[Ocfs2-tools-devel] [PATCH 2/2] o2hbmonitor: add lockfile

[Tristan Ye]

Comments inlined;)

Srinivas Eeda wrote:
> This patch creates file /var/run/o2hbmonitor.pid and takes exclusive lock to
> limit multiple processes getting spawned.
>
> Signed-off-by: Srinivas Eeda <srinivas.eeda at oracle.com>
> ---
>  o2monitor/o2hbmonitor.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 45 insertions(+), 0 deletions(-)
>
> diff --git a/o2monitor/o2hbmonitor.c b/o2monitor/o2hbmonitor.c
> index f01da76..ff12ceb 100644
> --- a/o2monitor/o2hbmonitor.c
> +++ b/o2monitor/o2hbmonitor.c
> @@ -61,6 +61,8 @@
>  #define SLOW_POLL_IN_SECS		10
>  #define FAST_POLL_IN_SECS		2
>  
> +#define LOCKFILE_NAME			"/var/run/o2hbmonitor.pid"
> +
>  char *progname;
>  int interactive;
>  int warn_threshold_percent;
> @@ -300,6 +302,48 @@ static void monitor(void)
>  	}
>  }
>  
> +static void lockfile(void)
> +{
> +	int fd, error;
> +	struct flock lock;
> +	char buf[33];
> +
> +	memset(buf, 0, 33);
> +
> +	fd = open(LOCKFILE_NAME, O_CREAT|O_WRONLY,
> +		  S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);
> +	if (fd < 0) {
> +		fprintf(stderr, "cannot open/create lock file %s\n",
> +			LOCKFILE_NAME);
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	lock.l_type = F_WRLCK;
> +	lock.l_whence = SEEK_SET;
> +	lock.l_start = 0;
> +	lock.l_len = 0;
> +
> +	error = fcntl(fd, F_SETLK, &lock);
> +	if (error) {
> +		fprintf(stderr, "o2hbmonitor is already running\n");
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	error = ftruncate(fd, 0);
> +	if (error) {
> +		fprintf(stderr, "cannot clear lock file %s\n", LOCKFILE_NAME);
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	sprintf(buf, "%d\n", getpid());
> +
> +	error = write(fd, buf, strlen(buf));
> +	if (error <= 0) {
> +		fprintf(stderr, "cannot write lock file %s\n", LOCKFILE_NAME);
> +		exit(EXIT_FAILURE);
> +	}
> +}
> +
Hi Srini,

Just curious why not using a in-memory semaphore for the exclusion:


---------------------------------------------------------------
#define O2HB_SEM_MAGIC_KEY    0x4A32594B

int main()
{
    ...
    daemon();
    semid = semget(O2HB_SEM_MAGIC_KEY, 1, IPC_CREAT|IPC_EXCL);
    if (semid < 0) {
       if (errno = EEXIST)
          syslog(LOG_INFO "o2hbmonitor is already running.\n");
       else
            fprintf(stderr, "failed to get semaphore.\n");
       exit(semid);
    }
    openlog();
    monitor();
    sem_close();
}
---------------------------------------------------------------

Lockfile solution has the possibility to allow duplicated monitors when
user remove lockfile arbitrarily.

>  static void usage(void)
>  {
>  	fprintf(stderr, "usage: %s [-w percent] -[ivV]\n", progname);
> @@ -359,6 +403,7 @@ int main(int argc, char **argv)
>  				strerror(errno));
>  	}
>  
> +	lockfile();
>  	openlog(progname, LOG_CONS|LOG_NDELAY, LOG_DAEMON);
>  	monitor();
>  	closelog();