SchOS/tools/posix/mkiso.sh

#!/bin/sh
# Build a bootable SchOS ISO.
#
#   tools/posix/mkiso.sh [output.iso]
#
# The disc carries one El Torito boot entry and a real directory tree:
#
#   /boot/efiboot.img      a FAT image holding the loader and the kernel
#   /EFI/BOOT/BOOTX64.EFI  the same loader, visible as a file on the disc
#   /bin /etc /usr ...     the staged sysroot, as an ordinary hierarchy
#
# --- Why only one entry -----------------------------------------------------
#
# There was a second, for BIOS: cdboot and stage2 concatenated with the kernel
# and loaded by El Torito in no-emulation mode. The BIOS loader is gone, so the
# entry that started it is too.
#
# What UEFI wants is not that mechanism at all. Firmware does not run
# no-emulation boot code; it looks for a FAT filesystem containing
# EFI/BOOT/BOOTX64.EFI and hands that volume to the application it finds. So
# the entry is a FAT image built with mtools, and it carries the kernel as well
# as the loader -- BOOTX64.EFI opens \schos\kernel on the volume it was itself
# loaded from, and for a UEFI boot that volume is this FAT image, not the ISO
# 9660 tree around it. Without the kernel in here the loader comes up and halts
# with EFI_NOT_FOUND, which is what it did.
#
# The loader is also copied into the ISO tree at /EFI/BOOT/BOOTX64.EFI, because
# some firmware looks there directly when booting from a USB stick.
#
# --- Booting from a USB stick -----------------------------------------------
#
# -isohybrid-gpt-basdat adds a GPT that marks the FAT image as a basic data
# partition, so writing this .iso to a stick with dd produces something UEFI
# will boot. That was already the only arrangement that worked from a stick:
# the firmware presents the medium as a hard disk, while the BIOS loader read
# the kernel back over ATAPI, so it never booted this way even when it existed.
#
# --- Rock Ridge and Joliet --------------------------------------------------
#
# Plain ISO 9660 gives 8.3 uppercase names with no permissions, so the sysroot
# would arrive as /BIN/TOYBOX.;1 with every file marked the same. Rock Ridge
# restores POSIX names, permissions and symlinks for Unix readers; Joliet does
# long names for Windows. Both are additions to the same image -- a reader that
# understands neither still sees a valid, if ugly, ISO 9660 disc.
#
# -cache-inodes matters more than it looks: the sysroot is a toybox multicall
# binary with a couple of hundred hard links to it. Without inode caching each
# link becomes its own copy and the disc grows by two orders of magnitude.

set -e

BUILD=${BUILD:-build}
OUT=${1:-schos.iso}
STAGING="$BUILD/iso"
SYSROOT=${SYSROOT:-sysroot}

KERNEL="$BUILD/kernel/kernel"
EFIAPP="$BUILD/uefi/BOOTX64.EFI"

[ -f "$KERNEL" ] || { echo "mkiso: missing $KERNEL -- run make first" >&2; exit 1; }
[ -f "$EFIAPP" ] || { echo "mkiso: missing $EFIAPP -- run 'make uefi' first" >&2; exit 1; }

# mtools is not optional any more. It used to be: without it the disc fell back
# to being BIOS-only, which was a degraded disc rather than no disc. There is no
# other entry to fall back to now, so a missing mformat means the ISO would not
# boot anything, and failing here says so instead of shipping it.
if ! command -v mformat >/dev/null 2>&1 || ! command -v mcopy >/dev/null 2>&1; then
    echo "mkiso: need mtools (mformat, mcopy) to build the EFI system partition" >&2
    echo "       Fedora: sudo dnf install mtools" >&2
    echo "       Debian/Ubuntu: apt install mtools" >&2
    exit 1
fi

rm -rf "$STAGING"
mkdir -p "$STAGING/boot" "$STAGING/EFI/BOOT"

cp "$EFIAPP" "$STAGING/EFI/BOOT/BOOTX64.EFI"

# The FAT image for the UEFI El Torito entry.
#
# It carries the kernel as well as the loader. BOOTX64.EFI opens \schos\kernel
# on the volume it was itself loaded from, and for a UEFI boot that volume is
# this FAT image -- not the ISO 9660 tree around it. Without the kernel in here
# the loader comes up and halts with EFI_NOT_FOUND, which is what it did.
#
# The ISO 9660 tree still carries the sysroot for a running system to read; the
# loader's own two files live in here because that is the volume it is handed.
#
# Sized from what actually goes in plus slack, rather than fixed: a hardcoded
# size is a thing that breaks quietly the first time the kernel grows.
EFI_IMG="$STAGING/boot/efiboot.img"
payload_kb=$(( ( $(wc -c < "$EFIAPP") + $(wc -c < "$KERNEL") + 1023 ) / 1024 ))
img_kb=$(( ( (payload_kb + 512 + 31) / 32 ) * 32 ))
[ "$img_kb" -lt 512 ] && img_kb=512

rm -f "$EFI_IMG"
if true; then
    # Create the file first and format it with an explicit geometry.
    #
    # Not `mformat -f`: that takes one of the standard floppy capacities
    # (360, 720, 1440, 2880 KB) and rejects anything else -- "Bad size 512".
    # Giving heads, sectors-per-track and a total sector count instead lets the
    # image be whatever the loader actually needs, which is the point of sizing
    # it from the file rather than hardcoding 1.44 MB.
    dd if=/dev/zero of="$EFI_IMG" bs=1024 count="$img_kb" status=none
    mformat -i "$EFI_IMG" -h 64 -s 32 -T $((img_kb * 2)) ::
    mmd   -i "$EFI_IMG" ::/EFI ::/EFI/BOOT ::/schos
    mcopy -i "$EFI_IMG" "$EFIAPP" ::/EFI/BOOT/BOOTX64.EFI
    mcopy -i "$EFI_IMG" "$KERNEL" ::/schos/kernel
fi

# The sysroot, as an ordinary hierarchy. Copied rather than linked so that
# whatever ends up on the disc is a snapshot, not a view of a tree that may be
# rebuilt underneath it.
if [ -d "$SYSROOT" ]; then
    for d in "$SYSROOT"/*; do
        [ -e "$d" ] || continue
        cp -a "$d" "$STAGING/"
    done
fi

# xorriso if it is here, mkisofs otherwise. Both accept the El Torito flags
# below unchanged -- xorriso's -as mkisofs mode exists precisely to be
# argument-compatible with it. The fallback is not academic: there is no xorriso
# package for Windows in scoop, where this is developed, but cdrtools provides
# mkisofs.exe.
if command -v xorriso >/dev/null 2>&1; then
    MKISOFS="xorriso -as mkisofs"
    HYBRID="-isohybrid-gpt-basdat"      # mkisofs proper does not know this one
elif command -v mkisofs >/dev/null 2>&1; then
    MKISOFS="mkisofs"
    HYBRID=""
else
    echo "mkiso: need xorriso or mkisofs on PATH" >&2
    echo "       Windows: scoop install cdrtools" >&2
    echo "       Debian/Ubuntu: apt install xorriso" >&2
    exit 1
fi

# shellcheck disable=SC2086  # EFI_ARGS is a deliberate word list
$MKISOFS \
    -quiet \
    -V SCHOS \
    -A "SchOS" \
    -R -J -joliet-long \
    -cache-inodes \
    -e boot/efiboot.img \
    -no-emul-boot \
    $HYBRID \
    -o "$OUT" \
    "$STAGING"

echo "==> $OUT ($(wc -c < "$OUT") bytes)"
echo "    UEFI: qemu-system-x86_64 -bios OVMF_CODE.fd -cdrom $OUT"
echo "    USB:  dd if=$OUT of=/dev/sdX bs=4M"