Chip 2007 January, February, March & April/Chip-Cover-CD-2007-02.iso/boot/i386/root/sbin/modify_resolvconf

Text File | 2006-11-29 | 25.3 KB | 816 lines

#!/bin/bash
#
# Copyright (c) 2001-2005 SuSE Linux Products GmbH, Nuernberg, Germany.
# 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., 59 Temple
# Place, Suite 330, Boston, MA 02111-1307 USA
#
# Author: Christian Zoz <[e-mail]>
#
# $Id: modify_resolvconf 1405 2006-02-13 15:08:56Z zoz $
#

if ! touch /tmp &>/dev/null; then
  echo "Filesystem read only: Cannot modify anything" >&2
  exit 1
fi

RESOLVCONF=/etc/resolv.conf
NAMEDCONF=/etc/named.d/forwarders.conf
PROGNAME=${0##*/}
RETVAL=0
if [ -x /usr/bin/fmt ] ; then
  FMT="/usr/bin/fmt -u -w 64"
else
  FMT="cat"
fi

usage () {
  cat << EOT >&2
  usage:   $PROGNAME <action> <options>
  action:  modify, restore, cleanup or check
  options:                               mandatory for:
    -s|--service <service>               modify, restore
    -e|--extension <string>
    -p|--process <process>               modify
    -i|--pid <pid>
    -f|--script <pathname of script>     modify
    -t|--text <text>                     modify
    -l|--searchlist <list of domains>
    -d|--domain <domain>
    -n|--nameservers <addresses>
    -o|--save_now <pathname of file>
    -a|--save_later <pathname of file>
    -k|--keep
       --resolv
       --named
       --no_restart
    -q|--quiet
    -v|--verbose
    -h|--help                            (does not need an action)
  cleanup and check ignore all options except -q and -v
EOT
  if [ -n "$1" ] ; then
     echo >&2
     ERROR="  ERROR:   "
     echo -e "$*\n" | while read line; do
       echo "${ERROR}${line}" >&2
       ERROR="           "
     done
  fi
  exit 1
}

debug () {
  test "$VERBOSE" = "yes" || return
  echo -e "debug: $*" >&2
}

warn () {
  test "$QUIET" = "yes" && return
  echo -e "$*" >&2
}

log () {
  logger -t "$PROGNAME" "$*"
  debug "$*"
  if [ "$ACTION" = "cleanup" -a "$QUIET" != "yes" ] ; then
    echo -e "$*" >&2
  fi
}

write_meta () {
  # At first we prepend a default text to TEXT
  TEXT="This is a temporary ${FILENAME##*/} created by service $SERVICE.\
        The previous file has been saved and will be restored later.\n\n\
        If you don't like your ${FILENAME##*/} to be changed, you\
        can set MODIFY_{RESOLV,NAMED}_CONF_DYNAMICALLY=no. This variables\
        are placed in /etc/sysconfig/network/config.\n\n\
        You can also configure service $SERVICE not to modify it.\n\n\
        $TEXT"
  cat << EOT > $FILENAME
### BEGIN INFO
#
# Modified_by:  $SERVICE
# Backup:       $BACKUP
# Process:      $PROC
# Process_id:   $PID
# Script:       $SCRIPT
# Saveto:       $SAVELATER
EOT
infoline="# Info:         "
echo -e "$TEXT" |
  $FMT |
  while read line ; do
    echo "$infoline$line";
    infoline="#               "
  done >> $FILENAME
  cat << EOT >> $FILENAME
#
### END INFO
EOT
}

read_resolvconf () {
  OLDDNS="`sed -n '/^[[:space:]]*nameserver[[:space:]]*/s///p' $TMP_DATA`"
}

write_resolvconf () {
  # Only one of $DOMAIN and $SEARCH does contain something
  if [ -n "$DOMAIN" ] ; then
    mv $TMP_DATA $TMP_FILE
    sed -e "/^[[:space:]]*\(domain\|search\)[[:space:]]/d" \
      $TMP_FILE > $TMP_DATA
    echo "domain $DOMAIN" >> $TMP_DATA
  fi
  if [ -n "$SEARCH" ] ; then
    mv $TMP_DATA $TMP_FILE
    sed -e "/^[[:space:]]*\(domain\|search\)[[:space:]]/d" \
      $TMP_FILE > $TMP_DATA
    echo "search $SEARCH" >> $TMP_DATA
  fi
  if [ -n "$DNS" ] ; then
    mv $TMP_DATA $TMP_FILE
    sed "/^[[:space:]]*nameserver[[:space:]]/d" $TMP_FILE > $TMP_DATA
    for a in $MODIFY_RESOLV_CONF_STATIC_DNS $DNS; do
      echo "nameserver $a" >> $TMP_DATA
    done
  fi
}

read_namedconf () {
  # At first normalize the forwarders entry, i.e. remove all comments and
  # linebreaks from it.
  mv $TMP_DATA $TMP_FILE
  sed -e '/^[[:space:]]*forwarders/{
      h
      :a
      s-/\*.*\*/--g
      s-#.*$--
      s-//.*$--
      s-[[:space:]\n]\+- -g
      /} *; *$/bb
      N
      ba
      :b
      x
      s-for.*$--
      G
      s-\n --
      s- ;-;-g
    } ' $TMP_FILE > $TMP_DATA
  # Then get the old Nameservers
  OLDDNS=`sed -n -e '/^[[:space:]]*forwarders/{
      s-[^0-9. ]*--g
      p
    } ' $TMP_DATA | tr -d '\n'`
}

write_namedconf () {
  # Put together a list of nameservers from the new servers and then the
  # old one, but stop after the third
  FORWDS=""
  declare -i n=0
  local a i
  for a in $DNS; do # $OLDDNS
    # named will fail if there are duplicate forwarders (bug 28459)
    for i in $FORWDS ; do
      if [ "$a;" == "$i" ] ; then
        continue 2
      fi
    done
    FORWDS="$FORWDS $a;"
    n=$((n+1))
    test $n = 3 && break
  done
  # replace the nameservers in the normalized file
  mv $TMP_DATA $TMP_FILE

  # Check whether there is an active "forwarders" directive
  grep "^[[:space:]]*forwarders" $TMP_FILE >/dev/null
  if [ $? == 0 ] ; then
    # Yes, replace that directive's argument
    sed -e "/^[[:space:]]*forwarders/{
        s-\(^.*forwarders\).*\$-\1 {$FORWDS };-
      } " $TMP_FILE > $TMP_DATA
  else
    # Check whether the default comment for the "forwarders" directive is present
    grep "^[[:space:]]*# your provider's name server." $TMP_FILE >/dev/null
    if [ $? == 0 ] ; then
      # Yes, put the comment right after that comment
      sed -e "/^[[:space:]]*# your provider's name server./a\        forwarders {$FORWDS };" $TMP_FILE > $TMP_DATA
    else
      # No, so just put the option right after the "options {" block opening
      sed -e "/^options {/a\        forwarders {$FORWDS };" $TMP_FILE > $TMP_DATA
    fi
  fi
}

write_file () {
  read_file
  write_meta
  case "$FILENAME" in
    *resolv*) write_resolvconf; ;;
    *named*)  write_namedconf; ;;
  esac
  cat $TMP_DATA >> $FILENAME
  chmod 644 $FILENAME
}

read_file () {
  sed "/### BEGIN INFO/,/### END INFO/d" $FILENAME > $TMP_DATA
  case "$FILENAME" in
    *resolv*) read_resolvconf; ;;
    *named*)  read_namedconf; ;;
  esac
}

notify_services () {
  test "$NO_RESTART" = "yes" && return
  case "$FILENAME" in
    *resolv*)
      if [ -d /var/spool/postfix/etc/ ] ; then
        cp $RESOLVCONF /var/spool/postfix/etc/
      fi
      if [ -x /etc/init.d/lwresd ] ; then
        warn "`/etc/init.d/lwresd reload`"
      fi
      ;;
    *named*)
      warn "`/etc/init.d/named reload`"
      ;;
  esac
}

remove_tmp_files () {
  rm $TMP_DATA $TMP_FILE 2>/dev/null
}

trap remove_tmp_files EXIT SIGINT SIGSEGV SIGQUIT SIGTERM

TMP_DATA=`mktemp /tmp/${PROGNAME}.XXXXXX`
TMP_FILE=`mktemp /tmp/${PROGNAME}.XXXXXX`

###########################################################
# Parse commandline
###########################################################

# Now set the parsed args but save the original commandline for recursive calls
COMMANDLINE="$@"
ACTION=""
VARIABLE=""
while true ; do
  case "$1" in
    -s|--service) VARIABLE=SERVICE;;
    -e|--extension) VARIABLE=EXT;;
    -p|--process) VARIABLE=PROC;;
    -i|--pid) VARIABLE=PID;;
    -f|--script) VARIABLE=SCRIPT;;
    -t|--text) VARIABLE=TEXT;;
    -l|--searchlist) VARIABLE=SEARCH;;
    -d|--domain) VARIABLE=DOMAIN;;
    -n|--nameservers) VARIABLE=DNS;;
    -q|--quiet) QUIET=yes;;
    -v|--verbose) VERBOSE=yes;;
    -h|--help) usage;;
    -o|--save_now) VARIABLE=SAVENOW;;
    -a|--save_later) VARIABLE=SAVELATER;;
    -k|--keep) KEEP=yes;;
       --resolv) FILENAME=$RESOLVCONF;;
       --named) FILENAME=$NAMEDCONF;;
       --no_restart) NO_RESTART=yes;;
    "") break ;;
    --)
      shift
      test -n "$ACTION" -o $# -gt 1 \
        && usage "Exactly one action may be given.\n"\
                 "Currently given actions: $ACTION $*"
      ACTION="$1"
      shift
      break
      ;;
    -*) usage Unknown option $1;;
    *)
      test -n "$ACTION" && usage "Exactly one action may be given.\n"\
                                 "Currently given actions: $ACTION $1"
      ACTION="$1"
      ;;
  esac
  if [ -n "$VARIABLE" ] ; then
    test -z "$2" && usage Option $1 needs an argument
    eval $VARIABLE=\$2
    shift
    VARIABLE=""
  fi
  shift
done
test -z "$ACTION" && usage No action was given

###########################################################
# Check if the arguments to the options are usefull
###########################################################

case $ACTION in
  modify)
#z#    case "$SERVICE" in
#z#      dhclient|dhcpcd|pppd|ipppd|pcmcia|hotplug) ;;
#z#      *) usage "service must be one of dhclient dhcpcd" \
#z#               " pppd ipppd pcmcia hotplug";;
#z#    esac
    test -z "$SERVICE" && usage "a vaild service must be set with --service"

    if [ "$SERVICE" != "hotplug" ] ; then
      if [ -z "$PROC" ] ; then
        usage "a running process/daemon must be set with --process"
      else
        PROCPID=`/sbin/pidofproc $PROC 2>/dev/null`
        if [ -z "$PROCPID" ] ; then
          usage "$PROC is not running currently, this may not happen"
        else
          debug "pid of prodess $PROC is $PROCPID"
        fi
      fi
    fi

    if [ -z "$PID" ] ; then
      PID="$PROCPID"
      # usage "you must set the pid of $PROC with --pid"
    else
      PIDPROC=`ps h $PID 2>/dev/null |(read a b c d e f; echo $e)`
      if [ -z "$PIDPROC" ] ; then
        warn "there is no process with id $PID"
      else
        debug "process with pid $PID is $PIDPROC"
      fi
    fi

#    if [ -z "$SCRIPT" ] ; then
#      usage "you must set the script that modifies $FILENAME with --script"
#    else
    if [ -n "$SCRIPT" ] ; then
      if [ -e "$SCRIPT" ] ; then
        debug "script $SCRIPT found"
      else
        usage "there is no script named $SCRIPT"
      fi
    fi

    if [ -z "$TEXT" ] ; then
      usage "You have to provide an descriptive text with --text\n" \
            "With --text=- you can use a here document"
    else
      # If TEXT="-" read it as here document
      if [ "$TEXT" = "-" ] ; then
        TEXT=""
        while read a; do
          test -z "$a" && a="\n\n"
          TEXT="$TEXT $a"
        done
      fi
    fi

    if [ -n "$DOMAIN" -a -n "$SEARCH" ] ; then
      usage "only one of --domain and --searchlist may be used\n" \
            "in resolv.conf search and domain are mutually exclusiv"
    fi

    FILENAME=""
    ;;
  restore)
#z#    case "$SERVICE" in
#z#      dhclient|dhcpcd|pppd|ipppd|pcmcia|hotplug) ;;
#z#      *) usage "service must be one of dhclient dhcpcd" \
#z#               " pppd ipppd pcmcia hotplug";;
#z#    esac
    test -z "$SERVICE" && usage "a vaild service must be set with --service"
    ;;
  cleanup)
    if [ -z "$FILENAME" ] ; then
      $0 $COMMANDLINE --resolv
      $0 $COMMANDLINE --named
      exit
    fi
    ;;
  check)
    # ignore all options
    if [ -z "$FILENAME" ] ; then
      FILENAME=$RESOLVCONF
    fi
    KEEP=""
    SAVENOW=""
    ;;
  *) usage "$ACTION is not a valid action" ;;
esac


###########################################################
# respect variables in config and choose right filenames
###########################################################

debug "pre-config: FILENAME=$FILENAME"

eval `grep "^[[:space:]]*\(\
MODIFY_RESOLV_CONF_DYNAMICALLY\|\
MODIFY_NAMED_CONF_DYNAMICALLY\|\
MODIFY_RESOLV_CONF_STATIC_DNS\
\)=" /etc/sysconfig/network/config 2>/dev/null`

if [ "$MODIFY_NAMED_CONF_DYNAMICALLY" = "yes" ] ; then
  test -z "$FILENAME" && FILENAME=$NAMEDCONF
fi
if [ "$MODIFY_RESOLV_CONF_DYNAMICALLY" = "yes" ] ; then
  test -z "$FILENAME" && FILENAME=$RESOLVCONF
fi

debug "post-config: FILENAME=$FILENAME"

case "$FILENAME" in
  "")
    log "Service $SERVICE tried to modify resolver configuration, but it"
    log "was not modified due to MODIFY_RESOLV\NAMED_CONF_DYNAMICALLY=no"
    exit
    ;;
  $NAMEDCONF)
    if ! [ -r "$FILENAME" -a -x /etc/init.d/named ] ; then
      if [ "$ACTION" = "cleanup" ] ; then
        exit 0
      else
        log "Service $SERVICE tried to modify $FILENAME, but named seems" \
            "not to be installed"
        log "Check your settings of MODIFY_RESOLV\NAMED_CONF_DYNAMICALLY"
        exit 1
      fi
    fi
    ;;
  $RESOLVCONF)
    if ! [ -r "$FILENAME" ] ; then
      touch $FILENAME
      chmod 644 $FILENAME
    fi
    ;;
esac
BACKUP="${FILENAME}.saved.by.$SERVICE"
test -n "$EXT" && BACKUP="${BACKUP}.${EXT}"

###########################################################
# Read current resolv.conf
###########################################################

read_meta () {
  if [ -e $FILENAME ] ; then
    RC_BLOCK=`sed -n "/### BEGIN INFO/,/### END INFO/s/^[[:space:]#]*//p" \
                                                                 $FILENAME`
    if [ -n "$RC_BLOCK" ] ; then
      while read NAME TOKEN; do
        # Note the quotes around RC_BLOCK. Without it we get all in one line.
        eval $NAME='`echo "$RC_BLOCK" | sed -n "/^$TOKEN:[[:space:]]*/s///p"`'
        debug "$NAME=${!NAME}"
      done << "        EOL"
        RC_SERVICE   Modified_by
        RC_BACKUP    Backup
        RC_PROC      Process
        RC_PID       Process_id
        RC_SCRIPT    Script
        RC_SAVELATER Saveto
        EOL
      # Here we want all in one line so we do not quote RC_BLOCK, but we lose
      # all formatting of the text (to be enhanced).
      RC_TEXT=`echo $RC_BLOCK | sed -e "s/^.*Info:[[:space:]]*//" \
                                    -e "s/ END INFO.*$//"`
      debug "RC_TEXT=${RC_TEXT:0:20} ..."
    fi
  fi
}

read_meta

###########################################################
# Divide all available backups
###########################################################

# . /sbin/modify_cf.lib

# Check all existing backups and divide them into valid direct, valid indirect
# and invalid backups.
# "all existing backups" = all files /etc/resolv.conf.saved.by.* and all
#                          files found in the backup field of another
#                          valid backup
# "valid direct" = file which the backup entry in resolv.conf points to
# "valid indirect" = file which the backup entry of another valid backup
#                    points to
# "invalid" = files /etc/resolv.conf.saved.by.* which are not valid
# All valid backups build a stack of files. These files are stored in three
# variables:
# DIRECT_BACKUP: Contains the only valid direct backup.
# INDIRECT_BACKUPS: Contains all indirect backups except the last of the stack.
#                  Files are ordered like the stack. The first is the backup
#                  of the valid direct backup.
# LAST_BACKUP: Contains the last file of the stack of valid indirect backups.
#              This file does not contain an info block or has an invalid
#              entry in its backup field.
# INVALID_BACKUPS: Contains all invalid backups sorted in chronological
# order, the newest first. This files are only used if there is no valid
# backup, but resolv.conf was modified dynamically.

read_field_backup () {
  ls "$*" &>/dev/null || return
  BAFI=`\
  sed -n \
    "/### BEGIN INFO/,/### END INFO/s/^[[:space:]#]*Backup:[[:space:]]*//p" \
    "$*"`
  ls "$BAFI" 2>/dev/null
}

# get all backups in chronoligical order, the newest first
for bp in `ls -t ${FILENAME}.saved.by* \
                 $(read_field_backup ${FILENAME}*) 2>/dev/null`; do
  for abp in $ALL_BACKUPS; do
    test "$bp" = "$abp" && continue 2
  done
  ALL_BACKUPS="$ALL_BACKUPS $bp"
done
test -r "$RC_BACKUP" && DIRECT_BACKUP="$RC_BACKUP"
debug "(0) DIRECT_BACKUP: $DIRECT_BACKUP"
debug "(0) ALL_BACKUPS: $ALL_BACKUPS"

if [ -n "$ALL_BACKUPS" ] ; then
  # At first put all except DIRECT_BACKUP from ALL_BACKUPS to INVALID_BACKUPS
  INVALID_BACKUPS=`\
  for a in $ALL_BACKUPS; do
    test "$a" != "$DIRECT_BACKUP" && echo "$a"
  done`
  # Then we are going to build a chain of backups and delete the chain elements
  # from INVALID_BACKUPS.
  NEXT_BACKUP=`read_field_backup "$DIRECT_BACKUP"`
  while [ -r "$NEXT_BACKUP" ] ; do
    debug "(searching stack) NEXT_BACKUP=$NEXT_BACKUP"
    # At first delete NEXT_BACKUP from INVALID_BACKUPS
    INVALID_BACKUPS=`\
    for a in $INVALID_BACKUPS; do
      test "$a" != "$NEXT_BACKUP" && echo "$a"
    done`
    # INDIRECT_BACKUPS contains all elements except the last ...
    INDIRECT_BACKUPS="$INDIRECT_BACKUPS $LAST_BACKUP"
    # ... which is always in LAST_BACKUP
    LAST_BACKUP="$NEXT_BACKUP"
    NEXT_BACKUP=`read_field_backup "$NEXT_BACKUP"`
    # Detect a loop
    for a in $DIRECT_BACKUP $INDIRECT_BACKUPS $LAST_BACKUP; do
      test "$NEXT_BACKUP" = "$a" && NEXT_BACKUP=""
    done
  done
  debug "(1) DIRECT_BACKUP: $DIRECT_BACKUP"
  debug "(1) INDIRECT_BACKUPS: $INDIRECT_BACKUPS"
  debug "(1) LAST_BACKUP: $LAST_BACKUP"
  debug "(1) INVALID_BACKUPS: $INVALID_BACKUPS"
fi

# The remaining invalid backups have to be reordered. First all backups
# without an infoblock then those with info block, both groups
# still chronologically ordered.
unset IB_1 IB_2 IB_3
for a in $INVALID_BACKUPS; do
  b=`sed -n "/### BEGIN INFO/,/### END INFO/p" $a`
  if [ -z "$b" ] ; then
    IB_1="$IB_1 $a"
  else
    IB_2="$IB_2 $a"
  fi
done
INVALID_BACKUPS="$IB_1 $IB_2"
debug "(2) INVALID_BACKUPS: $INVALID_BACKUPS"
# Then we select all backups with the correct service in the filename. We now
# have two groups, both ordered as before.
# Then we split the first group in those which additionally contain the
# given extension in the filename still sustainig the old order.
unset IB_1 IB_2 IB_3
for a in $INVALID_BACKUPS; do
  if echo $a | grep "$SERVICE" &>/dev/null; then
    if echo $a | grep "$SERVICE.$EXT" &>/dev/null; then
      IB_1="$IB_1 $a"
    else
      IB_2="$IB_2 $a"
    fi
  else
    IB_3="$IB_3 $a"
  fi
done
INVALID_BACKUPS="$IB_1 $IB_2 $IB_3"
debug "(3) INVALID_BACKUPS: $INVALID_BACKUPS"
# Now the list starts with backups that fit most regarding the  name of the
# backup and then at first these which seem to be backups of unmodified files.
# Now we choose the first one. If it has an info block we try to find an
# according stack as before and then take the last element of it.
CHOOSEN_BACKUP=`echo "$INVALID_BACKUPS" | (read a b; echo "$a")`
SUCC_BACKUP=`read_field_backup "$CHOOSEN_BACKUP"`
unset LOOP_STOP
while [ -r "$SUCC_BACKUP" ] ; do
  LOOP_STOP="$LOOP_STOP $SUCC_BACKUP"
  CHOOSEN_BACKUP="$SUCC_BACKUP"
  SUCC_BACKUP=`read_field_backup "$CHOOSEN_BACKUP"`
  # detect a loop
  for a in $LOOP_STOP; do
    test "$a" = "$SUCC_BACKUP" && SUCC_BACKUP=""
  done
done
# IMHO this should be the at least dynamically modified file of all invalid
# backups.
INVALID_BACKUPS="$CHOOSEN_BACKUP $INVALID_BACKUPS"
debug "(4) INVALID_BACKUPS: $INVALID_BACKUPS"

#  x=wird auch au▀erhalb verwendet
#
#    ALL_BACKUPS
#    BAFI
#    CHOOSEN_BACKUP
#  x DIRECT_BACKUP
#  x EXT                     ro
#  x FILENAME                ro
#    IB_1
#    IB_2
#    IB_3
#  x INDIRECT_BACKUPS
#  x INVALID_BACKUPS
#  x LAST_BACKUP
#    LOOP_STOP
#    NEXT_BACKUP
#  x RC_BACKUP               ro
#  x SERVICE                 ro
#    SUCC_BACKUP

###########################################################
# Finally execute the requested action
###########################################################

# If there is a resolv.conf and --save_now was set then lets do it:
test -n "$SAVENOW" -a -e "$FILENAME" && cp -p --backup=t $FILENAME $SAVENOW

debug "BACKUP=$BACKUP"
case $ACTION in
  modify)
    # maybe there is no resolv.conf or current resolv.conf points to
    # the same backup file that should be used now
    # We don't copy resolv.conf if there is an valid backup of the same
    # service with the same private extension or ...
    for a in $DIRECT_BACKUP $INDIRECT_BACKUPS $LAST_BACKUP; do
      test "$BACKUP" = "$a" && SAVE="no"
    done
    # ... there isn't any
    if [ -e $FILENAME -a "$SAVE" != "no" ] ; then
       cp -p $FILENAME $BACKUP
       debug "$FILENAME saved to $BACKUP"
    fi
    write_file
    log "Service $SERVICE modified $FILENAME. See info block in this file"
    notify_services
   ;;
  restore)
    # If __save_later was set when modifying then we save the temporary
    # resolv.conf
    test -n "$RC_SAVELATER" -a -e "$FILENAME" &&
      cp -p --backup=t $FILENAME $RC_SAVELATER
    # We only restore if a backup with the correct name (already in $BACKUP)
    # exists. If this backup is valid we have to save the integrity of a
    # possibly existing backup stack. If this backup is invalid (= not part
    # of a stack) then we just restore it, even if we invalidate an existing
    # stack.
    if [ -e "$BACKUP" ] ; then
      # Now we search the possibly existing stack and store the two
      # predecessors and one successor of it.
      # Don't remove the empty entry ("") from the list.
      for a in $FILENAME $DIRECT_BACKUP $INDIRECT_BACKUPS \
               $LAST_BACKUP ""; do
        P="$C"
        C="$S"
        S="$a"
        test "$C" = "$BACKUP" && break
      done
      # If we did not found the Backup in the stack of valid backups, we
      # write BACKUP to C and set FILENAME as its predecessor (P). Because
      # the Backup can have a successor even if it is called invalid, we have
      # to look for it.
      if [ "$C" != "$BACKUP" ] ; then
        P="$FILENAME"
        C="$BACKUP"
        S=`read_field_backup "$BACKUP"`
      fi
      debug "(restore) P=$P C=$C S=$S"
      # If we were called with --keep, we don't restore the backup but
      # keep the temporary settings.
      if [ "$KEEP" = "yes" ] ; then
        # We have to keep the resolver settings, but not the meta information
        # in the info block. There are two cases:
    # 1) The Backup (C) was the last in the stack (S="") then we remove the
    #    info block from its predecessor (P) and remove C.
        # 2) The Backup has itself a backup (S!="") then we have to replace the
        #    info block in the predecessor (P) with that from the Backup (C),
        #    but keep everything else from P. And remove C.
        cp -p $P $TMP_FILE
        if [ "$S" = "" ] ; then
          sed "/### BEGIN INFO/,/### END INFO/d" $TMP_FILE > $P
          log "kept $P and removed info block"
        else
          sed -n "/### BEGIN INFO/,/### END INFO/p" $C > $P
          sed "/### BEGIN INFO/,/### END INFO/d" $TMP_FILE >> $P
          log "kept $P and changed info block"
        fi
        rm $C
        log "removed $C"
      else
        # Don't keep the temporary settings, restore.
        # All we have to do is to move the Backup (C) to its predecessor (P),
        # because the backup field of the previous predecessor already points
        # to the filename of P and the backup field of C what then will be in
        # P points to S (if existing).
        mv $C $P
        log "restored $C to $P"
      fi
    else
      # If no extension was given we search for backup files of the calling
      # service with private extensions and call us recursivle for every
      # found extension.
      if [ "$EXT" = "" ] ; then
        for a in `ls -t "$BACKUP"* 2>/dev/null`; do
          EXT=${a##$BACKUP.}
          $0 $COMMANDLINE -e "$EXT" --no_restart
        done
        if [ "$EXT" = "" ] ; then
          log "no matching backup found, left everything alone"
        fi
      fi
    fi
    # If there is no backup left, make sure that $FILENAME does not contain
    # an info block
    if [ -z "`ls ${FILENAME}.saved.by.* $LAST_BACKUP $INDIRECT_BACKUPS \
                 $DIRECT_BACKUP $INVALID_BACKUPS 2>/dev/null`" ] ; then
      if grep -qs "### BEGIN INFO" $FILENAME 2>/dev/null; then
        log "removing info block from $FILENAME, because there is" \
            "no backup left"
        cp -p $FILENAME $TMP_FILE
        sed "/### BEGIN INFO/,/### END INFO/d" $TMP_FILE >  $FILENAME
        chmod 644 $FILENAME
      fi
    fi
    notify_services
    read_file
    ;;
  cleanup)
    # Peter wants to know the old nameservers before cleaning up
    if [ "$DNS" = "show" ] ; then
      read_file
      test -n "$OLDDNS" && echo $OLDDNS
    fi
    # If $FILENAME was modified (= RC_BLOCK nonempty) we have to restore it
    if [ -n "$RC_BLOCK" -a "$KEEP" != "yes" ] ; then
      # If --save_later was set when modifying then we save the temporary
      # resolv.conf
      test -n "$RC_SAVELATER" -a -e "$FILENAME" &&
        cp -p --backup=t $FILENAME $RC_SAVELATER
      # Search the most reasonable backup. That is (if existing) the LAST_BACKUP
      # then the DIRECT_BACKUP and last the first one of INVALID_BACKUPS
      BACKUP=`echo "$LAST_BACKUP $DIRECT_BACKUP $INVALID_BACKUPS" \
              | (read a b; echo $a)`
      if [ -e "$BACKUP" ] ; then
        mv $BACKUP $FILENAME
        log "restored $FILENAME from $BACKUP"
      fi
    fi
    # Now we remove all backups
    MSG=`rm -v $LAST_BACKUP $INDIRECT_BACKUPS $DIRECT_BACKUP \
               $INVALID_BACKUPS 2>/dev/null`
    test -n "$MSG" && log "Deleted the following stale backups: $MSG"
    # After cleaning up resolc.conf should not contain an INFO block that
    # marks it as modified. If it somehow happens that it has it, we remove it.
    if grep -qs "### BEGIN INFO" $FILENAME 2>/dev/null; then
      cp -p $FILENAME $TMP_FILE
      sed "/### BEGIN INFO/,/### END INFO/d" $TMP_FILE >  $FILENAME
      chmod 644 $FILENAME
    fi
    notify_services
    read_file
    ;;
  check)
    if [ -z "$RC_BLOCK" ] ; then
      warn "$FILENAME not modified"
    else
      warn $RC_TEXT
      RETVAL=1
    fi
    ;;
esac

# Don't delete empty file. See bug 40728
# test "`cat $FILENAME`" = "" && rm $FILENAME
debug "finished"
exit $RETVAL