Do not start getty on tty0 to avoid screen corruption

.spdxignore

@@ -14,3 +14,4 @@ pkg/kube/descheduler-job.yaml
 pkg/kube/descheduler_rbac.yaml
 pkg/kube/lh-cfg-v1.6.2.yaml
 pkg/vtpm/swtpm-vtpm/vendor/
+pkg/dom0-ztools/rootfs/usr/bin/rungetty.sh

.yetus/blanks-tabs.txt

@@ -3,3 +3,4 @@
 .*\.dts
 .*\.md
 ^.codespellignorelines
+pkg/dom0-ztools/rootfs/usr/bin/rungetty.sh

.yetus/excludes.txt

@@ -20,3 +20,4 @@
 ^.+/testdata/.+
 ^.codespellignorelines
 eve-tools/bpftrace-compiler/examples/.+\.bt
+pkg/dom0-ztools/rootfs/usr/bin/rungetty.sh

docs/LOCAL-TUI.md

@@ -12,13 +12,17 @@ The client communicates with the server over UNIX socket
 
 The UI is rendered on a local TTY (/dev/tty2) only i.e. on a physical monitor attached to the system. Neither Serial Console nor SSH connection has access to TUI. It is done to ensure the physical presence of the operator.
 
-## /dev/ttyX vs /dev/console
+## /dev/ttyX vs /dev/console vs /dev/tty0
 
-There are two distinguishable console devices in Linux `/dev/console` and `/dev/ttyX`. The later points to a particular virtual terminal device and the former points to *currently active* TTY device. The user can switch between virtual terminals by using `Alt+Fx` or `Alt+<,>` keys. When the current TTY is set `/dev/console` tracks this change and always points to to the current terminal
+There are three distinguishable console devices in Linux `/dev/console`, `/dev/tty0` and `/dev/ttyX` where X > 0. The latter points to a particular virtual terminal device i.e. a dedicated framebuffer for VGA console.  `/dev/tty0` points to *currently active* TTY device. This can be proven by reading `/sys/devices/virtual/tty/tty0/active` file. This file exists only for `/dev/tty0`. On the other hand `/dev/console` may point to several devices at a time. These are devices user specifies in `console=` kernel command line parameters. The list can be obtained by reading `/sys/devices/virtual/tty/console/active` file.
 
-Monitor application is spawned on a `/dev/tty2` using a `openvt` utility while the rest of the applications are spawned on the default kernel console defined by `console=` parameters on the kernel command line. When the application is in focus (`/dev/tty2` is an active console) writing to `/dev/console` which points to the same device corrupts TUI thus it cannot be used by other services in the system to produce the output. At least when `/dev/tty2` is a current console.
+The user can switch between virtual terminals by using `Alt+Fx` or `Alt+<,>` keys. When the current TTY is set `/dev/tty0` tracks this change and always points to to the current terminal
 
-From the other hand `/dev/tty`  (no digit at the end!) device always points to a TTY *in the context of running process*. This device can be used instead of `/dev/console` by other services for the output.
+Monitor application is spawned on a `/dev/tty2` using a `openvt` utility while the rest of the applications are spawned on the default kernel console defined by `console=` parameters on the kernel command line. When the application is in focus (`/dev/tty2` is an active console) writing to `/dev/console` or to `/dev/tty0` which points to the same device corrupts TUI thus it cannot be used by other services in the system to produce the output. At least when `/dev/tty2` is a current console.
+
+On the other hand `/dev/tty`  (no digit at the end!) device always points to a TTY *in the context of running process*. This device can be used instead of `/dev/console` by other services for the output.
+
+Mode details can be found in [https://www.kernel.org/doc/Documentation/admin-guide/serial-console.rst](https://www.kernel.org/doc/Documentation/admin-guide/serial-console.rst), [https://www.kernel.org/doc/html/v6.11/admin-guide/devices.html#virtual-consoles-and-the-console-device](https://www.kernel.org/doc/html/v6.11/admin-guide/devices.html#virtual-consoles-and-the-console-device) and in this blog post [https://www.baeldung.com/linux/monitor-keyboard-drivers](https://www.baeldung.com/linux/monitor-keyboard-drivers)
 
 ## Limitations of linux terminal
 

pkg/dom0-ztools/rootfs/usr/bin/rungetty.sh

@@ -0,0 +1,94 @@
+#!/bin/sh
+
+infinite_loop() {
+	while true; do
+		$@
+	done
+}
+
+# run getty on all known consoles
+start_getty() {
+	tty=${1%,*}
+	speed=${1#*,}
+	securetty="$2"
+	line=
+	term="linux"
+	[ "$speed" = "$1" ] && speed=115200
+
+	# if console=tty0 is specified on the kernel command line, we should not start a getty on tty0
+	# but instead start it on the first available tty. tty0 points to the current console, so if
+	# we start a getty from pillar of debug.enable.console=true we may start it on current tty
+	# which may be occupied by TUI monitor application and tty will be taken away by getty.
+	# replacing tty0 with tty1 should be ok because this is the user's intention
+	if [ "$tty" = "tty0" ]; then
+		tty="tty1"
+	fi
+
+	# did we already process this tty?
+	if $(echo "${PROCESSEDTTY}" | grep -q -w "$tty"); then
+		echo "getty: already processed tty for $tty, not starting twice" | tee /dev/tty
+		return
+	fi
+	# now indicate that we are processing it
+	PROCESSEDTTY="${PROCESSEDTTY} ${tty}"
+
+	# does the device even exist?
+	if [ ! -c /dev/$tty ]; then
+		echo "getty: cmdline has console=$tty but /dev/$tty is not a character device; not starting getty for $tty" | tee /dev/tty
+		return
+	fi
+
+	case "$tty" in
+	ttyS*|ttyAMA*|ttyUSB*|ttyMFD*)
+		line="-L"
+		term="vt100"
+		;;
+	tty?)
+		line=""
+		speed="38400"
+		term=""
+		;;
+	esac
+
+	# are we secure or insecure?
+	loginargs=
+	if [ "$INSECURE" == "true" ]; then
+		loginargs="-a root"
+	fi
+
+	if ! grep -q -w "$tty" "$securetty"; then
+		# we could not find the tty in securetty, so start a getty but warn that root login will not work
+		echo "getty: cmdline has console=$tty but does not exist in $securetty; will not be able to log in as root on this tty $tty." | tee /dev/$tty
+	fi
+	# respawn forever
+	echo "getty: starting getty for $tty"  | tee /dev/$tty
+	infinite_loop setsid.getty -w /sbin/agetty $loginargs $line $speed $tty $term &
+}
+
+
+# check if we are namespaced, and, if so, indicate in the PS1
+if [ -z "$INITGETTY" ]; then
+	cat >/etc/profile.d/namespace.sh <<"EOF"
+export PS1="(ns: getty) $PS1"
+EOF
+fi
+
+PROCESSEDTTY=
+
+# check if we have /etc/getty.shadow
+ROOTSHADOW=/hostroot/etc/getty.shadow
+if [ -f $ROOTSHADOW ]; then
+	cp $ROOTSHADOW /etc/shadow
+	# just in case someone forgot a newline
+	echo >> /etc/shadow
+fi
+
+for opt in $(cat /proc/cmdline); do
+	case "$opt" in
+	console=*)
+		start_getty ${opt#console=} /etc/securetty
+	esac
+done
+
+# if we are in a container (not in root init) wait for all our child process to exit; tini will handle subreaping, if necessary
+[ -n "$INITGETTY" ] || wait