linux-kernel - Re: [PATCH]trace: fix wrong help information about snapshot

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Date:	Thu, 12 Sep 2013 12:33:47 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Wang YanQing <udknight@...il.com>
Cc:	fweisbec@...il.com, mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH]trace: fix wrong help information about snapshot

On Thu, 12 Sep 2013 23:04:01 +0800
Wang YanQing <udknight@...il.com> wrote:

> 
> Cat snapshot give me:
> " tracer: nop
> 
>  * Snapshot is freed *
> 
>  Snapshot commands:
>  echo 0 > snapshot : Clears and frees snapshot buffer
>  echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.
>                       Takes a snapshot of the main buffer.
>  echo 2 > snapshot : Clears snapshot buffer (but does not allocate)
>                       (Doesn't have to be '2' works with any number that
>                        is not a '0' or '1')"
> 
> But after read the code, I found the right information about "echo 2 > snapshot"
> should looks like below:
> 
> " echo 2 > snapshot : Clears snapshot buffer (but does not free)
>                       (Doesn't have to be '2' works with any number that
>                        is not a '0' or '1')"

Actually, they both are correct:

	default:
		if (tr->allocated_snapshot) {
			if (iter->cpu_file == RING_BUFFER_ALL_CPUS)
				tracing_reset_online_cpus(&tr->max_buffer);
			else
				tracing_reset(&tr->max_buffer,	iter->cpu_file);
		}
		break;
	}

It does nothing if it isn't allocated.

Perhaps we need it to say "(but does not allocate or free)"

-- Steve



> 
> Signed-off-by: Wang YanQing <udknight@...il.com>
> ---
>  kernel/trace/trace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 7974ba2..d0da660 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2760,7 +2760,7 @@ static void show_snapshot_main_help(struct seq_file *m)
>  	seq_printf(m, "# echo 0 > snapshot : Clears and frees snapshot buffer\n");
>  	seq_printf(m, "# echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.\n");
>  	seq_printf(m, "#                      Takes a snapshot of the main buffer.\n");
> -	seq_printf(m, "# echo 2 > snapshot : Clears snapshot buffer (but does not allocate)\n");
> +	seq_printf(m, "# echo 2 > snapshot : Clears snapshot buffer (but does not free)\n");
>  	seq_printf(m, "#                      (Doesn't have to be '2' works with any number that\n");
>  	seq_printf(m, "#                       is not a '0' or '1')\n");
>  }

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