Add resizewin -z. It makes resizewin not do anything if the terminal

size is already set to something other than zero. It's supposed to be
called from eg /etc/profile - it's not neccessary to query terminal
size when logging in over the network, because the protocol used already
takes care of this, but it's neccessary when logging over a serial line.

Reviewed by:	cem, Daniel O'Connor <darius@dons.net.au>
MFC after:	2 weeks
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D10637

2 files changed, 43 insertions, 3 deletions

diff --git a/usr.bin/resizewin/resizewin.1 b/usr.bin/resizewin/resizewin.1
index b7376c79026e..ce15ce70283e 100644
--- a/usr.bin/resizewin/resizewin.1
+++ b/usr.bin/resizewin/resizewin.1
@@ -27,17 +27,27 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd July 9, 2016
+.Dd May 8, 2017
 .Dt RESIZEWIN 1
 .Os
 .Sh NAME
 .Nm resizewin
 .Nd update the kernel window size for the current TTY
+.Sh SYNOPSIS
+.Nm
+.Op Fl z
 .Sh DESCRIPTION
 Query the terminal emulator window size with the
 .Dv TIOCSWINSZ
 ioctl and set the window size known by the kernel to the new values.
 The terminal is assumed to be VT100/ANSI compatible.
+.Pp
+The following options are available:
+.Bl -tag -width ".Fl z"
+.It Fl z
+Do nothing unless the current kernel terminal size is zero.
+.El
+.Pp
 .Nm
 is functionally similar to
 .Xr resize 1 ,
diff --git a/usr.bin/resizewin/resizewin.c b/usr.bin/resizewin/resizewin.c
index 566577be4d70..20116b615088 100644
--- a/usr.bin/resizewin/resizewin.c
+++ b/usr.bin/resizewin/resizewin.c
@@ -47,20 +47,50 @@ static const char query[] =
     "\033[999;999H"	/* Move cursor */
     "\033[6n"		/* Get cursor position */
     "\0338";		/* Restore cursor position */
+
+static void
+usage(void)
+{
+
+	fprintf(stderr, "usage: resizewin [-z]\n");
+	exit(1);
+}
+
 int
-main(__unused int argc, __unused char **argv)
+main(int argc, char **argv)
 {
 	struct termios old, new;
 	struct winsize w;
-	int ret, fd, cnt, error;
+	int ret, fd, ch, cnt, error, zflag;
 	char data[20];
 	struct timeval then, now;
 
 	error = 0;
+	zflag = 0;
+	while ((ch = getopt(argc, argv, "z")) != -1) {
+		switch (ch) {
+		case 'z':
+			zflag = 1;
+			break;
+		case '?':
+		default:
+			usage();
+		}
+	}
+	argc -= optind;
+	if (argc != 0)
+		usage();
 
 	if ((fd = open("/dev/tty", O_RDWR | O_NONBLOCK)) == -1)
 		exit(1);
 
+	if (zflag) {
+		if (ioctl(fd, TIOCGWINSZ, &w) == -1)
+			exit(1);
+		if (w.ws_row != 0 && w.ws_col != 0)
+			exit(0);
+	}
+
 	/* Disable echo */
 	if (tcgetattr(fd, &old) == -1)
 		exit(1);