#!/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_BYTES=66688
MAX_PARMFILE_SIZE=896

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

# Cleanup on exit
cleanup()
{
	if [ -n "$binval" ]
	then
		rm -f $binval
	fi
	if [ -n "$image" -a $success = no ]
	then
		rm $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
EOF
}

# 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' $(expr $num % 256))$b"
		num=$(expr $num / 256) || true
	done
	printf $b
}

# 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
	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 $ramdisk | cut -f1)
		kernel_size=$(du -b $kernel | cut -f1)
		ramdisk_offset=$(du -b $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 [ "$parmfile" != "" ]
	then
		parmfile_size=$(du -b $parmfile | cut -f1)
		if [ $parmfile_size -le $MAX_PARMFILE_SIZE ]
		then
			dd seek=$OFFS_COMMANDLINE_BYTES bs=1 if=$parmfile \
			    of=$image conv=notrunc status=none
		else
			echo "$cmd: Size $parmfile_size of $parmfile exceeds command line limit of $MAX_PARMFILE_SIZE" >&2
			return 1
		fi
	fi

	# we've done it
	success=yes
}

# check args and build
args=$(getopt "r:p:h" $*)
if [ $? = 0 ]
then
	set -- $args
	while [ $1 != "" ]
	do
		case $1 in
			-r) ramdisk=$2; shift 2;;
			-p) parmfile=$2; shift 2;;
			-h) usage; exit 0;;
			--) shift; break;;
			*) echo "$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