linux-kernel - Re: [PATCH] tcp: tcp_drop adds `SNMP` and `reason` parameter for tracing

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Date:   Thu, 23 Sep 2021 13:31:21 +0800
From:   Zhongya Yan <yan2228598786@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brendan Gregg <brendan.d.gregg@...il.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        David Miller <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>, Yonghong Song <yhs@...com>,
        Zhongya Yan <2228598786@...com>
Subject: Re: [PATCH] tcp: tcp_drop adds `SNMP` and `reason` parameter for tracing

On Wed, 22 Sep 2021 23:08:15 -0400

Cong Wang <xiyou.wangcong@...il.com> wrote:

> I think you fail to explain why only TCP needs it?

Thanks for the suggestion, I will rewrite the description document.

> This should be useful for all kinds of drops, not just TCP, therefore
> you should consider extending net/core/drop_monitor.c instead of
> just tcp_drop().

Currently, I'll look at the code in `net/core/drop_monitor.c` later

 because it only extends tcp.

> Also, kernel does not have to explain it in strings, those SNMP
> counters are already available for user-space, so kernel could
> just use SNMP enums and let user-space interpret them. In many
> cases, you are just adding strings for those SNMP enums.
>
> Thanks.

Since these drops are hardly hot path, why not simply use a string ?
An ENUM will not really help grep games.
--Eric Dumazet

I think `Eric`s point is correct, so strings are used. SNMP is auxiliary,

I can remove it if you find it unfriendly