RaspberryPI IrToy - restore /dev/ttyACM0 interface in newer kernels automatically on kernel upgrade

etc_kernel_postinst.d__cdc-acm-irtoy-kludge

#!/bin/sh
# by Matija Nalis <mnalis-rpi@voyager.hr> GPLv3+ 20211112
# automatically kludge cdc_acm.ko for IrToy /dev/ttyACM0 usage "old-way"
#

#echo script: $0
#echo params: "$@"
#echo env:
#env


case "$DPKG_MAINTSCRIPT_PACKAGE::$DPKG_MAINTSCRIPT_NAME" in
   raspberrypi-kernel*::postrm)
      exit 0;;
esac

NEW_VER=$1
#echo "Detecting new kernel version base: $NEW_VER"
FLAVOUR=`uname -r | sed -e 's/^.*-v/-v/'`
#echo "Extracted current kernel flavour: $FLAVOUR"
#echo "Verifying correct flavor:"

if echo $NEW_VER | fgrep -q -- $FLAVOUR
then
        echo "FLAVOUR $FLAVOUR OK, continuing..."

        NEWDIR="/lib/modules/${NEW_VER}"
        echo "Checking kernel modules dir: $NEWDIR"
        if ! test -d ${NEWDIR}
        then
                echo "Failed to detect new kernel directory, ABORTING!"
                exit 3
        fi
        echo "Found, proceeding to kludge cdc_acm.ko..."

        # from https://gist.github.com/mnalis/2fed42a1abf8e98f45f6edf162bf609f
        # This changes blacklisting of USB ID `04d8:fd08` in cdc-acm, so IrToy gets recognized
        # as it was in previous kernel versions, and `/dev/ttyACM0` gets created for it instead of `/dev/lirc0`
        # For those who don't use lirc but IrToy directly and so need compatibility with that...
        #
        # works at least in Raspbian.org Buster raspberrypi-kernel 1:1.20211029-1~buster armhf

        cd ${NEWDIR}/kernel/drivers && \
          mv -n media/rc/ir_toy.ko media/rc/ir_toy.ko.DISABLED && \
          mv -n usb/class/cdc-acm.ko usb/class/cdc-acm.ko.DISABLED && \
          env -i sed -e 's/\xd8\x04\x08\xfd/\xff\x04\x08\xfd/' < usb/class/cdc-acm.ko.DISABLED > usb/class/cdc-acm.ko && \
          depmod -a && \
          echo "Kludge finished. Please reboot when ready to activate changes in ${NEWDIR}..." || (echo FAILED; exit 5)
else
        echo "FLAVOUR of $NEW_VER does not match $FLAVOUR, skipping..."
        exit 0
fi