From da22bdbc05c0014a0ceb6a14352c30fc2ae277c3 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 30 Jul 2018 20:57:22 +0200
Subject: [PATCH] ptyfwd: when we can't copy the window size from caller, use
 $LINES and $COLUMNS

This way users can directly influence the tty size if they like when
nspawn is invoked as a service and thus stdin/stdout/stderr are not
connected to a TTY.
---
 src/shared/ptyfwd.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/shared/ptyfwd.c b/src/shared/ptyfwd.c
index 942c3f31dc..1cb7ea3a19 100644
--- a/src/shared/ptyfwd.c
+++ b/src/shared/ptyfwd.c
@@ -20,6 +20,7 @@
 #include "log.h"
 #include "macro.h"
 #include "ptyfwd.h"
+#include "terminal-util.h"
 #include "time-util.h"
 
 struct PTYForward {
@@ -421,8 +422,17 @@ int pty_forward_new(
 
         f->master = master;
 
-        if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) >= 0)
-                (void) ioctl(master, TIOCSWINSZ, &ws);
+        if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) < 0) {
+                /* If we can't get the resolution from the output fd, then use our internal, regular width/height,
+                 * i.e. something derived from $COLUMNS and $LINES if set. */
+
+                ws = (struct winsize) {
+                        .ws_row = lines(),
+                        .ws_col = columns(),
+                };
+        }
+
+        (void) ioctl(master, TIOCSWINSZ, &ws);
 
         if (!(flags & PTY_FORWARD_READ_ONLY)) {
                 if (tcgetattr(STDIN_FILENO, &f->saved_stdin_attr) >= 0) {