linux-kernel - Re: [PATCH 7/8] perf daemon: Allow only one daemon over base directory

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Message-ID: <20201215154627.GH258566@kernel.org>
Date:   Tue, 15 Dec 2020 12:46:27 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Alexei Budankov <abudankov@...wei.com>
Subject: Re: [PATCH 7/8] perf daemon: Allow only one daemon over base
 directory

Em Sat, Dec 12, 2020 at 11:43:57AM +0100, Jiri Olsa escreveu:
> Add 'lock' file under daemon base and flock it, so only one
> perf daemon can run on top of it.
> 
>   # perf daemon --config ./config.daemon
>   # perf daemon --config ./config.daemon
>   failed: another perf daemon (pid 369675) owns /opt/perfdata

So the way to disambiguate is the "daemon base"?

- Arnaldo
 
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/perf/builtin-daemon.c | 43 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
> 
> diff --git a/tools/perf/builtin-daemon.c b/tools/perf/builtin-daemon.c
> index 855fed2fe364..1bd5432a57a3 100644
> --- a/tools/perf/builtin-daemon.c
> +++ b/tools/perf/builtin-daemon.c
> @@ -8,6 +8,7 @@
>  #include <string.h>
>  #include <sys/types.h>
>  #include <sys/wait.h>
> +#include <sys/file.h>
>  #include <signal.h>
>  #include <stdlib.h>
>  #include <time.h>
> @@ -639,6 +640,42 @@ static int handle_config_changes(struct daemon *daemon, int conf_fd,
>  	return 0;
>  }
>  
> +static int check_lock(struct daemon *daemon)
> +{
> +	char path[PATH_MAX];
> +	char buf[20];
> +	int fd, pid;
> +	ssize_t len;
> +
> +	scnprintf(path, sizeof(path), "%s/lock", daemon->base);
> +
> +	fd = open(path, O_RDWR|O_CREAT, 0640);
> +	if (fd < 0)
> +		return -1;
> +
> +	if (lockf(fd, F_TLOCK, 0) < 0) {
> +		filename__read_int(path, &pid);
> +		fprintf(stderr, "failed: another perf daemon (pid %d) owns %s\n",
> +			pid, daemon->base);
> +		return -1;
> +	}
> +
> +	scnprintf(buf, sizeof(buf), "%d", getpid());
> +	len = strlen(buf);
> +
> +	if (write(fd, buf, len) != len) {
> +		perror("write failed");
> +		return -1;
> +	}
> +
> +	if (ftruncate(fd, len)) {
> +		perror("ftruncate failed");
> +		return -1;
> +	}
> +
> +	return 0;
> +}
> +
>  static int go_background(struct daemon *daemon)
>  {
>  	int pid, fd;
> @@ -653,6 +690,9 @@ static int go_background(struct daemon *daemon)
>  	if (setsid() < 0)
>  		return -1;
>  
> +	if (check_lock(daemon))
> +		return -1;
> +
>  	umask(0);
>  
>  	if (chdir(daemon->base)) {
> @@ -704,6 +744,9 @@ static int __cmd_daemon(struct daemon *daemon, bool foreground, const char *conf
>  	if (setup_server_config(daemon))
>  		return -1;
>  
> +	if (foreground && check_lock(daemon))
> +		return -1;
> +
>  	if (!foreground && go_background(daemon))
>  		return -1;
>  
> -- 
> 2.26.2
> 

-- 

- Arnaldo