linux-kernel - Re: [PATCH] net: tcp_drop adds `reason` parameter for tracing

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Date:   Tue, 24 Aug 2021 07:20:49 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Zhongya Yan <yan2228598786@...il.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        edumazet@...gle.com, rostedt@...dmis.org, mingo@...hat.com,
        davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        hengqi.chen@...il.com, yhs@...com
Subject: Re: [PATCH] net: tcp_drop adds `reason` parameter for tracing

On Tue, 24 Aug 2021 05:51:40 -0700 Zhongya Yan wrote:
> +enum tcp_drop_reason {
> +	TCP_OFO_QUEUE = 1,
> +	TCP_DATA_QUEUE_OFO = 2,
> +	TCP_DATA_QUEUE = 3,
> +	TCP_PRUNE_OFO_QUEUE = 4,
> +	TCP_VALIDATE_INCOMING = 5,
> +	TCP_RCV_ESTABLISHED = 6,
> +	TCP_RCV_SYNSENT_STATE_PROCESS = 7,
> +	TCP_RCV_STATE_PROCESS = 8
> +};

This is basically tracking the caller, each may have multiple reasons
for dropping. Is tracking the caller sufficient? Should we at least
make this a bitmask so we can set multiple bits (caller and more
precise reason)? Or are we going to add another field in that case?

> -static void tcp_drop(struct sock *sk, struct sk_buff *skb)
> +static void __tcp_drop(struct sock *sk,
> +		   struct sk_buff *skb)
>  {
>  	sk_drops_add(sk, skb);
>  	__kfree_skb(skb);
>  }

Why keep this function if there is only one caller?

> +/* tcp_drop whit reason,for epbf trace
> + */

This comment is (a) misspelled, (b) doesn't add much value.

> +static void tcp_drop(struct sock *sk, struct sk_buff *skb,
> +		 enum tcp_drop_reason reason)
> +{
> +	trace_tcp_drop(sk, skb, reason);
> +	__tcp_drop(sk, skb);
> +}