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#!/bin/sh -eu
#
# SPDX-FileCopyrightText: 2021-2022 Alyssa Ross <hi@alyssa.is>
# SPDX-FileCopyrightText: 2022 Unikie
# SPDX-License-Identifier: EUPL-1.2+
#
# usage: make-gpt.sh GPT_PATH PATH:PARTTYPE[:PARTUUID[:PARTLABEL]]...
ONE_MiB=1048576
TWO_MiB=2097152
# Prints the number of 1MiB blocks required to store the file named
# $1. We use 1MiB blocks because that's what sfdisk uses for
# alignment. It would be possible to get a slightly smaller image
# using actual normal-sized 512-byte blocks, but it's probably not
# worth it to configure sfdisk to do that.
sizeMiB() {
wc -c "$1" | awk -v ONE_MiB=$ONE_MiB \
'{printf "%d\n", ($1 + ONE_MiB - 1) / ONE_MiB}'
}
# Copies from path $3 into partition number $2 in partition table $1.
fillPartition() {
sfdisk -J "$1" | jq -r --argjson index "$2" \
'.partitiontable.partitions[$index] | "\(.start) \(.size)"' |
(read -r start size;
dd if="$3" of="$1" seek="$start" count="$size" conv=notrunc)
}
# Prints the partition path from a PATH:PARTTYPE[:PARTUUID[:PARTLABEL]] string.
partitionPath() {
awk -F: '{print $1}' <<EOF
$1
EOF
}
scriptsDir="$(dirname "$0")"
out="$1"
shift
nl='
'
table="label: gpt"
# Keep 1MiB free at the start, and 1MiB free at the end.
gptBytes=$TWO_MiB
for partition; do
sizeMiB="$(sizeMiB "$(partitionPath "$partition")")"
table="$table${nl}size=${sizeMiB}MiB,$(awk -f "$scriptsDir/sfdisk-field.awk" -v partition="$partition")"
gptBytes="$((gptBytes + sizeMiB * ONE_MiB))"
done
rm -f "$out"
truncate -s "$gptBytes" "$out"
sfdisk "$out" <<EOF
$table
EOF
n=0
for partition; do
fillPartition "$out" "$n" "$(partitionPath "$partition")"
n="$((n + 1))"
done
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