path: root/rumba/model.py

#
# A library to manage ARCFIRE experiments
#
#    Copyright (C) 2017 Nextworks S.r.l.
#    Copyright (C) 2017 imec
#
#    Sander Vrijders   <sander.vrijders@ugent.be>
#    Dimitri Staessens <dimitri.staessens@ugent.be>
#    Vincenzo Maffione <v.maffione@nextworks.it>
#    Marco Capitani    <m.capitani@nextworks.it>
#    Nick Aerts        <nick.aerts@ugent.be>
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library 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
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., http://www.fsf.org/about/contact/.
#

import abc
import os
import stat
import time
import shutil
from enum import Enum

import rumba.log as log

logger = log.get_logger(__name__)


tmp_dir = '/tmp/rumba'
try:
    os.mkdir(tmp_dir)
    os.chmod(tmp_dir, stat.S_IRWXU | stat.S_IRWXG | stat.S_IRWXO)
except OSError:
    # Already there, nothing to do
    pass

cache_parent_dir = os.path.join(os.path.expanduser("~"), '.cache/')
try:
    os.mkdir(cache_parent_dir)
except OSError:
    # Already there, nothing to do
    pass
cache_dir = os.path.join(os.path.expanduser("~"), '.cache/rumba/')
try:
    os.mkdir(cache_dir)
except OSError:
    # Already there, nothing to do
    pass


# Represents generic testbed info
#
# @username [string] user name
# @password [string] password
# @proj_name [string] project name
# @exp_name [string] experiment name
#
class Testbed(object):
    def __init__(self,
                 exp_name,
                 username,
                 password,
                 proj_name,
                 http_proxy=None,
                 system_logs=None):
        self.username = username
        self.password = password
        self.proj_name = proj_name
        self.exp_name = exp_name
        self.http_proxy = http_proxy
        self.flags = {'no_vlan_offload': False}
        if system_logs is None:
            self.system_logs = ['/var/log/syslog']
        elif isinstance(system_logs, str):
            self.system_logs = [system_logs]
        else:
            self.system_logs = system_logs

    def swap_in(self, experiment):
        for node in experiment.nodes:
            node.executor = self.executor

        self._swap_in(experiment)

        for dif in experiment.dif_ordering:
            if isinstance(dif, ShimEthDIF):
                dif.link_quality.apply(dif)

    @abc.abstractmethod
    def _swap_in(self, experiment):
        logger.info("_swap_in(): nothing to do")

    @abc.abstractmethod
    def swap_out(self, experiment):
        logger.info("swap_out(): nothing to do")

# Base class for DIFs
#
# @name [string] DIF name
#
class DIF(object):
    def __init__(self, name, members=None):
        self.name = name
        if members is None:
            members = list()
        self.members = members
        self.ipcps = list()

    def __repr__(self):
        s = "DIF %s" % self.name
        return s

    def __hash__(self):
        return hash(self.name)

    def __eq__(self, other):
        return other is not None and self.name == other.name

    def __neq__(self, other):
        return not self == other

    def add_member(self, node):
        self.members.append(node)

    def del_member(self, node):
        self.members.remove(node)

    def get_ipcp_class(self):
        return IPCP


# Shim over UDP
#
class ShimUDPDIF(DIF):
    def __init__(self, name, members=None):
        DIF.__init__(self, name, members)

    def get_ipcp_class(self):
        return ShimUDPIPCP


# Shim over Ethernet
#
# @link_speed [int] Speed of the Ethernet network, in Mbps
#
class ShimEthDIF(DIF):

    def get_e_id(self):
        return "ShimEthDIF." + self.name

    def __init__(self, name, members=None, link_quality=None):
        DIF.__init__(self, name, members)
        self._link_quality = link_quality if link_quality is not None else LinkQuality()

    def get_ipcp_class(self):
        return ShimEthIPCP

    def add_member(self, node):
        super(ShimEthDIF, self).add_member(node)
        if len(self.members) > 2:
            raise Exception("More than 2 members in %s!" % self.name)

    @property
    def link_quality(self):
        return self._link_quality

    @link_quality.setter
    def link_quality(self, _link_quality):
        if not _link_quality:
            raise ValueError("Cannot set link_quality to None, use del "
                             "link_quality to reset")

        self._link_quality = _link_quality

        _link_quality.apply(self)

    @link_quality.deleter
    def link_quality(self):
        self._link_quality.deactivate(self)

    def set_delay(self, delay=0,
                  jitter=None,
                  correlation=None,
                  distribution=None):
        """
        Set the delay parameters of the underlying link.
        Parameters as in :py:meth:`.Delay.__init__`
        :param delay: average delay in ms
        :type delay: :py:class:`int`
        :param jitter: jitter in ms
        :type jitter: :py:class:`int`
        :param correlation: correlation in %
        :type correlation: :py:class:`int`
        :param distribution: delay distribution, defaults to a Normal
        distribution
        :type distribution: :py:class:`.Distribution`
        """
        new_delay = Delay(delay, jitter, correlation, distribution)
        new_quality = LinkQuality.clone(self.link_quality, delay=new_delay)
        self.link_quality = new_quality

    def set_loss(self,
                 loss=0,
                 correlation=None):
        """
        Set the loss parameter of the underlying link.
        Parameters as in :py:meth:`.Loss.__init__`
        :param loss: loss in percentage
        :type loss: :py:class:`int` or :py:class:`float`
        :param correlation: correlation in percentage
        :type correlation: :py:class:`int` or :py:class:`float`
        """
        new_loss = Loss(loss, correlation)
        new_quality = LinkQuality.clone(self.link_quality, loss=new_loss)
        self.link_quality = new_quality

    def set_rate(self, rate=None):
        """
        Set the rate parameter of the underlying link.
        :param rate: The desired rate in mbps
        :type rate: :py:class:`int`
        """
        new_quality = LinkQuality.clone(self.link_quality, rate=rate)
        self.link_quality = new_quality

    def set_quality(self, delay, loss, rate):
        """
        Configure the basic quality parameters of the
        underlying link
        :param delay: the link delay, in ms
        :type delay: :py:class:`int`
        :param loss: the link loss, as a percentage
        :type loss: :py:class:`float` or :py:class:`int`
        :param rate: the link rate in mbps
        :type rate: :py:class:`int`
        """
        new_quality = LinkQuality(delay, loss, rate)
        self.link_quality = new_quality


# Normal DIF
#
# @policies [dict] Policies of the normal DIF. Format:
#       dict( componentName: str --> comp_policy:
#               dict( policy_name: str --> parameters:
#                       dict( name: str --> value: str )))
#
class NormalDIF(DIF):
    def __init__(self, name, members=None, policy=None):
        DIF.__init__(self, name, members)
        if policy is None:
            policy = Policy(self)
        self.policy = policy

    def add_policy(self, comp, pol, **params):
        self.policy.add_policy(comp, pol, **params)

    def del_policy(self, comp=None, policy_name=None):
        self.policy.del_policy(comp, policy_name)

    def show(self):
        s = DIF.__repr__(self)
        for comp, pol_dict in self.policy.get_policies().items():
            for pol, params in pol_dict.items():
                s += "\n       Component %s has policy %s with params %s" \
                     % (comp, pol, params)
        return s


class Distribution(Enum):
    NORMAL = 1
    PARETO = 2
    PARETONORMAL = 3


class Delay(object):
    def __init__(self, delay=0, jitter=None, correlation=None,
                 distribution=None):
        """
        Configure link delay
        :param delay: average delay in ms
        :type delay: :py:class:`int`
        :param jitter: jitter in ms
        :type jitter: :py:class:`int`
        :param correlation: correlation in %
        :type correlation: :py:class:`int`
        :param distribution: delay distribution, defaults to a Normal
        distribution
        :type distribution: :py:class:`.Distribution`
        """

        if delay < 0:
            raise ValueError("Delay needs to be at least 0")

        if jitter and not jitter > 0:
            raise ValueError("Jitter needs to be higher than 0")

        if (not jitter) and correlation:
            raise ValueError("Correlation requires a value for jitter")

        if correlation and (correlation < 0 or correlation > 100):
            raise ValueError("Correlation needs to be between 0 and 100")

        self._delay = delay
        self._jitter = jitter
        self._correlation = correlation
        self._distribution = distribution

    @property
    def delay(self):
        return self._delay

    @property
    def jitter(self):
        return self._jitter

    @property
    def correlation(self):
        return self._correlation

    @property
    def distribution(self):
        return self._distribution

    def build_command(self):
        opts = ["delay %ims" % self.delay]

        if self.jitter:
            opts.append("%ims" % self.jitter)

            if self.correlation:
                opts.append("%f%%" % self.correlation)

        if self.distribution:
            opts.append("distribution %s" % self.distribution.name.lower())

        return " ".join(opts)


class Loss(object):
    def __init__(self, loss, correlation=None):
        """
        Configure link loss
        :param loss: loss in percentage
        :type loss: :py:class:`int` or :py:class:`float`
        :param correlation: correlation in percentage
        :type correlation: :py:class:`int` or :py:class:`float`
        """
        if loss and (loss < 0 or loss > 100):
            raise ValueError("Loss needs to be between 0 and 100")

        if correlation and (correlation < 0 or correlation > 100):
            raise ValueError("Correlation needs to be between 0 and 100")

        self._loss = loss
        self._correlation = correlation

    @property
    def loss(self):
        return self._loss

    @property
    def correlation(self):
        return self._correlation

    def build_command(self):
        opts = ["loss %f%%" % self.loss]

        if self.correlation:
            opts.append("%f%%" % self.correlation)

        return " ".join(opts)


class LinkQuality(object):
    _active = set()

    @classmethod
    def clone(cls, old_quality, delay=None, loss=None, rate=None):
        """
        Clone old_quality, updating it with the provided parameters
        if present

        :param old_quality: A :py:class`.LinkQuality` instance to
                            use as a base
        :type old_quality: :py:class`.LinkQuality`
        :param delay: Delay object holding delay configuration
                      or number corresponding to delay in ms
        :type delay: :py:class:`.Delay` or :py:class:`int`
        :param loss: Loss object holding delay configuration or
                     number corresponding to loss percentage
        :type loss: :py:class:`.Loss` or :py:class:`float`
        :param rate: The rate of the link in mbit
        :type rate: :py:class:`int`
        :return: a new :py:class`.LinkQuality` instance
        :rtype :py:class`LinkQuality`
        """
        if delay is None:
            delay = old_quality.delay
        if loss is None:
            loss = old_quality.loss
        if rate is None:
            rate = old_quality.rate
        return LinkQuality(delay, loss, rate)

    def __init__(self, delay=None, loss=None, rate=None):
        """
        Link quality configuration
        :param delay: Delay object holding delay configuration
                      or number corresponding to delay in ms
        :type delay: :py:class:`.Delay` or :py:class:`int`
        :param loss: Loss object holding delay configuration or
                     number corresponding to loss percentage
        :type loss: :py:class:`.Loss` or :py:class:`float`
        :param rate: The rate of the link in mbit
        :type rate: :py:class:`int`
        """

        if rate and not rate > 0:
            raise ValueError("Rate needs to be higher than 0")

        if isinstance(delay, int):
            delay = Delay(delay)
        if isinstance(loss, int) or isinstance(loss, float):
            loss = Loss(loss)
        self._delay = delay
        self._loss = loss
        self._rate = rate

    @property
    def delay(self):
        return self._delay

    @property
    def loss(self):
        return self._loss

    @property
    def rate(self):
        return self._rate

    def build_command(self, ipcp):
        cmd = []

        if ipcp in LinkQuality._active:
            cmd.append("tc qdisc change dev %s root netem" % ipcp.ifname)
        else:
            cmd.append("tc qdisc add dev %s root netem" % ipcp.ifname)

        if self.delay:
            cmd.append(self.delay.build_command())

        if self.loss:
            cmd.append(self.loss.build_command())

        if self.rate:
            cmd.append("rate %imbit" % self.rate)

        return " ".join(cmd)

    def apply(self, shim):
        if not (self.delay or self.loss or self.rate):
            self.deactivate(shim)
        else:
            for ipcp in shim.ipcps:
                if not ipcp.ifname:
                    logger.error("Could not apply LinkQuality to IPCP because "
                                 "the interface name is None")
                    continue

                ipcp.node.execute_command(self.build_command(ipcp),
                                          as_root=True)
                LinkQuality._active.add(ipcp)

    def deactivate(self, shim):
        for ipcp in shim.ipcps:
            if ipcp not in LinkQuality._active:
                continue
            if not ipcp.ifname:
                logger.error("Could not remove LinkQuality from IPCP because "
                             "the interface name is None")
                continue

            ipcp.node.execute_command("tc qdisc del dev %s root "
                                      "netem" % ipcp.ifname, as_root=True)
            LinkQuality._active.remove(ipcp)


# SSH Configuration
#
class SSHConfig(object):
    def __init__(self, hostname, port=22, proxy_server=None):
        self.username = None
        self.password = None
        self.hostname = hostname
        self.port = port
        self.proxy_server = proxy_server
        self.client = None
        self.proxy_client = None
        self.http_proxy = None

    def set_username(self, username):
        self.username = username

    def set_password(self, password):
        self.password = password

    def set_http_proxy(self, proxy):
        self.http_proxy = proxy


# A node in the experiment
#
# @difs: DIFs the node will have an IPCP in
# @dif_registrations: Which DIF is registered in which DIF
# @policies: dict of dif -> policy to apply for that dif in this node
#
#
class Node(object):

    def get_e_id(self):
        return "Node." + self.name

    def __init__(self, name, difs=None, dif_registrations=None,
                 policies=None, machine_type=None):
        self.name = name
        if difs is None:
            difs = list()
        self.difs = difs
        for dif in self.difs:
            dif.add_member(self)
        if dif_registrations is None:
            dif_registrations = dict()
        self.dif_registrations = dif_registrations
        self.machine_type = machine_type
        self.ssh_config = SSHConfig(name)
        self.ipcps = []
        self.policies = dict()
        self.has_tcpdump = False
        if policies is None:
            policies = dict()
        for dif in self.difs:
            if hasattr(dif, 'policy'):  # check if the dif supports policies
                self.policies[dif] = policies.get(dif, Policy(dif, self))

        self.executor = None # will be set by testbed on swap_in
        self.startup_command = None # will be set by prototype

        self._validate()

    def get_ipcp_by_dif(self, dif):
        for ipcp in self.ipcps:
            if ipcp.dif == dif:
                return ipcp

    def _undeclared_dif(self, dif):
        if dif not in self.difs:
            raise Exception("Invalid registration: node %s is not declared "
                            "to be part of DIF %s" % (self.name, dif.name))

    def _validate(self):
        # Check that DIFs referenced in self.dif_registrations
        # are part of self.difs
        for upper in self.dif_registrations:
            self._undeclared_dif(upper)
            for lower in self.dif_registrations[upper]:
                self._undeclared_dif(lower)

    def __repr__(self):
        s = "Node " + self.name + ":\n"

        s += "  DIFs: [ "
        s += " ".join([d.name for d in self.difs])
        s += " ]\n"

        s += "  DIF registrations: [ "
        rl = []
        for upper in self.dif_registrations:
            difs = self.dif_registrations[upper]
            x = "%s => [" % upper.name
            x += " ".join([lower.name for lower in difs])
            x += "]"
            rl.append(x)
        s += ", ".join(rl)
        s += " ]\n"

        return s

    def __hash__(self):
        return hash(self.name)

    def __eq__(self, other):
        return other is not None and self.name == other.name

    def __neq__(self, other):
        return not self == other

    def add_dif(self, dif):
        self.difs.append(dif)
        dif.add_member(self)
        if hasattr(dif, 'policy'):
            self.policies[dif] = Policy(dif, self)
        self._validate()

    def del_dif(self, dif):
        self.difs.remove(dif)
        dif.del_member(self)
        try:
            del self.policies[dif]
        except KeyError:
            # It was not in there, so nothing to do
            pass
        self._validate()

    def add_dif_registration(self, upper, lower):
        self.dif_registrations[upper].append(lower)
        self._validate()

    def del_dif_registration(self, upper, lower):
        self.dif_registrations[upper].remove(lower)
        self._validate()

    def add_policy(self, dif, component_name, policy_name, **parameters):
        self.policies[dif].add_policy(component_name, policy_name, **parameters)

    def del_policy(self, dif, component_name=None, policy_name=None):
        self.policies[dif].del_policy(component_name, policy_name)

    def get_policy(self, dif):
        return self.policies[dif]

    def execute_commands(self, commands, as_root=False, time_out=3,
                         use_proxy=False):
        return self.executor.execute_commands(self, commands, as_root, time_out)

    def execute_command(self, command, as_root=False, time_out=3,
                        use_proxy=False):
        return self.executor.execute_command(self, command, as_root, time_out)

    def write_text_to_file(self, text, file_name):
        # ssh_support.write_text_to_file(
        #     self.ssh_config,
        #     self.ssh_config,
        #     text,
        #     file_name
        # )
        return

    def copy_file(self, path, destination):
        self.executor.copy_file(self, path, destination)

    def copy_files(self, paths, destination):
        self.executor.copy_files(self, paths, destination)

    def fetch_files(self, paths, destination, sudo=False):
        self.executor.fetch_files(self, paths, destination, sudo)

    def fetch_file(self, path, destination, sudo=False):
        self.executor.fetch_file(self, path, destination, sudo)

    def set_link_state(self, dif, state):
        ipcp = self.get_ipcp_by_dif(dif)
        self.execute_command('ip link set dev ' + ipcp.ifname + ' ' + state,
                             as_root=True)


# Base class representing an IPC Process to be created in the experiment
#
# @name [string]: IPCP name
# @node: Node where the IPCP gets created
# @dif: the DIF the IPCP belongs to
#
class IPCP(object):
    def __init__(self, name, node, dif):
        self.name = name
        self.node = node
        self.dif = dif
        self.registrations = []

        # Is this IPCP the first in its DIF, so that it does not need
        # to enroll to anyone ?
        self.dif_bootstrapper = False

    def __repr__(self):
        return "{IPCP=%s,DIF=%s,N-1-DIFs=(%s)%s}" % \
                (self.name, self.dif.name,
                 ' '.join([dif.name for dif in self.registrations]),
                 ',bootstrapper' if self.dif_bootstrapper else ''
                 )

    def __hash__(self):
        return hash((self.name, self.dif.name))

    def __eq__(self, other):
        return other is not None and self.name == other.name \
                                and self.dif == other.dif

    def __neq__(self, other):
        return not self == other


class ShimEthIPCP(IPCP):
    def __init__(self, name, node, dif, ifname=None):
        IPCP.__init__(self, name, node, dif)
        self.ifname = ifname


class ShimUDPIPCP(IPCP):
    def __init__(self, name, node, dif):
        IPCP.__init__(self, name, node, dif)
        # TODO: add IP and port


# Class representing DIF and Node policies
#
# @dif: the dif this policy is applied to.
# @node: the node
#
class Policy(object):
    def __init__(self, dif, node=None, policies=None):
        self.dif = dif  # type: NormalDIF
        self.node = node
        if policies is None:
            self._dict = dict()
        else:
            self._dict = policies

    def add_policy(self, component_name, policy_name, **parameters):
        self._dict.setdefault(component_name, dict())[policy_name] = parameters

    #
    # Fetches effective policy info
    #
    def get_policies(self, component_name=None, policy_name=None):
        policy = self._superimpose()
        if component_name is None:
            return policy._dict
        elif policy_name is None:
            return policy._dict[component_name]
        else:
            return policy._dict[component_name][policy_name]

    def del_policy(self, component_name=None, policy_name=None):
        if component_name is None:
            self._dict = dict()
        elif policy_name is None:
            del self._dict[component_name]
        else:
            del self._dict[component_name][policy_name]

    #
    # Merges this policy into that of its dif, obtaining
    # the effective policy acting on self.node.
    #
    def _superimpose(self):
        if self.node is None:
            return self
        other = self.dif.policy
        base = dict(other._dict)
        base.update(self._dict)
        return Policy(self.dif, self.node, base)

    def __eq__(self, other):
        if not isinstance(other, Policy):
            return False
        else:
            return other.dif == self.dif \
                   and other.node == self.node \
                   and other._dict == self._dict

    def __str__(self):
        node_str = (" Node: " + self.node) if self.node is not None else ""
        return "Policy[Dif: %(dif)s,%(node_str)s Dict: %(dict)s]" \
               % {"dif": self.dif, "node_str": node_str, "dict": self._dict}

    def __repr__(self):
        node_str = (" Node: " + self.node) if self.node is not None else ""
        s = "Policy[ Dif: %(dif)s,%(node_str)s" \
            % {"dif": self.dif, "node_str": node_str}
        comps = []
        for component in self._dict:
            for policy in self._dict[component]:
                comps.append("\n  Component %s has policy %s with params %s"
                             % (component,
                                policy,
                                self._dict[component][policy]))
        s += ",".join(comps)
        s += "\n]\n"
        return s


# Base class for ARCFIRE experiments
#
# @name [string] Name of the experiment
# @nodes: Nodes in the experiment
#
class Experiment(object):
    __metaclass__ = abc.ABCMeta

    def __init__(self, testbed,
                 nodes=None,
                 git_repo=None,
                 git_branch=None,
                 log_dir=None,
                 prototype_logs=None):
        if nodes is None:
            nodes = list()
        self.nodes = nodes
        self.git_repo = git_repo
        self.git_branch = git_branch
        self.testbed = testbed
        # the strategy employed for completing the enrollment phase in
        # the different DIFs
        self.enrollment_strategy = 'minimal'  # 'full-mesh', 'manual'
        # the strategy employed for setting up the data transfer
        # networks in the DIFs after enrollment
        self.dt_strategy = 'full-mesh'  # 'minimal', 'manual'
        self.dif_ordering = []
        self.enrollments = []  # a list of per-DIF lists of enrollments
        self.dt_flows = []  # a list of per-DIF lists of data transfer flows
        self.mgmt_flows = []  # a list of per-DIF lists of management flows

        # Determine log directory
        if log_dir is None:
            # If it is None, use /tmp/rumba/{project}
            # Wipe it and make it again
            exp_name = self.testbed.exp_name.replace('/', '_')  # Just in case
            log_dir = os.path.join(tmp_dir, exp_name)
            shutil.rmtree(log_dir, ignore_errors=True)
            os.mkdir(log_dir)
        self.log_dir = log_dir
        if not os.path.isdir(self.log_dir):
            raise Exception('Destination "%s" is not a directory. '
                            'Cannot fetch logs.'
                            % self.log_dir)
        self.prototype_logs = prototype_logs \
            if prototype_logs is not None else []

        # Generate missing information
        self.generate()

    def __repr__(self):
        s = ""
        for n in self.nodes:
            s += "\n" + str(n)

        return s

    def add_node(self, node):
        self.nodes.append(node)
        self.generate()

    def del_node(self, node):
        self.nodes.remove(node)
        self.generate()

    # Compute registration/enrollment order for DIFs
    def compute_dif_ordering(self):
        # Compute DIFs dependency graph, as both adjacency and incidence list.
        difsdeps_adj = dict()
        difsdeps_inc = dict()

        for node in self.nodes:
            for dif in node.difs:
                if dif not in difsdeps_adj:
                    difsdeps_adj[dif] = set()

            for upper in node.dif_registrations:
                for lower in node.dif_registrations[upper]:
                    if upper not in difsdeps_inc:
                        difsdeps_inc[upper] = set()
                    if lower not in difsdeps_inc:
                        difsdeps_inc[lower] = set()
                    if upper not in difsdeps_adj:
                        difsdeps_adj[upper] = set()
                    if lower not in difsdeps_adj:
                        difsdeps_adj[lower] = set()
                    difsdeps_inc[upper].add(lower)
                    difsdeps_adj[lower].add(upper)

        # Kahn's algorithm below only needs per-node count of
        # incident edges, so we compute these counts from the
        # incidence list and drop the latter.
        difsdeps_inc_cnt = dict()
        for dif in difsdeps_inc:
            difsdeps_inc_cnt[dif] = len(difsdeps_inc[dif])
        del difsdeps_inc

        # Init difsdeps_inc_cnt for those DIFs that do not
        # act as lower IPCPs nor upper IPCPs for registration
        # operations
        for node in self.nodes:
            for dif in node.difs:
                if dif not in difsdeps_inc_cnt:
                    difsdeps_inc_cnt[dif] = 0

        # Run Kahn's algorithm to compute topological
        # ordering on the DIFs graph.
        frontier = set()
        self.dif_ordering = []
        for dif in difsdeps_inc_cnt:
            if difsdeps_inc_cnt[dif] == 0:
                frontier.add(dif)

        while len(frontier):
            cur = frontier.pop()
            self.dif_ordering.append(cur)
            for nxt in difsdeps_adj[cur]:
                difsdeps_inc_cnt[nxt] -= 1
                if difsdeps_inc_cnt[nxt] == 0:
                    frontier.add(nxt)
            difsdeps_adj[cur] = set()

        circular_set = [dif for dif in difsdeps_inc_cnt
                        if difsdeps_inc_cnt[dif] != 0]
        if len(circular_set):
            raise Exception("Fatal error: The specified DIFs topology"
                            "has one or more"
                            "circular dependencies, involving the following"
                            " DIFs: %s" % circular_set)

        logger.debug("DIF topological ordering: %s", self.dif_ordering)

    # Compute all the enrollments, to be called after compute_dif_ordering()
    def compute_enrollments(self):
        dif_graphs = dict()
        self.enrollments = []
        self.mgmt_flows = []
        self.dt_flows = []

        for dif in self.dif_ordering:
            neighsets = dict()
            dif_graphs[dif] = dict()
            first = None

            # For each N-1-DIF supporting this DIF, compute the set of nodes
            # that share such N-1-DIF. This set will be called the 'neighset' of
            # the N-1-DIF for the current DIF.

            for node in self.nodes:
                if dif in node.dif_registrations:
                    dif_graphs[dif][node] = []  # init for later use
                    if first is None:  # pick any node for later use
                        first = node
                    for lower_dif in node.dif_registrations[dif]:
                        if lower_dif not in neighsets:
                            neighsets[lower_dif] = []
                        neighsets[lower_dif].append(node)

            # Build the graph, represented as adjacency list
            for lower_dif in neighsets:
                # Each neighset corresponds to a complete (sub)graph.
                for node1 in neighsets[lower_dif]:
                    for node2 in neighsets[lower_dif]:
                        if node1 != node2:
                            dif_graphs[dif][node1].append((node2, lower_dif))

            self.enrollments.append([])
            self.dt_flows.append([])
            self.mgmt_flows.append([])

            if first is None:
                # This is a shim DIF, nothing to do
                continue

            er = []
            for node in dif_graphs[dif]:
                for edge in dif_graphs[dif][node]:
                    er.append("%s --[%s]--> %s" % (node.name,
                                                   edge[1].name,
                                                   edge[0].name))
            logger.debug("DIF graph for %s: %s", dif, ', '.join(er))

            # To generate the list of mgmt flows, minimal enrollments
            # and minimal dt flows, we simulate it, using
            # breadth-first traversal.
            enrolled = {first}
            frontier = {first}
            while len(frontier):
                cur = frontier.pop()
                for edge in dif_graphs[dif][cur]:
                    if edge[0] not in enrolled:
                        enrolled.add(edge[0])
                        enrollee = edge[0].get_ipcp_by_dif(dif)
                        assert(enrollee is not None)
                        enroller = cur.get_ipcp_by_dif(dif)
                        assert(enroller is not None)
                        if self.enrollment_strategy == 'minimal':
                            self.enrollments[-1].append({'dif': dif,
                                                         'enrollee': enrollee,
                                                         'enroller': enroller,
                                                         'lower_dif': edge[1]})
                        self.mgmt_flows[-1].append({'src': enrollee,
                                                    'dst': enroller})
                        if self.dt_strategy == 'minimal':
                            self.dt_flows[-1].append({'src': enrollee,
                                                      'dst': enroller})
                        frontier.add(edge[0])
            if len(dif.members) != len(enrolled):
                raise Exception("Disconnected DIF found: %s" % (dif,))

            # In case of a full mesh enrollment or dt flows
            for cur in dif_graphs[dif]:
                for edge in dif_graphs[dif][cur]:
                    if cur.name < edge[0].name:
                        enrollee = cur.get_ipcp_by_dif(dif)
                        assert(enrollee is not None)
                        enroller = edge[0].get_ipcp_by_dif(dif)
                        assert(enroller is not None)
                        if self.enrollment_strategy == 'full-mesh':
                            self.enrollments[-1].append({'dif': dif,
                                                         'enrollee': enrollee,
                                                         'enroller': enroller,
                                                         'lower_dif': edge[1]})
                        if self.dt_strategy == 'full-mesh':
                            self.dt_flows[-1].append({'src': enrollee,
                                                      'dst': enroller})

            if not (self.dt_strategy == 'minimal'
                    or self.dt_strategy == 'full-mesh') \
                    or not (self.enrollment_strategy == 'full-mesh'
                            or self.enrollment_strategy == 'minimal'):
                # This is a bug
                assert False

        log_string = "Enrollments:\n"
        for el in self.enrollments:
            for e in el:
                log_string += ("    [%s] %s --> %s through N-1-DIF %s\n"
                               % (e['dif'],
                                  e['enrollee'].name,
                                  e['enroller'].name,
                                  e['lower_dif']))
        logger.debug(log_string)

        log_string = "Mgmt flows:\n"
        for el in self.mgmt_flows:
            for e in el:
                log_string += ("    %s --> %s \n"
                               % (e['src'].name,
                                  e['dst'].name))
        logger.debug(log_string)

        log_string = "Dt flows:\n"
        for el in self.dt_flows:
            for e in el:
                log_string += ("    %s --> %s \n"
                               % (e['src'].name,
                                  e['dst'].name))
        logger.debug(log_string)

    def compute_ipcps(self):
        # For each node, compute the required IPCP instances, and associated
        # registrations
        for node in self.nodes:
            node.ipcps = []
            # We want also the node.ipcps list to be generated in
            # topological ordering
            for dif in self.dif_ordering:
                if dif not in node.difs:
                    continue

                # Create an instance of the required IPCP class
                ipcp = dif.get_ipcp_class()(
                    name='%s.%s' % (dif.name, node.name),
                    node=node, dif=dif)

                if dif in node.dif_registrations:
                    for lower in node.dif_registrations[dif]:
                        ipcp.registrations.append(lower)

                node.ipcps.append(ipcp)
                dif.ipcps.append(ipcp)

    def compute_bootstrappers(self):
        for node in self.nodes:
            for ipcp in node.ipcps:
                ipcp.dif_bootstrapper = True
                for el in self.enrollments:
                    for e in el:
                        if e['dif'] != ipcp.dif:
                            # Skip this DIF
                            break
                        if e['enrollee'] == ipcp:
                            ipcp.dif_bootstrapper = False
                            # Exit the loops
                            break
                    if not ipcp.dif_bootstrapper:
                        break

    def dump_ssh_info(self):
        f = open(os.path.join(tmp_dir, 'ssh_info'), 'w')
        for node in self.nodes:
            f.write("%s;%s;%s;%s;%s\n" % (node.name,
                                          self.testbed.username,
                                          node.ssh_config.hostname,
                                          node.ssh_config.port,
                                          node.ssh_config.proxy_server))
        f.close()

    # Examine the nodes and DIFs, compute the registration and enrollment
    # order, the list of IPCPs to create, registrations, ...
    def generate(self):
        start = time.time()
        self.compute_dif_ordering()
        self.compute_ipcps()
        self.compute_enrollments()
        self.compute_bootstrappers()
        for node in self.nodes:
            logger.info("IPCPs for node %s: %s", node.name, node.ipcps)
        end = time.time()
        logger.info("Layer ordering computation took %.2f seconds", end - start)

    def install_prototype(self):
        start = time.time()
        self._install_prototype()
        end = time.time()
        logger.info("Install took %.2f seconds", end - start)

    def set_startup_command(self, command):
        for node in self.nodes:
            node.startup_command = command

    def bootstrap_prototype(self):
        start = time.time()
        self._bootstrap_prototype()
        end = time.time()
        logger.info("Bootstrap took %.2f seconds", end - start)

    @abc.abstractmethod
    def _install_prototype(self):
        raise Exception('install_prototype() method not implemented')

    @abc.abstractmethod
    def _bootstrap_prototype(self):
        raise Exception('bootstrap_prototype() method not implemented')

    @abc.abstractmethod
    def prototype_name(self):
        raise Exception('prototype_name() method not implemented')

    @abc.abstractmethod
    def _terminate_prototype(self):
        raise Exception('terminate_prototype() method not implemented')

    def swap_in(self):
        # Realize the experiment testbed (testbed-specific)
        start = time.time()
        self.testbed.swap_in(self)
        self.dump_ssh_info()
        end = time.time()
        logger.info("Swap-in took %.2f seconds", end - start)

    def swap_out(self):
        start = time.time()
        # Terminate prototype gracefully
        self._terminate_prototype()
        for node in self.nodes:
            if node.ssh_config.client is not None:
                node.ssh_config.client.close()
            if node.ssh_config.proxy_client is not None:
                node.ssh_config.proxy_client.close()
        # Undo the testbed (testbed-specific)
        self.testbed.swap_out(self)
        end = time.time()
        logger.info("Swap-out took %.2f seconds", end - start)


class Executor:
    __metaclass__ = abc.ABCMeta

    @abc.abstractmethod
    def execute_command(self, node, command, as_root=False, time_out=3):
        # Execute command on a node
        return

    def execute_commands(self, node, commands, as_root=False, time_out=3):
        for command in commands:
            self.execute_command(node, command, as_root, time_out)

    @abc.abstractmethod
    def copy_file(self, node, path, destination):
        return

    def copy_files(self, node, paths, destination):
        for path in paths:
            self.copy_file(node, path, destination)

    @abc.abstractmethod
    def fetch_file(self, node, path, destination, sudo=False):
        return

    def fetch_files(self, node, paths, destination, sudo=False):
        for path in paths:
            self.fetch_file(node, path, destination, sudo)