cifs RDMA restrictions

[David Howells <dhowells@redhat.com>]

Hi Tom,

I'm looking at cleaning up the "struct page" instances in smbdirect.c as much
as possible.  Can you tell me what are the restrictions on the size of a
segment attached to an SGE?  For instance, by:

	static bool smb_set_sge(struct smb_extract_to_rdma *rdma,
				struct page *lowest_page, size_t off, size_t len)
	{
		struct ib_sge *sge = &rdma->sge[rdma->nr_sge];
		u64 addr;

		addr = ib_dma_map_page(rdma->device, lowest_page,
				       off, len, rdma->direction);
		if (ib_dma_mapping_error(rdma->device, addr))
			return false;

		sge->addr   = addr;
		sge->length = len;
		sge->lkey   = rdma->local_dma_lkey;
		rdma->nr_sge++;
		return true;
	}

Thanks,
David