#!/usr/bin/env bash
# Build the FIT image GL.iNet's U-Boot boots from the GL-MT6000's `kernel'
# partition (p6, 32 MiB), for one Guix system generation:
#   kernel-1  the system's Image, LZMA-compressed, loaded at 0x48000000
#   fdt-1     mt7986a-glinet-gl-mt6000.dtb with the Guix command line in
#             /chosen/bootargs-append (GL's U-Boot passes empty bootargs;
#             linux-mt6000 carries OpenWrt's bootargs-append patch)
#   initrd-1  the system's initrd
# Same layout as OpenWrt's MT6000 FIT (kernel-1, fdt-1, config-1), plus the
# ramdisk OpenWrt's initramfs image also carries.
#
# Usage: scripts/mt6000-fit.sh /gnu/store/...-system OUTPUT.itb
set -euo pipefail

sys=${1:?usage: $0 SYSTEM OUTPUT.itb}
out=$(realpath -m "${2:?usage: $0 SYSTEM OUTPUT.itb}")
limit=$((32 * 1024 * 1024))

export PATH=$HOME/.local/bin:$PATH
# The package's main output: name-version, no -static/-doc suffix.
tool() { guix build "$1" 2>/dev/null | grep -E -- "-$1-[0-9][^-]*\$"; }
mkimage=$(tool u-boot-tools)/bin/mkimage
dtc=$(tool dtc)/bin
fdtput=$dtc/fdtput
xz=$(tool xz)/bin/xz

params=$(cat "$sys/parameters")
# root=LABEL or root=UUID, as Guix's bootloader configurations do.  (`guix
# system image' gives the image's system its root partition's UUID.)
root=$(sed -n 's/.*(root-device (file-system-label "\([^"]*\)")).*/\1/p' <<<"$params")
if [ -z "$root" ]; then
	bytes=$(sed -n 's/.*(root-device (uuid [a-z0-9]* #vu8(\([0-9 ]*\)))).*/\1/p' <<<"$params")
	[ -n "$bytes" ] || { echo "$0: no label or UUID root in $sys/parameters" >&2; exit 1; }
	hex=$(printf '%02x' $bytes)
	root=${hex:0:8}-${hex:8:4}-${hex:12:4}-${hex:16:4}-${hex:20:12}
fi
kargs=$(sed -n 's/.*(kernel-arguments (\([^)]*\))).*/\1/p' <<<"$params" | tr -d '"')
cmdline="root=$root gnu.system=$sys gnu.load=$sys/boot $kargs"

kernel=$(readlink -f "$sys/kernel")
initrd=$(readlink -f "$sys/initrd")
dtb=$kernel/lib/dtbs/mediatek/mt7986a-glinet-gl-mt6000.dtb
[ -f "$dtb" ] || { echo "$0: $dtb missing" >&2; exit 1; }

work=$(mktemp -d)
trap 'rm -rf "$work"' EXIT
"$xz" --format=lzma -9 -c "$kernel/Image" > "$work/Image.lzma"
cp "$dtb" "$work/board.dtb"
chmod u+w "$work/board.dtb"
# Leading space: appended to whatever U-Boot passes (nothing, here).
"$fdtput" -t s "$work/board.dtb" /chosen bootargs-append " $cmdline"
# (Board fixes for GL's firmware and this kernel: in the DTB, from
# mt7986a-glinet-gl-mt6000-guix.dtsi.)
cp "$initrd" "$work/initrd"

cat > "$work/image.its" <<EOF
/dts-v1/;

/ {
	description = "Guix System for the GL-MT6000";
	#address-cells = <1>;

	images {
		kernel-1 {
			description = "Linux ($(basename "$kernel"))";
			data = /incbin/("Image.lzma");
			type = "kernel";
			arch = "arm64";
			os = "linux";
			compression = "lzma";
			load = <0x48000000>;
			entry = <0x48000000>;
			hash-1 { algo = "crc32"; };
			hash-2 { algo = "sha1"; };
		};
		fdt-1 {
			description = "mt7986a-glinet-gl-mt6000";
			data = /incbin/("board.dtb");
			type = "flat_dt";
			arch = "arm64";
			compression = "none";
			hash-1 { algo = "crc32"; };
		};
		initrd-1 {
			description = "Guix initrd";
			data = /incbin/("initrd");
			type = "ramdisk";
			arch = "arm64";
			os = "linux";
			compression = "none";
			hash-1 { algo = "crc32"; };
		};
	};

	configurations {
		default = "config-1";
		config-1 {
			description = "$(basename "$sys")";
			kernel = "kernel-1";
			fdt = "fdt-1";
			ramdisk = "initrd-1";
		};
	};
};
EOF
# mkimage runs dtc; /incbin paths are relative to the work directory.
(cd "$work" && PATH=$dtc:$PATH "$mkimage" -f image.its "$out" >/dev/null)

size=$(stat -c %s "$out")
if [ "$size" -gt "$limit" ]; then
	echo "$0: $out is $size bytes, over the 32 MiB kernel partition" >&2
	exit 1
fi
echo "$out: $size bytes; command line: $cmdline"