
#!/bin/sh

dbdir=/var/lib/dpkg

# Backup the 7 last versions of dpkg databases containing user data.
if cd /var/backups ; then
  # We backup all relevant database files if any has changed, so that
  # the rotation number always contains an internally consistent set.
  dbchanged=no
  dbfiles="arch status diversions statoverride"
  for db in $dbfiles ; do
    if ! [ -s "dpkg.${db}.0" ] && ! [ -s "$dbdir/$db" ]; then
      # Special case the files not existing or being empty as being equal.
      continue
    elif ! cmp -s "dpkg.${db}.0" "$dbdir/$db"; then
      dbchanged=yes
      break
    fi
  done
  if [ "$dbchanged" = "yes" ] ; then
    for db in $dbfiles ; do
      if [ -e "$dbdir/$db" ]; then
        cp -p "$dbdir/$db" "dpkg.$db"
      else
        touch "dpkg.$db"
      fi
      savelog -c 7 "dpkg.$db" >/dev/null
    done
  fi

  # The alternatives database is independent from the dpkg database.
  dbalt=alternatives

  # XXX: Ideally we'd use --warning=none instead of discarding stderr, but
  # as of GNU tar 1.27.1, it does not seem to work reliably (see #749307).
  if ! test -e ${dbalt}.tar.0 ||
     ! tar -df ${dbalt}.tar.0 -C $dbdir $dbalt >/dev/null 2>&1 ;
  then
    tar -cf ${dbalt}.tar -C $dbdir $dbalt >/dev/null 2>&1
    savelog -c 7 ${dbalt}.tar >/dev/null
  fi
fi