init: add re-exec capability

This will allow the re-execution of the init process after upgrading
OpenRC.

man/openrc-shutdown.8

@@ -19,11 +19,13 @@
 .Op Fl H , -halt
 .Op Fl k , -kexec
 .Op Fl p , -poweroff
+.Op Fl R , -reexec
 .Op Fl r , -reboot
 .Sh DESCRIPTION
 .Nm
 is the utility that communicates with openrc-init(8) to bring down the
-system.  The following options affect how the system is brought down:
+system or instruct openrc-init to re-execute itself. It supports the
+following options:
 .Bl -tag -width "poweroff"
 .It Fl H , -halt
 Stop all services, kill all remaining processes and halt the system.
@@ -32,6 +34,9 @@ Stop all services, kill all processes and boot directly into a new
 kernel loaded via kexec(8).
 .It Fl p , -poweroff
 Stop all services, kill all processes and power off the system.
+.It Fl R , -reexec
+instruct openrc-init to re-exec itself. This should be used after an
+upgrade of OpenRC if you are using openrc-init as your init process.
 .It Fl r , -reboot
 Stop all services, kill all processes and reboot the system.
 .El

src/rc/openrc-init.c

@@ -20,6 +20,7 @@
 
 #include <errno.h>
 #include <signal.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -79,6 +80,12 @@ static void init(const char *default_runlevel)
 	waitpid(pid, NULL, 0);
 }
 
+static void handle_reexec(char *my_name)
+{
+	execl(my_name, my_name, "reexec", NULL);
+	return;
+}
+
 static void handle_shutdown(const char *runlevel, int cmd)
 {
 	pid_t pid;
@@ -123,10 +130,11 @@ static void signal_handler(int sig)
 
 int main(int argc, char **argv)
 {
-	char *default_runlevel = NULL;
+	char *default_runlevel;
 	char buf[2048];
 	int count;
 	FILE *fifo;
+	bool reexec = false;
 	struct sigaction sa;
 
 	if (getpid() != 1)
@@ -134,16 +142,22 @@ int main(int argc, char **argv)
 
 	if (argc > 1)
 		default_runlevel = argv[1];
+	else
+		default_runlevel = NULL;
+
+	if (default_runlevel && strcmp(default_runlevel, "reexec") == 0)
+		reexec = true;
 
 	printf("OpenRC init version %s starting\n", VERSION);
-	init(default_runlevel);
+	if (! reexec)
+		init(default_runlevel);
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = signal_handler;
 	sigaction(SIGCHLD, &sa, NULL);
 	sigaction(SIGINT, &sa, NULL);
 	reboot(RB_DISABLE_CAD);
 
-	if (mkfifo(RC_INIT_FIFO, 0600) == -1)
+	if (mkfifo(RC_INIT_FIFO, 0600) == -1 && errno != EEXIST)
 		perror("mkfifo");
 
 	for (;;) {
@@ -166,6 +180,8 @@ int main(int argc, char **argv)
 			handle_shutdown("shutdown", RB_POWER_OFF);
 		else if (strcmp(buf, "reboot") == 0)
 			handle_shutdown("reboot", RB_AUTOBOOT);
+		else if (strcmp(buf, "reexec") == 0)
+			handle_reexec(argv[0]);
 	}
 	return 0;
 }

src/rc/openrc-shutdown.c

@@ -35,11 +35,12 @@
 
 const char *applet = NULL;
 const char *extraopts = NULL;
-const char *getoptstring = "kpr" getoptstring_COMMON;
+const char *getoptstring = "HkpRr" getoptstring_COMMON;
 const struct option longopts[] = {
 	{ "halt",        no_argument, NULL, 'H'},
 	{ "kexec",        no_argument, NULL, 'k'},
 	{ "poweroff",        no_argument, NULL, 'p'},
+	{ "reexec",        no_argument, NULL, 'R'},
 	{ "reboot",        no_argument, NULL, 'r'},
 	longopts_COMMON
 };
@@ -47,11 +48,13 @@ const char * const longopts_help[] = {
 	"halt the system",
 	"reboot the system using kexec",
 	"power off the system",
+	"re-execute init (use after upgrading)",
 	"reboot the system",
 	longopts_help_COMMON
 };
 const char *usagestring = NULL;
-const char *exclusive = "Select one of --halt, --kexec, --poweroff or --reboot";
+const char *exclusive = "Select one of "
+"--halt, --kexec, --poweroff, --reexec or --reboot";
 
 static void send_cmd(const char *cmd)
 {
@@ -79,6 +82,7 @@ int main(int argc, char **argv)
 	bool do_kexec = false;
 	bool do_poweroff = false;
 	bool do_reboot = false;
+	bool do_reexec = false;
 
 	applet = basename_c(argv[0]);
 if (geteuid() != 0)
@@ -99,6 +103,10 @@ if (geteuid() != 0)
 			do_poweroff = true;
 			cmd_count++;
 			break;
+		case 'R':
+			do_reexec = true;
+			cmd_count++;
+			break;
 		case 'r':
 			do_reboot = true;
 			cmd_count++;
@@ -118,5 +126,7 @@ if (geteuid() != 0)
 		send_cmd("poweroff");
 	else if (do_reboot)
 		send_cmd("reboot");
+	else if (do_reexec)
+		send_cmd("reexec");
 	return 0;
 }