linux-kernel - Re: [PATCH v3 net-next 2/5] net: tracepoint: replace tcp_set_state tracepoint with inet_sock_set

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Date:   Sun, 31 Dec 2017 11:06:25 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Brendan Gregg <brendan.d.gregg@...il.com>
Cc:     Song Liu <songliubraving@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brendan Gregg <bgregg@...flix.com>, netdev@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 net-next 2/5] net: tracepoint: replace tcp_set_state
 tracepoint with inet_sock_set_state tracepoint

On Sun, Dec 31, 2017 at 6:33 AM, Brendan Gregg
<brendan.d.gregg@...il.com> wrote:
> On Tue, Dec 19, 2017 at 7:12 PM, Yafang Shao <laoar.shao@...il.com> wrote:
>> As sk_state is a common field for struct sock, so the state
>> transition tracepoint should not be a TCP specific feature.
>> Currently it traces all AF_INET state transition, so I rename this
>> tracepoint to inet_sock_set_state tracepoint with some minor changes and move it
>> into trace/events/sock.h.
>
> The tcp:tcp_set_state probe is tcp_set_state(), so it's only going to
> fire for TCP sessions. It's not broken, and we could add a
> sctp:sctp_set_state as well. Replacing tcp:tcp_set_state with
> inet_sk_set_state is feeling like we might be baking too much
> implementation detail into the tracepoint API.
>
> If we must have inet_sk_set_state, then must we also delete tcp:tcp_set_state?
>

Hi Brendan,

The reason we have to make this change could be got from this mail
thread, https://patchwork.kernel.org/patch/10099243/ .

The original tcp:tcp_set_state probe doesn't traced all TCP state transitions.
There're some state transitions in inet_connection_sock.c and
inet_hashtables.c are missed.
So we have to place this probe into these two files to fix the issue.
But as inet_connection_sock.c and inet_hashtables.c are common files
for all IPv4 protocols, not only for TCP, so it is not proper to place
a tcp_ function in these two files.
That's why we decide to rename tcp:tcp_set_state probe to
sock:inet_sock_set_state.

Thanks
Yafang