tinyramfs/init

#!/bin/sh -ef
#
# tiny init
#
# word splitting is safe by design
# shellcheck disable=2068,2046,2086
#
# false positive
# shellcheck disable=2154,2163,1091

print()
{
    printf "%b %s\n" "${2:-\033[1;37m>>\033[m}" "$1"
    shell
}

panic()
{
    print "$1" "\033[1;31m!!\033[m" >&2
    shell
}

shell()
{
    # see https://busybox.net/FAQ.html#job_control
    setsid sh -c "exec sh <> /dev/${console:-tty1} 2>&1" || sh
}

findfs()
{
    value=0; device=

    case "${1%%=*}" in
        /dev/*)
            device="$1"
        ;;
        UUID)
            device="/dev/disk/by-uuid/${1##*=}"
        ;;
        LABEL)
            device="/dev/disk/by-label/${1##*=}"
        ;;
        PARTUUID)
            device="/dev/disk/by-partuuid/${1##*=}"
        ;;
    esac

    # avoid race condition
    while [ ! -e "$device" ]; do
        [ "$value" = 30 ] && panic "failed to lookup partition"
        value=$(( value + 1 )); sleep 1
    done
}

prepare_environment()
{
    . /etc/config

    export \
        SHELL=/bin/sh \
        TERM=linux \
        HOME=/root \
        PATH=/bin:/sbin:/usr/bin:/usr/sbin \
        PS1="# " \
        LC_ALL=C \
        LANG=C \
        OLD_IFS="$IFS"

    # fix for ubase mount
    :> /etc/fstab

    mount -t proc     -o nosuid,noexec,nodev     proc /proc
    mount -t sysfs    -o nosuid,noexec,nodev     sys  /sys
    mount -t devtmpfs -o nosuid,noexec,mode=0755 dev  /dev

    ln -s /proc/self/fd   /dev/fd
    ln -s /proc/self/fd/0 /dev/stdin
    ln -s /proc/self/fd/1 /dev/stdout
    ln -s /proc/self/fd/2 /dev/stderr

    trap 'panic "something went wrong"' EXIT

    # false positive
    # shellcheck disable=2015
    [ "$modules" ] && modprobe -a "$modules" 2> /dev/null ||:
}

parse_cmdline()
{
    read -r cmdline < /proc/cmdline

    for line in $cmdline; do case "$line" in
        debug | debug=1)
            set -x
        ;;
        rootfstype=*)
            root_type="$line"
        ;;
        rootflags=*)
            root_opts="$line"
        ;;
        ro | rw)
            rorw="-o $line"
        ;;
        *.*)
            # TODO implement backward compatibilty with dracut, mkinitcpio, etc
            : no operation
        ;;
        *=*)
            export "$line"
        ;;
        *)
            export "${line}=1"
        ;;
    esac; done
}

setup_devmgr()
{
    [ "$break" = devmgr ] && print "break before setup device manager"

    case "$devmgr" in
        udev)
            udevd -d -N never
            udevadm trigger -c add -t subsystems
            udevadm trigger -c add -t devices
            udevadm settle
        ;;
        mdev)
            mdev -df 2> /dev/null & mdev_pid="$!"

            [ "$monolith" != 1 ] && {
                set -- $(find /sys -name modalias -type f -exec sort -u {} +)
                modprobe -a "$@" 2> /dev/null ||:
            }
        ;;
        mdevd)
            mdevd 2> /dev/null & mdevd_pid="$!"
            mdevd-coldplug
        ;;
    esac
}

unlock_luks()
{
    [ "$break" = luks ] && print "break before unlock LUKS"

    { IFS=,; set -- $luks_opts; IFS="$OLD_IFS"; }

    for opt; do case "$opt" in
        discard | discard=1)
            luks_discard="--allow-discards"
        ;;
        header=*)
            luks_header="--${opt}"
        ;;
        name=*)
            luks_name="${opt##*=}"
        ;;
        key=*)
            luks_key="-d ${opt##*=}"
        ;;
    esac; done

    findfs "$luks_root"

    set -- \
        "--disable-locks" \
        "$luks_key" "$luks_header" \
        "$luks_discard" "$device" \
        "${luks_name:-luks-${device##*/}}"

    cryptsetup open $@ || panic "failed to unlock LUKS"
}

trigger_lvm()
{
    [ "$break" = lvm ] && print "break before trigger LVM"

    { IFS=,; set -- $lvm_opts; IFS="$OLD_IFS"; }

    for opt; do case "$opt" in
        discard | discard=1)
            lvm_discard="--config=devices{issue_discards=1}"
        ;;
        config=0)
            :> /etc/lvm/lvm.conf
        ;;
        group=*)
            lvm_group="${opt##*=}"
        ;;
        name=*)
            lvm_name="/${opt##*=}"
        ;;
        tag=*)
            lvm_tag="@${opt##*=}"
        ;;
    esac; done

    set -- "--sysinit" "-qq" "-ay" "$lvm_discard"

    if [ "$lvm_group" ] && [ "$lvm_name" ]; then
        lvchange $@ "${lvm_group}${lvm_name}"
    elif [ "$lvm_group" ]; then
        vgchange $@ "$lvm_group"
    elif [ "$lvm_tag" ]; then
        lvchange $@ "$lvm_tag"
    else
        vgchange $@
    fi
}

mount_root()
{
    [ "$break" = root ] && print "break before mount root"

    findfs "$root"

    set -- \
        "${root_type:+-t $root_type}" \
        "${rorw:--o ro}${root_opts:+,$root_opts}" \
        "$device" "/mnt/root"

    mount $@ || panic "failed to mount root"
}

cleanup()
{
    [ "$break" = cleanup ] && print "break before cleanup"

    case "$devmgr" in
        udev)  udevadm control -e ;;
        mdev)  kill "$mdev_pid"   ;;
        mdevd) kill "$mdevd_pid"  ;;
    esac

    # temporary workaround until util-linux release a new version
    # see https://github.com/karelzak/util-linux/issues/997
    for dir in dev sys proc; do
        mount -o move "$dir" "/mnt/root/${dir}" || mount --move "$dir" "/mnt/root/${dir}"
    done
}

boot_system()
{
    [ "$break" = boot ] && print "break before boot system"

    set -- "/mnt/root" "${init:-/sbin/init}"
    exec switch_root $@ 2> /dev/null || panic "failed to boot system"
}

# int main()
{
    prepare_environment
    parse_cmdline
    setup_devmgr

    # trigger lvm twice to handle both LUKS on LVM and LVM on LUKS
    [ "$lvm"  = 1 ] && trigger_lvm
    [ "$luks" = 1 ] && unlock_luks
    [ "$lvm"  = 1 ] && trigger_lvm

    mount_root
    cleanup
    boot_system
}