On Tue, Nov 29, 2016 at 02:21:23PM +0100, Thomas Graf wrote:

Adds a series of test to verify the functionality of attaching
BPF programs at LWT hooks.

Also adds a sample which collects a histogram of packet sizes which
pass through an LWT hook.

$ ./lwt_len_hist.sh
Starting netserver with host 'IN(6)ADDR_ANY' port '12865' and family AF_UNSPEC
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.253.2 () port 0 AF_INET : demo
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    10.00    39857.69

Nice!

+	ret = bpf_redirect(ifindex, 0);
+	if (ret < 0) {
+		printk("bpf_redirect() failed: %d\n", ret);
+		return BPF_DROP;
+	}

this 'if' looks a bit weird. You're passing 0 as flags,
so this helper will always succeed.
Other sample code often does 'return bpf_redirect(...)'
due to this reasoning.