From 37b5835028cb170fdffb35e33fdf1fdcc402df9a Mon Sep 17 00:00:00 2001
From: Warner Losh <imp@FreeBSD.org>
Date: Wed, 22 Mar 2017 19:00:41 +0000
Subject: [PATCH] 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.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D10037
---
 include/ttyent.h         |  1 +
 lib/libc/gen/getttyent.c | 22 ++++++++++++++++++++++
 libexec/getty/ttys.5     |  8 +++++++-
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/include/ttyent.h b/include/ttyent.h
index f2220ad73b94..c173bb81803b 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"
diff --git a/lib/libc/gen/getttyent.c b/lib/libc/gen/getttyent.c
index 8e9ac9883a51..aa08632f60fc 100644
--- a/lib/libc/gen/getttyent.c
+++ b/lib/libc/gen/getttyent.c
@@ -97,6 +97,26 @@ done:
 	return (0);
 }
 
+static int
+auto_exists_status(const char *ty_name)
+{
+	struct stat sb;
+	char *dev;
+	int rv;
+
+	rv = 0;
+	if (*ty_name == '/')
+		asprintf(&dev, "%s", ty_name);
+	else
+		asprintf(&dev, "/dev/%s", ty_name);
+	if (dev == NULL)
+		return 0;
+	if (stat(dev, &sb) == 0)
+		rv = TTY_ON;
+	free(dev);
+	return (rv);
+}
+
 struct ttyent *
 getttyent(void)
 {
@@ -161,6 +181,8 @@ 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 d4c7f1d1a249..1150909752a8 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.