netdev - eBPF: how to check the flow table

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Date:   Sun, 18 Sep 2016 14:02:15 +0200
From:   Eric Leblond <eric@...it.org>
To:     netdev@...r.kernel.org
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        daniel@...earbox.net
Subject: eBPF: how to check the flow table

Hello,

I'm currently testing a code implementing AF_PACKET bypass for
Suricata. The idea is that Suricata is updating a hash table containing
a list of flows it does not want to see anymore.

I want to check flow timeout from the userspace, so my current
algorithm is doing:

    while (bpf_get_next_key(mapfd, &key, &next_key) == 0) {
        bpf_lookup_elem(mapfd, &next_key, &value);
        FlowCallback(mapfd, &next_key, &value, data);
        key = next_key;
    }

In the FlowCallback, I check the timing in the flow entry and I remove
the key if the flow is timeout.

This is currently working well when there is only a few flows but on a
real system with log of insertion in the table, the loop is never
returning because we dequeue slower than we enqueue.

Is there a better algorithm or an other way to do it ? 

BR,
-- 
Eric Leblond <eric@...it.org>
Blog: https://home.regit.org/