linux-kernel - Re: [PATCH 1/3] perf top: Fix stdio interface input handling with glibc 2.28+

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Date:   Thu, 5 Mar 2020 11:49:43 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Tommi Rantala <tommi.t.rantala@...ia.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] perf top: Fix stdio interface input handling with
 glibc 2.28+

Em Thu, Mar 05, 2020 at 10:37:12AM +0200, Tommi Rantala escreveu:
> Since glibc 2.28 when running 'perf top --stdio', input handling no
> longer works, but hitting any key always just prints the "Mapped keys"
> help text.
> 
> To fix it, call clearerr() in the display_thread() loop to clear any EOF
> sticky errors, as instructed in the glibc NEWS file
> (https://sourceware.org/git/?p=glibc.git;a=blob;f=NEWS):
> 
>  * All stdio functions now treat end-of-file as a sticky condition.  If you
>    read from a file until EOF, and then the file is enlarged by another
>    process, you must call clearerr or another function with the same effect
>    (e.g. fseek, rewind) before you can read the additional data.  This
>    corrects a longstanding C99 conformance bug.  It is most likely to affect
>    programs that use stdio to read interactive input from a terminal.
>    (Bug #1190.)

Thanks for fixing this, I had stumbled on it at some point, but since I
mostly use the TUI interface, it fell thru the cracks.

Do you prefer it over the TUI one?

Thanks, tested and applied.

- Arnaldo
 
> Signed-off-by: Tommi Rantala <tommi.t.rantala@...ia.com>
> ---
>  tools/perf/builtin-top.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index f6dd1a63f159e..d2539b793f9d4 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -684,7 +684,9 @@ static void *display_thread(void *arg)
>  	delay_msecs = top->delay_secs * MSEC_PER_SEC;
>  	set_term_quiet_input(&save);
>  	/* trash return*/
> -	getc(stdin);
> +	clearerr(stdin);
> +	if (poll(&stdin_poll, 1, 0) > 0)
> +		getc(stdin);
>  
>  	while (!done) {
>  		perf_top__print_sym_table(top);
> -- 
> 2.21.1
> 

-- 

- Arnaldo