tcgetwinsize(3) and tcsetwinsize(3) have existed in POSIX for years, and
been supported on the other BSDs for just as long. This patch implements
them in libc.

diff 11d817a3382201927643a2ae0a36dcc4048bfb0b HEAD
commit - 11d817a3382201927643a2ae0a36dcc4048bfb0b
commit + c077581a317e8f39c250c631d6d29b01a97e7f8a
blob - 6eb2cca93e5f1c834a57a03af4a4b3fe27c64ce1
blob + 18cf144e7a06b88f2514407c57cda12d192d7709
--- lib/libc/Symbols.list
+++ lib/libc/Symbols.list
@@ -1700,9 +1700,11 @@ tcflush
 tcgetattr
 tcgetpgrp
 tcgetsid
+tcgetwinsize
 tcsendbreak
 tcsetattr
 tcsetpgrp
+tcsetwinsize
 
 /* thread */
 _rthread_debug
blob - 85c1d52273c9cb24478c2c7e67a79bbdd86dae51
blob + a1aff88ae34741f62149e88c69c93f6b5b7326c6
--- lib/libc/termios/Makefile.inc
+++ lib/libc/termios/Makefile.inc
@@ -4,6 +4,7 @@
 
 SRCS+=	cfgetispeed.c cfgetospeed.c cfmakeraw.c cfsetispeed.c cfsetospeed.c \
 	cfsetspeed.c tcdrain.c tcflow.c tcflush.c tcgetattr.c tcgetpgrp.c \
-	tcsendbreak.c tcsetattr.c tcsetpgrp.c tcgetsid.c
+	tcsendbreak.c tcsetattr.c tcsetpgrp.c tcgetsid.c tcgetwinsize.c \
+	tcsetwinsize.c
 
 MAN+=	tcgetpgrp.3 tcsendbreak.3 tcsetattr.3 tcsetpgrp.3 tcgetsid.3
blob - /dev/null
blob + c41b49129a7c60230f20f727ce90f7e4b089cd30 (mode 644)
--- /dev/null
+++ lib/libc/termios/tcgetwinsize.c
@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2025 Finxx <me@finxx.xyz>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/ioctl.h>
+#include <termios.h>
+
+int
+tcgetwinsize(int fd, struct winsize *winsize_p)
+{
+	return (ioctl(fd, TIOCGWINSZ, winsize_p));
+}
blob - /dev/null
blob + 7e652d5f8457bb752b724c14cbfbdd9dc15f0564 (mode 644)
--- /dev/null
+++ lib/libc/termios/tcsetwinsize.c
@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2025 Finxx <me@finxx.xyz>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/ioctl.h>
+#include <termios.h>
+
+int
+tcsetwinsize(int fd, const struct winsize *winsize_p)
+{
+	return (ioctl(fd, TIOCSWINSZ, winsize_p));
+}
blob - 681c29489138850507516a8ef6bc346bed04e4e9
blob + 62a2d7a676481ae3fd947c15e237d4a5b018c1ca
--- sys/sys/termios.h
+++ sys/sys/termios.h
@@ -272,6 +272,8 @@ int	tcdrain(int);
 int	tcflow(int, int);
 int	tcflush(int, int);
 int	tcsendbreak(int, int);
+int	tcgetwinsize(int, struct winsize *);
+int	tcsetwinsize(int, const struct winsize *);
 
 #if __XPG_VISIBLE >= 420 || __POSIX_VISIBLE >= 200809
 pid_t	tcgetsid(int);