Add logic for writing a pidfile on startup

The systemd service really wants a pidfile for a 'forking' daemon, so
add the '--pidfile/-P' option to specify a path and add logic to
write the pid after we've finished configuring. Added the option
to the systemd service file as well.

Signed-off-by: Clark Williams <williams@redhat.com>

5 files changed, 44 insertions, 8 deletions

diff --git a/Makefile b/Makefile
index cf4879a..b5c2d76 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 NAME	:= starvation_monitor
-VERSION	:= 0.1
+VERSION	:= 0.2
 
 
 INSTALL=install
diff --git a/redhat/starvation_monitor.conf b/redhat/starvation_monitor.conf
index 9e256bf..8d9753d 100644
--- a/redhat/starvation_monitor.conf
+++ b/redhat/starvation_monitor.conf
@@ -42,3 +42,7 @@ LOGGING=
 # ex: FG=--foreground
 # note: when using this should change the service Type to be simple
 FG=
+
+# Write a pidfile
+# ex: PF=--pidfile /run/starvation_monitor.pid
+PF="--pidfile /run/starvation_monitor.pid"
diff --git a/redhat/starvation_monitor.service b/redhat/starvation_monitor.service
index d20f871..fced98e 100644
--- a/redhat/starvation_monitor.service
+++ b/redhat/starvation_monitor.service
@@ -5,7 +5,7 @@ Description=Starvation Monitor
 # Type=simple
 Type=forking
 EnvironmentFile=/etc/systemd/starvation_monitor.conf
-ExecStart=/usr/bin/starvation_monitor $CLIST $AGGR $BP $BR $BD $THRESH $LOGGING $FG
+ExecStart=/usr/bin/starvation_monitor $CLIST $AGGR $BP $BR $BD $THRESH $LOGGING $FG $PF
 
 [Install]
 WantedBy=multi-user.target
diff --git a/redhat/starvation_monitor.spec b/redhat/starvation_monitor.spec
index 33aab67..fc05903 100644
--- a/redhat/starvation_monitor.spec
+++ b/redhat/starvation_monitor.spec
@@ -1,5 +1,5 @@
 Name:		starvation_monitor
-Version:	0.1
+Version:	0.2
 Release:	1%{?dist}
 Summary:	daemon that finds starving tasks and gives them a temporary boost
 
@@ -38,11 +38,14 @@ make DESTDIR=$RPM_BUILD_ROOT -C redhat install
 
 
 %changelog
-* Thu Aug 20 2020 williams@redhat.com
+* Fri Aug 21 2020 williams@redhat.com - 0.2-1
+- add pidfile logic
+
+* Thu Aug 20 2020 williams@redhat.com - 0.1-1
 - Added systemd service to redhat subdirectory
 - added make and rpm logic for systemd files
 
-* Wed Aug 19 2020 williams@redhat.com
+* Wed Aug 19 2020 williams@redhat.com - 0.0-1
 - initial version of specfile
 - Makefile mods for RPM builds
 - added systemd service and config files
diff --git a/src/starvation_monitor.c b/src/starvation_monitor.c
index c312478..445484c 100644
--- a/src/starvation_monitor.c
+++ b/src/starvation_monitor.c
@@ -4,7 +4,7 @@
  * This program was born after Daniel and Juri started debugging once again
  * problems caused kernel threads starving due to busy-loop sched FIFO threads.
  *
- * The idea is simple: after detecting a thread starving on a given CPU for a 
+ * The idea is simple: after detecting a thread starving on a given CPU for a
  * given period, this thread will receive a "bounded" chance to run, using
  * SCHED_DEADLINE. In this way, the starving thread is able to make progress
  * causing a bounded Operating System noise (OS Noise).
@@ -121,6 +121,11 @@ int config_monitor_all_cpus = 1;
 char *config_monitored_cpus;
 
 
+/*
+ * path to file for storing daemon pid
+ */
+char pidfile[MAXPATHLEN];
+
 void log_msg(const char *fmt, ...)
 {
 	const char *log_prefix = "starvation_monitor: ";
@@ -185,6 +190,19 @@ void die(const char *fmt, ...)
 	exit(ret);
 }
 
+void write_pidfile(void)
+{
+	FILE *f = fopen(pidfile, "w");
+	if (f != NULL) {
+		fprintf(f, "%d", getpid());
+		fclose(f);
+	}
+	else
+		die("unable to open pidfile %s: %s\n", pidfile, strerror(errno));
+}
+
+
+
 /*
  * Based on:
  * https://github.com/pasce/daemon-skeleton-linux-c
@@ -496,7 +514,7 @@ long get_variable_long_value(char *buffer, const char *variable)
 	return get_long_after_colon(start);
 }
 
-/* 
+/*
  * Example:
  * ' S           task   PID         tree-key  switches  prio     wait-time             sum-exec        sum-sleep'
  * '-----------------------------------------------------------------------------------------------------------'
@@ -662,7 +680,7 @@ int boost_starving_task(int pid)
 	struct sched_attr new_attr;
 	struct sched_attr old_attr;
 
-	memset(&new_attr, 0, sizeof(new_attr)); 
+	memset(&new_attr, 0, sizeof(new_attr));
 	new_attr.size = sizeof(new_attr);
 	new_attr.sched_policy   = SCHED_DEADLINE;
 	new_attr.sched_runtime  = config_dl_runtime;
@@ -794,6 +812,7 @@ void print_usage(void)
 		"          -A/--aggressive_mode: dispatch one thread per run queue, even when there is no starving",
 		"                               threads on all CPU (uses more CPU/power).",
 		"	misc:",
+		"          --pidfile: write daemon pid to specified file",
 		"          -h/--help: print this menu",
 		NULL,
 	};
@@ -883,6 +902,9 @@ int parse_args(int argc, char **argv)
 {
 	int c;
 
+	/* ensure the pidfile is an empty string */
+	pidfile[0] = '\0';
+
 	while (1) {
 		static struct option long_options[] = {
 			{"cpu",			required_argument, 0, 'c'},
@@ -897,6 +919,7 @@ int parse_args(int argc, char **argv)
 			{"boost_runtime",	required_argument, 0, 'r'},
 			{"boost_duration",	required_argument, 0, 'd'},
 			{"starving_threshold",	required_argument, 0, 't'},
+			{"pidfile",             required_argument, 0, 'P'},
 			{0, 0, 0, 0}
 		};
 
@@ -970,6 +993,9 @@ int parse_args(int argc, char **argv)
 			print_usage();
 			exit(EXIT_SUCCESS);
 			break;
+		case 'P':
+			strncpy(pidfile, optarg, sizeof(pidfile)-1);
+			break;
 		case '?':
 			usage("Invalid option");
 			break;
@@ -1134,6 +1160,9 @@ int main(int argc, char **argv)
 	if (!config_foreground)
 		deamonize();
 
+	if (strlen(pidfile) > 0)
+		write_pidfile();
+
 	if (config_aggressive)
 		aggressive_main(cpus, nr_cpus);
 	else