linux-kernel - Re: [PATCH v2 1/2] tools subcmd: Add non-waitpid check_if_command

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Message-ID: <ZoTETvgcPdl9EUJV@google.com>
Date: Tue, 2 Jul 2024 20:23:58 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	James Clark <james.clark@....com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 1/2] tools subcmd: Add non-waitpid
 check_if_command_finished()

Hi Ian,

On Sun, Jun 30, 2024 at 09:42:35PM -0700, Ian Rogers wrote:
> Using waitpid can cause stdout/stderr of the child process to be
> lost. Use Linux's /prod/<pid>/status file to determine if the process
> has reached the zombie state. Use the 'status' file rather than 'stat'
> to avoid issues around skipping the process name.
> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/lib/subcmd/run-command.c | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/tools/lib/subcmd/run-command.c b/tools/lib/subcmd/run-command.c
> index 4e3a557a2f37..ec06683e77a0 100644
> --- a/tools/lib/subcmd/run-command.c
> +++ b/tools/lib/subcmd/run-command.c
> @@ -2,6 +2,7 @@
>  #include <unistd.h>
>  #include <sys/types.h>
>  #include <sys/stat.h>
> +#include <ctype.h>
>  #include <fcntl.h>
>  #include <string.h>
>  #include <linux/string.h>
> @@ -217,8 +218,40 @@ static int wait_or_whine(struct child_process *cmd, bool block)
>  
>  int check_if_command_finished(struct child_process *cmd)
>  {
> +#ifdef __linux__

Is this really necessary?  I don't think we plan to support other OS..

Thanks,
Namhyung


> +	char filename[FILENAME_MAX + 12];
> +	char status_line[256];
> +	FILE *status_file;
> +
> +	/*
> +	 * Check by reading /proc/<pid>/status as calling waitpid causes
> +	 * stdout/stderr to be closed and data lost.
> +	 */
> +	sprintf(filename, "/proc/%d/status", cmd->pid);
> +	status_file = fopen(filename, "r");
> +	if (status_file == NULL) {
> +		/* Open failed assume finish_command was called. */
> +		return true;
> +	}
> +	while (fgets(status_line, sizeof(status_line), status_file) != NULL) {
> +		char *p;
> +
> +		if (strncmp(status_line, "State:", 6))
> +			continue;
> +
> +		fclose(status_file);
> +		p = status_line + 6;
> +		while (isspace(*p))
> +			p++;
> +		return *p == 'Z';
> +	}
> +	/* Read failed assume finish_command was called. */
> +	fclose(status_file);
> +	return true;
> +#else
>  	wait_or_whine(cmd, /*block=*/false);
>  	return cmd->finished;
> +#endif
>  }
>  
>  int finish_command(struct child_process *cmd)
> -- 
> 2.45.2.803.g4e1b14247a-goog
>