geniso

#!/bin/sh
set -eu

# Required packages:
for x in \
    dev-libs/libisoburn \
    sys-boot/grub \
    sys-fs/mtools \
    sys-fs/squashfs-tools \
    sys-kernel/dracut
do
    qlist -Ie "$x" > /dev/null || emerge --ask=y -1 "$x"
done

ROOT="${1:-$PWD/root}"
ISO="${2:-$PWD/iso}"
OUT="${3:-$PWD/image.iso}"

mkdir -p "$ISO/LiveOS"

test -f "$ISO/LiveOS/squashfs.img" || mksquashfs "$ROOT" "$ISO/LiveOS/squashfs.img" -comp xz

kver="$(readlink "$ROOT/usr/src/linux")"
kver="${kver#linux-}"

# -r/--sysroot option currently *heavily* broken (dracut 059)
test -f "$ISO/LiveOS/initramfs.img" || dracut "$ISO/LiveOS/initramfs.img" "$kver" \
    --xz \
    --omit plymouth \
    --add dmsquash-live

test -f "$ISO/LiveOS/bzImage" || cp "$ROOT/usr/src/linux/arch/x86/boot/bzImage" "$ISO/LiveOS/bzImage"

mkdir -p "$ISO/boot/grub"
cat > "$ISO/boot/grub/grub.cfg" << 'EOF'
set timeout=1
set gfxpayload=keep
insmod all_video
menuentry 'boot' {
    linux /LiveOS/bzImage root=live:CDLABEL=ISOIMAGE loglevel=0
    initrd /LiveOS/initramfs.img
}
EOF
grub-mkrescue -joliet -iso-level 3 -o "$OUT" "$ISO"