[v2] ulogd: Implement PID file writing

The deamon currently does not have the ability to write a PID file to track its
process ID. This is very useful to an init script and to ensure there is only
one running instance. This patch implements this functionality.

Signed-off-by: Chris Boot <bootc@bootc.net>
---

Changes since v1:
 - Added documentation about the option to ulogd.8.
 - Move check for NULL ulogd_pidfile into main(), so it's more obvious that the
   code does nothing unless the --pidfile option is present.
 - Check for stale PID files and overwrite if that's the case, instead of
   bailing out.
 - Lock the pidfile with fcntl(); this is a good check to guard against running
   multiple instances with the same pidfile. (from atd)
 - Only unlink the pidfile at exit if we have created it. This prevents us
   removing another running ulogd process's pidfile if we exit because there is
   another running instance.

 src/ulogd.c |  147 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 ulogd.8     |    3 ++
 2 files changed, 149 insertions(+), 1 deletion(-)

On 12/05/13 13:47, Chris Boot wrote:
> The deamon currently does not have the ability to write a PID file to track its
> process ID. This is very useful to an init script and to ensure there is only
> one running instance. This patch implements this functionality.
>
> Signed-off-by: Chris Boot <bootc@bootc.net>
> ---
>
> Changes since v1:
>  - Added documentation about the option to ulogd.8.
>  - Move check for NULL ulogd_pidfile into main(), so it's more obvious that the
>    code does nothing unless the --pidfile option is present.
>  - Check for stale PID files and overwrite if that's the case, instead of
>    bailing out.
>  - Lock the pidfile with fcntl(); this is a good check to guard against running
>    multiple instances with the same pidfile. (from atd)
>  - Only unlink the pidfile at exit if we have created it. This prevents us
>    removing another running ulogd process's pidfile if we exit because there is
>    another running instance.
>
>  src/ulogd.c |  147 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  ulogd.8     |    3 ++
>  2 files changed, 149 insertions(+), 1 deletion(-)
>
> diff --git a/src/ulogd.c b/src/ulogd.c
> index 8a144e3..b835220 100644
> --- a/src/ulogd.c
> +++ b/src/ulogd.c
> @@ -4,6 +4,7 @@
>   *
>   * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
>   * (C) 2013 by Eric Leblond <eric@regit.org>
> + * (C) 2013 Chris Boot <bootc@bootc.net>
>   *
>   *  This program is free software; you can redistribute it and/or modify
>   *  it under the terms of the GNU General Public License version 2 
> @@ -55,12 +56,14 @@
>  #include <signal.h>
>  #include <dlfcn.h>
>  #include <sys/types.h>
> +#include <fcntl.h>
>  #include <dirent.h>
>  #include <getopt.h>
>  #include <pwd.h>
>  #include <grp.h>
>  #include <syslog.h>
>  #include <sys/time.h>
> +#include <sys/stat.h>
>  #include <ulogd/conffile.h>
>  #include <ulogd/ulogd.h>
>  #ifdef DEBUG
> @@ -78,11 +81,13 @@
>  static FILE *logfile = NULL;		/* logfile pointer */
>  static char *ulogd_logfile = NULL;
>  static const char *ulogd_configfile = ULOGD_CONFIGFILE;
> +static const char *ulogd_pidfile = NULL;
>  static FILE syslog_dummy;
>  
>  static int info_mode = 0;
>  
>  static int verbose = 0;
> +static int created_pidfile = 0;
>  
>  /* linked list for all registered plugins */
>  static LLIST_HEAD(ulogd_plugins);
> @@ -94,6 +99,7 @@ static LLIST_HEAD(ulogd_pi_stacks);
>  static int load_plugin(const char *file);
>  static int create_stack(const char *file);
>  static int logfile_open(const char *name);
> +static void cleanup_pidfile();
>  
>  static struct config_keyset ulogd_kset = {
>  	.num_ces = 4,
> @@ -457,6 +463,8 @@ void __ulogd_log(int level, char *file, int line, const char *format, ...)
>  
>  static void warn_and_exit(int daemonize)
>  {
> +	cleanup_pidfile();
> +
>  	if (!daemonize) {
>  		if (logfile && !verbose) {
>  			fprintf(stderr, "Fatal error, check logfile \"%s\""
> @@ -1002,6 +1010,131 @@ static int parse_conffile(const char *section, struct config_keyset *ce)
>  	return 1;
>  }
>  
> +/*
> + * Apply F_WRLCK to fd using fcntl().
> + *
> + * This function is copied verbatim from atd's daemon.c file, published under
> + * the GPL2+ license with the following copyright statement:
> + * Copyright (C) 1996 Thomas Koenig
> + */
> +static int lock_fd(int fd)
> +{
> +	struct flock lock;
> +
> +	lock.l_type = F_WRLCK;
> +	lock.l_whence = SEEK_SET;
> +	lock.l_start = 0;
> +	lock.l_len = 0;
> +
> +	return fcntl(fd, F_SETLK, &lock);
> +}
> +
> +/*
> + * Manage ulogd's pidfile.
> + *
> + * This function is based on atd's daemon.c:daemon_setup() function, published
> + * under the GPL2+ license with the following copyright statement:
> + * Copyright (C) 1996 Thomas Koenig
> + */
> +static int write_pidfile()
> +{
> +	int fd;
> +	FILE *fp;
> +	pid_t pid = -1;
> +
> +	fd = open(ulogd_pidfile, O_RDWR | O_CREAT | O_EXCL, 0644);
> +	if (fd < 0) {
> +		if (errno != EEXIST) {
> +			ulogd_log(ULOGD_ERROR, "cannot open %s: %d\n",
> +					ulogd_pidfile, errno);
> +			return -1;
> +		}
> +
> +		fd = open(ulogd_pidfile, O_RDWR);
> +		if (fd < 0) {
> +			ulogd_log(ULOGD_ERROR, "cannot open %s: %d\n",
> +					ulogd_pidfile, errno);
> +			return -1;
> +		}
> +
> +		fp = fdopen(fd, "rw");
> +		if (fp == NULL) {
> +			ulogd_log(ULOGD_ERROR, "cannot fdopen %s: %d\n",
> +					ulogd_pidfile, errno);
> +			return -1;
> +		}
> +
> +		if ((fscanf(fp, "%d", &pid) != 1) || (pid == getpid())
> +				|| (lock_fd(fd) == 0)) {
> +			ulogd_log(ULOGD_NOTICE,
> +				"removing stale pidfile for pid %d\n", pid);
> +
> +			if (unlink(ulogd_pidfile) < 0) {
> +				ulogd_log(ULOGD_ERROR, "cannot unlink %s: %d\n",
> +						ulogd_pidfile, errno);
> +				return -1;
> +			}
> +		} else {
> +			ulogd_log(ULOGD_FATAL,
> +				"another ulogd already running with pid %d\n",
> +				pid);
> +			return -1;
> +		}
> +
> +		fclose(fp);
> +		unlink(ulogd_pidfile);
> +
> +		fd = open(ulogd_pidfile, O_RDWR | O_CREAT | O_EXCL, 0644);
> +
> +		if (fd < 0) {
> +			ulogd_log(ULOGD_ERROR,
> +				"cannot open %s (2nd time round): %d\n",
> +				ulogd_pidfile, errno);
> +			return -1;
> +		}
> +	}
> +
> +	if (lock_fd(fd) < 0) {
> +		ulogd_log(ULOGD_ERROR, "cannot lock %s: %d\n", ulogd_pidfile,
> +				errno);
> +		return -1;
> +	}
> +
> +	fp = fdopen(fd, "w");
> +	if (fp == NULL) {
> +		ulogd_log(ULOGD_ERROR, "cannot fdopen %s: %d\n", ulogd_pidfile,
> +				errno);
> +		return -1;
> +	}
> +
> +	fprintf(fp, "%d\n", getpid());
> +	fflush(fp);
> +
> +	if (ftruncate(fileno(fp), ftell(fp)) < 0)
> +		ulogd_log(ULOGD_NOTICE, "cannot ftruncate %s: %d\n",
> +				ulogd_pidfile, errno);
> +
> +	/*
> +	 * We do NOT close fd, since we want to keep the lock. However, we don't
> +	 * want to keep the file descriptor in case of an exec().
> +	 */
> +	fcntl(fd, F_SETFD, FD_CLOEXEC);
> +
> +	created_pidfile = 1;
> +
> +	return 0;
> +}
> +
> +static void cleanup_pidfile()
> +{
> +	if (!ulogd_pidfile || !created_pidfile)
> +		return;
> +
> +	if (unlink(ulogd_pidfile) != 0)
> +		ulogd_log(ULOGD_ERROR, "PID file %s could not be deleted: %d\n",
> +				ulogd_pidfile, errno);
> +}
> +
>  static void deliver_signal_pluginstances(int signal)
>  {
>  	struct ulogd_pluginstance_stack *stack;
> @@ -1080,6 +1213,8 @@ static void sigterm_handler(int signal)
>  
>  	config_stop();
>  
> +	cleanup_pidfile();
> +
>  	exit(0);
>  }
>  
> @@ -1121,6 +1256,7 @@ static void print_usage(void)
>  	printf("\t-v --verbose\tOutput info on standard output\n");
>  	printf("\t-l --loglevel\tSet log level\n");
>  	printf("\t-c --configfile\tUse alternative Configfile\n");
> +	printf("\t-p --pidfile\tRecord ulogd PID in file\n");
>  	printf("\t-u --uid\tChange UID/GID\n");
>  	printf("\t-i --info\tDisplay infos about plugin\n");
>  }
> @@ -1134,6 +1270,7 @@ static struct option opts[] = {
>  	{ "info", 1, NULL, 'i' },
>  	{ "verbose", 0, NULL, 'v' },
>  	{ "loglevel", 1, NULL, 'l' },
> +	{ "pidfile", 1, NULL, 'p' },
>  	{NULL, 0, NULL, 0}
>  };
>  
> @@ -1150,7 +1287,7 @@ int main(int argc, char* argv[])
>  
>  	ulogd_logfile = strdup(ULOGD_LOGFILE_DEFAULT);
>  
> -	while ((argch = getopt_long(argc, argv, "c:dvl:h::Vu:i:", opts, NULL)) != -1) {
> +	while ((argch = getopt_long(argc, argv, "c:p:dvl:h::Vu:i:", opts, NULL)) != -1) {
>  		switch (argch) {
>  		default:
>  		case '?':
> @@ -1179,6 +1316,9 @@ int main(int argc, char* argv[])
>  		case 'c':
>  			ulogd_configfile = optarg;
>  			break;
> +		case 'p':
> +			ulogd_pidfile = optarg;
> +			break;
>  		case 'u':
>  			change_uid = 1;
>  			user = strdup(optarg);
> @@ -1280,6 +1420,11 @@ int main(int argc, char* argv[])
>  		setsid();
>  	}
>  
> +	if (ulogd_pidfile) {
> +		if (write_pidfile() < 0)
> +			warn_and_exit(daemonize);
> +	}
> +
>  	signal(SIGTERM, &sigterm_handler);
>  	signal(SIGINT, &sigterm_handler);
>  	signal(SIGHUP, &signal_handler);
> diff --git a/ulogd.8 b/ulogd.8
> index 9cbad7c..9d16aeb 100644
> --- a/ulogd.8
> +++ b/ulogd.8
> @@ -57,6 +57,9 @@ change UID/GID
>  .TP
>  .B -i <pluginpath>, --info <pluginpath>
>  display infos about plugin
> +.TP
> +.B -p <filename>, --pidfile <filename>
> +record the ulogd process ID to the given file name
>  .SH FILES
>  .I /etc/ulogd.conf
>  .br

Hi folks,

Any comments about my revised patch? Is this likely to be taken up into
ulogd?

Cheers,
Chris

Hi,

Le vendredi 17 mai 2013 à 08:33 +0100, Chris Boot a écrit :
> On 12/05/13 13:47, Chris Boot wrote:
> > The deamon currently does not have the ability to write a PID file to track its
> > process ID. This is very useful to an init script and to ensure there is only
> > one running instance. This patch implements this functionality.
> >
> > Signed-off-by: Chris Boot <bootc@bootc.net>

I've applied this patch to my tree and made incremental modification to
fix some issues as explained in the upcoming patch.

BR,
--
Eric