path: root/geo-replication/syncdaemon/master.py

import os
import sys
import time
import stat
import random
import signal
import json
import logging
import socket
import string
import errno
from shutil import copyfileobj
from errno import ENOENT, ENODATA, EPIPE, EEXIST
from threading import currentThread, Condition, Lock
from datetime import datetime

from gconf import gconf
from tempfile import mkdtemp, NamedTemporaryFile
from syncdutils import FreeObject, Thread, GsyncdError, boolify, escape, \
                       unescape, select, gauxpfx, md5hex, selfkill, entry2pb

URXTIME = (-1, 0)

# Utility functions to help us to get to closer proximity
# of the DRY principle (no, don't look for elevated or
# perspectivistic things here)

def _xtime_now():
    t = time.time()
    sec = int(t)
    nsec = int((t - sec) * 1000000)
    return (sec, nsec)

def _volinfo_hook_relax_foreign(self):
    volinfo_sys = self.get_sys_volinfo()
    fgn_vi = volinfo_sys[self.KFGN]
    if fgn_vi:
        expiry = fgn_vi['timeout'] - int(time.time()) + 1
        logging.info('foreign volume info found, waiting %d sec for expiry' % \
                     expiry)
        time.sleep(expiry)
        volinfo_sys = self.get_sys_volinfo()
    self.volinfo_state, state_change = self.volinfo_state_machine(self.volinfo_state,
                                                                  volinfo_sys)
    if self.inter_master:
        raise GsyncdError("cannot be intermediate master in special mode")
    return (volinfo_sys, state_change)


# The API!

def gmaster_builder(excrawl=None):
    """produce the GMaster class variant corresponding
       to sync mode"""
    this = sys.modules[__name__]
    modemixin = gconf.special_sync_mode
    if not modemixin:
        modemixin = 'normal'
    changemixin = isinstance(excrawl, str) and excrawl or gconf.change_detector
    logging.info('setting up %s change detection mode' % changemixin)
    modemixin = getattr(this, modemixin.capitalize() + 'Mixin')
    crawlmixin = getattr(this, 'GMaster' + changemixin.capitalize() + 'Mixin')
    sendmarkmixin = boolify(gconf.use_rsync_xattrs) and SendmarkRsyncMixin or SendmarkNormalMixin
    purgemixin = boolify(gconf.ignore_deletes) and PurgeNoopMixin or PurgeNormalMixin
    class _GMaster(crawlmixin, modemixin, sendmarkmixin, purgemixin):
        pass
    return _GMaster


# Mixin classes that implement the data format
# and logic particularities of the certain
# sync modes

class NormalMixin(object):
    """normal geo-rep behavior"""

    minus_infinity = URXTIME

    # following staticmethods ideally would be
    # methods of an xtime object (in particular,
    # implementing the hooks needed for comparison
    # operators), but at this point we don't yet
    # have a dedicated xtime class

    @staticmethod
    def serialize_xtime(xt):
        return "%d.%d" % tuple(xt)

    @staticmethod
    def deserialize_xtime(xt):
        return tuple(int(x) for x in xt.split("."))

    @staticmethod
    def native_xtime(xt):
        return xt

    @staticmethod
    def xtime_geq(xt0, xt1):
        return xt0 >= xt1

    def make_xtime_opts(self, is_master, opts):
        if not 'create' in opts:
            opts['create'] = is_master
        if not 'default_xtime' in opts:
            opts['default_xtime'] = URXTIME

    def xtime_low(self, server, path, **opts):
        xt = server.xtime(path, self.uuid)
        if isinstance(xt, int) and xt != ENODATA:
            return xt
        if xt == ENODATA or xt < self.volmark:
            if opts['create']:
                xt = _xtime_now()
                server.aggregated.set_xtime(path, self.uuid, xt)
            else:
                xt = opts['default_xtime']
        return xt

    def keepalive_payload_hook(self, timo, gap):
        # first grab a reference as self.volinfo
        # can be changed in main thread
        vi = self.volinfo
        if vi:
            # then have a private copy which we can mod
            vi = vi.copy()
            vi['timeout'] = int(time.time()) + timo
        else:
            # send keep-alives more frequently to
            # avoid a delay in announcing our volume info
            # to slave if it becomes established in the
            # meantime
            gap = min(10, gap)
        return (vi, gap)

    def volinfo_hook(self):
        volinfo_sys = self.get_sys_volinfo()
        self.volinfo_state, state_change = self.volinfo_state_machine(self.volinfo_state,
                                                                      volinfo_sys)
        return (volinfo_sys, state_change)

    def xtime_reversion_hook(self, path, xtl, xtr):
        if xtr > xtl:
            raise GsyncdError("timestamp corruption for " + path)

    def need_sync(self, e, xte, xtrd):
        return xte > xtrd

    def set_slave_xtime(self, path, mark):
        self.slave.server.set_xtime(path, self.uuid, mark)
        self.slave.server.set_xtime_remote(path, self.uuid, mark)

class PartialMixin(NormalMixin):
    """a variant tuned towards operation with a master
       that has partial info of the slave (brick typically)"""

    def xtime_reversion_hook(self, path, xtl, xtr):
        pass

class WrapupMixin(NormalMixin):
    """a variant that differs from normal in terms
       of ignoring non-indexed files"""

    @staticmethod
    def make_xtime_opts(is_master, opts):
        if not 'create' in opts:
            opts['create'] = False
        if not 'default_xtime' in opts:
            opts['default_xtime'] = URXTIME

    @staticmethod
    def keepalive_payload_hook(self, timo, gap):
        return (None, gap)

    def volinfo_hook(self):
        return _volinfo_hook_relax_foreign(self)

class BlindMixin(object):
    """Geo-rep flavor using vectored xtime.

    Coordinates are the master, slave uuid pair;
    in master coordinate behavior is normal,
    in slave coordinate we force synchronization
    on any value difference (these are in disjunctive
    relation, ie. if either orders the entry to be
    synced, it shall be synced.
    """

    minus_infinity = (URXTIME, None)

    @staticmethod
    def serialize_xtime(xt):
        a = []
        for x in xt:
            if not x:
                x = ('None', '')
            a.extend(x)
        return '.'.join(str(n) for n in a)

    @staticmethod
    def deserialize_xtime(xt):
        a = xt.split(".")
        a = (tuple(a[0:2]), tuple(a[3:4]))
        b = []
        for p in a:
            if p[0] == 'None':
                p = None
            else:
                p = tuple(int(x) for x in p)
            b.append(p)
        return tuple(b)

    @staticmethod
    def native_xtime(xt):
        return xt[0]

    @staticmethod
    def xtime_geq(xt0, xt1):
        return (not xt1[0] or xt0[0] >= xt1[0]) and \
               (not xt1[1] or xt0[1] >= xt1[1])

    @property
    def ruuid(self):
        if self.volinfo_r:
            return self.volinfo_r['uuid']

    @staticmethod
    def make_xtime_opts(is_master, opts):
        if not 'create' in opts:
            opts['create'] = is_master
        if not 'default_xtime' in opts:
            opts['default_xtime'] = URXTIME

    def xtime_low(self, server, path, **opts):
        xtd = server.xtime_vec(path, self.uuid, self.ruuid)
        if isinstance(xtd, int):
            return xtd
        xt = (xtd[self.uuid], xtd[self.ruuid])
        if not xt[1] and (not xt[0] or xt[0] < self.volmark):
            if opts['create']:
                # not expected, but can happen if file originates
                # from interrupted gsyncd transfer
                logging.warn('have to fix up missing xtime on ' + path)
                xt0 = _xtime_now()
                server.aggregated.set_xtime(path, self.uuid, xt0)
            else:
                xt0 = opts['default_xtime']
            xt = (xt0, xt[1])
        return xt

    @staticmethod
    def keepalive_payload_hook(self, timo, gap):
        return (None, gap)

    def volinfo_hook(self):
        res = _volinfo_hook_relax_foreign(self)
        volinfo_r_new = self.slave.server.aggregated.native_volume_info()
        if volinfo_r_new['retval']:
            raise GsyncdError("slave is corrupt")
        if getattr(self, 'volinfo_r', None):
            if self.volinfo_r['uuid'] != volinfo_r_new['uuid']:
                raise GsyncdError("uuid mismatch on slave")
        self.volinfo_r = volinfo_r_new
        return res

    def xtime_reversion_hook(self, path, xtl, xtr):
        if not isinstance(xtr[0], int) and \
          (isinstance(xtl[0], int) or xtr[0] > xtl[0]):
            raise GsyncdError("timestamp corruption for " + path)

    def need_sync(self, e, xte, xtrd):
        if xte[0]:
            if not xtrd[0] or xte[0] > xtrd[0]:
                # there is outstanding diff at 0th pos,
                # we can short-cut to true
                return True
        # we arrived to this point by either of these
        # two possiblilites:
        # - no outstanding difference at 0th pos,
        #   wanna see 1st pos if he raises veto
        #   against "no need to sync" proposal
        # - no data at 0th pos, 1st pos will have
        #   to decide (due to xtime assignment,
        #   in this case 1st pos does carry data
        #   -- iow, if 1st pos did not have data,
        #   and 0th neither, 0th would have been
        #   force-feeded)
        if not xte[1]:
            # no data, no veto
            return False
        # the hard work: for 1st pos,
        # the conduct is fetch corresponding
        # slave data and do a "blind" comparison
        # (ie. do not care who is newer, we trigger
        # sync on non-identical xitmes)
        xtr = self.xtime(e, self.slave)
        return isinstance(xtr, int) or xte[1] != xtr[1]

    def set_slave_xtime(self, path, mark):
        xtd = {}
        for (u, t) in zip((self.uuid, self.ruuid), mark):
            if t:
                xtd[u] = t
        self.slave.server.set_xtime_vec(path, xtd)


# Further mixins for certain tunable behaviors

class SendmarkNormalMixin(object):

    def sendmark_regular(self, *a, **kw):
        return self.sendmark(*a, **kw)

class SendmarkRsyncMixin(object):

    def sendmark_regular(self, *a, **kw):
        pass


class PurgeNormalMixin(object):

    def purge_missing(self, path, names):
        self.slave.server.purge(path, names)

class PurgeNoopMixin(object):

    def purge_missing(self, path, names):
        pass

class GMasterCommon(object):
    """abstract class impementling master role"""

    KFGN = 0
    KNAT = 1

    def get_sys_volinfo(self):
        """query volume marks on fs root

        err out on multiple foreign masters
        """
        fgn_vis, nat_vi = self.master.server.aggregated.foreign_volume_infos(), \
                          self.master.server.aggregated.native_volume_info()
        fgn_vi = None
        if fgn_vis:
            if len(fgn_vis) > 1:
                raise GsyncdError("cannot work with multiple foreign masters")
            fgn_vi = fgn_vis[0]
        return fgn_vi, nat_vi

    @property
    def uuid(self):
        if self.volinfo:
            return self.volinfo['uuid']

    @property
    def volmark(self):
        if self.volinfo:
            return self.volinfo['volume_mark']

    @property
    def inter_master(self):
        """decide if we are an intermediate master
        in a cascading setup
        """
        return self.volinfo_state[self.KFGN] and True or False

    def xtime(self, path, *a, **opts):
        """get amended xtime

        as of amending, we can create missing xtime, or
        determine a valid value if what we get is expired
        (as of the volume mark expiry); way of amendig
        depends on @opts and on subject of query (master
        or slave).
        """
        if a:
            rsc = a[0]
        else:
            rsc = self.master
        self.make_xtime_opts(rsc == self.master, opts)
        return self.xtime_low(rsc.server, path, **opts)

    def get_initial_crawl_data(self):
        default_data = {'sync_time': 0, 'files_synced': 0, 'bytes_synced': 0}
        if getattr(gconf, 'state_detail_file', None):
            try:
                return json.load(open(gconf.state_detail_file))
            except (IOError, OSError):
                ex = sys.exc_info()[1]
                if ex.errno == ENOENT:
                    # Create file with initial data
                    with open(gconf.state_detail_file, 'wb') as f:
                        json.dump(default_data, f)
                    return default_data
                else:
                    raise

        return default_data

    def update_crawl_data(self):
        if getattr(gconf, 'state_detail_file', None):
            try:
                same_dir = os.path.dirname(gconf.state_detail_file)
                with NamedTemporaryFile(dir=same_dir, delete=False) as tmp:
                    json.dump(self.total_crawl_stats, tmp)
                    os.rename(tmp.name, gconf.state_detail_file)
            except (IOError, OSError):
                raise

    def __init__(self, master, slave):
        self.master = master
        self.slave = slave
        self.jobtab = {}
        self.syncer = Syncer(slave)
        # crawls vs. turns:
        # - self.crawls is simply the number of crawl() invocations on root
        # - one turn is a maximal consecutive sequence of crawls so that each
        #   crawl in it detects a change to be synced
        # - self.turns is the number of turns since start
        # - self.total_turns is a limit so that if self.turns reaches it, then
        #   we exit (for diagnostic purposes)
        # so, eg., if the master fs changes unceasingly, self.turns will remain 0.
        self.crawls = 0
        self.turns = 0
        self.total_turns = int(gconf.turns)
        self.lastreport = {'crawls': 0, 'turns': 0, 'time': 0}
        self.crawl_stats = {'sync_time': 0, 'last_synctime': 0, 'crawl_starttime': 0,
                            'crawl_time': 0, 'files_synced': 0, 'bytes_synced' :0}
        self.total_crawl_stats = self.get_initial_crawl_data()
        self.start = None
        self.change_seen = None
        # the authoritative (foreign, native) volinfo pair
        # which lets us deduce what to do when we refetch
        # the volinfos from system
        uuid_preset = getattr(gconf, 'volume_id', None)
        self.volinfo_state = (uuid_preset and {'uuid': uuid_preset}, None)
        # the actual volinfo we make use of
        self.volinfo = None
        self.terminate = False
        self.sleep_interval = 1
        self.checkpoint_thread = None

    def init_keep_alive(cls):
        """start the keep-alive thread """
        timo = int(gconf.timeout or 0)
        if timo > 0:
            def keep_alive():
                while True:
                    vi, gap = cls.keepalive_payload_hook(timo, timo * 0.5)
                    cls.slave.server.keep_alive(vi)
                    time.sleep(gap)
            t = Thread(target=keep_alive)
            t.start()

    def volinfo_query(self):
        """volume info state machine"""
        volinfo_sys, state_change = self.volinfo_hook()
        if self.inter_master:
            self.volinfo = volinfo_sys[self.KFGN]
        else:
            self.volinfo = volinfo_sys[self.KNAT]
        if state_change == self.KFGN or (state_change == self.KNAT and not self.inter_master):
            logging.info('new master is %s', self.uuid)
            if self.volinfo:
                logging.info("%s master with volume id %s ..." % \
                                 (self.inter_master and "intermediate" or "primary",
                                  self.uuid))
        if state_change == self.KFGN:
            gconf.configinterface.set('volume_id', self.uuid)
        if self.volinfo:
            if self.volinfo['retval']:
                raise GsyncdError ("master is corrupt")
            self.start_checkpoint_thread()
        else:
            if should_display_info or self.crawls == 0:
                if self.inter_master:
                    logging.info("waiting for being synced from %s ..." % \
                                     self.volinfo_state[self.KFGN]['uuid'])
                else:
                    logging.info("waiting for volume info ...")
            return True

    def should_crawl(cls):
        return (gconf.glusterd_uuid in cls.master.server.node_uuid())

    def register(self):
        self.register()

    def crawlwrap(self, oneshot=False):
        if oneshot:
            # it's important to do this during the oneshot crawl as
            # for a passive gsyncd (ie. in a replicate scenario)
            # the keepalive thread would keep the connection alive.
            self.init_keep_alive()
        self.lastreport['time'] = time.time()
        self.crawl_stats['crawl_starttime'] = datetime.now()

        logging.info('crawl interval: %d seconds' % self.sleep_interval)
        t0 = time.time()
        crawl = self.should_crawl()
        while not self.terminate:
            if self.volinfo_query():
                continue
            t1 = time.time()
            if int(t1 - t0) >= 60: #lets hardcode this check to 60 seconds
                crawl = self.should_crawl()
                t0 = t1
            if not crawl:
                time.sleep(5)
                continue
            if self.start:
                logging.debug("... crawl #%d done, took %.6f seconds" % \
                                  (self.crawls, time.time() - self.start))
            self.start = t1
            should_display_info = self.start - self.lastreport['time'] >= 60
            if should_display_info:
                logging.info("%d crawls, %d turns",
                             self.crawls - self.lastreport['crawls'],
                             self.turns - self.lastreport['turns'])
                self.lastreport.update(crawls = self.crawls,
                                       turns = self.turns,
                                       time = self.start)
            self.crawl()
            if oneshot:
                return
            time.sleep(self.sleep_interval)

    @classmethod
    def _checkpt_param(cls, chkpt, prm, xtimish=True):
        """use config backend to lookup a parameter belonging to
           checkpoint @chkpt"""
        cprm = getattr(gconf, 'checkpoint_' + prm, None)
        if not cprm:
            return
        chkpt_mapped, val = cprm.split(':', 1)
        if unescape(chkpt_mapped) != chkpt:
            return
        if xtimish:
            val = cls.deserialize_xtime(val)
        return val

    @classmethod
    def _set_checkpt_param(cls, chkpt, prm, val, xtimish=True):
        """use config backend to store a parameter associated
           with checkpoint @chkpt"""
        if xtimish:
            val = cls.serialize_xtime(val)
        gconf.configinterface.set('checkpoint_' + prm, "%s:%s" % (escape(chkpt), val))

    @staticmethod
    def humantime(*tpair):
        """format xtime-like (sec, nsec) pair to human readable format"""
        ts = datetime.fromtimestamp(float('.'.join(str(n) for n in tpair))).\
               strftime("%Y-%m-%d %H:%M:%S")
        if len(tpair) > 1:
            ts += '.' + str(tpair[1])
        return ts

    def get_extra_info(self):
        str_info = "\nFilesSynced=%d;" % (self.crawl_stats['files_synced'])
        str_info += "BytesSynced=%s;" % (self.crawl_stats['bytes_synced'])

        self.crawl_stats['crawl_time'] = datetime.now() - self.crawl_stats['crawl_starttime']

        str_info += "Uptime=%s;" % (self._crawl_time_format(self.crawl_stats['crawl_time']))
        str_info += "SyncTime=%s;" % (self.crawl_stats['sync_time'])
        str_info += "TotalSyncTime=%s;" % (self.total_crawl_stats['sync_time'])
        str_info += "TotalFilesSynced=%d;" % (self.total_crawl_stats['files_synced'])
        str_info += "TotalBytesSynced=%s;" % (self.total_crawl_stats['bytes_synced'])
        str_info += "\0"
        logging.debug(str_info)
        return str_info

    def _crawl_time_format(self, crawl_time):
        # Ex: 5 years, 4 days, 20:23:10
        years, days = divmod(crawl_time.days, 365.25)
        years = int(years)
        days = int(days)

        date=""
        m, s = divmod(crawl_time.seconds, 60)
        h, m = divmod(m, 60)

        if years != 0:
            date += "%s %s " % (years, "year" if years == 1 else "years")
        if days != 0:
            date += "%s %s " % (days, "day" if days == 1 else "days")

        date += "%s:%s:%s" % (string.zfill(h, 2), string.zfill(m, 2), string.zfill(s, 2))
        return date

    def checkpt_service(self, chan, chkpt, tgt):
        """checkpoint service loop

        monitor and verify checkpoint status for @chkpt, and listen
        for incoming requests for whom we serve a pretty-formatted
        status report"""
        if not chkpt:
            # dummy loop for the case when there is no checkpt set
            while True:
                select([chan], [], [])
                conn, _ = chan.accept()
                conn.send(self.get_extra_info())
                conn.close()
        completed = self._checkpt_param(chkpt, 'completed', xtimish=False)
        if completed:
            completed = tuple(int(x) for x in completed.split('.'))
        while True:
            s,_,_ = select([chan], [], [], (not completed) and 5 or None)
            # either request made and we re-check to not
            # give back stale data, or we still hunting for completion
            if self.native_xtime(tgt) and self.native_xtime(tgt) < self.volmark:
                # indexing has been reset since setting the checkpoint
                status = "is invalid"
            else:
                xtr = self.xtime('.', self.slave)
                if isinstance(xtr, int):
                    raise GsyncdError("slave root directory is unaccessible (%s)",
                                      os.strerror(xtr))
                ncompleted = self.xtime_geq(xtr, tgt)
                if completed and not ncompleted: # stale data
                    logging.warn("completion time %s for checkpoint %s became stale" % \
                                 (self.humantime(*completed), chkpt))
                    completed = None
                    gconf.confdata.delete('checkpoint-completed')
                if ncompleted and not completed: # just reaching completion
                    completed = "%.6f" % time.time()
                    self._set_checkpt_param(chkpt, 'completed', completed, xtimish=False)
                    completed = tuple(int(x) for x in completed.split('.'))
                    logging.info("checkpoint %s completed" % chkpt)
                status = completed and \
                  "completed at " + self.humantime(completed[0]) or \
                  "not reached yet"
            if s:
                conn = None
                try:
                    conn, _ = chan.accept()
                    try:
                        conn.send("  | checkpoint %s %s %s" % (chkpt, status, self.get_extra_info()))
                    except:
                        exc = sys.exc_info()[1]
                        if (isinstance(exc, OSError) or isinstance(exc, IOError)) and \
                           exc.errno == EPIPE:
                            logging.debug('checkpoint client disconnected')
                        else:
                            raise
                finally:
                    if conn:
                        conn.close()

    def start_checkpoint_thread(self):
        """prepare and start checkpoint service"""
        if self.checkpoint_thread or not (
          getattr(gconf, 'state_socket_unencoded', None) and getattr(gconf, 'socketdir', None)
        ):
            return
        chan = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
        state_socket = os.path.join(gconf.socketdir, md5hex(gconf.state_socket_unencoded) + ".socket")
        try:
            os.unlink(state_socket)
        except:
            if sys.exc_info()[0] == OSError:
                pass
        chan.bind(state_socket)
        chan.listen(1)
        checkpt_tgt = None
        if gconf.checkpoint:
            checkpt_tgt = self._checkpt_param(gconf.checkpoint, 'target')
            if not checkpt_tgt:
                checkpt_tgt = self.xtime('.')
                if isinstance(checkpt_tgt, int):
                    raise GsyncdError("master root directory is unaccessible (%s)",
                                      os.strerror(checkpt_tgt))
                self._set_checkpt_param(gconf.checkpoint, 'target', checkpt_tgt)
            logging.debug("checkpoint target %s has been determined for checkpoint %s" % \
                          (repr(checkpt_tgt), gconf.checkpoint))
        t = Thread(target=self.checkpt_service, args=(chan, gconf.checkpoint, checkpt_tgt))
        t.start()
        self.checkpoint_thread = t

    def add_job(self, path, label, job, *a, **kw):
        """insert @job function to job table at @path with @label"""
        if self.jobtab.get(path) == None:
            self.jobtab[path] = []
        self.jobtab[path].append((label, a, lambda : job(*a, **kw)))

    def add_failjob(self, path, label):
        """invoke .add_job with a job that does nothing just fails"""
        logging.debug('salvaged: ' + label)
        self.add_job(path, label, lambda: False)

    def wait(self, path, *args):
        """perform jobs registered for @path

        Reset jobtab entry for @path,
        determine success as the conjuction of
        success of all the jobs. In case of
        success, call .sendmark on @path
        """
        jobs = self.jobtab.pop(path, [])
        succeed = True
        for j in jobs:
            ret = j[-1]()
            if not ret:
                succeed = False
        if succeed and not args[0] == None:
            self.sendmark(path, *args)
        return succeed

    def sendmark(self, path, mark, adct=None):
        """update slave side xtime for @path to master side xtime

        also can send a setattr payload (see Server.setattr).
        """
        if adct:
            self.slave.server.setattr(path, adct)
        self.set_slave_xtime(path, mark)

    @staticmethod
    def volinfo_state_machine(volinfo_state, volinfo_sys):
        """compute new volinfo_state from old one and incoming
           as of current system state, also indicating if there was a
           change regarding which volume mark is the authoritative one

        @volinfo_state, @volinfo_sys are pairs of volume mark dicts
        (foreign, native).

        Note this method is marked as static, ie. the computation is
        pure, without reliance on any excess implicit state. State
        transitions which are deemed as ambiguous or banned will raise
        an exception.

        """
        # store the value below "boxed" to emulate proper closures
        # (variables of the enclosing scope are available inner functions
        # provided they are no reassigned; mutation is OK).
        param = FreeObject(relax_mismatch = False, state_change = None, index=-1)
        def select_vi(vi0, vi):
            param.index += 1
            if vi and (not vi0 or vi0['uuid'] == vi['uuid']):
                if not vi0 and not param.relax_mismatch:
                    param.state_change = param.index
                # valid new value found; for the rest, we are graceful about
                # uuid mismatch
                param.relax_mismatch = True
                return vi
            if vi0 and vi and vi0['uuid'] != vi['uuid'] and not param.relax_mismatch:
                # uuid mismatch for master candidate, bail out
                raise GsyncdError("aborting on uuid change from %s to %s" % \
                                   (vi0['uuid'], vi['uuid']))
            # fall back to old
            return vi0
        newstate = tuple(select_vi(*vip) for vip in zip(volinfo_state, volinfo_sys))
        srep = lambda vi: vi and vi['uuid'][0:8]
        logging.debug('(%s, %s) << (%s, %s) -> (%s, %s)' % \
                      tuple(srep(vi) for vi in volinfo_state + volinfo_sys + newstate))
        return newstate, param.state_change

class GMasterChangelogMixin(GMasterCommon):
    """ changelog based change detection and syncing """

    # index for change type and entry
    IDX_START = 0
    IDX_END   = 2

    POS_GFID   = 0
    POS_TYPE   = 1
    POS_ENTRY1 = 2
    POS_ENTRY2 = 3  # renames

    _CL_TYPE_DATA_PFX     = "D "
    _CL_TYPE_METADATA_PFX = "M "
    _CL_TYPE_ENTRY_PFX    = "E "

    TYPE_GFID  = [_CL_TYPE_DATA_PFX] # ignoring metadata ops
    TYPE_ENTRY = [_CL_TYPE_ENTRY_PFX]

    # flat directory heirarchy for gfid based access
    FLAT_DIR_HIERARCHY = '.'

    def fallback_xsync(self):
        logging.info('falling back to xsync mode')
        gconf.configinterface.set('change-detector', 'xsync')
        selfkill()

    def setup_working_dir(self):
        workdir = os.path.join(gconf.working_dir, md5hex(gconf.local_path))
        logfile = os.path.join(workdir, 'changes.log')
        logging.debug('changelog working dir %s (log: %s)' % (workdir, logfile))
        return (workdir, logfile)

    def lstat(self, e):
        try:
            return os.lstat(e)
        except (IOError, OSError):
            ex = sys.exc_info()[1]
            if ex.errno == ENOENT:
                return ex.errno
            else:
                raise

    # sync data
    def syncdata(self, datas):
        logging.debug('datas: %s' % (datas))
        for data in datas:
            logging.debug('candidate for syncing %s' % data)
            pb = self.syncer.add(data)
            timeA = datetime.now()
            def regjob(se, xte, pb):
                rv = pb.wait()
                if rv[0]:
                    logging.debug('synced ' + se)
                    # update stats
                    timeB = datetime.now()
                    self.crawl_stats['last_synctime'] = timeB - timeA
                    self.crawl_stats['sync_time'] += ((self.crawl_stats['last_synctime'].microseconds) / (10.0 ** 6))
                    self.crawl_stats['files_synced'] += 1
                    self.crawl_stats['bytes_synced'] += self.syncer.bytes_synced

                    # cumulative statistics
                    self.total_crawl_stats['bytes_synced'] += self.syncer.bytes_synced
                    self.total_crawl_stats['sync_time'] += ((self.crawl_stats['last_synctime'].microseconds) / (10.0 ** 6))
                    self.total_crawl_stats['files_synced'] += 1
                    return True
                else:
                    if rv[1] in [23, 24]:
                        # stat to check if the file exist
                        st = self.lstat(se)
                        if isinstance(st, int):
                            # file got unlinked in the interim
                            return True
                    logging.warn('Rsync: %s [errcode: %d]' % (se, rv[1]))
            self.add_job(self.FLAT_DIR_HIERARCHY, 'reg', regjob, data, None, pb)
        if self.wait(self.FLAT_DIR_HIERARCHY, None):
            self.update_crawl_data()
            return True

    def process_change(self, change, done):
        clist   = []
        entries = []
        purges = set()
        links = set()
        datas = set()
        pfx = gauxpfx()
        try:
            f = open(change, "r")
            clist = f.readlines()
            f.close()
        except IOError:
            raise

        def edct(op, **ed):
            dct = {}
            dct['op'] = op
            for k in ed:
                if k == 'stat':
                    st = ed[k]
                    dst = dct['stat'] = {}
                    dst['uid'] = st.st_uid
                    dst['gid'] = st.st_gid
                    dst['mode'] = st.st_mode
                else:
                    dct[k] = ed[k]
            return dct
        for e in clist:
            e = e.strip()
            et = e[self.IDX_START:self.IDX_END]
            ec = e[self.IDX_END:].split(' ')
            if et in self.TYPE_ENTRY:
                ty = ec[self.POS_TYPE]
                en = unescape(os.path.join(pfx, ec[self.POS_ENTRY1]))
                gfid = ec[self.POS_GFID]
                # definitely need a better way bucketize entry ops
                if ty in ['UNLINK', 'RMDIR']:
                  entries.append(edct(ty, gfid=gfid, entry=en))
                  purges.update([os.path.join(pfx, gfid)])
                  continue
                if not ty == 'RENAME':
                    go = os.path.join(pfx, gfid)
                    st = self.lstat(go)
                    if isinstance(st, int):
                        logging.debug('file %s got purged in the interim' % go)
                        continue
                if ty in ['CREATE', 'MKDIR', 'MKNOD']:
                    entries.append(edct(ty, stat=st, entry=en, gfid=gfid))
                elif ty == 'LINK':
                    entries.append(edct(ty, stat=st, entry=en, gfid=gfid))
                    links.update([os.path.join(pfx, gfid)])
                elif ty == 'SYMLINK':
                    entries.append(edct(ty, stat=st, entry=en, gfid=gfid, link=os.readlink(en)))
                elif ty == 'RENAME':
                    e2 = unescape(os.path.join(pfx, ec[self.POS_ENTRY2]))
                    entries.append(edct(ty, gfid=gfid, entry=en, entry1=e2))
                else:
                    pass
            elif et in self.TYPE_GFID:
                da = os.path.join(pfx, ec[0])
                st = self.lstat(da)
                if isinstance(st, int):
                    logging.debug('file %s got purged in the interim' % da)
                    continue
                datas.update([da])
        logging.debug('entries: %s' % repr(entries))
        # sync namespace
        if (entries):
            self.slave.server.entry_ops(entries)
        # sync data
        if self.syncdata(datas - (purges - links)):
            if done:
                self.master.server.changelog_done(change)
            return True

    def process(self, changes, done=1):
        for change in changes:
            times = 0
            while True:
                times += 1
                logging.debug('processing change %s [%d time(s)]' % (change, times))
                if self.process_change(change, done):
                    break
                # it's either entry_ops() or Rsync that failed to do it's
                # job. Mostly it's entry_ops() [which currently has a problem
                # of failing to create an entry but failing to return an errno]
                # Therefore we do not know if it's either Rsync or the freaking
                # entry_ops() that failed... so we retry the _whole_ changelog
                # again.
                # TODO: remove entry retries when it's gets fixed.
                logging.warn('incomplete sync, retrying changelog: %s' % change)
                time.sleep(0.5)
            self.turns += 1

    def upd_stime(self, stime):
        if stime:
            self.sendmark(self.FLAT_DIR_HIERARCHY, stime)

    def crawl(self):
        changes = []
        try:
            self.master.server.changelog_scan()
            self.crawls += 1
        except OSError:
            self.fallback_xsync()
        changes = self.master.server.changelog_getchanges()
        if changes:
            xtl = self.xtime(self.FLAT_DIR_HIERARCHY)
            if isinstance(xtl, int):
                raise GsyncdError('master is corrupt')
            logging.debug('processing changes %s' % repr(changes))
            self.process(changes)
            self.upd_stime(xtl)

    def register(self):
        (workdir, logfile) = self.setup_working_dir()
        self.sleep_interval = int(gconf.change_interval)
        # register with the changelog library
        try:
            # 9 == log level (DEBUG)
            # 5 == connection retries
            self.master.server.changelog_register(gconf.local_path,
                                                  workdir, logfile, 9, 5)
        except OSError:
            self.fallback_xsync()
            # control should not reach here
            raise

class GMasterXsyncMixin(GMasterChangelogMixin):
    """

    This crawl needs to be xtime based (as of now
    it's not. this is beacuse we generate CHANGELOG
    file during each crawl which is then processed
    by process_change()).
    For now it's used as a one-shot initial sync
    mechanism and only syncs directories, regular
    files and symlinks.
    """

    def register(self):
        self.sleep_interval = 60
        self.tempdir = self.setup_working_dir()[0]
        self.tempdir = os.path.join(self.tempdir, 'xsync')
        logging.info('xsync temp directory: %s' % self.tempdir)
        try:
            os.makedirs(self.tempdir)
        except OSError:
            ex = sys.exc_info()[1]
            if ex.errno == EEXIST and os.path.isdir(self.tempdir):
                pass
            else:
                raise

    def write_entry_change(self, prefix, data=[]):
        self.fh.write("%s %s\n" % (prefix, ' '.join(data)))

    def open(self):
        try:
            self.xsync_change = os.path.join(self.tempdir, 'XSYNC-CHANGELOG.' + str(int(time.time())))
            self.fh = open(self.xsync_change, 'w')
        except IOError:
            raise

    def close(self):
        self.fh.close()

    def fname(self):
        return self.xsync_change

    def crawl(self, path='.', xtr=None, done=0):
        """ generate a CHANGELOG file consumable by process_change """
        if path == '.':
            self.open()
            self.crawls += 1
        if not xtr:
            # get the root stime and use it for all comparisons
            xtr = self.xtime('.', self.slave)
            if isinstance(xtr, int):
                if xtr != ENOENT:
                    raise GsyncdError('slave is corrupt')
                xtr = self.minus_infinity
        xtl = self.xtime(path)
        if isinstance(xtl, int):
            raise GsyncdError('master is corrupt')
        if xtr == xtl:
            if path == '.':
                self.close()
            return
        self.xtime_reversion_hook(path, xtl, xtr)
        logging.debug("entering " + path)
        dem = self.master.server.entries(path)
        pargfid = self.master.server.gfid(path)
        if isinstance(pargfid, int):
            logging.warn('skipping directory %s' % (path))
        for e in dem:
            bname = e
            e = os.path.join(path, e)
            st = self.lstat(e)
            if isinstance(st, int):
                logging.warn('%s got purged in the interim..' % e)
                continue
            gfid = self.master.server.gfid(e)
            if isinstance(gfid, int):
                logging.warn('skipping entry %s..' % (e))
                continue
            xte = self.xtime(e)
            if isinstance(xte, int):
                raise GsyncdError('master is corrupt')
            if not self.need_sync(e, xte, xtr):
                continue
            mo = st.st_mode
            if stat.S_ISDIR(mo):
                self.write_entry_change("E", [gfid, 'MKDIR', escape(os.path.join(pargfid, bname))])
                self.crawl(e, xtr)
            elif stat.S_ISREG(mo):
                self.write_entry_change("E", [gfid, 'CREATE', escape(os.path.join(pargfid, bname))])
                self.write_entry_change("D", [gfid])
            elif stat.S_ISLNK(mo):
                self.write_entry_change("E", [gfid, 'SYMLINK', escape(os.path.join(pargfid, bname))])
            else:
                logging.info('ignoring %s' % e)
        if path == '.':
            logging.info('processing xsync changelog %s' % self.fname())
            self.close()
            self.process([self.fname()], done)
            self.upd_stime(xtl)

class GMasterXtimeMixin(GMasterCommon):
    """ xtime based change detection and syncing """

    def register(self):
        pass

    def crawl(self, path='.', xtl=None):
        """crawling...

          Standing around
          All the right people
          Crawling
          Tennis on Tuesday
          The ladder is long
          It is your nature
          You've gotta suntan
          Football on Sunday
          Society boy

        Recursively walk the master side tree and check if updates are
        needed due to xtime differences. One invocation of crawl checks
        children of @path and do a recursive enter only on
        those directory children where there is an update needed.

        Way of updates depend on file type:
        - for symlinks, sync them directy and synchronously
        - for regular children, register jobs for @path (cf. .add_job) to start
          and wait on their rsync
        - for directory children, register a job for @path which waits (.wait)
          on jobs for the given child
        (other kind of filesystem nodes are not considered)

        Those slave side children which do not exist on master are simply
        purged (see Server.purge).

        Behavior is fault tolerant, synchronization is adaptive: if some action fails,
        just go on relentlessly, adding a fail job (see .add_failjob) which will prevent
        the .sendmark on @path, so when the next crawl will arrive to @path it will not
        see it as up-to-date and  will try to sync it again. While this semantics can be
        supported by funky design principles (http://c2.com/cgi/wiki?LazinessImpatienceHubris),
        the ultimate reason which excludes other possibilities is simply transience: we cannot
        assert that the file systems (master / slave) underneath do not change and actions
        taken upon some condition will not lose their context by the time they are performed.
        """
        logging.debug("entering " + path)
        if not xtl:
            xtl = self.xtime(path)
            if isinstance(xtl, int):
                self.add_failjob(path, 'no-local-node')
                return
        xtr = self.xtime(path, self.slave)
        if isinstance(xtr, int):
            if xtr != ENOENT:
                self.slave.server.purge(path)
            try:
                self.slave.server.mkdir(path)
            except OSError:
                self.add_failjob(path, 'no-remote-node')
                return
            xtr = self.minus_infinity
        else:
            self.xtime_reversion_hook(path, xtl, xtr)
            if xtl == xtr:
                if path == '.' and self.change_seen:
                    self.turns += 1
                    self.change_seen = False
                    if self.total_turns:
                        logging.info("finished turn #%s/%s" % \
                                     (self.turns, self.total_turns))
                        if self.turns == self.total_turns:
                            logging.info("reached turn limit")
                            self.terminate = True
                return
        if path == '.':
            self.change_seen = True
        try:
            dem = self.master.server.entries(path)
        except OSError:
            self.add_failjob(path, 'local-entries-fail')
            return
        random.shuffle(dem)
        try:
            des = self.slave.server.entries(path)
        except OSError:
            self.slave.server.purge(path)
            try:
                self.slave.server.mkdir(path)
                des = self.slave.server.entries(path)
            except OSError:
                self.add_failjob(path, 'remote-entries-fail')
                return
        dd = set(des) - set(dem)
        if dd:
            self.purge_missing(path, dd)
        chld = []
        for e in dem:
            e = os.path.join(path, e)
            xte = self.xtime(e)
            if isinstance(xte, int):
                logging.warn("irregular xtime for %s: %s" % (e, errno.errorcode[xte]))
            elif self.need_sync(e, xte, xtr):
                chld.append((e, xte))
        def indulgently(e, fnc, blame=None):
            if not blame:
                blame = path
            try:
                return fnc(e)
            except (IOError, OSError):
                ex = sys.exc_info()[1]
                if ex.errno == ENOENT:
                    logging.warn("salvaged ENOENT for " + e)
                    self.add_failjob(blame, 'by-indulgently')
                    return False
                else:
                    raise
        for e, xte in chld:
            st = indulgently(e, lambda e: os.lstat(e))
            if st == False:
                continue

            mo = st.st_mode
            adct = {'own': (st.st_uid, st.st_gid)}
            if stat.S_ISLNK(mo):
                if indulgently(e, lambda e: self.slave.server.symlink(os.readlink(e), e)) == False:
                    continue
                self.sendmark(e, xte, adct)
            elif stat.S_ISREG(mo):
                logging.debug("syncing %s ..." % e)
                pb = self.syncer.add(e)
                timeA = datetime.now()
                def regjob(e, xte, pb):
                    if pb.wait()[0]:
                        logging.debug("synced " + e)
                        self.sendmark_regular(e, xte)
                        # update stats
                        timeB = datetime.now()
                        self.crawl_stats['last_synctime'] = timeB - timeA
                        self.crawl_stats['sync_time'] += ((self.crawl_stats['last_synctime'].microseconds) / (10.0 ** 6))
                        self.crawl_stats['files_synced'] += 1
                        self.total_crawl_stats['sync_time'] += ((self.crawl_stats['last_synctime'].microseconds) / (10.0 ** 6))
                        self.total_crawl_stats['files_synced'] += 1
                        self.update_crawl_data()
                        return True
                    else:
                        logging.warn("failed to sync " + e)
                self.add_job(path, 'reg', regjob, e, xte, pb)
            elif stat.S_ISDIR(mo):
                adct['mode'] = mo
                if indulgently(e, lambda e: (self.add_job(path, 'cwait', self.wait, e, xte, adct),
                                             self.crawl(e, xte),
                                             True)[-1], blame=e) == False:
                    continue
            else:
                # ignore fifos, sockets and special files
                pass
        if path == '.':
            self.wait(path, xtl)


class BoxClosedErr(Exception):
    pass

class PostBox(list):
    """synchronized collection for storing things thought of as "requests" """

    def __init__(self, *a):
        list.__init__(self, *a)
        # too bad Python stdlib does not have read/write locks...
        # it would suffivce to grab the lock in .append as reader, in .close as writer
        self.lever = Condition()
        self.open = True
        self.done = False

    def wait(self):
        """wait on requests to be processed"""
        self.lever.acquire()
        if not self.done:
            self.lever.wait()
        self.lever.release()
        return self.result

    def wakeup(self, data):
        """wake up requestors with the result"""
        self.result = data
        self.lever.acquire()
        self.done = True
        self.lever.notifyAll()
        self.lever.release()

    def append(self, e):
        """post a request"""
        self.lever.acquire()
        if not self.open:
            raise BoxClosedErr
        list.append(self, e)
        self.lever.release()

    def close(self):
        """prohibit the posting of further requests"""
        self.lever.acquire()
        self.open = False
        self.lever.release()

class Syncer(object):
    """a staged queue to relay rsync requests to rsync workers

    By "staged queue" its meant that when a consumer comes to the
    queue, it takes _all_ entries, leaving the queue empty.
    (I don't know if there is an official term for this pattern.)

    The queue uses a PostBox to accumulate incoming items.
    When a consumer (rsync worker) comes, a new PostBox is
    set up and the old one is passed on to the consumer.

    Instead of the simplistic scheme of having one big lock
    which synchronizes both the addition of new items and
    PostBox exchanges, use a separate lock to arbitrate consumers,
    and rely on PostBox's synchronization mechanisms take
    care about additions.

    There is a corner case racy situation, producers vs. consumers,
    which is not handled by this scheme: namely, when the PostBox
    exchange occurs in between being passed to the producer for posting
    and the post placement. But that's what Postbox.close is for:
    such a posting will find the PostBox closed, in which case
    the producer can re-try posting against the actual PostBox of
    the queue.

    To aid accumlation of items in the PostBoxen before grabbed
    by an rsync worker, the worker goes to sleep a bit after
    each completed syncjob.
    """

    def __init__(self, slave):
        """spawn worker threads"""
        self.slave = slave
        self.lock = Lock()
        self.pb = PostBox()
        self.bytes_synced = 0
        for i in range(int(gconf.sync_jobs)):
            t = Thread(target=self.syncjob)
            t.start()

    def syncjob(self):
        """the life of a worker"""
        while True:
            pb = None
            while True:
                self.lock.acquire()
                if self.pb:
                    pb, self.pb = self.pb, PostBox()
                self.lock.release()
                if pb:
                    break
                time.sleep(0.5)
            pb.close()
            po = self.slave.rsync(pb)
            if po.returncode == 0:
                ret = (True, 0)
            elif po.returncode in (23, 24):
                # partial transfer (cf. rsync(1)), that's normal
                ret = (False, po.returncode)
            else:
                po.errfail()
            pb.wakeup(ret)

    def add(self, e):
        while True:
            pb = self.pb
            try:
                pb.append(e)
                return pb
            except BoxClosedErr:
                pass