linux-kernel - Re: [PATCH 2/3] perf kvm: Allow running without stdin

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Message-ID: <20191023104245.GL22919@krava>
Date:   Wed, 23 Oct 2019 12:42:45 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Igor Lubashev <ilubashe@...mai.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] perf kvm: Allow running without stdin

On Tue, Oct 22, 2019 at 09:54:52PM -0400, Igor Lubashev wrote:
> Allow perf kvm --stdio to run without access to stdin.
> This lets perf kvm to run in a batch mode until interrupted.
> 
> The following now works as expected:
> 
>   $ perf kvm top --stdio < /dev/null
> 
> Signed-off-by: Igor Lubashev <ilubashe@...mai.com>
> ---
>  tools/perf/builtin-kvm.c | 33 ++++++++++++++++++++-------------
>  1 file changed, 20 insertions(+), 13 deletions(-)
> 
> diff --git a/tools/perf/builtin-kvm.c b/tools/perf/builtin-kvm.c
> index 858da896b518..5217aa3596c7 100644
> --- a/tools/perf/builtin-kvm.c
> +++ b/tools/perf/builtin-kvm.c
> @@ -930,18 +930,20 @@ static int fd_set_nonblock(int fd)
>  
>  static int perf_kvm__handle_stdin(void)
>  {
> -	int c;
> -
> -	c = getc(stdin);
> -	if (c == 'q')
> +	switch (getc(stdin)) {
> +	case 'q':
> +		done = 1;
>  		return 1;
> -
> -	return 0;
> +	case EOF:
> +		return 0;
> +	default:
> +		return 1;
> +	}
>  }
>  
>  static int kvm_events_live_report(struct perf_kvm_stat *kvm)
>  {
> -	int nr_stdin, ret, err = -EINVAL;
> +	int nr_stdin = -1, ret, err = -EINVAL;
>  	struct termios save;
>  
>  	/* live flag must be set first */
> @@ -972,13 +974,16 @@ static int kvm_events_live_report(struct perf_kvm_stat *kvm)
>  	if (evlist__add_pollfd(kvm->evlist, kvm->timerfd) < 0)
>  		goto out;
>  
> -	nr_stdin = evlist__add_pollfd(kvm->evlist, fileno(stdin));
> -	if (nr_stdin < 0)
> -		goto out;
> -
>  	if (fd_set_nonblock(fileno(stdin)) != 0)
>  		goto out;
>  
> +	/* add stdin, if it is connected */
> +	if (getc(stdin) != EOF) {
> +		nr_stdin = evlist__add_pollfd(kvm->evlist, fileno(stdin));
> +		if (nr_stdin < 0)
> +			goto out;
> +	}
> +
>  	/* everything is good - enable the events and process */
>  	evlist__enable(kvm->evlist);
>  
> @@ -994,8 +999,10 @@ static int kvm_events_live_report(struct perf_kvm_stat *kvm)
>  		if (err)
>  			goto out;
>  
> -		if (fda->entries[nr_stdin].revents & POLLIN)
> -			done = perf_kvm__handle_stdin();
> +		if (nr_stdin >= 0 && fda->entries[nr_stdin].revents & POLLIN) {
> +			if (!perf_kvm__handle_stdin())

can this return 0 ? if stdin is EOF then nr_stdin stays -1

> +				fda->entries[nr_stdin].events = 0;

why do you need to set events to 0 in here?

thanks,
jirka