add console options from boot cmdline to inittab

This will make sure that you get a login console that corresponds to the
boot option.

Signed-off-by: Natanael Copa <natanael.copa@docker.com>

alpine/init

@@ -1,7 +1,43 @@
 #!/bin/sh
 
+setup_console() {
+	tty=${1%,*}
+	speed=${1#*,}
+	inittab="$2"
+	securetty="$3"
+	line=
+	term="linux"
+	[ "$speed" = "$1" ] && speed=115200
+
+	case "$tty" in
+	ttyS*|ttyAMA*|ttyUSB*|ttyMFD*)
+		line="-L"
+		term="vt100"
+		;;
+	tty0)
+		# skip current console
+		return 0
+		;;
+	esac
+	# skip consoles already in inittab
+	grep -q "^$tty:" "$inittab" && return
+
+	echo "$tty::respawn:/sbin/getty $line $speed $tty $term" >> "$inittab"
+	if ! grep -q -w "$tty" "$securetty"; then
+		echo "$tty" >> "$securetty"
+	fi
+}
+
 /bin/mount -t tmpfs tmpfs /mnt
 
 /bin/cp -a / /mnt 2>/dev/null
 
+/bin/mount -t proc -o noexec,nosuid,nodev proc /proc
+for opt in $(cat /proc/cmdline); do
+	case "$opt" in
+	console=*)
+		setup_console ${opt#console=} /mnt/etc/inittab /mnt/etc/securetty;;
+	esac
+done
+
 exec /bin/busybox switch_root /mnt /sbin/init