diff options
Diffstat (limited to 'unmkinitramfs')
| -rwxr-xr-x | unmkinitramfs | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/unmkinitramfs b/unmkinitramfs new file mode 100755 index 0000000..a296029 --- /dev/null +++ b/unmkinitramfs @@ -0,0 +1,174 @@ +#!/bin/sh + +set -eu + +usage() +{ + cat << EOF + +Usage: unmkinitramfs [-v] initramfs-file directory + +Options: + -v Display verbose messages about extraction + +See unmkinitramfs(8) for further details. + +EOF +} + +usage_error() +{ + usage >&2 + exit 2 +} + +# Extract a compressed cpio archive +xcpio() +{ + archive="$1" + dir="$2" + shift 2 + + if gzip -t "$archive" >/dev/null 2>&1 ; then + gzip -c -d "$archive" + elif zstd -q -c -t "$archive" >/dev/null 2>&1 ; then + zstd -q -c -d "$archive" + elif xzcat -t "$archive" >/dev/null 2>&1 ; then + xzcat "$archive" + elif lz4cat -t < "$archive" >/dev/null 2>&1 ; then + lz4cat "$archive" + elif bzip2 -t "$archive" >/dev/null 2>&1 ; then + bzip2 -c -d "$archive" + elif lzop -t "$archive" >/dev/null 2>&1 ; then + lzop -c -d "$archive" + # Ignoring other data, which may be garbage at the end of the file + fi | ( + if [ -n "$dir" ]; then + mkdir -p -- "$dir" + cd -- "$dir" + fi + cpio "$@" + ) +} + +# Read bytes out of a file, checking that they are valid hex digits +readhex() +{ + dd < "$1" bs=1 skip="$2" count="$3" 2> /dev/null | \ + LANG=C grep -E "^[0-9A-Fa-f]{$3}\$" +} + +# Check for a zero byte in a file +checkzero() +{ + dd < "$1" bs=1 skip="$2" count=1 2> /dev/null | \ + LANG=C grep -q -z '^$' +} + +# Split an initramfs into archives and call xcpio on each +splitinitramfs() +{ + initramfs="$1" + dir="$2" + shift 2 + + count=0 + start=0 + while true; do + # There may be prepended uncompressed archives. cpio + # won't tell us the true size of these so we have to + # parse the headers and padding ourselves. This is + # very roughly based on linux/lib/earlycpio.c + end=$start + while true; do + if checkzero "$initramfs" $end; then + # This is the EOF marker. There might + # be more zero padding before the next + # archive, so read through all of it. + end=$((end + 4)) + while checkzero "$initramfs" $end; do + end=$((end + 4)) + done + break + fi + magic="$(readhex "$initramfs" $end 6)" || break + test "$magic" = 070701 || test "$magic" = 070702 || break + namesize=0x$(readhex "$initramfs" $((end + 94)) 8) + filesize=0x$(readhex "$initramfs" $((end + 54)) 8) + end=$((end + 110)) + end=$(((end + namesize + 3) & ~3)) + end=$(((end + filesize + 3) & ~3)) + done + if [ $end -eq $start ]; then + break + fi + + # Extract to early, early2, ... subdirectories + count=$((count + 1)) + if [ $count -eq 1 ]; then + subdir=early + else + subdir=early$count + fi + dd < "$initramfs" skip=$start count=$((end - start)) iflag=skip_bytes,count_bytes 2> /dev/null | + ( + if [ -n "$dir" ]; then + mkdir -p -- "$dir/$subdir" + cd -- "$dir/$subdir" + fi + cpio -i "$@" + ) + start=$end + done + + if [ "$end" -gt 0 ]; then + # Extract to main subdirectory + subarchive=$(mktemp "${TMPDIR:-/var/tmp}/unmkinitramfs_XXXXXX") + trap 'rm -f "$subarchive"' EXIT + dd < "$initramfs" skip="$end" iflag=skip_bytes 2> /dev/null \ + > "$subarchive" + xcpio "$subarchive" "${dir:+$dir/main}" -i "$@" + else + # Don't use subdirectories (for backward compatibility) + xcpio "$initramfs" "$dir" -i "$@" + fi +} + +OPTIONS=$(getopt -o hv --long help,list,verbose -n "$0" -- "$@") || usage_error + +cpio_opts="--preserve-modification-time --no-absolute-filenames --quiet" +expected_args=2 +eval set -- "$OPTIONS" + +while true; do + case "$1" in + -h|--help) + usage + exit 0 + ;; + --list) + # For lsinitramfs + cpio_opts="${cpio_opts:+${cpio_opts} --list}" + expected_args=1 + shift + ;; + -v|--verbose) + cpio_opts="${cpio_opts:+${cpio_opts} --verbose}" + shift + ;; + --) + shift + break + ;; + *) + echo "Internal error!" >&2 + exit 1 + esac +done + +if [ $# -ne $expected_args ]; then + usage_error +fi + +# shellcheck disable=SC2086 +splitinitramfs "$1" "${2:-}" $cpio_opts |