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| | #!/bin/sh -eu
#
# SPDX-FileCopyrightText: 2021-2023, 2025 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[:PARTMiB]]]...
ONE_MiB=1048576
# 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 $1.
fillPartition() {
start="$(sfdisk -J "$1" | jq -r --argjson index "$2" \
'.partitiontable.partitions[$index].start * 512')"
# GNU cat will use copy_file_range(2) if possible, whereas dd
# will always do a userspace copy, which is significantly slower.
lseek -S 1 "$start" cat "$3" 1<>"$1"
}
scriptsDir="$(dirname "$0")"
out="$1"
shift
table=$(for partition; do
awk -f "$scriptsDir/sfdisk-field.awk" \
-v partition="$partition" \
-v size="$(sizeMiB "${partition%%:*}")"
done)
# Keep 1MiB free at the start, and 1MiB free at the end.
gptMiB=2
while read -r partition; do
# Here we rely on sfdisk-field.awk always putting size last.
: $((gptMiB += ${partition##*=}))
done <<EOF
$table
EOF
rm -f "$out"
truncate -s "${gptMiB}M" "$out"
sfdisk --no-reread --no-tell-kernel "$out" <<EOF
label: gpt
sector-size: $ONE_MiB
$table
EOF
n=0
for partition; do
fillPartition "$out" "$n" "${partition%%:*}"
n="$((n + 1))"
done
|