initrd-do

#!/bin/sh
# initrd-do - run a command within an initrd
# Copyright (C) 2008 Loïc Minier <lool@dooz.org>
# Copyright (C) 2011 Linaro Limited
#
# Permission is hereby granted, free of charge, to any person obtaining a
# copy of this software and associated documentation files (the "Software"),
# to deal in the Software without restriction, including without limitation
# the rights to use, copy, modify, merge, publish, distribute, sublicense,
# and/or sell copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
# SOFTWARE IN THE PUBLIC INTEREST, INC. BE LIABLE FOR ANY CLAIM, DAMAGES OR
# OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
# ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
# DEALINGS IN THE SOFTWARE.
#
# Except as contained in this notice, the name of the author shall not be used
# in advertising or otherwise to promote the sale, use or other dealings in
# this Software without prior written authorization from the author.
#
# depends: sudo

set -e

self="$(basename "$0")"
work_dir=""
new_initrd=""

log() {
    echo "$*" >&2
}

log_i() {
    log "I:" "$@"
}

log_w() {
    log "W:" "$@"
}

die() {
    log "E:" "$@"
    exit 1
}

usage() {
    log "Usage: $self --initrd <initrd-file> [-c <command> [<arg> ...]]"
}

getshell() {
    if [ -n "$SHELL" ]; then
        echo "$SHELL"
        return
    fi
    PASSWD="$(getent passwd $(id -u) | sed -n 's/.*://p')"
    if [ -n "$PASSWD" ]; then
        echo "$PASSWD"
        return
    fi
    echo "/bin/sh"
}

escape() {
    echo "$*" | sed "s/'/'\"'\"'/g; s/.*/'&'/"
}

# unused; use eval
unescape () {
    eval "echo" "$*"
}

cleanup() {
    if [ -n "$new_initrd" ]; then
        rm -f "$new_initrd"
    fi
    if [ -n "$work_dir" ]; then
        rm -rf "$work_dir"
    fi
}

trap "cleanup" 0 1 2 3 9 11 13 15

initrd=""
command="$(escape "$(getshell)")"

while [ $# -gt 0 ]; do
    case $1 in
      --help)
        usage
        exit 0
      ;;
      -i|--initrd)
        shift
        initrd="$1"
        if ! shift; then
            die "Need an initrd file after --initrd"
        fi
      ;;
      -c)
        shift
        if [ $# -le 0 ]; then
            die "Need a command after -c"
        fi
        command=""
        while :; do
            command="$command $(escape "$1")"
            shift
            if [ $# -eq 0 ]; then
                break
            fi
        done
        break
      ;;
      *)
        # clever handling of args: set initrd first if unset, otherwise set
        # command
        if [ -z "$initrd" ]; then
            initrd="$1"
            shift
        else
            command=""
            while :; do
                command="$command $(escape "$1")"
                shift
                if [ $# -eq 0 ]; then
                    break
                fi
            done
        fi
      ;;
    esac
done

if [ -z "$initrd" ]; then
    usage
    exit 1
fi

work_dir="$(mktemp -dt "$self.XXXXXXXXXX")"

# subshell to not touch cwd as we will nuke it
(   cd "$work_dir"
    log_i "Unpacking initrd $initrd"
    gunzip -c <"$initrd" | cpio -i --quiet
    log_i "Running command:" $command
    eval $command
)

err=$?

if [ 0 != $err ]; then
    log_w "Command exited with $err; aborting"
    exit 1
fi

log_i "Generating new initrd"
new_initrd="$(mktemp -t "$self.XXXXXXXXXX")"
# subshell to not touch cwd as we will nuke it
(   cd "$work_dir"
    find . | cpio -o -H newc -R 0:0 --quiet | gzip -c >"$new_initrd"
)

log_i "Moving new initrd to $initrd"
mv -f "$new_initrd" "$initrd"