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Filename : apt_clone.py
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# Copyright (C) 2011 Canonical
#
# Authors:
#  Michael Vogt
#
# 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; version 3.
#
# 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 Street, Fifth Floor, Boston, MA 02110-1301 USA

from __future__ import print_function

import apt
from apt.cache import FetchFailedException
import apt_pkg
import difflib
import fnmatch
import glob
import hashlib
import logging
import os
import re
import shutil
import stat
import subprocess
import tarfile
import tempfile
import time

from io import BytesIO, open

if "APT_CLONE_DEBUG_RESOLVER" in os.environ:
    apt_pkg.config.set("Debug::pkgProblemResolver", "1")
    apt_pkg.config.set("Debug::pkgDepCache::AutoInstall", "1")

class LowLevelCommands(object):
    """ calls to the lowlevel operations to install debs
        or repack a deb
    """
    dpkg_repack = "/usr/bin/dpkg-repack"

    def install_debs(self, debfiles, targetdir):
        if not debfiles:
            return True
        install_cmd = ["dpkg", "-i"]
        if targetdir != "/":
            install_cmd.insert(0, "chroot")
            install_cmd.insert(1, targetdir)
        ret = subprocess.call(install_cmd + debfiles)
        return (ret == 0)

    def repack_deb(self, pkgname, targetdir):
        """ dpkg-repack pkgname into targetdir """
        if not os.path.exists(self.dpkg_repack):
            raise IOError("no '%s' found" % self.dpkg_repack)
        repack_cmd = [self.dpkg_repack]
        if not os.getuid() == 0:
            if not os.path.exists("/usr/bin/fakeroot"):
                return
            repack_cmd = ["fakeroot", "-u"] + repack_cmd
        ret = subprocess.call(repack_cmd + [pkgname], cwd=targetdir)
        return (ret == 0)

    def debootstrap(self, targetdir, distro=None):
        if distro is None:
            import lsb_release
            distro = lsb_release.get_distro_information()['CODENAME']
        ret = subprocess.call(["debootstrap", distro, targetdir])
        return (ret == 0)

    def merge_keys(self, fromkeyfile, intokeyfile):
        ret = subprocess.call(['apt-key', '--keyring', intokeyfile,
                               'add', fromkeyfile])
        return (ret == 0)

    def bind_mount(self, olddir, newdir):
        ret = subprocess.call(["mount", "--bind", olddir, newdir])
        return (ret == 0)

    def bind_umount(self, binddir):
        ret = subprocess.call(["umount", binddir])
        return (ret == 0)


class AptClone(object):
    """ clone the package selection/installation of a existing system
        using the information that apt provides

        If dpkg-repack is installed, it will be used to generate debs
        for the obsolete ones.
    """
    CLONE_FILENAME = "apt-clone-state-%s.tar.gz" % os.uname()[1]

    TARPREFIX = "./"

    def __init__(self, fetch_progress=None, install_progress=None,
                 cache_cls=None):
        self.not_downloadable = set()
        self.version_mismatch = set()
        self.commands = LowLevelCommands()
        # fetch
        if fetch_progress:
            self.fetch_progress = fetch_progress
        else:
            self.fetch_progress =  apt.progress.text.AcquireProgress()
        # install
        if install_progress:
            self.install_progress = install_progress
        else:
            self.install_progress = apt.progress.base.InstallProgress()
        # FIXME: SIIIIILLLLLLLYYYYYYYYY use mock.patch instead to patch
        #        the apt.Cache() to a mock
        # cache class (e.g. apt.Cache)
        if cache_cls:
            self._cache_cls = cache_cls
        else:
            self._cache_cls = apt.Cache

    # save
    def save_state(self, sourcedir, target,
                   with_dpkg_repack=False, with_dpkg_status=False,
                   scrub_sources=False, extra_files=None):
        """ save the current system state (installed pacakges, enabled
            repositories ...) into the apt-state.tar.gz file in targetdir
        """
        if os.path.isdir(target):
            target = os.path.join(target, self.CLONE_FILENAME)
        else:
            if not target.endswith(".tar.gz"):
                target += ".apt-clone.tar.gz"

        if sourcedir != '/':
            apt_pkg.init_config()
            apt_pkg.config.set("Dir", sourcedir)
            apt_pkg.config.set("Dir::State::status",
                               os.path.join(sourcedir, 'var/lib/dpkg/status'))
            apt_pkg.init_system()

        with tarfile.open(name=target, mode="w:gz") as tar:
            self._write_uname(tar)
            self._write_state_installed_pkgs(sourcedir, tar)
            self._write_state_auto_installed(tar)
            self._write_state_sources_list(tar, scrub_sources)
            self._write_state_apt_preferences(tar)
            self._write_state_apt_keyring(tar)
            self._write_state_extra_files(extra_files, tar)
            if with_dpkg_status:
                self._write_state_dpkg_status(tar)
            if with_dpkg_repack:
                self._dpkg_repack(tar)

    def _get_host_info_dict(self):
        # not really uname
        host_info = { 'hostname'   : os.uname()[1],
                       'kernel'     : os.uname()[2],
                       'uname_arch' : os.uname()[4],
                       'arch'       : apt_pkg.config.find("APT::Architecture")
                     }
        return host_info

    def _write_uname(self, tar):
        host_info = self._get_host_info_dict()
        # save it
        f = tempfile.NamedTemporaryFile(mode='w')
        info = "\n".join(["%s: %s" % (key, value)
                          for (key, value) in host_info.items()])
        f.write(info+"\n")
        f.flush()
        tar.add(f.name, arcname="./var/lib/apt-clone/uname")

    def _write_state_extra_files(self, extra_files, tar):
        if extra_files is None:
            return
        for p in extra_files:
            for f in glob.glob(p):
                tar.add(f, arcname="./extra-files"+f)
                
    def _write_state_installed_pkgs(self, sourcedir, tar):
        cache = self._cache_cls(rootdir=sourcedir)
        s = ""
        foreign = ""
        for pkg in cache:
            if pkg.is_installed:
                # a version identifies the pacakge
                s += "%s %s %s\n" % (
                    pkg.name, pkg.installed.version, int(pkg.is_auto_installed))
                if not pkg.candidate or not pkg.candidate.downloadable:
                    self.not_downloadable.add(pkg.name)
                elif not (pkg.installed.downloadable and
                          pkg.candidate.downloadable):
                    self.version_mismatch.add(pkg.name)
                for o in pkg.installed.origins:
                    if o.archive == "now" and o.origin == "":
                        continue
                    import lsb_release
                    distro_id = lsb_release.get_distro_information()['ID']
                    if o.origin != distro_id:
                        foreign += "%s %s %s\n" % (
                            pkg.name, pkg.installed.version,
                            o.origin if o.origin != "" else "unknown")
                    break
        # store the installed.pkgs
        tarinfo = tarfile.TarInfo("./var/lib/apt-clone/installed.pkgs")
        s = s.encode('utf-8')
        tarinfo.size = len(s)
        tarinfo.mtime = time.time()
        tar.addfile(tarinfo, BytesIO(s))
        # store the foreign packages
        tarinfo = tarfile.TarInfo("./var/lib/apt-clone/foreign.pkgs")
        foreign = foreign.encode('utf-8')
        tarinfo.size = len(foreign)
        tarinfo.mtime = time.time()
        tar.addfile(tarinfo, BytesIO(foreign))

    def _write_state_dpkg_status(self, tar):
        # store dpkg-status, this is not strictly needed as installed.pkgs
        # should contain all we need, but we still keep it for debugging
        # reasons
        dpkg_status = apt_pkg.config.find_file("dir::state::status")
        tar.add(dpkg_status, arcname="./var/lib/apt-clone/dpkg-status")

    def _write_state_auto_installed(self, tar):
        extended_states = apt_pkg.config.find_file(
            "Dir::State::extended_states")
        if os.path.exists(extended_states):
            tar.add(extended_states, "./var/lib/apt-clone/extended_states")

    def _write_state_apt_preferences(self, tar):
        f = apt_pkg.config.find_file("Dir::Etc::preferences")
        if os.path.exists(f):
            tar.add(f, arcname="./etc/apt/preferences")
        p = apt_pkg.config.find_dir("Dir::Etc::preferencesparts",
                                    "/etc/apt/preferences.d")
        if os.path.exists(p):
            tar.add(p, arcname="./etc/apt/preferences.d")

    def _write_state_apt_keyring(self, tar):
        f = apt_pkg.config.find_file("Dir::Etc::trusted")
        if os.path.exists(f):
            tar.add(f, arcname="./etc/apt/trusted.gpg")
        p = apt_pkg.config.find_dir("Dir::Etc::trustedparts",
                                    "/etc/apt/trusted.gpg.d")
        if os.path.exists(p):
            tar.add(p, arcname="./etc/apt/trusted.gpg.d")

    def _write_state_sources_list(self, tar, scrub=False):
        sources_list = apt_pkg.config.find_file("Dir::Etc::sourcelist")
        self._add_file_to_tar_with_password_check(tar, sources_list, scrub,
            "./etc/apt/sources.list")
        source_parts = apt_pkg.config.find_dir("Dir::Etc::sourceparts")
        if os.path.exists(source_parts):
            tar.add(source_parts, arcname="./etc/apt/sources.list.d",
                    recursive=False)
            for source in os.listdir(source_parts):
                if source.startswith('.'):
                    continue
                if not source.endswith('.list'):
                    continue
                sources_file_name = '%s/%s' % (source_parts, source)
                if os.path.isdir(sources_file_name):
                    continue
                self._add_file_to_tar_with_password_check(tar,
                    sources_file_name, scrub,
                    "./etc/apt/sources.list.d/"+source)

    def _add_file_to_tar_with_password_check(self, tar, sources, scrub, arcname):
        if scrub:
            with tempfile.NamedTemporaryFile(mode='wb') as source_copy, open(sources, 'rb') as f:
                for line in f.readlines():
                    # compat with both py2/py3
                    if type(line) is bytes:
                        line = line.decode("UTF-8")
                    if re.search('/[^/@:]*:[^/@:]*@', line):
                        line = re.sub('/[^/@:]*:[^/@:]*@',
                            '/USERNAME:PASSWORD@', line)
                    # tempfile.NamedTemporaryFile cannot easily be made to
                    # open in Unicode mode in Python 2.  We can remove this
                    # once ubuntu-release-upgrader is run under Python 3
                    # (i.e. after Ubuntu 14.04).
                    source_copy.write(line.encode("utf-8"))
                    source_copy.flush()
                tar.add(source_copy.name, arcname=arcname)
        else:
            tar.add(sources, arcname=arcname)

    def _write_modified_files_from_etc(self, tar):
        #etcdir = os.path.join(apt_pkg.config.get("Dir"), "etc")
        pass

    def _dpkg_repack(self, tar):
        tdir = tempfile.mkdtemp()
        for pkgname in self.not_downloadable:
            self.commands.repack_deb(pkgname, tdir)
        tar.add(tdir, arcname="./var/lib/apt-clone/debs")
        shutil.rmtree(tdir)
        #print(tdir)

    # detect prefix
    def _detect_tarprefix(self, tar):
        #print(tar.getnames())
        if tar.getnames()[-1].startswith("./"):
            self.TARPREFIX = "./"
        else:
            self.TARPREFIX = ""

    # info
    def _get_info_distro(self, statefile):
        with tarfile.open(statefile) as tar:
            self._detect_tarprefix(tar)
            # guess distro infos
            f = tar.extractfile(self.TARPREFIX+"etc/apt/sources.list")
            for line in f.readlines():
                line = line.decode("utf-8")
                if line.startswith("#") or line.strip() == "":
                    continue
                l = line.split()
                if len(l) > 2 and not l[2].endswith("/"):
                    return l[2]
        return None

    def _get_clone_info_dict(self, statefile):
        distro = self._get_info_distro(statefile) or "unknown"
        # nr installed
        with tarfile.open(statefile) as tar:
            f = tar.extractfile(
                self.TARPREFIX + "var/lib/apt-clone/installed.pkgs")
            installed = autoinstalled = 0
            meta = []
            for line in f.readlines():
                line = line.decode("utf-8")
                (name, version, auto) = line.strip().split()
                installed += 1
                if int(auto):
                    autoinstalled += 1
                # FIXME: this is a bad way to figure out about the
                # meta-packages
                if name.endswith("-desktop"):
                    meta.append(name)
            # date
            m = tar.getmember(
                self.TARPREFIX + "var/lib/apt-clone/installed.pkgs")
            date = m.mtime
            # check hostname (if found)
            hostname = "unknown"
            arch = "unknown"
            if self.TARPREFIX+"var/lib/apt-clone/uname" in tar.getnames():
                info = tar.extractfile(
                    self.TARPREFIX + "var/lib/apt-clone/uname").read()
                section = apt_pkg.TagSection(info)
                hostname = section.get("hostname", "unknown")
                arch = section.get("arch", "unknown")
            return { 'hostname' : hostname,
                     'distro' : distro,
                     'meta' : ", ".join(meta),
                     'installed' : installed,
                     'autoinstalled' : autoinstalled,
                     'date' : time.ctime(date),
                     'arch' : arch,
                   }

    def info(self, statefile):
        return "Hostname: %(hostname)s\n"\
               "Arch: %(arch)s\n"\
               "Distro: %(distro)s\n"\
               "Meta: %(meta)s\n"\
               "Installed: %(installed)s pkgs (%(autoinstalled)s automatic)\n"\
               "Date: %(date)s\n" % self._get_clone_info_dict(statefile)

    # show-diff
    def _get_file_diff_against_clone(self, statefile, system_file, targetdir):
        with tarfile.open(statefile) as tar:
            self._detect_tarprefix(tar)
            clone_file = tar.extractfile(self.TARPREFIX+system_file[1:])
            clone_file_lines = []
            # FIXME: is there a better way for this? something to tell
            #        tarfile that really its all utf8?
            for line in clone_file.readlines():
                clone_file_lines.append(line.decode("utf-8"))
        system_file = targetdir+system_file
        if os.path.exists(system_file):
            with open(system_file) as fp:
                system_file_lines = fp.readlines()
        else:
            system_file_lines = []
        gen = difflib.unified_diff(
            system_file_lines, clone_file_lines,
            fromfile="current-system%s" % system_file, tofile=system_file)
        diff = []
        for line in gen:
            diff.append(line)
        return diff

    def show_diff(self, statefile, targetdir="/"):
        if targetdir != "/":
            apt_pkg.config.set("DPkg::Chroot-Directory", targetdir)

        # show info/uname diff
        print("Clone info differences: ")
        host_info = self._get_host_info_dict()
        clone_info = self._get_clone_info_dict(statefile)
        for key in host_info:
            if host_info.get(key, None) != clone_info.get(key, None):
                print(" '%s': clone='%s' system='%s'" % (
                        key, clone_info.get(key, None),
                        host_info.get(key, None)))
        print("")

        # show sources.list{,.d} diff
        sources_list_system = "/etc/apt/sources.list"
        diff = self._get_file_diff_against_clone(
            statefile, sources_list_system, targetdir)
        if diff:
            print("".join(diff))

        # FIXME: do sources.list.d diff too
        # FIXME: do apt-keyring diff
        #self._restore_package_selection(statefile, targetdir, protect_installed)
        # create new cache in the rootdir
        cache = self._cache_cls(rootdir=targetdir)
        with tarfile.open(statefile) as tar:
            f = tar.extractfile(
                self.TARPREFIX + "var/lib/apt-clone/installed.pkgs")
            # get the data
            installed_in_clone = {}
            for line in f.readlines():
                line = line.strip().decode('utf-8')
                if line.startswith("#") or line == "":
                    continue
                (name, version, auto) = line.split()
                installed_in_clone[name] = (version, auto)
        installed_on_system = {}
        for pkg in cache:
            if not pkg.installed:
                continue
            installed_on_system[pkg.name] = (
                pkg.installed.version, str(pkg.is_auto_installed))

        only_on_system = set(installed_on_system.keys()) - set(installed_in_clone.keys())
        if only_on_system:
            print("Installed on the system but not in the clone-file:")
            print(" ".join(sorted(only_on_system)))
            print("\n")

        only_in_clone =  set(installed_in_clone.keys()) - set(installed_on_system.keys())
        if only_in_clone:
            print("Installed in the clone-file but not in the system:")
            print(" ".join(sorted(only_in_clone)))
            print("\n")

        # show version differences
        pkgversion_differences = set()
        for pkgname in sorted(installed_in_clone):
            if not pkgname in installed_on_system:
                continue
            clone_file_pkgversion, clone_is_auto = installed_in_clone[pkgname]
            system_pkgversion, sys_is_auto = installed_on_system[pkgname]
            if clone_file_pkgversion != system_pkgversion:
                pkgversion_differences.add(
                    (pkgname, clone_file_pkgversion, system_pkgversion))
        if pkgversion_differences:
            print("Version differences: ")
            print("Pkgname <clone-file-version> <system-version>")
            for pkgname, clone_ver, system_ver in pkgversion_differences:
                print(" %s  <%s>   <%s>" % (pkgname, clone_ver, system_ver))


    # restore
    def restore_state(self, statefile, targetdir="/", exclude_pkgs=None,
                      new_distro=None, protect_installed=False, mirror=None):
        """ take a statefile produced via (like apt-state.tar.gz)
            save_state() and restore the packages/repositories
            into targetdir (that is usually "/")
        """

        if targetdir != "/":
            apt_pkg.config.set("DPkg::Chroot-Directory", targetdir)
            self.commands.bind_mount("/proc", os.path.join(targetdir, "proc"))
            self.commands.bind_mount("/sys", os.path.join(targetdir, "sys"))

        # detect prefix
        with tarfile.open(statefile) as tar:
            self._detect_tarprefix(tar)

        if not os.path.exists(targetdir):
            print("Dir '%s' does not exist, need to bootstrap first" % targetdir)
            distro = self._get_info_distro(statefile)
            self.commands.debootstrap(targetdir, distro)

        self._restore_sources_list(statefile, targetdir, mirror=mirror)
        self._restore_apt_keyring(statefile, targetdir)
        if new_distro:
            self._rewrite_sources_list(targetdir, new_distro)
        self._restore_package_selection(statefile, targetdir, protect_installed, exclude_pkgs)
        # FIXME: this needs to check if there are conflicts, e.g. via
        #        gdebi
        self._restore_not_downloadable_debs(statefile, targetdir)
        # restore after package to avoid e.g. conffile prompts
        self._restore_extra_files(statefile, targetdir)

        # and umount again
        if targetdir != "/":
            self.commands.bind_umount(os.path.join(targetdir, "proc"))
            self.commands.bind_umount(os.path.join(targetdir, "sys"))

    # simulate restore and return list of missing pkgs
    def simulate_restore_state(self, statefile, exclude_pkgs, new_distro=None):
        # create tmp target (with host system dpkg-status) to simulate in
        target = tempfile.mkdtemp()
        dpkg_status = apt_pkg.config.find_file("dir::state::status")
        if not os.path.exists(target+os.path.dirname(dpkg_status)):
            os.makedirs(target+os.path.dirname(dpkg_status))
        shutil.copy(dpkg_status, target+dpkg_status)
        # restore sources.list and update cache in tmp target
        self._restore_sources_list(statefile, target)
        # optionally rewrite on new distro
        if new_distro:
            self._rewrite_sources_list(target, new_distro)
        cache = self._cache_cls(rootdir=target)
        try:
            cache.update(apt.progress.base.AcquireProgress())
        except FetchFailedException:
            # This cannot be resolved here, but it should not be interpreted as
            # a fatal error.
            pass
        cache.open()
        # try to replay cache and see thats missing
        missing = self._restore_package_selection_in_cache(statefile, cache, exclude_pkgs=exclude_pkgs)
        shutil.rmtree(target)
        return missing

    def _restore_sources_list(self, statefile, targetdir, mirror=None):
        with tarfile.open(statefile) as tar:
            existing = os.path.join(targetdir, "etc", "apt", "sources.list")
            if os.path.exists(existing):
                shutil.copy(existing, '%s.apt-clone' % existing)
            tar.extract(self.TARPREFIX+"etc/apt/sources.list", targetdir)
            td_sources = os.path.join(targetdir, "etc", "apt", "sources.list")
            os.chmod(td_sources, stat.S_IRUSR | stat.S_IWUSR | stat.S_IRGRP |
                     stat.S_IROTH)
            if mirror:
                from aptsources.sourceslist import SourcesList
                apt_pkg.config.set("Dir::Etc::sourcelist", td_sources)
                sources = SourcesList()
                for entry in sources.list[:]:
                    if entry.uri != mirror:
                       entry.uri = mirror
                sources.save()
            try:
                tar.extract(self.TARPREFIX+"etc/apt/sources.list.d", targetdir)
            except KeyError:
                pass

    def _restore_apt_keyring(self, statefile, targetdir):
        existing = os.path.join(targetdir, "etc", "apt", "trusted.gpg")
        backup = '%s.apt-clone' % existing
        if os.path.exists(existing):
            shutil.copy(existing, backup)
        with tarfile.open(statefile) as tar:
            try:
                tar.extract(self.TARPREFIX+"etc/apt/trusted.gpg", targetdir)
            except KeyError:
                pass
            try:
                tar.extract(self.TARPREFIX+"etc/apt/trusted.gpg.d", targetdir)
            except KeyError:
                pass
            if os.path.exists(backup):
                self.commands.merge_keys(backup, existing)
                os.remove(backup)

    def _restore_package_selection_in_cache(self, statefile, cache, protect_installed=False, exclude_pkgs=None):
        # deal with excludes
        if exclude_pkgs is None:
            exclude_pkgs = []
        exclude_pkgs = set(exclude_pkgs)
        # reinstall packages
        missing = set()
        pkgs = set()
        # procted installed pkgs
        resolver = apt_pkg.ProblemResolver(cache._depcache)
        if protect_installed:
            for pkg in cache:
                if pkg.is_installed:
                    resolver.protect(pkg._pkg)
        # get the installed.pkgs data
        with tarfile.open(statefile) as tar:
            f = tar.extractfile(
                self.TARPREFIX + "var/lib/apt-clone/installed.pkgs")
            # the actiongroup will help libapt to speed up the following loop
            with cache.actiongroup():
                for line in f.readlines():
                    line = line.strip().decode('utf-8')
                    if line.startswith("#") or line == "":
                        continue
                    (name, version, auto) = line.split()
                    # tiny helper
                    def is_excluded(name, exclude_pkgs):
                        for excl in exclude_pkgs:
                            if fnmatch.fnmatch(name, excl):
                                return True
                    if is_excluded(name, exclude_pkgs):
                        continue
                    pkgs.add(name)
                    auto_installed = int(auto)
                    from_user = not auto_installed
                    if name in cache:
                        try:
                            # special mode, most useful for release-upgrades
                            if protect_installed:
                                cache[name].mark_install(from_user=from_user, auto_fix=False)
                                if cache.broken_count > 0:
                                    resolver.resolve()
                                    if not cache[name].marked_install:
                                        raise SystemError("pkg %s not marked upgrade" % name)
                            else:
                                # normal mode, this assume the system is consistent
                                cache[name].mark_install(from_user=from_user)
                        except SystemError as e:
                            logging.warning("can't add %s (%s)" % (name, e))
                            missing.add(name)
                        # ensure the auto install info is
                        cache[name].mark_auto(auto_installed)
        # check what is broken and try to fix
        if cache.broken_count > 0:
            resolver.resolve()
        # now go over and see what is missing
        for pkg in pkgs:
            if not pkg in cache:
                missing.add(pkg)
                continue
            if not (cache[pkg].is_installed or cache[pkg].marked_install):
                missing.add(pkg)
        return missing

    def _restore_package_selection(self, statefile, targetdir, protect_installed, exclude_pkgs):
        # create new cache
        cache = self._cache_cls(rootdir=targetdir)
        # python-apt Cache(rootdir=) will mangle dir::bin, fix that
        apt.apt_pkg.config.set("Dir::Bin", "/")
        apt.apt_pkg.config.set("Dir::Bin::dpkg", "/usr/bin/dpkg")
        try:
            cache.update(self.fetch_progress)
        except FetchFailedException:
            # This cannot be resolved here, but it should not be interpreted as
            # a fatal error.
            pass
        cache.open()
        self._restore_package_selection_in_cache(statefile, cache, protect_installed, exclude_pkgs)
        # do it
        cache.commit(self.fetch_progress, self.install_progress)

    def _restore_extra_files(self, statefile, targetdir):
        with tarfile.open(statefile) as tar:
            for m in tar.getmembers():
                prefix = self.TARPREFIX+"extra-files/"
                if m.name.startswith(prefix):
                    # strip prefix on extract
                    m.name = m.name[len(prefix):]
                    tar.extract(m, targetdir)

    def _restore_not_downloadable_debs(self, statefile, targetdir):
        with tarfile.open(statefile) as tar:
            try:
                debsdir = [ tarinfo for tarinfo in tar.getmembers() if tarinfo.name.startswith(self.TARPREFIX+"var/lib/apt-clone/debs/")]
                tar.extractall(targetdir,debsdir)
            except KeyError:
                return
        debs = []
        path = os.path.join(targetdir, "./var/lib/apt-clone/debs")
        for deb in glob.glob(os.path.join(path, "*.deb")):
            debpath = os.path.join(path, deb)
            debs.append(debpath)
        self.commands.install_debs(debs, targetdir)

    def _rewrite_sources_list(self, targetdir, new_distro):
        from aptsources.sourceslist import SourcesList, SourceEntry
        apt_pkg.config.set(
            "Dir::Etc::sourcelist",
            os.path.abspath(os.path.join(targetdir, "etc", "apt", "sources.list")))
        apt_pkg.config.set(
            "Dir::Etc::sourceparts",
            os.path.abspath(os.path.join(targetdir, "etc", "apt", "sources.list.d")))
        sources = SourcesList()

        for entry in sources.list[:]:
            if entry.invalid or entry.disabled:
                continue
            replacement = ''
            for pocket in ('updates', 'security', 'backports'):
                if entry.dist.endswith('-%s' % pocket):
                    replacement = '%s-%s' % (new_distro, pocket)
                    break
            if replacement:
                entry.dist = replacement
            else:
                entry.dist = new_distro

        existing = os.path.join(targetdir, "etc", "apt",
                                "sources.list.apt-clone")
        sourcelist = apt_pkg.config.find_file("Dir::Etc::sourcelist")
        if os.path.exists(existing):
            with open(existing, 'r') as fp:
                for line in fp:
                    src = SourceEntry(line, sourcelist)
                    if (src.invalid or src.disabled) or src not in sources:
                        sources.list.append(src)
            os.remove(existing)

        for entry in sources.list:
            if entry.uri.startswith('cdrom:'):
                # Make sure CD entries come first.
                sources.list.remove(entry)
                sources.list.insert(0, entry)
                entry.disabled = True
        sources.save()

    def _find_unowned_in_etc(self, sourcedir=""):
        if sourcedir:
            etcdir = os.path.join(sourcedir, "etc")
        else:
            etcdir = "/etc"
        # get all the files that dpkg "owns"
        owned = set()
        dpkg_basedir = os.path.dirname(apt_pkg.config.get("Dir::State::status"))
        for f in glob.glob(os.path.join(dpkg_basedir, "info", "*.list")):
            with open(f, encoding="utf-8") as fp:
                for line in fp:
                    if line.startswith("/etc/"):
                        owned.add(line.strip())
        # now go over etc
        unowned = set()
        for dirpath, dirnames, filenames in os.walk(etcdir):
            for name in filenames:
                fullname = os.path.join(dirpath[len(sourcedir):], name)
                if not fullname in owned:
                    unowned.add(fullname)
        return unowned

    def _find_modified_conffiles(self, sourcedir="/"):
        dpkg_status = sourcedir+apt_pkg.config.find("Dir::State::status")
        modified = set()
        # iterate dpkg-status file
        with open(dpkg_status) as fp:
            tag = apt_pkg.TagFile(fp)
            for entry in tag:
                if "conffiles" in entry:
                    for line in entry["conffiles"].split("\n"):
                        obsolete = None
                        if len(line.split()) == 3:
                            name, md5sum, obsolete = line.split()
                        else:
                            name, md5sum = line.split()
                        # update
                        path = sourcedir+name
                        md5sum = md5sum.strip()
                        # ignore oboslete conffiles
                        if obsolete == "obsolete":
                            continue
                        # user removed conffile
                        if not os.path.exists(path):
                            logging.debug("conffile %s removed" % path)
                            modified.add(path)
                            continue
                        # check content
                        md5 = hashlib.md5()
                        with open(path, 'rb') as fp:
                            md5.update(fp.read())
                        if md5.hexdigest() != md5sum:
                            logging.debug("conffile %s (%s != %s)" % (
                                    path, md5.hexdigest(), md5sum))
                            modified.add(path)
        return modified

    def _dump_debconf_database(self, sourcedir):
        print("not implemented yet")
        # debconf-copydb configdb newdb --config=Name:newdb --config=Driver:File --config=Filename:/tmp/lala.db
        #
        # debconf-copydb newdb configdb --config=Name:newdb --config=Driver:File --config=Filename:/tmp/lala.db
        #
        # dump to text with:
        #  debconf-copydb configdb pipe --config=Name:pipe
        #                 --config=Driver:Pipe --config=InFd:none
        #
        # restore from text with:
        #   ssh remotehost debconf-copydb pipe configdb --config=Name:pipe --config=Driver:Pipe