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#!/bin/bash

shopt -s nullglob

not() {
    if "$@"; then
        return 1
    else
        return 0
    fi
}

set-vars() {
    KERNEL="$1"
    TARGET="usr/lib/modules/$KERNEL"
    PRESERVE_MODULES_DIR=/run/linux-preserve-modules

    TARGET_DIR="/$TARGET"
    PRESERVE_DIR="$PRESERVE_MODULES_DIR/modules/$KERNEL"

    # exit early if kernel version empty
    if [[ -z "$KERNEL" ]]; then
        echo "error: unknown kernel version" >&2
        exit 1
    fi
}

preserve-modules-copy() {
    if [[ $# -gt 1 ]]; then
        echo "usage: linux-preserve-modules copy [release]" >&2
        exit 1
    elif [[ $# -eq 1 ]]; then
        set-vars "$1"
    fi

    # exit early if the target directory does not exist
    if [[ ! -f "$TARGET_DIR/modules.builtin" ]]; then
        echo "info: nothing to copy" >&2
        exit 0
    fi

    # exit early if kernel modules already copied
    if [[ -d "$PRESERVE_DIR/modules.builtin" ]]; then
        echo "info: already copied" >&2
        exit 0
    fi

    # exit early if kernel modules already copied
    if [[ -f "$TARGET_DIR/.preserved" ]]; then
        echo "info: already linked" >&2
        exit 0
    fi

    # copy over kernel modules and dep files
    mkdir -p "$PRESERVE_DIR"
    cp -r "$TARGET_DIR/modules".* "$PRESERVE_DIR/"
    [[ -d "$TARGET_DIR/kernel" ]] && cp -r "$TARGET_DIR/kernel" "$PRESERVE_DIR/kernel"
    [[ -d "$TARGET_DIR/updates" ]] && cp -r "$TARGET_DIR/updates" "$PRESERVE_DIR/updates"

    echo "info: copied modules" >&2
    exit 0
}

preserve-modules-link() {
    if [[ $# -gt 1 ]]; then
        echo "usage: linux-preserve-modules link [release]" >&2
        exit 1
    elif [[ $# -eq 1 ]]; then
        set-vars "$1"
    fi

    # exit early if no kernel modules copied
    if [[ ! -f "$PRESERVE_DIR/modules.builtin" ]]; then
        echo "info: nothing to link" >&2
        exit 0
    fi

    # exit early if mount targets still owned by a package
    OWNERS=(
        $(pacman -Qoq "$TARGET_DIR/kernel" 2>/dev/null)
        $(pacman -Qoq "$TARGET_DIR/updates" 2>/dev/null)
    )
    if [[ "${#OWNERS[@]}" -ne 0 ]]; then
        echo "info: modules still there" >&2
        exit 0
    fi

    # exit early if kernel modules already copied
    if [[ -f "$TARGET_DIR/.preserved" ]]; then
        echo "info: already linked" >&2
        exit 0
    fi

    # copy over dep files and mark kernel version as preserved
    mkdir -p "$TARGET_DIR/"
    touch "$TARGET_DIR/.preserved"
    cp -r "$PRESERVE_DIR/modules".* "$TARGET_DIR/"

    # bind mount preserved kernel modules
    mkdir -p "$TARGET_DIR/kernel"
    mkdir -p "$TARGET_DIR/updates"
    [[ -d "$PRESERVE_DIR/kernel" ]] && mount --bind "$PRESERVE_DIR/kernel" "$TARGET_DIR/kernel"
    [[ -d "$PRESERVE_DIR/updates" ]] && mount --bind "$PRESERVE_DIR/updates" "$TARGET_DIR/updates"

    # trigger depmod
    depmod "$KERNEL"

    echo "info: linked modules" >&2
    exit 0
}

preserve-modules-unlink() {
    if [[ $# -gt 1 ]]; then
        echo "usage: linux-preserve-modules unlink [release]" >&2
        exit 1
    elif [[ $# -eq 1 ]]; then
        set-vars "$1"
    fi

    # exit early if kernel modules not already copied
    if [[ ! -f "$TARGET_DIR/.preserved" ]]; then
        echo "info: not linked" >&2
        exit 0
    fi

    # clean preserved files
    rm "$TARGET_DIR/.preserved"
    rm "$TARGET_DIR/modules".*
    mountpoint -q "$TARGET_DIR/kernel" && umount "$TARGET_DIR/kernel"
    mountpoint -q "$TARGET_DIR/updates" && umount "$TARGET_DIR/updates"

    # remove mount points if empty
    rmdir --ignore-fail-on-non-empty "$TARGET_DIR/kernel"
    rmdir --ignore-fail-on-non-empty "$TARGET_DIR/updates"
    rmdir --ignore-fail-on-non-empty "$TARGET_DIR"

    echo "info: unlinked modules" >&2
    exit 0
}

preserve-modules-unlink-all() {
    if [[ $# -gt 0 ]]; then
        echo "usage: linux-preserve-modules unlink-all" >&2
        exit 1
    fi

    # find kernels with .preserved marker file
    LINKED_KERNELS=( $(find /usr/lib/modules -maxdepth 2 -type f -name .preserved | cut -d/ -f5) )
    echo "info: found ${#LINKED_KERNELS[@]} kernels with linked modules" >&2

    # unlink modules for each
    for kernel in ${LINKED_KERNELS[@]}; do
        linux-preserve-modules unlink "$kernel"
    done

    exit 0
}

usage() {
    echo "usage: linux-preserve-modules <copy|link|unlink|unlink-all> [release]" >&2
    exit 1
}

main() {
    if [[ "$(id -u)" -ne 0 ]]; then
        echo "error: this script needs to run as root" >&2
        usage
    fi

    set-vars "$(uname -r)"

    if [[ "$#" -eq 0 ]]; then
        usage
    fi

    CMD="$1"
    shift
    case "$CMD" in
        copy) preserve-modules-copy "$@";;
        link) preserve-modules-link "$@";;
        unlink) preserve-modules-unlink "$@";;
        unlink-all) preserve-modules-unlink-all "$@";;
        *) usage;;
    esac
}

main "$@"