffer is not overlayed with data.
Additionally, the hypervisor may offset further than 8 bytes into the buffer for the start of the payload if it so desires. The offset is also written to the rx queue.

Another option which would solve this problem would be if the get_inbuf interface also returned an offset into the original data buffer where the payload starts.