netdev - Re: [PATCH bpf v2 1/2] fprobe: samples: Add use_trace option and show hit/missed counter

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Date:   Fri, 17 Jun 2022 12:06:51 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf v2 1/2] fprobe: samples: Add use_trace option and
 show hit/missed counter

On Wed,  8 Jun 2022 01:11:02 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

>  
>  static void sample_entry_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs)
>  {
> -	pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
> +	if (use_trace)
> +		trace_printk("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);

Could we add a comment stating something like "this is just an example, no
kernel code should call trace_printk() except when actively debugging".

-- Steve


> +	else
> +		pr_info("Enter <%pS> ip = 0x%p\n", (void *)ip, (void *)ip);
> +	nhit++;
>  	if (stackdump)
>  		show_backtrace();
>  }
> @@ -49,8 +56,13 @@ static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_r
>  {
>  	unsigned long rip = instruction_pointer(regs);
>  
> -	pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
> -		(void *)ip, (void *)ip, (void *)rip, (void *)rip);
> +	if (use_trace)
> +		trace_printk("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
> +			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
> +	else
> +		pr_info("Return from <%pS> ip = 0x%p to rip = 0x%p (%pS)\n",
> +			(void *)ip, (void *)ip, (void *)rip, (void *)rip);
> +	nhit++;
>  	if (stackdump)
>  		show_backtrace();