Refactor fallback shell handling, run as regular service

This patch re-enables the fallback shell handling after the big TTY
refactor.  We do this by allowing the fallback shell to run as a
regular service.

Note: this also adds the "hidden" support for 'notty' option for
      tty configurations stanzas.  This is just to pick up from
      where the kernel left us, reusing stdin + stdout.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/conf.c

@@ -737,6 +737,10 @@ int conf_reload(void)
 
 	globfree(&gl);
 
+	/* Verify config, do we have at least one TTY available? */
+	if (tty_fallback(FINIT_CONF))
+		logit(LOG_WARNING, "warning, no getty enabled on local TTYs.");
+
 	/* Mark any reverse deps as chenaged. */
 	service_update_rdeps();
 

src/service.c

@@ -1248,6 +1248,7 @@ int service_register(int type, char *cfg, struct rlimit rlimit[], char *file)
 		svc->noclear = tty.noclear;
 		svc->nowait  = tty.nowait;
 		svc->nologin = tty.nologin;
+		svc->notty   = tty.notty;
 
 		/* TTYs cannot be redirected */
 		log = NULL;

src/svc.c

@@ -431,6 +431,10 @@ svc_t *svc_find_by_tty(char *dev)
 {
 	svc_t *svc, *iter = NULL;
 
+	/* this is valid for fallback shells */
+	if (!dev)
+		return NULL;
+
 	for (svc = svc_iterator(&iter, 1); svc; svc = svc_iterator(&iter, 0)) {
 		if (!svc_is_tty(svc))
 			continue;

src/svc.h

@@ -143,9 +143,10 @@ typedef struct svc {
 			char  dev[32];
 			char  baud[10];
 			char  term[10];
-			int   noclear;
-			int   nowait;
-			int   nologin;
+			char  noclear;
+			char  nowait;
+			char  nologin;
+			char  notty;
 		};
 	};
 

src/tty.c

@@ -35,14 +35,11 @@
 #include "finit.h"
 #include "conf.h"
 #include "helpers.h"
+#include "service.h"
 #include "tty.h"
 #include "util.h"
 #include "utmp-api.h"
 
-#ifdef FALLBACK_SHELL
-static pid_t fallback = 0;
-#endif
-
 char *tty_canonicalize(char *dev)
 {
 	static char path[80];
@@ -134,12 +131,18 @@ int tty_parse_args(char *cmd, struct tty *tty)
 			tty->nowait  = 1;
 		else if (!strcmp(cmd, "nologin"))
 			tty->nologin = 1;
+		else if (!strcmp(cmd, "notty"))
+			tty->notty = 1;	/* for fallback shell */
 		else
 			tty->args[tty->num++] = cmd;
 
 		cmd = strtok(NULL, " \t");
 	} while (cmd && tty->num < NELEMS(tty->args));
 
+	/* skip /dev probe, we just want a bríngup shell */
+	if (tty->notty)
+		return 0;
+
 	/* Iterate over all args */
 	for (i = 0; i < tty->num; i++) {
 		_d("Checking arg %s for dev and cmd ...", tty->args[i]);
@@ -214,6 +217,18 @@ int tty_exec(svc_t *tty)
 	char *dev;
 	int rc;
 
+	if (tty->notty) {
+		/*
+		 * Become session leader and set controlling TTY
+		 * to enable Ctrl-C and job control in shell.
+		 */
+		setsid();
+		ioctl(STDIN_FILENO, TIOCSCTTY, 1);
+
+		prctl(PR_SET_NAME, "finitsh", 0, 0, 0);
+		return execl(_PATH_BSHELL, _PATH_BSHELL, NULL);
+	}
+
 	dev = tty_canonicalize(tty->dev);
 	if (!dev) {
 		_d("%s: Cannot find TTY device: %s", tty->dev, strerror(errno));
@@ -243,39 +258,27 @@ int tty_exec(svc_t *tty)
 /*
  * Fallback shell if no TTYs are active
  */
-int tty_fallback(pid_t lost)
+int tty_fallback(char *file)
 {
-#ifdef FALLBACK_SHELL
-	if (lost == 1) {
-		if (fallback) {
-			kill(fallback, SIGKILL);
-			fallback = 0;
-		}
+	svc_t *svc, *iter = NULL;
+	size_t num = 0;
 
-		return 0;
+	for (svc = svc_iterator(&iter, 1); svc; svc = svc_iterator(&iter, 0)) {
+		if (!svc_is_tty(svc) || svc_is_removed(svc))
+			continue;
+		num++;
 	}
 
-	if (fallback != lost || tty_num_active())
-		return 0;
+#ifdef FALLBACK_SHELL
+	char line[32] = "tty [12345789] notty noclear";
 
-	fallback = fork();
-	if (fallback)
-		return 1;
+	if (!num) {
+		_d("No TTY active in configuration, enabling fallback shell.");
+		return service_register(SVC_TYPE_TTY, line, global_rlimit, file);
+	}
+#endif
 
-	/*
-	 * Become session leader and set controlling TTY
-	 * to enable Ctrl-C and job control in shell.
-	 */
-	setsid();
-	ioctl(STDIN_FILENO, TIOCSCTTY, 1);
-
-	prctl(PR_SET_NAME, "finitsh", 0, 0, 0);
-	_exit(execl(_PATH_BSHELL, _PATH_BSHELL, NULL));
-#else
-	(void)lost;
-#endif /* FALLBACK_SHELL */
-
-	return 0;
+	return num == 0;
 }
 
 /**

src/tty.h

@@ -36,9 +36,10 @@ struct tty {
 	char	*dev;
 	char	*baud;
 	char	*term;
-	int	 noclear;
-	int	 nowait;
-	int	 nologin;
+	char	 noclear;
+	char	 nowait;
+	char	 nologin;
+	char	 notty;
 };
 
 char	*tty_canonicalize (char *dev);
@@ -49,6 +50,7 @@ int	 tty_atcon        (char *buf, size_t len);
 int	 tty_parse_args   (char *cmdline, struct tty *tty);
 
 int	 tty_exec	  (svc_t *tty);
+int	 tty_fallback	  (char *file);
 
 #endif /* FINIT_TTY_H_ */