debvm-create: autodetect size of serial consoles

We now extend /etc/profile to invoke setterm -resize when detecting an
interactive login on a serial console. This should fix 90% of wrongly
sized serial consoles.

2 files changed, 17 insertions, 2 deletions

diff --git a/bin/debvm-run b/bin/debvm-run
index 81114e6..e45f350 100755
--- a/bin/debvm-run
+++ b/bin/debvm-run
@@ -67,7 +67,8 @@ F<rootfs.ext4>, resulting in an ephemeral run.
 
 Make sure C<$TERM> is set to a value known inside the VM.
 You may need to install B<ncurses-term> for more definitions.
-It also helps to run C<setterm --resize> after boot and when resizing the terminal emulator.
+The serial console will miss events of resizing the terminal emulator.
+You may run C<setterm -resize> in that case.
 
 =item How can I kill debvm-run?
 
diff --git a/share/customize-autologin.sh b/share/customize-autologin.sh
index 9effa29..da40342 100755
--- a/share/customize-autologin.sh
+++ b/share/customize-autologin.sh
@@ -4,12 +4,26 @@
 #
 # This is a mmdebstrap customize hook that configures automatic root login on a
 # serial console. It also parses the TERM kernel cmdline and passes it as
-# TERM to agetty.
+# TERM to agetty. Since serial consoles do not transmit SIGWINCH, it causes
+# the shell to run setterm -resize on interactive, serial logins.
 
 set -eu
 
 TARGET=$1
 
+cat >"$TARGET/etc/profile.d/resize_serial_term.sh" <<'EOF'
+if test -n "${TERM-}" && test -n "${PS1-}"; then
+	case "$(tty)" in
+		/dev/tty[0-9]*)
+		;;
+		/dev/tty*)
+			# Assume that every other tty is serial and should be resized.
+			setterm -resize
+		;;
+	esac
+fi
+EOF
+
 if test "$(dpkg-query --root "$TARGET" -f '${db:Status-Status}' -W systemd-sysv 2>/dev/null)" = installed; then
 	UNIT=serial-getty@.service