linux-kernel - Re: [PATCH] net/tcp: introduce TRACE_EVENT for TCP/IPv4 state transition

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Date:   Thu, 9 Nov 2017 18:34:08 +0000
From:   Song Liu <songliubraving@...com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Yafang Shao <laoar.shao@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net/tcp: introduce TRACE_EVENT for TCP/IPv4 state
 transition


> On Nov 9, 2017, at 10:18 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> On Thu, 9 Nov 2017 15:43:29 +0900
> Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> 
>>> +TRACE_EVENT(tcp_set_state,
>>> +	TP_PROTO(struct sock *sk, int oldstate, int newstate),
>>> +	TP_ARGS(sk, oldstate, newstate),
>>> +
>>> +	TP_STRUCT__entry(
>>> +		__field(__be32, dst)
>>> +		__field(__be32, src)
>>> +		__field(__u16, dport)
>>> +		__field(__u16, sport)
>>> +		__field(int, oldstate)
>>> +		__field(int, newstate)
>>> +	),
>>> +
>>> +	TP_fast_assign(
>>> +		if (oldstate == TCP_TIME_WAIT) {
>>> +			__entry->dst = inet_twsk(sk)->tw_daddr;
>>> +			__entry->src = inet_twsk(sk)->tw_rcv_saddr;
>>> +			__entry->dport = ntohs(inet_twsk(sk)->tw_dport);
>>> +			__entry->sport = ntohs(inet_twsk(sk)->tw_sport);
>>> +		} else if (oldstate == TCP_NEW_SYN_RECV) {
>>> +			__entry->dst = inet_rsk(inet_reqsk(sk))->ir_rmt_addr;
>>> +			__entry->src = inet_rsk(inet_reqsk(sk))->ir_loc_addr;
>>> +			__entry->dport =
>>> +				ntohs(inet_rsk(inet_reqsk(sk))->ir_rmt_port);
>>> +			__entry->sport = inet_rsk(inet_reqsk(sk))->ir_num;
>>> +		} else {
>>> +			__entry->dst = inet_sk(sk)->inet_daddr;
>>> +			__entry->src = inet_sk(sk)->inet_rcv_saddr;
>>> +			__entry->dport = ntohs(inet_sk(sk)->inet_dport);
>>> +			__entry->sport = ntohs(inet_sk(sk)->inet_sport);
>>> +		}
>>> +
>>> +		__entry->oldstate = oldstate;
>>> +		__entry->newstate = newstate;
>>> +	),
>>> +
>>> +	TP_printk("%08X:%04X %08X:%04X, %02x %02x",
>>> +		__entry->src, __entry->sport, __entry->dst, __entry->dport,
>>> +		__entry->oldstate, __entry->newstate)  
>> 
>> direct %x of state is not allowed.
>> This has to use show_tcp_state_name() like it's done in trace_tcp_set_state
> 
> Hmm, I need to look at trace_tcp_set_state. I'm guessing it is in
> net-next too?

Yes, in net-next. There are 6 tracepoints under tcp group:

  tcp_destroy_sock  
  tcp_receive_reset  
  tcp_retransmit_skb  
  tcp_retransmit_synack  
  tcp_send_reset  
  tcp_set_state

They are all added recently.
 
> 
>> 
>> Also I'm missing the reason to introduce another tracepoint
>> that looks just like trace_tcp_set_state.
> 
> I want to make sure that perf and trace-cmd can parse the TP_printk(),
> if it is having helper functions like that in the TP_printk() part,
> then the libtraceevent needs to be aware of that.
> 

tcp_set_state uses __print_symbolic to show state in text format. I found
trace-cmd cannot parse that part:

[011] 147338.660560: tcp_set_state:        sport=16262 dport=48346 \
    saddr=127.0.0.6 daddr=127.0.0.6 saddrv6=2401:db00:30:317e:face:0:1f:0 \
    daddrv6=2401:db00:30:31e5:face:0:7f:0 oldstate= newstate=

Other parts of the output looks good to me.

Thanks,
Song