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"
}

panic()
{
    print "${1:-unexpected error occurred}" \
          "\033[1;31m!!\033[m"      >&2; sh
}

resolve_device()
{
    count=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

    # prevent race condition
    while [ ! -b "$device" ]; do sleep 1
        [ "$(( count += 1 ))" != 30 ] || {
            panic "failed to lookup partition"
            break
        }
    done
}

prepare_environment()
{
    . /etc/tinyramfs/config

    export \
        PATH=/bin TERM=linux SHELL=/bin/sh \
        LANG=C LC_ALL=C PS1="# " HOME=/root \

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

    mkdir -p /run/cryptsetup /run/lock /run/lvm

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

    trap panic EXIT

    [ ! "$modules" ] || modprobe -a "$modules"
}

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 $line"    ;;
        --*)             init_args="${cmdline##*--}"; break ;;
        *=*)             command export "$line"     ;;
        *)               command export "${line}=1" ;;
    esac 2> /dev/null || continue; done
}

setup_devmgr()
{
    [ "$break" = devmgr ] && { print "break before setup_devmgr()"; sh; }

    case "$devmgr" in
        udev)
            udevd -N never & devmgr_pid="$!"
            udevadm trigger -c add -t subsystems
            udevadm trigger -c add -t devices
            udevadm settle
        ;;
        mdev)
            mdev -s
            mdev -df & devmgr_pid="$!"

            find /sys/devices -name uevent |

            while read -r uevent; do
                printf add > "$uevent"
            done
        ;;
        mdevd)
            mdevd & devmgr_pid="$!"
            mdevd-coldplug
        ;;
    esac 2> /dev/null
}

unlock_luks()
{
    [ "$break" = luks ] && { print "break before unlock_luks()"; sh; }

    { IFS=,; set -- $luks_opts; unset 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

    resolve_device "$luks_root"

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

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

trigger_lvm()
{
    [ "$break" = lvm ] && { print "break before trigger_lvm()"; sh; }

    { IFS=,; set -- $lvm_opts; unset 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" "-aay" "$lvm_discard"

    if [ "$lvm_group" ] && [ "$lvm_name" ]; then
        lvm lvchange $@ "${lvm_group}${lvm_name}"
    elif [ "$lvm_group" ]; then
        lvm vgchange $@ "$lvm_group"
    elif [ "$lvm_tag" ]; then
        lvm lvchange $@ "$lvm_tag"
    else
        lvm vgchange $@
    fi || panic "failed to trigger LVM"
}

mount_root()
{
    [ "$break" = root ] && { print "break before mount_root()"; sh; }

    resolve_device "$root"

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

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

boot_system()
{
    [ "$break" = boot ] && { print "break before boot_system()"; sh; }

    kill "$devmgr_pid"

    # temporary workaround until util-linux release a new version
    # see https://github.com/karelzak/util-linux/issues/997
    for dir in run dev sys proc; do
        mount -o move "$dir" "/mnt/root/${dir}" ||
        mount  --move "$dir" "/mnt/root/${dir}"
    done 2> /dev/null

    set -- "/mnt/root" "${init:-/sbin/init}" "$init_args"

    # use 'env -i' to prevent leaking exported variables
    exec env -i \
        TERM=linux \
        PATH=/bin:/sbin:/usr/bin:/usr/sbin \
        switch_root $@ || 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
    boot_system
}