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+ started 20211112
# automatically kludge cdc_acm.ko for IrToy /dev/ttyACM0 usage "old-way"
# updated by Matija Nalis <mnalis-rpi@voyager.hr> 20251022 for RpiOS-Trixie (6.12.47+rpt-rpi-v8)
#
# put this file with +rx permissions in /etc/kernel/postinst.d/cdc-acm-irtoy-kludge
#

#echo script: $0
#echo params: "$@"
#echo  "\$DPKG_MAINTSCRIPT_PACKAGE::\$DPKG_MAINTSCRIPT_NAME=$DPKG_MAINTSCRIPT_PACKAGE::$DPKG_MAINTSCRIPT_NAME"
#echo env: ; env


case "$DPKG_MAINTSCRIPT_PACKAGE::$DPKG_MAINTSCRIPT_NAME" in
   raspberrypi-kernel*::postrm|linux-image-*+rpt*::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, trying 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...
        #
        # should work at least in Raspbian.org Buster raspberrypi-kernel 1:1.20211029-1~buster armhf
        # and in RaspberryPi OS Trixie linux-image-6.12.47+rpt-rpi-v8 arm64

        MODULE=`echo ${NEWDIR}/kernel/drivers/usb/class/cdc-acm.ko*`
        EXT=${MODULE##*.}
        case $EXT in
                DISABLED)
                    echo "cdc-acm module already kludged. Skipping."
                    exit 0
                    ;;
                ko) COMP="cat"; DECOMP="cat"; EEXT="";;
                xz) COMP="xz"; DECOMP="xz -dc"; EEXT=".$EXT";;
                gz) COMP="gzip"; DECOMP="gzip -dc"; EEXT=".$EXT";;
                bz2) COMP="bzip2"; DECOMP="bzip2 -dc"; EEXT=".$EXT";;
                *)
                    echo "Failed to find cdc-acm kernel module (got extension $EXT from $MODULE). ABORTING!"
                    exit 0
                    ;;
        esac

        #echo "COMP=$COMP DECOMP=$DECOMP EXT=$EXT EEXT=$EEXT from MODULE=$MODULE"
        echo "    cdc-acm.ko${EEXT} found, proceeding to kludge it..."

        cd ${NEWDIR}/kernel/drivers && \
          mv -n media/rc/ir_toy.ko${EEXT} media/rc/ir_toy.ko${EEXT}.DISABLED && \
          mv -n usb/class/cdc-acm.ko${EEXT} usb/class/cdc-acm.ko${EEXT}.DISABLED && \
          $DECOMP < usb/class/cdc-acm.ko${EEXT}.DISABLED | env -i sed -e 's/\xd8\x04\x08\xfd/\xff\x04\x08\xfd/' | $COMP  > usb/class/cdc-acm.ko${EEXT} && \
          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