#!/bin/sh
# SPDX-License-Identifier: GPL-2.0-or-later
#
# Build a partitioned SchOS disk: the image a real machine boots from.
#
#   tools/posix/mkdisk.sh <esp-dir> <schfs.img> <output.img>
#
# A GUID partition table with two entries:
#
#   1  EFI system partition   FAT, holding <esp-dir> (the loader and kernel)
#   2  SchFS                  <schfs.img>, byte for byte, typed
#                             47138FA9-B79C-47A6-9F7D-AC1F7F572D5E
#
# This is the layout every UEFI machine expects: the firmware finds the ESP by
# its type and runs EFI/BOOT/BOOTX64.EFI from it, and the kernel finds the root
# by scanning the same table -- the SchFS type first, anything else after (see
# rootdev_mount() in kernel/proc/proc.c). Write it to a USB stick or a disk
# with dd and it boots; attach it to QEMU's q35 as its only disk and it boots
# the same way.
#
# The SchFS partition holds the volume unchanged. A filesystem addresses
# blocks from the start of whatever it is on, and the kernel hands a partition
# to it as a device whose block 0 is the partition's first sector -- so the
# image mkschfs writes for a whole disk is already the right content for a
# partition, and so is anything a Linux SchFS driver is given as /dev/sdX2.
#
# Needs sfdisk (util-linux) and mtools. Nothing here needs root or loop
# devices: the FAT is built in a file and copied in at its offset.

set -eu

esp=$1
vol=$2
out=$3

SCHFS_TYPE=47138FA9-B79C-47A6-9F7D-AC1F7F572D5E
ESP_TYPE=C12A7328-F81F-11D2-BA4B-00A0C93EC93B

for t in sfdisk mformat mcopy; do
    command -v $t >/dev/null || { echo "mkdisk: needs $t" >&2; exit 1; }
done

# Sizes in 512-byte sectors. The ESP is 64 MB, which leaves room for the
# kernel to grow by an order of magnitude; partitions start on 1 MB
# boundaries, which is what every partitioning tool does and what flash
# media erase in.
esp_mb=64
esp_start=2048
esp_sectors=$((esp_mb * 2048))
vol_bytes=$(wc -c < "$vol")
vol_start=$((esp_start + esp_sectors))
vol_sectors=$(( (vol_bytes + 511) / 512 ))
# 1 MB at the end for the backup GPT, rounded the same way.
total=$((vol_start + vol_sectors + 2048))

rm -f "$out" "$out.esp"
dd if=/dev/zero of="$out" bs=512 count=0 seek=$total 2>/dev/null

sfdisk --quiet --label gpt "$out" <<EOF
start=$esp_start, size=$esp_sectors, type=$ESP_TYPE, name="EFI system"
start=$vol_start, size=$vol_sectors, type=$SCHFS_TYPE, name="SchOS"
EOF

# The ESP, built apart and copied in.
dd if=/dev/zero of="$out.esp" bs=1M count=$esp_mb 2>/dev/null
mformat -i "$out.esp" -F -v SCHOS ::
mcopy -i "$out.esp" -s "$esp"/* ::
dd if="$out.esp" of="$out" bs=512 seek=$esp_start conv=notrunc 2>/dev/null
rm -f "$out.esp"

dd if="$vol" of="$out" bs=512 seek=$vol_start conv=notrunc 2>/dev/null

echo "mkdisk: $out -- ESP ${esp_mb} MB, SchFS $((vol_bytes >> 20)) MB"