linux-kernel - Re: [PATCH tip/master] tracing/probes: Fix a warning message to show correct maximum length

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Message-ID: <20170207074148.GA24528@gmail.com>
Date:   Tue, 7 Feb 2017 08:41:48 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH tip/master] tracing/probes: Fix a warning message to show
 correct maximum length


* Masami Hiramatsu <mhiramat@...nel.org> wrote:

> Since tracing/*probe_events will accept a probe definition
> up to 4096 - 2 ('\n' and '\0') bytes, it must show 4094 instead
> of 4096 in warning message.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  kernel/trace/trace_probe.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 8c0553d..7138fea 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -673,8 +673,9 @@ ssize_t traceprobe_probes_write(struct file *file, const char __user *buffer,
>  			*tmp = '\0';
>  			size = tmp - kbuf + 1;
>  		} else if (done + size < count) {
> +			/* This can accept WRITE_BUFSIZE - 2 ('\n' + '\0') */
>  			pr_warn("Line length is too long: Should be less than %d\n",
> -				WRITE_BUFSIZE);
> +				WRITE_BUFSIZE - 2);

The message should also indicate which kernel subsystem generated it - which is 
useful if the message is not immediately noticed in the kernel log.

You can do this by having something like this at the top of the trace_probe file:

  #define pr_fmt(fmt) "trace_probe: " fmt

Thanks,

	Ingo