bootprep-btrfs

#!/usr/bin/env bash
#
# bootprep-btrfs
#
# A btrfs orchestrator
#
# Version: 2.1.0
# License: GPL-3.0-or-later
#
# Copyright (C) 2026 Scott McClain
# SPDX-License-Identifier: GPL-3.0-or-later

set -euo pipefail

# Wrap once so nested installer/engine calls share the same bounded run log.
if [[ $EUID -eq 0 && "${BOOTPREP_LOG_ACTIVE:-}" != 1 && "${1:-}" == activate ]]; then
    command -v python3 >/dev/null 2>&1 || { echo "Please install Python 3 for BootPrep logging." >&2; exit 1; }
    BOOTPREP_LOG_HELPER="/usr/lib/bootprep/bootprep-log.py"
    [[ -f "$BOOTPREP_LOG_HELPER" ]] || { echo "Missing BootPrep logging helper: $BOOTPREP_LOG_HELPER" >&2; exit 1; }
    exec python3 "$BOOTPREP_LOG_HELPER" /bin/bash "${BASH_SOURCE[0]}" "$@"
fi


readonly BTRFS="/usr/bin/btrfs"
readonly BOOTPREP="/usr/sbin/bootprep"

die() {
    printf '[ERROR] %s\n' "$1" >&2
    exit 1
}

require_root() {
    [[ ${EUID} -eq 0 ]] || die "Please run with sudo."
}

activate() {
    local snapshot_num="${1:-}"
    local mount_point="${2:-/}"
    local base_mount
    local target
    local subvol_id

    [[ $# -le 2 ]] \
        || die "Usage: bootprep-btrfs activate <snapshot-number> [mount-point]"

    [[ -n "${snapshot_num}" && "${snapshot_num}" =~ ^[0-9]+$ ]] \
        || die "Usage: bootprep-btrfs activate <snapshot-number> [mount-point]"

    [[ -d "${mount_point}" ]] \
        || die "Mount point does not exist: ${mount_point}"

    base_mount="${mount_point%/}/"
    target="${base_mount}.snapshots/${snapshot_num}/snapshot"

    [[ -d "${target}" ]] \
        || die "Snapshot directory does not exist: ${target}"

    "${BTRFS}" subvolume show "${target}" >/dev/null 2>&1 \
        || die "Snapshot path is not a Btrfs subvolume: ${target}"

    subvol_id="$("${BTRFS}" inspect-internal rootid "${target}")"

    [[ "${subvol_id}" =~ ^[0-9]+$ ]] \
        || die "Unable to resolve Btrfs subvolume ID for: ${target}"

    printf '\n'
    printf '=========================================\n'
    printf ' BootPrep Btrfs\n'
    printf '=========================================\n'
    printf 'Snapshot    : #%s\n' "${snapshot_num}"
    printf 'Path        : %s\n' "${target}"
    printf 'Mount Point : %s\n' "${mount_point}"
    printf '\n'

    printf '[1/3] Making snapshot writable...\n'
    "${BTRFS}" property set "${target}" ro false

    printf '[2/3] Setting default Btrfs subvolume...\n'
    "${BTRFS}" subvolume set-default "${subvol_id}" "${mount_point}"

    printf '[3/3] Preparing snapshot for boot...\n'
    "${BOOTPREP}" prepare "${snapshot_num}"

    printf '\n'
    printf '[ OK ] Snapshot #%s is activated and ready for reboot.\n' "${snapshot_num}"
}

require_root

case "${1:-}" in
    activate)
        shift
        activate "$@"
        ;;
    *)
        exec "${BTRFS}" "$@"
        ;;
esac