Re: [PATCH RFC net-next 13/14] samples: bpf: example of stateful socket filtering

On Fri, Jun 27, 2014 at 5:06 PM, Alexei Starovoitov [off-list ref] wrote:

this socket filter example does:

- creates a hashtable in kernel with key 4 bytes and value 8 bytes

- populates map[6] = 0; map[17] = 0;  // 6 - tcp_proto, 17 - udp_proto

- loads eBPF program:
  r0 = skb[14 + 9]; // load one byte of ip->proto
  *(u32*)(fp - 4) = r0;
  value = bpf_map_lookup_elem(map_id, fp - 4);
  if (value)
       (*(u64*)value) += 1;

In the code below, this is XADD.  Is there anything that validates
that shared things like this can only be poked at by atomic
operations?

--Andy