From 9606d987722ee5b89bbfae230389d3385a3884b0 Mon Sep 17 00:00:00 2001
From: David Oberhollenzer <goliath@infraroot.at>
Date: Thu, 14 May 2020 17:49:44 +0200
Subject: Replace standard signal handling in initd with signalfd + epoll

Signed-off-by: David Oberhollenzer <goliath@infraroot.at>
---
 initd/init.h   |  2 ++
 initd/main.c   | 65 ++++++++++++++++++++++++++++++++++++++++++++++------------
 initd/runsvc.c | 17 +++++----------
 3 files changed, 59 insertions(+), 25 deletions(-)

diff --git a/initd/init.h b/initd/init.h
index 5618ccd..5ac6d22 100644
--- a/initd/init.h
+++ b/initd/init.h
@@ -16,7 +16,9 @@
 #include <poll.h>
 
 #include <linux/reboot.h>
+#include <sys/signalfd.h>
 #include <sys/reboot.h>
+#include <sys/epoll.h>
 #include <sys/prctl.h>
 #include <stdbool.h>
 #include <signal.h>
diff --git a/initd/main.c b/initd/main.c
index d92a823..9c4bf78 100644
--- a/initd/main.c
+++ b/initd/main.c
@@ -58,13 +58,17 @@ static void start_service(svc_run_data_t *rt)
 	print_status(rt);
 }
 
-static void handle_signal(int signo)
+static void handle_signal(int fd)
 {
+	struct signalfd_siginfo info;
 	svc_run_data_t *rt;
 	int status;
 	pid_t pid;
 
-	switch (signo) {
+	if (read(fd, &info, sizeof(info)) < (ssize_t)sizeof(info))
+		return;
+
+	switch (info.ssi_signo) {
 	case SIGTERM:
 		config_set_target(TGT_SHUTDOWN);
 		break;
@@ -96,20 +100,43 @@ static void handle_signal(int signo)
 
 int main(void)
 {
+	struct epoll_event ev;
 	svc_run_data_t *rt;
-	struct sigaction act;
+	int ret, sfd, epfd;
+	sigset_t sigmask;
+
+	cli(NULL);
 
 	if (config_load())
 		return EXIT_FAILURE;
 
-	memset(&act, 0, sizeof(act));
-	act.sa_handler = handle_signal;
+	epfd = epoll_create1(EPOLL_CLOEXEC);
+	if (epfd < 0) {
+		perror("epoll_create");
+		return EXIT_FAILURE;
+	}
 
-	sigaction(SIGTERM, &act, NULL);
-	sigaction(SIGINT, &act, NULL);
-	sigaction(SIGHUP, &act, NULL);
-	sigaction(SIGUSR1, &act, NULL);
-	sigaction(SIGCHLD, &act, NULL);
+	sigemptyset(&sigmask);
+	sigaddset(&sigmask, SIGTERM);
+	sigaddset(&sigmask, SIGINT);
+	sigaddset(&sigmask, SIGHUP);
+	sigaddset(&sigmask, SIGUSR1);
+	sigaddset(&sigmask, SIGCHLD);
+
+	sfd = signalfd(-1, &sigmask, SFD_CLOEXEC);
+	if (sfd < 0) {
+		perror("signalfd");
+		return EXIT_FAILURE;
+	}
+
+	memset(&ev, 0, sizeof(ev));
+	ev.events = EPOLLIN;
+	ev.data.fd = sfd;
+
+	if (epoll_ctl(epfd, EPOLL_CTL_ADD, sfd, &ev)) {
+		perror("adding signalfd to epoll");
+		return EXIT_FAILURE;
+	}
 
 	if (reboot(LINUX_REBOOT_CMD_CAD_OFF))
 		perror("cannot disable CTRL+ALT+DEL");
@@ -117,10 +144,22 @@ int main(void)
 	for (;;) {
 		rt = config_dequeue();
 
-		if (rt == NULL) {
-			pause();
-		} else {
+		if (rt != NULL) {
 			start_service(rt);
+			continue;
+		}
+
+		ret = epoll_wait(epfd, &ev, 1, -1);
+		if (ret == 0)
+			continue;
+
+		if (ret < 0) {
+			perror("epoll wait");
+			return EXIT_FAILURE;
+		}
+
+		if (ev.data.fd == sfd) {
+			handle_signal(sfd);
 		}
 	}
 
diff --git a/initd/runsvc.c b/initd/runsvc.c
index 5495f15..682f4c6 100644
--- a/initd/runsvc.c
+++ b/initd/runsvc.c
@@ -195,18 +195,6 @@ pid_t runsvc(service_t *svc)
 		perror("fork");
 
 	if (pid == 0) {
-		cli(NULL);
-
-		memset(&act, 0, sizeof(act));
-		act.sa_handler = runsvc_sighandler;
-		sigaction(SIGTERM, &act, NULL);
-		sigaction(SIGINT, &act, NULL);
-		sigaction(SIGHUP, &act, NULL);
-
-		act.sa_handler = SIG_DFL;
-		sigaction(SIGUSR1, &act, NULL);
-		sigaction(SIGCHLD, &act, NULL);
-
 		if (setup_env())
 			exit(EXIT_FAILURE);
 
@@ -218,6 +206,11 @@ pid_t runsvc(service_t *svc)
 			exit(EXIT_FAILURE);
 		}
 
+		memset(&act, 0, sizeof(act));
+		act.sa_handler = runsvc_sighandler;
+		sigaction(SIGTERM, &act, NULL);
+		sigaction(SIGINT, &act, NULL);
+		sigaction(SIGHUP, &act, NULL);
 		sti(NULL);
 
 		if (svc->flags & SVC_FLAG_SUB_REAPER) {
-- 
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