From 78ea3f31e616b9da05f8bd61b550abed92f678d9 Mon Sep 17 00:00:00 2001
From: Mattias Andrée <maandree@kth.se>
Date: Sat, 24 Feb 2024 20:33:55 +0100
Subject: Add support for SIGHUP
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Signed-off-by: Mattias Andrée <maandree@kth.se>
---
 Makefile     |  3 ++-
 config.mk    | 18 +++++++++++-------
 coreupdown.c | 48 ++++++++++++++++++++++++++++++++++++++----------
 3 files changed, 51 insertions(+), 18 deletions(-)

diff --git a/Makefile b/Makefile
index f9850e0..63eedf7 100644
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,8 @@ CPPFLAGS_CONFS =\
 	-D'COREDOWN_THRESHOLD_TIME=$(COREDOWN_THRESHOLD_TIME)'\
 	-D'COREDOWN_COOLDOWN=$(COREDOWN_COOLDOWN)'\
 	-D'DAEMON_INTERVAL_SEC=$(DAEMON_INTERVAL_SEC)'\
-	-D'DAEMON_INTERVAL_NSEC=$(DAEMON_INTERVAL_NSEC)'
+	-D'DAEMON_INTERVAL_NSEC=$(DAEMON_INTERVAL_NSEC)'\
+	-D'DAEMON_PATH="$(PREFIX)/bin/coreupdownd"'
 
 OBJ =\
 	coreupdown.o
diff --git a/config.mk b/config.mk
index f833645..01bd595 100644
--- a/config.mk
+++ b/config.mk
@@ -1,14 +1,18 @@
 PREFIX    = /usr
 MANPREFIX = $(PREFIX)/share/man
+# It is important that PREFIX is properly set when building, not just installing
 
-COREUP_THRESHOLD_CPU = 95
-COREUP_THRESHOLD_TIME = 2
-COREUP_COOLDOWN = 4
-COREDOWN_THRESHOLD_CPU = 50
+# In percent of one CPU (integer)
+COREUP_THRESHOLD_CPU    = 95
+COREDOWN_THRESHOLD_CPU  = 50
+# In multiples of the update interval (integer)
+COREUP_THRESHOLD_TIME   = 2
 COREDOWN_THRESHOLD_TIME = 2
-COREDOWN_COOLDOWN = 4
-DAEMON_INTERVAL_SEC = 1
-DAEMON_INTERVAL_NSEC = 0
+COREUP_COOLDOWN         = 4
+COREDOWN_COOLDOWN       = 4
+# Update interval (integer)
+DAEMON_INTERVAL_SEC     = 1
+DAEMON_INTERVAL_NSEC    = 0
 
 CC = c99
 
diff --git a/coreupdown.c b/coreupdown.c
index 403bdf6..70015ec 100644
--- a/coreupdown.c
+++ b/coreupdown.c
@@ -3,6 +3,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
+#include <signal.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -11,6 +12,7 @@
 #include <unistd.h>
 
 static const char *argv0;
+static volatile sig_atomic_t caught_sighup = 0;
 
 #define coreup() coreupdown(ULONG_MAX)
 #define coredown() coreupdown(1)
@@ -226,14 +228,25 @@ line_done:
 #undef IDLE_FIELD
 }
 
+static void
+sighup_handler(int signo)
+{
+	(void) signo;
+	caught_sighup = 1;
+}
+
 static int
-daemon_main(int argc, char **argv)
+daemon_main(int argc, char **argv, int orig_argc, char **orig_argv, int reexeced)
 {
 	uintmax_t total, idle;
 	size_t cpus;
-	int up_time = 0, down_time = 0, cooldown = 0;
+	int up_time = 0, down_time = 0, cooldown = 0, err;
 	struct timespec interval, rem;
 
+restart:
+	if (reexeced)
+		argv[0] = "coreupdownd";
+
 	if (argc && !strcmp(argv[0], "--")) {
 		argv++;
 		argc--;
@@ -244,11 +257,14 @@ daemon_main(int argc, char **argv)
 		return 1;
 	}
 
-	/* TODO configurations should be configurable */
+	if (!reexeced) {
+		/* TODO add proper daemonisation */
+	}
 
-	/* TODO add SIGHUP support */
+	/* TODO configurations should be configurable */
 
-	/* TODO add proper daemonisation */
+	if (signal(SIGHUP, sighup_handler) == SIG_ERR)
+		fprintf(stderr, "%s: signal SIGHUP <function>: %s\n", argv0, strerror(errno));
 
 	interval.tv_sec = DAEMON_INTERVAL_SEC;
 	interval.tv_nsec = DAEMON_INTERVAL_NSEC;
@@ -260,16 +276,26 @@ daemon_main(int argc, char **argv)
 	close(STDOUT_FILENO);
 
 	for (;;) {
-		if (clock_nanosleep(CLOCK_REALTIME /* = monotonic */, 0, &interval, &rem)) {
+		if (caught_sighup) {
+			caught_sighup = 0;
+			orig_argv[0] = "coreupdownd ";
+			execv(DAEMON_PATH, orig_argv);
+			fprintf(stderr, "%s: execv %s: %s\n", argv0, DAEMON_PATH, strerror(errno));
+			reexeced = 1;
+			argv = &orig_argv[1];
+			argc = orig_argc - 1;
+			goto restart;
+		}
+
+		if ((err = clock_nanosleep(CLOCK_REALTIME /* = monotonic */, 0, &interval, &rem))) {
 			do {
-				if (errno != EINTR) {
+				if (err != EINTR) {
 					fprintf(stderr, "%s: clock_nanosleep CLOCK_REALTIME: %s\n",
 					        argv0, strerror(errno));
 					return 1;
 				}
-			} while (clock_nanosleep(CLOCK_REALTIME, 0, &rem, &rem));
+			} while ((err = clock_nanosleep(CLOCK_REALTIME, 0, &rem, &rem)));
 		}
-		sleep(1);
 		if (getusage(&total, &idle, &cpus))
 			return 1;
 		if (cooldown) {
@@ -313,7 +339,9 @@ main(int argc, char **argv)
 		if (!strcmp(command, "coredown"))
 			return oneshot_main(argc, argv, 1);
 		if (!strcmp(command, "coreupdownd"))
-			return daemon_main(argc, argv);
+			return daemon_main(argc, argv, argc + 1, &argv[-1], 0);
+		if (!strcmp(command, "coreupdownd "))
+			return daemon_main(argc, argv, argc + 1, &argv[-1], 1);
 	}
 
 	fprintf(stderr, "usage: coreup [count]\n"
-- 
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