Make init(8) slightly more robust when /dev/console is missing.

If the environment doesn't offer a working /dev/console, the existing
version of init(8) will simply refuse running rc(8) scripts. This means
you'll only have a system running init(8) and nothing else.

Change the code to do the following:

- Open /dev/console like we used to do, but make it more robust to use
  O_NONBLOCK to prevent blocking on a carrier.
- If this fails, use /dev/null as stdin and /var/log/init.log as stdout
  and stderr.
- If even this fails, use /dev/null as stdin, stdout and stderr.

So why us this useful? Well, if you remove the `getpid() == 1' check in
main(), you can now use init(8) inside jails to properly execute rc(8).
It still requires some polishing, as existing tools assume init(8) has
PID 1.

Also it is now possible to use use init(8) on `headless' devices that
don't even have a serial boot console.

etc/newsyslog.conf

@@ -24,6 +24,7 @@
 /var/log/cron				600  3	   100	*     JC
 /var/log/daily.log			640  7	   *	@T00  JN
 /var/log/debug.log			600  7     100  *     JC
+/var/log/init.log			644  3	   100	*     J
 /var/log/kerberos.log			600  7	   100	*     J
 /var/log/lpd-errs			644  7	   100	*     JC
 /var/log/maillog			640  7	   *	@T00  JC

sbin/init/init.8

@@ -31,7 +31,7 @@
 .\"     @(#)init.8	8.3 (Berkeley) 4/18/94
 .\" $FreeBSD$
 .\"
-.Dd February 11, 2012
+.Dd March 14, 2012
 .Dt INIT 8
 .Os
 .Sh NAME
@@ -293,22 +293,22 @@ as follows:
 file
 .El
 .Sh FILES
-.Bl -tag -width /etc/rc.shutdown -compact
+.Bl -tag -width /var/log/init.log -compact
 .It Pa /dev/console
 system console device
 .It Pa /dev/tty*
 terminal ports found in
 .Xr ttys 5
-.It Pa /var/run/utx.active
-record of current users on the system
-.It Pa /var/log/utx.log
-record of all logins and logouts
 .It Pa /etc/ttys
 the terminal initialization information file
 .It Pa /etc/rc
 system startup commands
 .It Pa /etc/rc.shutdown
 system shutdown commands
+.It Pa /var/log/init.log
+log of
+.Xr rc 8
+output if the system console device is not available
 .El
 .Sh DIAGNOSTICS
 .Bl -diag

sbin/init/init.c

@@ -138,7 +138,7 @@ static void transition(state_t);
 static state_t requested_transition;
 static state_t current_state = death_single;
 
-static void setctty(const char *);
+static void open_console(void);
 static const char *get_shell(void);
 static void write_stderr(const char *message);
 
@@ -568,19 +568,35 @@ transition(state_t s)
  * Only called by children of init after forking.
  */
 static void
-setctty(const char *name)
+open_console(void)
 {
 	int fd;
 
-	revoke(name);
-	if ((fd = open(name, O_RDWR)) == -1) {
-		stall("can't open %s: %m", name);
+	/* Try to open /dev/console. */
+	revoke(_PATH_CONSOLE);
+	if ((fd = open(_PATH_CONSOLE, O_RDWR | O_NONBLOCK)) != -1) {
+		if (login_tty(fd) == 0)
+			return;
+		close(fd);
+	}
+
+	/* No luck.  Log output to file if possible. */
+	if ((fd = open(_PATH_DEVNULL, O_RDWR)) == -1) {
+		stall("cannot open null device.");
 		_exit(1);
 	}
-	if (login_tty(fd) == -1) {
-		stall("can't get %s for controlling terminal: %m", name);
-		_exit(1);
+	if (fd != STDIN_FILENO) {
+		dup2(fd, STDIN_FILENO);
+		close(fd);
 	}
+	fd = open(_PATH_INITLOG, O_WRONLY | O_APPEND | O_CREAT, 0644);
+	if (fd == -1)
+		dup2(STDIN_FILENO, STDOUT_FILENO);
+	else if (fd != STDOUT_FILENO) {
+		dup2(fd, STDOUT_FILENO);
+		close(fd);
+	}
+	dup2(STDOUT_FILENO, STDERR_FILENO);
 }
 
 static const char *
@@ -638,7 +654,7 @@ single_user(void)
 		/*
 		 * Start the single user session.
 		 */
-		setctty(_PATH_CONSOLE);
+		open_console();
 
 #ifdef SECURE
 		/*
@@ -798,7 +814,7 @@ run_script(const char *script)
 		sigaction(SIGTSTP, &sa, (struct sigaction *)0);
 		sigaction(SIGHUP, &sa, (struct sigaction *)0);
 
-		setctty(_PATH_CONSOLE);
+		open_console();
 
 		char _sh[]		= "sh";
 		char _autoboot[]	= "autoboot";
@@ -1572,7 +1588,7 @@ runshutdown(void)
 		sigaction(SIGTSTP, &sa, (struct sigaction *)0);
 		sigaction(SIGHUP, &sa, (struct sigaction *)0);
 
-		setctty(_PATH_CONSOLE);
+		open_console();
 
 		char _sh[]	= "sh";
 		char _reboot[]	= "reboot";

sbin/init/pathnames.h

@@ -35,6 +35,7 @@
 
 #include <paths.h>
 
+#define	_PATH_INITLOG	"/var/log/init.log"
 #define	_PATH_SLOGGER	"/sbin/session_logger"
 #define	_PATH_RUNCOM	"/etc/rc"
 #define _PATH_RUNDOWN   "/etc/rc.shutdown"