From 8194f460daaa9343ce9863838b14132d0ad8037c Mon Sep 17 00:00:00 2001
From: sin <sin@2f30.org>
Date: Fri, 7 Feb 2014 12:47:15 +0000
Subject: Refactor code

We no longer have two processes, one for reaping children and
another for handling the FIFO.

Use signalfd() to multiplex signal handling and reading from the
FIFO.

This setup will also allow us to capture ctrl-alt-del and to work
with a read-only rootfs.

To create the FIFO, we send a SIGHUP signal to init from our init
scripts.
---
 config.def.h |   2 -
 sinit.c      | 123 +++++++++++++++++++++++++++++++++++++++++------------------
 2 files changed, 86 insertions(+), 39 deletions(-)

diff --git a/config.def.h b/config.def.h
index ac9cf9b..9bfe505 100644
--- a/config.def.h
+++ b/config.def.h
@@ -1,8 +1,6 @@
 /* See LICENSE file for copyright and license details. */
 
 static const char *rcinitcmd[] = { "/bin/rc.init", NULL };
-static Arg rcinitarg = { .v = rcinitcmd };
-
 static const char *rcrebootcmd[] = { "/bin/rc.shutdown", "reboot", NULL };
 static const char *rcpoweroffcmd[] = { "/bin/rc.shutdown", "poweroff", NULL };
 
diff --git a/sinit.c b/sinit.c
index 3942457..14ee7ca 100644
--- a/sinit.c
+++ b/sinit.c
@@ -7,6 +7,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/select.h>
+#include <sys/signalfd.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
@@ -23,57 +24,78 @@ typedef struct {
         const Arg arg;
 } Command;
 
+volatile sig_atomic_t signum;
+
+typedef struct {
+	int sig;
+	void (*func)(void);
+} Sigmap;
+
 static void dispatchcmd(int);
+static void sigfifo(void);
+static void sigreap(void);
+static void sigreboot(void);
 static void spawn(const Arg *);
 
+static Sigmap dispatchsig[] = {
+	{ SIGHUP,  sigfifo   },
+	{ SIGCHLD, sigreap   },
+	{ SIGINT,  sigreboot },
+};
+
+static int sigfd = -1;
+static int fifofd = -1;
+
 #include "config.h"
 
 int
 main(void)
 {
-	sigset_t set;
-	pid_t pid;
+	struct signalfd_siginfo siginfo;
+	sigset_t sigset;
+	int maxfd, i, ret;
+	ssize_t n;
 	fd_set rfds;
-	int status, fd, n;
 
 	if (getpid() != 1)
 		return EXIT_FAILURE;
 	setsid();
 
-	sigfillset(&set);
-	sigprocmask(SIG_BLOCK, &set, 0);
-
-	pid = fork();
-	if (pid < 0)
-		return EXIT_FAILURE;
-	if (pid > 0)
-		for (;;)
-			wait(&status);
-
-	sigprocmask(SIG_UNBLOCK, &set, 0);
-
-	spawn(&rcinitarg);
-
-	if (!fifopath)
-		return EXIT_SUCCESS;
-
-	unlink(fifopath);
-	umask(0);
-	if (mkfifo(fifopath, 0600) < 0)
-		weprintf("sinit: mkfifo %s:", fifopath);
-
-	fd = open(fifopath, O_RDWR | O_NONBLOCK);
-	if (fd < 0)
-		weprintf("sinit: open %s:", fifopath);
-	if (fd >= 0) {
-		while (1) {
-			FD_ZERO(&rfds);
-			FD_SET(fd, &rfds);
-			n = select(fd + 1, &rfds, NULL, NULL, NULL);
-			if (n < 0)
-				eprintf("sinit: select:");
-			if (FD_ISSET(fd, &rfds))
-				dispatchcmd(fd);
+	sigemptyset(&sigset);
+	for (i = 0; i < LEN(dispatchsig); i++)
+		sigaddset(&sigset, dispatchsig[i].sig);
+	sigprocmask(SIG_BLOCK, &sigset, NULL);
+
+	sigfd = signalfd(-1, &sigset, 0);
+	if (sigfd < 0)
+		eprintf("sinit: signalfd:");
+
+	spawn(&(Arg){ .v = rcinitcmd });
+
+	while (1) {
+		FD_ZERO(&rfds);
+		FD_SET(sigfd, &rfds);
+		maxfd = sigfd;
+		if (fifofd != -1) {
+			FD_SET(fifofd, &rfds);
+			if (fifofd > maxfd)
+				maxfd = fifofd;
+		}
+		ret = select(maxfd + 1, &rfds, NULL, NULL, NULL);
+		if (ret < 0)
+			eprintf("sinit: select:");
+		if (ret > 0) {
+			if (FD_ISSET(sigfd, &rfds)) {
+				n = read(sigfd, &siginfo, sizeof(siginfo));
+				if (n <= 0)
+					continue;
+				for (i = 0; i < LEN(dispatchsig); i++)
+					if (dispatchsig[i].sig == siginfo.ssi_signo)
+						dispatchsig[i].func();
+			}
+			if (fifofd != -1)
+				if (FD_ISSET(fifofd, &rfds))
+					dispatchcmd(fifofd);
 		}
 	}
 
@@ -102,6 +124,33 @@ dispatchcmd(int fd)
 	}
 }
 
+static void
+sigfifo(void)
+{
+	if (!fifopath)
+		return;
+	unlink(fifopath);
+	umask(0);
+	if (mkfifo(fifopath, 0600) < 0)
+		weprintf("sinit: mkfifo %s:", fifopath);
+	fifofd = open(fifopath, O_RDWR | O_NONBLOCK);
+	if (fifofd < 0)
+		weprintf("sinit: open %s:", fifopath);
+}
+
+static void
+sigreap(void)
+{
+	while (waitpid(-1, NULL, WNOHANG) > 0)
+		;
+}
+
+static void
+sigreboot(void)
+{
+	spawn(&(Arg){ .v = rcrebootcmd });
+}
+
 static void
 spawn(const Arg *arg)
 {
-- 
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