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

[Andy Lutomirski <luto@amacapital.net>]

On Fri, Jun 27, 2014 at 5:06 PM, Alexei Starovoitov <ast@plumgrid.com> 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