#!/bin/bash
#
# netboot - PXE-style boot for KVM on s390
#
# Sample script to build a single s390 boot image consisting of
# kernel, an initial ramdisk and kernel parameters from
# individual components. Note that bash is required to run this script!
#
# Sample invocation:
#
# ./mk-s390image /boot/image -r /boot/initrd image
#
# The resulting image can be used to build a bootable
# ISO or as firmware image for KVM.
#
# Copyright IBM Corp. 2017
#
# s390-tools is free software; you can redistribute it and/or modify
# it under the terms of the MIT license. See LICENSE for details.

# Offsets
OFFS_INITRD_START_BYTES=66568
OFFS_INITRD_SIZE_BYTES=66576
OFFS_COMMANDLINE_MAX_SIZE_BYTES=66608
OFFS_COMMANDLINE_BYTES=66688
LEGACY_MAX_PARMFILE_SIZE=896

# Variables
cmd=$(basename -- "$0")
kernel=
ramdisk=
parmfile=
image=
binval=
success=no

# Cleanup on exit
# shellcheck disable=SC2317
cleanup()
{
	if [ -n "$binval" ]; then
		rm -f -- "$binval"
	fi
	if [ -n "$image" ] && [ "$success" = no ]; then
		rm -f -- "$image"
	fi
}
trap cleanup EXIT

# Usage
usage()
{
	cat <<- EOF
		Usage: $cmd KERNEL BOOT_IMAGE [-r RAMDISK] [-p PARMFILE]

		Build an s390 image BOOT_IMAGE suitable for CD/tape/network boot or as a
		KVM firmware image using a stripped Linux kernel file KERNEL.

		OPTIONS
		-p        Use PARMFILE with kernel parameters in the image
		-r        Include RAMDISK in the image
		-h        Print this help, then exit
		-v        Print version information, then exit
	EOF
}

printversion()
{
	cat <<- EOD
		$cmd: version %S390_TOOLS_VERSION%
		Copyright IBM Corp. 2017
	EOD
}

# Convert decimal number to big endian doubleword
dec2be64()
{
	local num=$1
	local b
	local i
	for i in $(seq 1 8); do
		b="\\x$(printf '%x' "$((num % 256))")$b"
		num=$((num / 256)) || true
	done
	printf '%b' "$b"
}

max_kernel_cmdline_size()
{
	local __kernel=$1 size v

	size_be="$(od -A n -j "${OFFS_COMMANDLINE_MAX_SIZE_BYTES}" -N 8 -t uL -- "$__kernel")"
	# If little endian then swap bytes
	if (("$(printf '\1' | od -dAn)" == 1)); then
		v="$(printf '%016x0' "$size_be")"
		size="0x${v:14:2}${v:12:2}${v:10:2}${v:8:2}${v:6:2}${v:4:2}${v:2:2}${v:0:2}"
	else
		size="$size_be"
	fi
	if ((size == 0)); then
		size="${LEGACY_MAX_PARMFILE_SIZE}"
	fi
	# Use arithmetic expression to remove leading and trailing whitespace.
	printf '%s' "$((size))"
}

# Do the image build
dobuild()
{
	local i
	local kernel_size
	local ramdisk_size
	local ramdisk_offset
	local parmfile_size
	# check whether all specified files exist
	for i in $kernel $ramdisk $parmfile; do
		if [ ! -f "$i" ]; then
			echo "$cmd: File $i not found" >&2
			return 1
		fi
		if [ ! -r "$i" ]; then
			echo "$cmd: File $i cannot be read, no read permission" >&2
			return 1
		fi
	done
	if ! file -b -- "$(readlink -f -- "$kernel")" | grep "Linux S390" > /dev/null; then
		echo "$cmd: Unrecognized file format for $kernel" >&2
		return 1
	fi

	# from now on we SHOULD only fail on disk shortage
	# or file permissions, let the shell handle that
	set -e

	# copy over kernel padded with zeroes to page boundary
	dd if="$kernel" of="$image" bs=4096 conv=sync status=none

	# append ramdisk if specified
	if [ "$ramdisk" != "" ]; then
		ramdisk_size=$(du -b -L -- "$ramdisk" | cut -f1)
		# shellcheck disable=SC2034
		kernel_size=$(du -b -L -- "$kernel" | cut -f1)
		ramdisk_offset=$(du -b -L -- "$image" | cut -f1)
		cat -- "$ramdisk" >> "$image"
		binval=$(mktemp)
		dec2be64 "$ramdisk_offset" > "$binval"
		dd seek=$OFFS_INITRD_START_BYTES if="$binval" of="$image" bs=1 \
			count=8 conv=notrunc status=none
		dec2be64 "$ramdisk_size" > "$binval"
		dd seek=$OFFS_INITRD_SIZE_BYTES if="$binval" of="$image" bs=1 \
			count=8 conv=notrunc status=none
	fi

	# set cmdline
	if [ "$parmfile" != "" ]; then
		max_parmfile_size=$(max_kernel_cmdline_size "$kernel")
		parmfile_size=$(du -b -L -- "$parmfile" | cut -f1)
		if ((parmfile_size <= max_parmfile_size)); then
			# Clear any previous parameters
			dd seek=$OFFS_COMMANDLINE_BYTES bs=1 count="$max_parmfile_size" \
				if=/dev/zero of="$image" conv=notrunc status=none
			dd seek=$OFFS_COMMANDLINE_BYTES bs=1 count="$parmfile_size" \
				if="$parmfile" of="$image" conv=notrunc status=none
		else
			echo "$cmd: Size $parmfile_size of $parmfile exceeds command line limit of $max_parmfile_size bytes" >&2
			return 1
		fi
	fi

	# we've done it
	success=yes
}

# check args and build
# shellcheck disable=SC2086,SC2048
if args=$(getopt "r:p:hv" $*); then
	# shellcheck disable=SC2086
	set -- $args
	while [ "$1" != "" ]; do
		case $1 in
			-r)
				ramdisk=$2
				shift 2
				;;
			-p)
				parmfile=$2
				shift 2
				;;
			-h)
				usage
				exit 0
				;;
			-v)
				printversion
				exit 0
				;;
			--)
				shift
				break
				;;
			*)
				echo "$cmd: Unexpected argument $1, exiting..." >&2
				exit 1
				;;
		esac
	done
fi

if [ $# = 2 ]; then
	kernel=$1
	image=$2
	dobuild
	exit 0
fi

# something wasn't right
usage >&2
exit 1