#!/bin/sh
# -------
# File:        chroot-tool
# Description: Simple script to prepare environment to run commands in a chrooted directory
# Author:      Luis Garcia Gisbert <garcia_luigis@gva.es>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin St, Fifth Floor, Boston MA 02110-1301 USA
# --------


CHT_REQ_BIND_DIRS="/dev /proc /sys"
# export CHT_BIND_DIRS to get additional directories available to chroot
CHT_BIND_DIRS="${CHT_BIND_DIRS} /tmp /net"
BIND_DIRS="$CHT_REQ_BIND_DIRS $CHT_BIND_DIRS"

DPKG_DIVERT="/usr/sbin/dpkg-divert"

# export CHT_LOCAL_FILES and/or CHT_DIVERT_FILES
CHT_LOCAL_FILES="$CHT_LOCAL_FILES /etc/resolv.conf"
ALTERNATE_DIR="/usr/share/chroot-tool"
if [ -d "${ALTERNATE_DIR}" ] ; then
   for f in $(find ${ALTERNATE_DIR} -type f -printf "%P\n") ; do
      CHT_DIVERT_FILES="$CHT_DIVERT_FILES /${f}"
   done
fi

#****f chroot-tool/chroot_divert
# NAME
#   chroot_divert -- divert/restore a single file in chroot
# SYNOPSIS
#   removes/restores files in the chroot. 
chroot_divert(){
   f="$2"
   f_div="${f}.chroot-tool"
   f_alt="$3"
   F="${CHROOT_DIR}${f}"
   F_DIV="${CHROOT_DIR}${f_div}"
   if [ "$1" = "divert" ] ; then
      # do diversion
      if [ -x "${CHROOT_DIR}${DPKG_DIVERT}" ] ; then
         # OK use dpkg-diversion method
         chroot $CHROOT_DIR ${DPKG_DIVERT} --divert ${f_div} --rename ${f} || true
      else
         # poor man's method
         if [ -f "${F}" -a ! -f "${F_DIV}" ] ; then
            mv -f "${F}" "${F_DIV}"
         fi
      fi
      if [ "$f_alt" -a -f "$f_alt" ] ; then
         # install replacememnt
         cp -f "$f_alt" "$F"
      fi
   else
      # remove diversions
      rm -f "${F}"
      if [ -x "${CHROOT_DIR}${DPKG_DIVERT}" ] ; then
         # OK use dpkg-diversion method
         chroot $CHROOT_DIR ${DPKG_DIVERT} --rename --remove ${f} || true
      else
         # poor man's method
         if [ -f "${F_DIV}" ] ; then
            mv -f "${F_DIV}" "${F}"
         fi
      fi
   fi
}

already_mounted(){
   if mount |grep -q "^$1\b.*\b${CHROOT_DIR}${d}\b.*\(\bbind\b\)" ; then
      return 0
   fi
   return 1
}

die(){
   while [ "$1" ] ; do
      echo "$1" >&2
      shift
   done
   unbind_dirs
   exit 1
}

mount_dir(){
   if ! already_mounted "$1" ; then
      if ! mount --bind "$1" "${CHROOT_DIR}${1}" 2>/dev/null >/dev/null ; then
         return 1
      fi
   fi
   return 0
}

bind_dirs(){
   for d in $CHT_REQ_BIND_DIRS ; do
      [ -d "${d}" -a -d "${CHROOT_DIR}${d}" ] || return 1
      mount_dir "$d" || return 1
   done
   for d in $CHT_BIND_DIRS ; do
      mount_dir "$d" || true
   done
   return 0
}

bind_dirs_verbose(){
      bind_dirs || die "Error, unable to bind some of the required dirs: $BIND_DIRS"
   return 0
}

unbind_dirs(){
   for d in $BIND_DIRS ; do
      umount "${CHROOT_DIR}${d}" 2>/dev/null >/dev/null || true
   done
   return 0
}

prepare_chroot(){
   for f in $CHT_REMOVE_FILES ; do
      chroot_divert divert "$f"
   done
   for f in $CHT_LOCAL_FILES ; do
      chroot_divert divert "$f" "$f"
   done
   for f in $CHT_DIVERT_FILES ; do
      chroot_divert divert "$f" "${ALTERNATE_DIR}${f}"
   done
}

restore_chroot(){
   for f in $CHT_REMOVE_FILES $CHT_LOCAL_FILES $CHT_DIVERT_FILES ; do
      chroot_divert restore "$f"
   done
}

usage(){
   die "Usage: $0 {chroot|bind|unbind} CHROOT_DIR" \
       "       $0 run CHROOT_DIR COMMAND_CMD"
}

# main
# tests

[ $(id -u) -eq 0 ] || die "Please, run this program as root"
ACTION="$1"
CHROOT_DIR="$2"
[ "$CHROOT_DIR" -a -d "$CHROOT_DIR" ] || usage
shift 2

case $ACTION in
   bind)
      bind_dirs_verbose
      ;;
   unbind)
      unbind_dirs
      ;;
   chroot)
      bind_dirs_verbose
      prepare_chroot
      chroot $CHROOT_DIR || true
      restore_chroot
      unbind_dirs
      ;;
   run)
      [ "$1" ] || usage
      bind_dirs_verbose
      prepare_chroot
      chroot $CHROOT_DIR "$@" || true
      restore_chroot
      unbind_dirs
      ;;
   *)
      usage
      ;;
esac

exit 0