linux-kernel - Re: [PATCH v3 linux-trace 4/8] samples: bpf: simple tracing example in C

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Date:	Mon, 9 Feb 2015 23:12:16 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-api@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 linux-trace 4/8] samples: bpf: simple tracing example
 in C

On Mon,  9 Feb 2015 19:45:57 -0800
Alexei Starovoitov <ast@...mgrid.com> wrote:

> +static void print_netif_receive_skb(void *data, int size)
> +{
> +	struct ftrace_raw_netif_receive_skb {
> +		struct trace_entry t;
> +		void *skb;
> +		__u32 len;
> +		__u32 name;
> +	} *e = data;

Same here, there's no guarantee that this structure will always match.

cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/format 
name: netif_receive_skb
ID: 975
format:
	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	field:int common_pid;	offset:4;	size:4;	signed:1;

	field:void * skbaddr;	offset:8;	size:8;	signed:0;
	field:unsigned int len;	offset:16;	size:4;	signed:0;
	field:__data_loc char[] name;	offset:20;	size:4;	signed:1;

print fmt: "dev=%s skbaddr=%p len=%u", __get_str(name), REC->skbaddr, REC->len

-- Steve
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