Re: [PATCH] net: tcp_drop adds `reason` parameter for tracing v2

On Wed, 25 Aug 2021 08:47:46 -0700 Eric Dumazet wrote:

On Wed, Aug 25, 2021 at 8:41 AM Zhongya Yan [off-list ref] wrote:

quoted

@@ -5703,15 +5700,15 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
                        TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
                tcp_send_challenge_ack(sk, skb);
-               goto discard;
+               tcp_drop(sk, skb, TCP_DROP_MASK(__LINE__, TCP_VALIDATE_INCOMING));  

I'd rather use a string. So that we can more easily identify _why_ the
packet was drop, without looking at the source code
of the exact kernel version to locate line number 1057

Yeah, the line number seems like a particularly bad idea. Hopefully
strings won't be problematic, given we can expect most serious users 
to feed the tracepoints via BPF. enum would be more convenient there,
I'd think.

You can be sure that we will get reports in the future from users of
heavily modified kernels.
Having to download a git tree, or apply semi-private patches is a no go.

I'm slightly surprised by this angle. Are there downstream kernels with
heavily modified TCP other than Google's?

If you really want to include __FILE__ and __LINE__, these both can be
stringified and included in the report, with the help of macros.