postmarketos-base: configure getty using deviceinfo_getty variable (!771)

On some devices a getty should run on the serial console.
Configure the getty by setting the deviceinfo_getty variable. The
format is "<port>;<baud rate>". For example, "ttyS0;115200".

A post-installation trigger in postmarketos-base checks
/etc/deviceinfo, and modifies /etc/inittab if the device should run
a getty.

main/postmarketos-base/APKBUILD

@@ -1,6 +1,6 @@
 pkgname=postmarketos-base
 pkgver=3
-pkgrel=29
+pkgrel=30
 pkgdesc="Meta package for minimal postmarketOS base"
 url="https://postmarketos.org"
 arch="noarch"
@@ -26,6 +26,7 @@ depends="
 	pulseaudio
 	pulseaudio-alsa"
 install="$pkgname.post-install"
+triggers="$pkgname.trigger=/etc"
 subpackages="$pkgname-x11"
 source="
 	firmwareload.sh

main/postmarketos-base/postmarketos-base.trigger

@@ -0,0 +1,40 @@
+#!/bin/sh -e
+
+# Each argument to this shell script is a path that caused the trigger to execute. 
+# If /etc/deviceinfo was installed (which should be the case for any device) and 
+# deviceinfo_getty is set, then configure a getty. 
+
+deviceinfo="false"
+
+for i in "$@"; do
+	case "$i" in
+		/etc)
+			if [ -f /etc/deviceinfo ]; then 
+				deviceinfo="true"
+			fi
+			break ;;
+	esac
+done
+
+if [ "$deviceinfo" = "true" ]; then
+	deviceinfo_getty=""
+
+	# shellcheck disable=SC1091
+	. /etc/deviceinfo
+
+	if [ -n "${deviceinfo_getty}" ]; then
+		port=$(echo "${deviceinfo_getty}" | cut -s -d ";" -f 1)
+		baudrate=$(echo "${deviceinfo_getty}" | cut -s -d ";" -f 2)
+
+		if [ -n "${port}" ] && [ -n "${baudrate}" ]; then
+			echo "Configuring a getty on port ${port} with baud rate ${baudrate}"
+			sed -i -e "s/#ttyS0::respawn:\/sbin\/getty -L ttyS0 115200 vt100/${port}::respawn:\/sbin\/getty -L ${port} ${baudrate} vt100/" /etc/inittab
+		else
+			echo "ERROR: Invalid value for deviceinfo_getty: ${deviceinfo_getty}"
+			exit 1
+		fi
+	fi
+fi
+
+sync
+exit 0