tinyramfs/storage-device

#!/bin/sh
# Copyright (c) 2012-2019, Piotr Karbowski <piotr.karbowski@gmail.com>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without modification, are
# permitted provided that the following conditions are met:
#
#    * Redistributions of source code must retain the above copyright notice, this list
#      of conditions and the following disclaimer.
#    * Redistributions in binary form must reproduce the above copyright notice, this list
#      of conditions and the following disclaimer in the documentation and/or other
#      materials provided with the distribution.
#    * Neither the name of the Piotr Karbowski nor the names of its contributors may be
#      used to endorse or promote products derived from this software without specific
#      prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
# THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
# OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE US
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

# This script meant to create /dev/disk/by-* and /dev/mapper/* symlinks.
# and remove them after storage device is removed.
# the /dev/disk/by-* handling based on the idea and proof of concept from BitJam.

# debug
#exec >> /run/debug-mdev 2>&1
#set -x
#echo '### ENV:'
#env
#echo '### CODE:'
#

umask 077

# TODO use /tmp
storage_dir="/tmp/.mdev-like-a-boss"
[ -d "$storage_dir" ] || mkdir "$storage_dir"

[ "$MDEV" ] || exit 2

create_uuid_label_symlink() {
    target_dir="/dev/disk/by-${1}"
    target_symlink="${target_dir}/${2}"
    [ -e "$target_symlink" ] && return
    mkdir -p "$target_dir"
    ln -sf "/dev/${MDEV}" "$target_symlink"
    printf "%s\n" "$target_symlink" > "${storage_dir}/storage_symlink_${1}_${MDEV}"
}

add_symlinks() {
    # Skip temp cryptsetup nodes.
    case "$MDEV" in
        "dm-"[0-9]*)
            case "$(cat "/sys/block/${MDEV}/dm/name")" in
                "temporary-cryptsetup-"[0-9]*)
                    return 0
                    ;;
            esac
            ;;
    esac

    if command -v blkid > /dev/null 2>&1; then
        blkid_output=$(blkid "/dev/${MDEV}")
        eval "${blkid_output#*: }"

        [ "$UUID" ] && create_uuid_label_symlink uuid "$UUID"
        [ "$LABEL" ] && create_uuid_label_symlink label "$LABEL"
        [ "$PARTUUID" ] && create_uuid_label_symlink partuuid "$PARTUUID"
    fi

    if [ -f "/sys/block/${MDEV}/dm/name" ]; then
        [ -d /dev/mapper ] || mkdir /dev/mapper
        if ! [ -c /dev/mapper/control ]; then
            #awk '$2 == "device-mapper" { foo = system("mknod /dev/mapper/control c 10 " $1); exit foo }' /proc/misc || exit 1
            while read -r dm; do
                [ "${dm#* }" = device-mapper ] && {
                    mknod /dev/mapper/control c 10 "${dm% *}" || exit 1
                }
            done < /proc/misc
        fi

        dmname=$(cat "/sys/block/${MDEV}/dm/name")
        if [ "$dmname" ]; then
            target_symlink="/dev/mapper/${dmname}"
            [ -e "$target_symlink" ] && return
            ln -sf "/dev/${MDEV}" "$target_symlink"
            printf "%s\n" "$target_symlink" > "${storage_dir}/storage_symlink_mapper_${MDEV}"
        fi
    fi
}

set_readahead() {
    read_ahead_kb_control="/sys/class/block/${MDEV}/queue/read_ahead_kb"
    new_read_ahead_kb="2048"

    if [ -f "$read_ahead_kb_control" ]; then
        read_ahead_kb=$(cat "$read_ahead_kb_control")
        if [ "$read_ahead_kb" -lt "$new_read_ahead_kb" ]; then
            logger -t mdev "Changing $MDEV read_ahead_kb from $read_ahead_kb to $new_read_ahead_kb"
            printf "%s" "$new_read_ahead_kb" > "$read_ahead_kb_control"
        fi
    fi
}

drop_symlinks() {
    for type in uuid label mapper; do
        [ -f "${storage_dir}/storage_symlink_${type}_${MDEV}" ] || continue
        target_symlink=$(cat "${storage_dir}/storage_symlink_${type}_${MDEV}" 2> /dev/null)
        [ "$target_symlink" ] || continue

        target_symlink_device=$(readlink "$target_symlink")
        if [ "$target_symlink_device" = "/dev/${MDEV}" ]; then
            rm "$target_symlink"
        fi

        rm "${storage_dir}/storage_symlink_${type}_${MDEV}"
    done
}

case "$ACTION" in
    add | "")
        add_symlinks
        set_readahead
        ;;
    remove)
        drop_symlinks
        ;;
esac