lsinitrd-quick

#! /bin/bash

trap 'echo error in $BASH_COMMAND >&2; exit 1' ERR

MG_CPIO=$'\x71\xc7'
MG_CPIO1=070701
MG_GZ=$'\x1f\x8b'
MG_GZ1=$'\x1f\x9e'
MG_BZ="BZh"
MG_XZ=$'\xfd7zXZ'
MG_LZ4=$'\x02\x21'
MG_LZO=$'\x89LZO'
MG_ZSTD=$'\x28\xB5\x2F\xFD'

check_fmt() {
    case $1 in
	$MG_CPIO*|$MG_CPIO1)
	    echo cpio;;
	$MG_GZ*|$MG_GZ1*)
	    echo gzip;;
	$MG_BZ*)
	    echo bz2;;
	$MG_XZ*)
	    echo xz;;
	$MG_LZ4*)
	    echo lz4;;
	$MG_LZO*)
	    echo lzo;;
	$MG_ZSTD*)
	    echo zstd;;
    esac
}

uncomp() {
    case $1 in
	$MG_CPIO*|$MG_CPIO1)
	    cat;;
	$MG_GZ*)
	    zcat;;
	$MG_BZ*)
	    bzcat;;
	$MG_XZ*)
	    xzcat;;
	$MG_LZ4*)
	    lz4 -d -c;;
	$MG_LZO*)
	    lzop -d -c;;
	$MG_ZSTD*)
	    zstd -d -c;;
    esac
}

check_size () {
    [[ "$SIZE" -gt $1 ]] || {
	echo "$INITRD: file too small, cannot read magic" >&2
	exit 1
    }
}

INITRD=$1
[[ "$INITRD" && -f "$INITRD" ]] || {
    echo "$INITRD: file not found" >&2
    exit 1
}
SIZE=$(stat -L -c %s "$INITRD")
check_size 6

read -r -d'\0' -n 6 MAGIC <"$INITRD"
FMT=$(check_fmt "$MAGIC")
BYTES=0
if [[ ! $FMT ]]; then
    echo "$INITRD: unknown format" >&2
    exit 1
elif [[ "$FMT" = cpio ]]; then
    # check for "early CPIO" image
    TMPFILE=$(mktemp "${TMPDIR:-/tmp}/initrd-XXXXXX")
    EARLY=$(cpio -t early_cpio "kernel/*/microcode/*.bin" \
		 <"$INITRD" 2>"$TMPFILE")
    BLOCKS=$(cut -d" " -f1 "$TMPFILE")
    rm -f "$TMPFILE"
    if [[ -z "$EARLY" ]]; then
	# just plain uncompressed cpio
	cpio -t <"$INITRD" 2>/dev/null
	exit
    fi
    BYTES=$((512*BLOCKS))
    check_size $((BYTES + 6))
    read -r -d '\0' -n 6 MAGIC \
	 < <(dd if="$INITRD" bs=1b count=1 skip=$BLOCKS 2>/dev/null)
fi

tail -c +$((BYTES + 1)) "$INITRD" | uncomp "$MAGIC" | cpio -t 2>/dev/null