Re: [PATCH 12/22] perf daemon: Allow only one daemon over base directory

[Namhyung Kim]

On Sun, Jan 3, 2021 at 7:05 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Add 'lock' file under daemon base and flock it, so only one
> perf daemon can run on top of it.
>
> Example:
>
>   # cat ~/.perfconfig
>   [daemon]
>   base=/opt/perfdata
>
>   [session-cycles]
>   run = -m 10M -e cycles --overwrite --switch-output -a
>
>   [session-sched]
>   run = -m 20M -e sched:* --overwrite --switch-output -a
>
> Starting the daemon:
>
>   # perf daemon start
>
> And try once more:
>
>   # perf daemon start
>   failed: another perf daemon (pid 775594) owns /opt/perfdata
>
> will end up with an error, because there's already one running
> on top of /opt/perfdata.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  tools/perf/builtin-daemon.c | 49 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
>
> diff --git a/tools/perf/builtin-daemon.c b/tools/perf/builtin-daemon.c
> index 45748bb471ec..1982eedd3f3f 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>
> @@ -562,12 +563,18 @@ static int cmd_session_list(struct daemon *daemon, union cmd *cmd, FILE *out)
>                         /* output */
>                         csv_sep, daemon->base, SESSION_OUTPUT);
>
> +               fprintf(out, "%c%s/%s",
> +                       /* lock */
> +                       csv_sep, daemon->base, "lock");
> +
>                 fprintf(out, "\n");
>         } else {
>                 fprintf(out, "[%d:daemon] base: %s\n", getpid(), daemon->base);
>                 if (cmd->list.verbose) {
>                         fprintf(out, "  output:  %s/%s\n",
>                                 daemon->base, SESSION_OUTPUT);
> +                       fprintf(out, "  lock:    %s/lock\n",
> +                               daemon->base);
>                 }
>         }
>
> @@ -761,6 +768,42 @@ 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|O_CLOEXEC, 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;
> +       }

So the fd is (a kind of) leaked and the lock is released only when
the daemon is going to die, right?

Thanks,
Namhyung

> +
> +       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;
> @@ -775,6 +818,9 @@ static int go_background(struct daemon *daemon)
>         if (setsid() < 0)
>                 return -1;
>
> +       if (check_lock(daemon))
> +               return -1;
> +
>         umask(0);
>
>         if (chdir(daemon->base)) {
> @@ -861,6 +907,9 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
>         if (setup_server_config(daemon))
>                 return -1;
>
> +       if (foreground && check_lock(daemon))
> +               return -1;
> +
>         if (!foreground && go_background(daemon))
>                 return -1;
>
> --
> 2.26.2
>