Naive local initrd updater

initrd-rpm-update.sh

#!/usr/bin/bash
# SPDX-FileCopyrightText: 2023 SUSE LLC
#
# SPDX-License-Identifier: GPL-2.0-only

# Naive emergency tool to update existing initrd from RPM.
# Primary usecase is to PTF update saltboot initrd

set -e

function usage() {
cat << EOF
$0 - Update existing initrd based on RPM

Usage: $0 initrd rpm

If RPM poinst to the directory, it will source all present RPMs and update
initrd in alphabetical order.
EOF
exit 1
}

if [ -z "$1" ]; then
  echo "ERROR: Missing initrd argument!"
  usage
fi
if [ ! -f "$1" ]; then
  echo "Provided initrd '$1' does not exists!"
  usage
fi
INITRD=$(realpath "$1")

if [ -z "$2" ]; then
  echo "EROR: Missing RPM argument!"
  usage
fi
if [ ! -e "$2" ]; then
  echo "Provided RPM path '$2' does not exists!"
  usage
fi
RPMDIR=$(realpath "$2")
RPMS=()
if [ -d "$RPMDIR" ]; then
  readarray -d '' RPMS < <(find "$RPMDIR" -type f -print0)
else
  RPMS=("$RPMDIR")
fi

WORKDIR=$(dirname "$INITRD")
BACKUP=$(mktemp --tmpdir="$WORKDIR" "$(basename ${INITRD}).XXX")
echo "Backing up initrd to the '$BACKUP'"
cp -f "$INITRD" "$BACKUP"

TMPDIR=$(mktemp -d --tmpdir="$WORKDIR")
pushd "$TMPDIR"
for RPM in "${RPMS[@]}"; do
  echo "Extracting $RPM"
  rpm2cpio "$RPM" | cpio -idm
done

echo "Updating initrd"
find . | cpio -H newc -o | zstd >> "$INITRD"

HASH=$(md5sum "$INITRD")
SIZE=$(stat -c "%s" "$INITRD")
popd
rm -r "$TMPDIR"

echo -e "All done.\n New initrd size: $SIZE\n New initrd hash: $HASH"