MFC r315733, r315737, r315740, r330054:

 r315733 (imp):
  Impelemnt ttys onifexists in init.

  Implement a new init(8) option in /etc/ttys. If this option is present
  on the entry in /etc/ttys, the entry will be active if and only if it
  exists.  If the name starts with a '/', it will be considered an
  absolute path. If not, it will be a path relative to /dev.

  This allows one to turn off video console getty that aren't present
  (while running a getty on them even when they aren't the system
  console). Likewise with serial ports.

  It differs from onifconsole in only requiring the device exist rather
  than it be listed as one of the system consoles.

 r315737 (ngie):
  Unbreak world by adding sys/stat.h for stat(2)

 r315740 (imp):
  Simplify the code a little.

 r330054 (trasz):
  Improve missing tty handling in init(8).  This removes a check that did
  nothing - it was checking for ENXIO, which, with devfs, is no longer
  returned - and was badly placed anyway, and replaces it with similar
  one that works, and is done just before starting getty, instead of being
  done when rereading ttys(5).

  From the practical point of view, this makes init(8) handle disappearing
  terminals (eg /dev/ttyU*) gracefully, without unneccessary getty restarts
  and resulting error messages.

Reported by:	Bart Ender, Andre Albsmeier
PR:		228315
Blocks:		11.2-BETA2
Approved by:	re (marius)
Sponsored by:	The FreeBSD Foundation

5 files changed, 80 insertions, 19 deletions

diff --git a/include/ttyent.h b/include/ttyent.h
index f2220ad..928da81 100644
--- a/include/ttyent.h
+++ b/include/ttyent.h
@@ -38,6 +38,7 @@
 #define	_TTYS_OFF	"off"
 #define	_TTYS_ON	"on"
 #define	_TTYS_ONIFCONSOLE "onifconsole"
+#define	_TTYS_ONIFEXISTS "onifexists"
 #define	_TTYS_SECURE	"secure"
 #define	_TTYS_INSECURE	"insecure"
 #define	_TTYS_WINDOW	"window"
@@ -54,6 +55,8 @@ struct ttyent {
 #define	TTY_SECURE	0x02	/* allow uid of 0 to login */
 #define	TTY_DIALUP	0x04	/* is a dialup tty */
 #define	TTY_NETWORK	0x08	/* is a network tty */
+#define	TTY_IFEXISTS	0x10	/* configured as "onifexists" */
+#define	TTY_IFCONSOLE	0x20	/* configured as "onifconsole" */
 	int	ty_status;	/* status flags */
 	char 	*ty_window;	/* command to start up window manager */
 	char	*ty_comment;	/* comment field */
diff --git a/lib/libc/gen/getttyent.3 b/lib/libc/gen/getttyent.3
index 18c3f07..43b2ace 100644
--- a/lib/libc/gen/getttyent.3
+++ b/lib/libc/gen/getttyent.3
@@ -75,6 +75,8 @@ struct ttyent {
 #define	TTY_SECURE	0x02	/* allow uid of 0 to login */
 #define	TTY_DIALUP	0x04	/* is a dialup tty */
 #define	TTY_NETWORK	0x08	/* is a network tty */
+#define	TTY_IFEXISTS	0x10	/* configured as "onifexists" */
+#define	TTY_IFCONSOLE	0x20	/* configured as "onifconsole" */
 	int	ty_status;	/* status flags */
 	char	*ty_window;	/* command to start up window manager */
 	char	*ty_comment;	/* comment field */
@@ -115,6 +117,10 @@ Identifies a tty used for network connections.
 If this flag is set, then
 .Fn isnettty
 will return a non-zero value.
+.It Dv TTY_IFEXISTS
+Identifies a tty that does not neccessarily exist.
+.It Dv TTY_IFCONSOLE
+Identifies a tty that might be a system console.
 .El
 .It Fa ty_window
 The command to execute for a window system associated with the line.
diff --git a/lib/libc/gen/getttyent.c b/lib/libc/gen/getttyent.c
index 266f631..e0b2698 100644
--- a/lib/libc/gen/getttyent.c
+++ b/lib/libc/gen/getttyent.c
@@ -34,6 +34,7 @@ static char sccsid[] = "@(#)getttyent.c	8.1 (Berkeley) 6/4/93";
 __FBSDID("$FreeBSD$");
 
 #include <sys/types.h>
+#include <sys/stat.h>
 #include <sys/sysctl.h>
 
 #include <ctype.h>
@@ -72,11 +73,14 @@ auto_tty_status(const char *ty_name)
 {
 	size_t len;
 	char *buf, *cons, *nextcons;
+	int rv;
+
+	rv = TTY_IFCONSOLE;
 
 	/* Check if this is an enabled kernel console line */
 	buf = NULL;
 	if (sysctlbyname("kern.console", NULL, &len, NULL, 0) == -1)
-		return (0); /* Errors mean don't enable */
+		return (rv); /* Errors mean don't enable */
 	buf = malloc(len);
 	if (sysctlbyname("kern.console", buf, &len, NULL, 0) == -1)
 		goto done;
@@ -87,14 +91,32 @@ auto_tty_status(const char *ty_name)
 	nextcons = buf;
 	while ((cons = strsep(&nextcons, ",")) != NULL && strlen(cons) != 0) {
 		if (strcmp(cons, ty_name) == 0) {
-			free(buf);
-			return (TTY_ON);
+			rv |= TTY_ON;
+			break;
 		}
 	}
 
 done:
 	free(buf);
-	return (0);
+	return (rv);
+}
+
+static int
+auto_exists_status(const char *ty_name)
+{
+	struct stat sb;
+	char *dev;
+	int rv;
+
+	rv = TTY_IFEXISTS;
+	if (*ty_name == '/')
+		asprintf(&dev, "%s", ty_name);
+	else
+		asprintf(&dev, "/dev/%s", ty_name);
+	if (dev != NULL && stat(dev, &sb) == 0)
+		rv |= TTY_ON;
+	free(dev);
+	return (rv);
 }
 
 struct ttyent *
@@ -161,6 +183,8 @@ getttyent(void)
 			tty.ty_status |= TTY_ON;
 		else if (scmp(_TTYS_ONIFCONSOLE))
 			tty.ty_status |= auto_tty_status(tty.ty_name);
+		else if (scmp(_TTYS_ONIFEXISTS))
+			tty.ty_status |= auto_exists_status(tty.ty_name);
 		else if (scmp(_TTYS_SECURE))
 			tty.ty_status |= TTY_SECURE;
 		else if (scmp(_TTYS_INSECURE))
diff --git a/libexec/getty/ttys.5 b/libexec/getty/ttys.5
index d4c7f1d..1150909 100644
--- a/libexec/getty/ttys.5
+++ b/libexec/getty/ttys.5
@@ -28,7 +28,7 @@
 .\"     from: @(#)ttys.5	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\" "
-.Dd March 9, 2014
+.Dd March 16, 2017
 .Dt TTYS 5
 .Os
 .Sh NAME
@@ -105,6 +105,12 @@ should (should not) execute the command given in the second field.
 ``onifconsole'' will cause this line to be enabled if and only if it is
 an active kernel console device (it is equivalent to ``on'' in this
 case).
+The flag ``onifexists'' will cause this line to be enabled if and only
+if the name exists.
+If the name starts with a ``/'', it will be considered an absolute
+path.
+Otherwise, it is considered a path relative to
+.Pa /dev .
 The flag ``secure'' (if the console is enabled) allows users with a
 uid of 0 to login on
 this line.
diff --git a/sbin/init/init.c b/sbin/init/init.c
index f4206c4..12cf9a7 100644
--- a/sbin/init/init.c
+++ b/sbin/init/init.c
@@ -154,6 +154,8 @@ typedef struct init_session {
 	int	se_flags;		/* status of session */
 #define	SE_SHUTDOWN	0x1		/* session won't be restarted */
 #define	SE_PRESENT	0x2		/* session is in /etc/ttys */
+#define	SE_IFEXISTS	0x4		/* session defined as "onifexists" */
+#define	SE_IFCONSOLE	0x8		/* session defined as "onifconsole" */
 	int	se_nspace;		/* spacing count */
 	char	*se_device;		/* filename of port */
 	char	*se_getty;		/* what to run on that port */
@@ -1260,7 +1262,6 @@ static session_t *
 new_session(session_t *sprev, struct ttyent *typ)
 {
 	session_t *sp;
-	int fd;
 
 	if ((typ->ty_status & TTY_ON) == 0 ||
 	    typ->ty_name == 0 ||
@@ -1271,21 +1272,15 @@ new_session(session_t *sprev, struct ttyent *typ)
 
 	sp->se_flags |= SE_PRESENT;
 
+	if ((typ->ty_status & TTY_IFEXISTS) != 0)
+		sp->se_flags |= SE_IFEXISTS;
+
+	if ((typ->ty_status & TTY_IFCONSOLE) != 0)
+		sp->se_flags |= SE_IFCONSOLE;
+
 	if (asprintf(&sp->se_device, "%s%s", _PATH_DEV, typ->ty_name) < 0)
 		err(1, "asprintf");
 
-	/*
-	 * Attempt to open the device, if we get "device not configured"
-	 * then don't add the device to the session list.
-	 */
-	if ((fd = open(sp->se_device, O_RDONLY | O_NONBLOCK, 0)) < 0) {
-		if (errno == ENXIO) {
-			free_session(sp);
-			return (0);
-		}
-	} else
-		close(fd);
-
 	if (setupargv(sp, typ) == 0) {
 		free_session(sp);
 		return (0);
@@ -1505,6 +1500,30 @@ start_getty(session_t *sp)
 }
 
 /*
+ * Return 1 if the session is defined as "onifexists"
+ * or "onifconsole" and the device node does not exist.
+ */
+static int
+session_has_no_tty(session_t *sp)
+{
+	int fd;
+
+	if ((sp->se_flags & SE_IFEXISTS) == 0 &&
+	    (sp->se_flags & SE_IFCONSOLE) == 0)
+		return (0);
+
+	fd = open(sp->se_device, O_RDONLY | O_NONBLOCK, 0);
+	if (fd < 0) {
+		if (errno == ENOENT)
+			return (1);
+		return (0);
+	}
+
+	close(fd);
+	return (0);
+}
+
+/*
  * Collect exit status for a child.
  * If an exiting login, start a new login running.
  */
@@ -1522,7 +1541,8 @@ collect_child(pid_t pid)
 	del_session(sp);
 	sp->se_process = 0;
 
-	if (sp->se_flags & SE_SHUTDOWN) {
+	if (sp->se_flags & SE_SHUTDOWN ||
+	    session_has_no_tty(sp)) {
 		if ((sprev = sp->se_prev) != NULL)
 			sprev->se_next = sp->se_next;
 		else
@@ -1608,6 +1628,8 @@ multi_user(void)
 	for (sp = sessions; sp; sp = sp->se_next) {
 		if (sp->se_process)
 			continue;
+		if (session_has_no_tty(sp))
+			continue;
 		if ((pid = start_getty(sp)) == -1) {
 			/* serious trouble */
 			requested_transition = clean_ttys;