mirror of
https://github.com/flatcar/scripts.git
synced 2025-10-25 22:31:09 +02:00
79 lines
2.3 KiB
Bash
Executable File
79 lines
2.3 KiB
Bash
Executable File
#!/bin/bash
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# Does as it says on the tin.
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#
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# Example: extract-initramfs-from-vmlinuz /boot/flatcar/vmlinuz-a out-dir
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#
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# This will create one or more out-dir/rootfs-N directories that contain the contents of the initramfs.
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set -euo pipefail
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# check for xzcat. Will abort the script with an error message if the tool is not present.
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xzcat -V >/dev/null
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fail() {
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echo "${*}" >&2
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exit 1
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}
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find_xz_headers() {
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grep --fixed-strings --text --byte-offset --only-matching $'\xFD\x37\x7A\x58\x5A\x00' "$1" | cut -d: -f1
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}
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decompress_at() {
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# Data may not really be a valid xz, so allow for errors.
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tail "-c+$((${2%:*} + 1))" "$1" | xzcat 2>/dev/null || true
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}
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try_extract() {
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# cpio can do strange things when given garbage, so do a basic check.
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[[ $(head -c6 "$1") == 070701 ]] || return 0
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while {
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# cpio needs the directory to exist first. Fail if it's already there.
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{ mkdir "${out}/rootfs-${ROOTFS_IDX}" || return $?; } &&
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# There may be multiple concatenated archives so try cpio till it fails.
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cpio --quiet --extract --make-directories --directory="${out}/rootfs-${ROOTFS_IDX}" --nonmatching 'dev/*' 2>/dev/null
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}; do
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ROOTFS_IDX=$(( ROOTFS_IDX + 1 ))
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done < "$1"
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# Last cpio attempt may or may not leave an empty directory.
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rmdir "${out}/rootfs-${ROOTFS_IDX}" 2>/dev/null || ROOTFS_IDX=$(( ROOTFS_IDX + 1 ))
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}
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me="${0##*/}"
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if [[ $# -ne 2 ]]; then
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fail "Usage: ${me} <vmlinuz> <output_directory>"
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fi
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image="${1}"
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out="${2}"
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if [[ ! -s "${image}" ]]; then
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fail "The image file '${image}' either does not exist or is empty"
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fi
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mkdir -p "${out}"
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tmp=$(mktemp --directory -t eifv-XXXXXX)
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trap 'rm -rf -- "${tmp}"' EXIT
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ROOTFS_IDX=0
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# arm64 kernels are not compressed, so try decompressing once.
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# Other kernels are compressed, so also try decompressing twice.
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for OFF1 in $(find_xz_headers "${image}")
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do
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decompress_at "${image}" "${OFF1}" > "${tmp}/initrd.maybe_cpio_or_elf"
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try_extract "${tmp}/initrd.maybe_cpio_or_elf"
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for OFF2 in $(find_xz_headers "${tmp}/initrd.maybe_cpio_or_elf")
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do
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decompress_at "${tmp}/initrd.maybe_cpio_or_elf" "${OFF2}" > "${tmp}/initrd.maybe_cpio"
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try_extract "${tmp}/initrd.maybe_cpio"
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done
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done
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if [[ ${ROOTFS_IDX} -eq 0 ]]; then
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fail "no initramfs found in ${image}"
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fi
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echo "done, found ${ROOTFS_IDX} rootfs(es)"
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