sd-card-images/scripts/build-image

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#!/bin/sh
# Build empty image
IMAGE="${1}"
set -ex
# Aim for a 4 GB image default but with 5% unpartitioned as a margin, and a minimum of 1 GB
# >>> (0.95 * 4000000000 // 512) * 512
# 3800000000.0
IMAGE_SIZE=${IMAGE_SIZE:-3800000000}
if [ $IMAGE_SIZE -lt 1000000000 ]; then
echo "IMAGE_SIZE of 1GB or less unsupported!"
exit 1
fi
rm -f "${IMAGE}"
# fallocate fails on some (git CI) COW filesystems, so have a coreutils alternative.
fallocate -v -l "${IMAGE_SIZE}" "${IMAGE}" || truncate --size "${IMAGE_SIZE}" "${IMAGE}" # 3,800,000,000 bytes
parted -s "${IMAGE}" mklabel msdos
parted -s "${IMAGE}" mkpart primary fat32 -- 4MiB 32MiB # 28 MiB (29,360,128 bytes)
parted -s "${IMAGE}" mkpart primary ext2 -- 32MiB -1
parted -s "${IMAGE}" set 2 boot on
# Create empty FAT partition
rm -f vfat.img
# fallocate fails on some (git CI) COW filesystems, so have a coreutils alternative.
fallocate -l 28MiB vfat.img || truncate --size 28MiB vfat.img
mkfs.vfat vfat.img
# Leave a friendly note about this partition
echo "The boot process for this SoC does not use this partition." >> PARTITION_INTENTIONALLY_EMPTY.TXT
mcopy -v -i vfat.img PARTITION_INTENTIONALLY_EMPTY.TXT ::
# Copy FAT partition to image
dd if=vfat.img of="${IMAGE}" bs=1K seek=4K conv=notrunc