#!/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=$((end - start)) iflag=skip_bytes,count_bytes 2> /dev/null |
(
# shellcheck disable=SC2030
if [ -n "$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 \
> "$subarchive"
# shellcheck disable=SC2030,SC2031
xcpio "$subarchive" "${dir:+$dir/main}" -i "$@"
else
# Don't use subdirectories (for backward compatibility)
# shellcheck disable=SC2031
xcpio "$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
Mini Shell