netdev - Re: [PATCH bpf-next v1] bpf, sockmap: Introduce tracing capability for sockmap

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Message-ID: <20250409121125.48510acb@gandalf.local.home>
Date: Wed, 9 Apr 2025 12:11:25 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>
Cc: bpf@...r.kernel.org, mrpre@....com, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, John Fastabend
 <john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>, Martin
 KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP
 Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo
 <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Jakub Sitnicki
 <jakub@...udflare.com>, Masami Hiramatsu <mhiramat@...nel.org>, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
 <horms@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v1] bpf, sockmap: Introduce tracing capability
 for sockmap

On Wed,  9 Apr 2025 18:29:33 +0800
Jiayuan Chen <jiayuan.chen@...ux.dev> wrote:

> +#define trace_sockmap_skmsg_redirect(sk, prog, msg, act)	\
> +	trace_sockmap_redirect((sk), "msg", (prog), (msg)->sg.size, (act))
> +
> +#define trace_sockmap_skb_redirect(sk, prog, skb, act)		\
> +	trace_sockmap_redirect((sk), "skb", (prog), (skb)->len, (act))
> +
> +TRACE_EVENT(sockmap_redirect,
> +	    TP_PROTO(const struct sock *sk, const char *type,
> +		     const struct bpf_prog *prog, int length, int act),
> +	    TP_ARGS(sk, type, prog, length, act),
> +
> +	TP_STRUCT__entry(
> +		__field(const void *, sk)
> +		__field(const char *, type)

On 64bit, const char * is 8 bytes, and you are pointing it to a string of
size 4 bytes (3 chars and '\0'). Why not just make it a constant string, or
better yet, an enum?

-- Steve

> +		__field(__u16, family)
> +		__field(__u16, protocol)
> +		__field(int, prog_id)
> +		__field(int, length)
> +		__field(int, act)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->sk		= sk;
> +		__entry->type		= type;
> +		__entry->family		= sk->sk_family;
> +		__entry->protocol	= sk->sk_protocol;
> +		__entry->prog_id	= prog->aux->id;
> +		__entry->length		= length;
> +		__entry->act		= act;
> +	),
> +