#!/usr/bin/perl -w
# (c) 2010 Thomas Schoebel-Theuer / 1&1 Internet AG

use strict;
use English;
use warnings;

umask 0077;

##################################################################

# messaging

my $error_count = 0;
my $notify = "";

sub lprint {
  my ($text) = @_;
  print $text;
  if ($notify) {
    system("/usr/bin/logger -t marsadm \"$notify $text\"");
  }
}

sub lprint_stderr {
  my ($text) = @_;
  print STDERR $text;
  if ($notify) {
    system("/usr/bin/logger -t marsadm \"$notify $text\"");
  }
}

sub ldie {
  my ($text) = @_;
  $error_count++;
  lprint_stderr "DYING: $text";
  die "\n";
}

sub lwarn {
  my ($text) = @_;
  lprint_stderr "WARNING: $text";
}

##################################################################

# low-level infrastructure

my @link_list = ();
my %link_hash;
my $verbose = 0;

sub get_link {
  my ($path, $unchecked) = @_;
  my $result = readlink($path);
  if (!defined($result)) {
    ldie  "cannot read symlink '$path'\n" unless $unchecked;
    lwarn "cannot read symlink '$path'\n" if $unchecked == 1;
  }
  return $result;
}

sub is_link_recent {
  my ($path) = @_;
  my @stat = lstat($path);
  return 0 if (!@stat);
  return 1 if $stat[9] + 15 >= mars_time();
  return 0;
}

sub to_tmp {
  my $path = shift;
  $path =~ s:^(.*)/:$1/.tmp.:;
  return $path;
}

sub from_tmp {
  my $path = shift;
  $path =~ s:^(.*)/\.tmp\.:$1/:;
  return $path;
}

sub set_link {
  my ($src, $dst) = @_;
  my $dst_tmp = to_tmp($dst);
  unlink($dst_tmp);
  symlink($src, $dst_tmp) or ldie "cannot create symlink '$dst' -> '$src'\n";
  # the _order_ is important! remove existing intermediate element before re-appanding
  if (exists($link_hash{$dst})) {
    my @copy = @link_list;
    @link_list = ();
    foreach my $elem (@copy) {
      next if $elem eq $dst;
      push @link_list, $elem;
    }
  }
  $link_hash{$dst} = $src;
  push @link_list, $dst;
}

sub finish_links {
  return unless @link_list;
  my $timestamp = mars_time();
  lprint "using lamport timestamp $timestamp\n" if $verbose;
  while (my $link = shift @link_list) {
    my $link_tmp = to_tmp($link);
    my $target = readlink($link_tmp);
    my $this_timestamp = $timestamp;
    # allow overriding of secondaries in partitioned clusters by use of small timestamps
    if ($target eq "(none)") {
      my @stat = lstat($link);
      $this_timestamp = $stat[9] + 1 if @stat;
    }
    system("touch -h -d \"\@$this_timestamp\" $link_tmp") == 0 or ldie "cannot set mtime on symlink '$link_tmp'\n";
    rename($link_tmp, $link) or ldie "cannot finalize symlink '$link'\n";
    if ($verbose) {
      lprint "created symlink '$link' -> '$target'\n";
    }
  }
  _trigger();
}

##################################################################

# global variables and checks

my $Id = '$Id$ ';
my $user_version = 0.1;
my $mars = "/mars";
my $host = `uname -n` or ldie "cannot determine my network node name\n";
chomp $host;
my $force = 0;
my $timeout = -1;
my $ip = _get_ip() or ldie "cannot determine my IP address\n";

my $kernel_version = 0;
unless ($ARGV[0] =~ m/cluster|cat/) {
  $kernel_version = get_link("$mars/tree-$host", 1);
  if ($kernel_version && $user_version != $kernel_version) {
    lwarn "kernel_version=$kernel_version user_version=$user_version\n";
    if ($user_version < $kernel_version) {
      ldie "Sorry, your MARS kernel module uses version $kernel_version, but my $0 userspace version is only $user_version. That cannot work. Please upgrade your userspace scripts!\n";
    } elsif (int($user_version) > int($kernel_version) + 1) {
      ldie "MAJOR VERSION mismatch : only one major upgrade step is supported.\n";
    }
    lwarn "using different minor versions is possible, but you should upgrade your kernel module ASAP\n";
  }
}

sub get_alive_links {
  my $res = shift || "all";
  my $alive = shift || "alive";
  my $glob = "$mars/$alive-*";
  if ($res ne "all") {
    $glob = "$mars/$alive-{";
    my $count = 0;
    foreach my $peer (glob("$mars/resource-$res/data-*")) {
      $peer =~ m:/data-(.+):;
      $glob .= "," if $count++;
      $glob .= $1;
    }
    $glob .= "}";
  }
  my %links;
  foreach my $path (glob($glob)) {
    $path =~ m:/$alive-(.+):;
    my $peer = $1;
    $links{$peer} = get_link($path);
  }
  return %links;
}

##################################################################

# timeout handling

#
# return the lamport clock time in nanosecond resolution
# fallback to system time()
#
sub mars_time {
  my $lamport_time;
  if (open(my $lamport_clock, "<", "/proc/sys/mars/lamport_clock")) {
    while (<$lamport_clock>) {
      $lamport_time = $1 if /^lamport_now=(.*)/;
    }
    close($lamport_clock);
  }
  return $lamport_time || time() . "." . '0' x 9;
}

sub sleep_timeout {
  my $sleeptime = shift || 5;
  if ($timeout < 0) {
    sleep($sleeptime);
    return;
  }
  ldie "Timeout reached. You may retry with --timeout=-1 to ensure waiting until progress is possible.\n" if !$timeout;
  my $rest = $timeout;
  $rest = $sleeptime if $rest > $sleeptime;
  sleep($rest);
  $timeout -= $rest;
}

# wait for some condition
sub wait_cond {
  my ($cmd, $res, $specific) = @_;
  my $is_actual = ($specific =~ s/^(is|has)-//);
  my $is_on = !($specific =~ s/-off$//);
  $specific =~ s/-on$//;
  if ($is_actual) {
    if ($specific eq "device") {
      check_mars_device($cmd, $res, 1, !$is_on);
      return;
    }
    my %table =
      (
       "attach" => "is-attached",
       "attached" => "is-attached",
       "replay"   => "is-replaying",
       "replaying"=> "is-replaying",
       "copy"     => "is-copying",
       "copying"  => "is-copying",
       "sync"     => "is-syncing",
       "syncing"  => "is-syncing",
       "primary" => "is-primary",
      );
    my $name = $table{$specific};
    ldie "actual indicator '$specific' does not exist\n" unless exists($table{$specific});
    check_status($cmd, $res, $name, $is_on ? 1 : 0, 1);
  } else {
    my %table =
      (
       "attach" => "attach",
       "attached" => "attach",
       "connect" => "connect",
       "replay" => "allow-replay",
       "sync" => "sync",
      );
    my $name = $table{$specific};
    ldie "button '$specific' does not exist\n" unless exists($table{$specific});
    check_todo($cmd, $res, $name, $is_on ? 1 : 0, 1);
  }
}

# wait until some communication has occurred
sub wait_cluster {
  return wait_cond(@_) if int(@_) >= 3;
  my $cmd = shift;
  my $res = shift || "all";
  my $start_time = mars_time();
  _trigger();
  my $delta = $timeout > 0 ? $timeout : 30;
  while (1) {
    my $dead_count = 0;
    my $alive_count = 0;
    my $unknown_count = 0;
    my %status = get_alive_links($res, "time");
    my $now = mars_time();
    foreach my $peer (keys(%status)) {
      next if $peer eq $host;
      if ($status{$peer} >= $start_time) {
	$alive_count++;
      } elsif ($status{$peer} + $delta < $now) {
	$dead_count++;
      } else {
	$unknown_count++;
      }
    }
    if (!$dead_count && !$unknown_count) {
      lprint "all $alive_count peer(s) seem to be alive\n";
      last;
    }
    if (!$unknown_count) {
      lwarn "$alive_count peer(s) seem to be alive, and $dead_count peer(s) seem to be dead / not reachable\n";
      ldie "--force not given\n" unless $force;
      last;
    }
    sleep(1);
  }
}

##################################################################

# syntactic checks

sub check_id {
  my $str = shift;
  ldie "identifier '$str' has disallowed characters" unless $str =~ m/^[A-Za-z_][-A-Za-z0-9_]*$/;
  ldie "identifier '$str' is too long (only 16 chars allowed)" if length($str) > 16;
}

##################################################################

# semantic checks

sub check_res {
  my $res = shift;
  if (not -d "$mars/resource-$res") {
    # DO WHAT I MEAN: try to substitute a device name for a badly given resource name if it is unique
    my $count = 0;
    my $found;
    my @tests = glob("$mars/resource-*/device-$host");
    foreach my $test (@tests) {
      my $target = get_link($test, 2);
      if ($target eq $res) {
	$found = $test;
	$count++;
      }
    }
    if (!$count) {
      @tests = glob("$mars/resource-*/_direct-*-$host");
      foreach my $test (@tests) {
	my $target = get_link($test, 2);
	$target =~ s/^.*,//;
	if ($target eq $res) {
	  $found = $test;
	  $count++;
	}
    }
    }
    ldie "resource '$res' does not exist ($count replacements found)\n" unless $count == 1 and $found;
    $found =~ s:^.*/resource-(.*)/.*$:$1:;
    lwarn "substituting bad resource name '$res' by uniquely matching resource name '$found'\n";
    $res = $found;
  }
  return $res;
}

sub check_sizes {
  my ($res, $host) = @_;
  my $logical_size = get_link("$mars/resource-$res/size");
  my $physical_size = get_link("$mars/resource-$res/actsize-$host", 1);
  if (defined($physical_size) && $physical_size < $logical_size) {
    ldie "physical device on host '$host' has size $physical_size, which is smaller than the logical resource size $logical_size\n";
  }
}

sub check_res_member {
  my $res = shift;
  ldie "sorry, I have not yet joined to resource '$res'\n" unless -e "$mars/resource-$res/data-$host";
  check_sizes($res, $host);
}

sub check_sync_finished {
  my ($res, $host) = @_;
  check_sizes(@_);
  my $lnk = "$mars/resource-$res/syncstatus-$host";
  if (lstat($lnk)) {
    my $syncstatus = get_link($lnk, 1);
    my $size = get_link("$mars/resource-$res/size");
    ldie "sync has not yet finished, only $syncstatus / $size bytes transferred\n" unless $syncstatus >= $size;
  }
  lprint "OK, it seems that sync has finished on $host.\n";
}

sub check_primary {
  my ($cmd, $res) = @_;
  my $lnk = "$mars/resource-$res/actual-$host/is-primary";
  my $is_primary = get_link($lnk);
  if (!$is_primary) { # give it a second chance
    my $name = get_link("$mars/resource-$res/device-$host");
    my $dev = "/dev/mars/$name";
    $is_primary = 1 if -b $dev;
  }
  ldie "for operation '$cmd' I need to be primary\n" unless $is_primary;
  my $primary = _get_designated_primary($res);
  ldie "for operation '$cmd', I also must be the designated primary\n" unless $primary eq $host;
}

sub check_not_primary {
  my ($cmd, $res) = @_;
  my $lnk = "$mars/resource-$res/actual-$host/is-primary";
  my $is_primary = get_link($lnk);
  if ($is_primary) {
    ldie "operation '$cmd' cannot be executed on primary\n";
  }
  # also check whether we intend to become primary
  my $primary = _get_designated_primary($res);
  ldie "operation '$cmd' cannot be executed on designated primary\n" if $primary eq $host;
}

sub check_primary_gone {
  my ($res) = @_;
  for (;;) {
    my $pri = _get_actual_primary($res);
    last if !$pri;
    last if $pri eq $host;
    lprint "waiting for other primary host ($pri) to disappear....\n";
    sleep_timeout();
  }
}

sub check_todo {
  my ($cmd, $res, $key, $val, $wait, $unchecked, $inv) = @_;
  my $path = "$mars/resource-$res/todo-$host/$key";
  my $link;
  for (;;) {
    $link = get_link($path, $unchecked);
    return unless defined($link);
    if (defined($inv) && $inv) {
      last if $link != $val;
      ldie "cannot execute $cmd: switch '$key' must not have value '$val'\n" if !$wait;
      lprint "waiting until switch '$key' leaves the value '$val'....\n";
    } else {
      last if $link == $val;
      ldie "cannot execute $cmd: switch '$key' must have value '$val', but actually has value '$link'\n" if !$wait;
      lprint "waiting until switch '$key' reaches the value '$val'....\n";
    }
    sleep_timeout();
  }
  lprint "OK, '$path' has acceptable value '$link'\n";
}

sub check_status {
  my ($cmd, $res, $key, $val, $wait, $unchecked, $inv) = @_;
  my $path = "$mars/resource-$res/actual-$host/$key";
  my $link;
  for (;;) {
    $link = get_link($path, $unchecked);
    return unless defined($link);
    if (defined($inv) && $inv) {
      last if $link != $val;
      ldie "cannot execute $cmd: '$path' must not have value '$val'\n" if !$wait;
      lprint "waiting until '$key' leaves the value '$val'...\n";
    } else {
      last if $link == $val;
      ldie "cannot execute $cmd: '$path' must have value '$val'\n" if !$wait;
      lprint "waiting until '$key' reaches the value '$val'...\n";
    }
    sleep_timeout();
  }
  lprint "OK, '$path' has acceptable value '$link'\n";
}

sub check_mars_device {
  my ($cmd, $res, $wait, $inv) = @_;
  my $name = get_link("$mars/resource-$res/device-$host");
  my $dev = "/dev/mars/$name";
  my $backoff = 1;
  my $round = 0;
  if ($inv) {
    while (-b $dev) {
      ldie "cannot execute $cmd: device '$dev' has not yet disappeared\n" if !$wait;
      lwarn "device '$dev' has not yet disappeared\n";
      sleep_timeout($backoff);
      # very slowly increasing backoff
      if ($backoff < 10 && $round++ > 5) {
	$round = 0;
	$backoff++;
      }
    }
    lprint "device '$dev' is no longer present\n" unless -b $dev;
    return;
  }
  # !$inv
  my $primary = _get_designated_primary($res);
  ldie "for operation '$cmd', I should be the designated primary\n" unless $primary eq $host;
  while (! -e $dev) {
    my $text = get_error_text($cmd, $res);
    lprint $text if $text;
    ldie "aborting due to errors\n" if $text =~ m/error/mi;
    ldie "cannot execute $cmd: device '$dev' not yet present\n" if !$wait;
    lprint "device '$dev' not yet present\n";
    sleep_timeout($backoff);
    # very slowly increasing backoff
    if ($backoff < 10 && $round++ > 5) {
      $round = 0;
      $backoff++;
    }
  }
  lprint "device '$dev' is present\n" if -b $dev;
}

sub check_userspace {
  my ($dst) = @_;
  if ($dst !~ m:/userspace/:) {
    ldie "your path '$dst' must be inside $mars/userspace/ or $mars/resource-*/userspace/\n" unless $force;
    lwarn "your path '$dst' is outside $mars/userspace/ or $mars/resource-*/userspace/ and you gave --force, hopefully YOU KNOW WHAT YOU ARE DOING\n";
  }
}

##################################################################

# state inspection routines

sub _get_minmax {
  my ($res, $glob, $take_symlink) = @_;
  my $min = -1;
  my $max = -1;
  my @paths = glob($glob) or ldie "cannot find '$glob'\n";
  foreach my $path (@paths) {
    my $nr = $path;
    if ($take_symlink) {
      $nr = get_link($path);
    }
    $nr =~ s:^.*[a-z]+-([0-9]+)(-[^/]*)?$:$1:;
    $min = $nr if ($nr < $min || $min < 0);
    $max = $nr if ($nr > $max || $max < 0);
  }
  return ($min, $max);
}

sub get_minmax_logfiles {
  my ($res) = @_;
  return _get_minmax($res, "$mars/resource-$res/log-*", 0);
}

sub get_minmax_versions {
  my ($res) = @_;
  return _get_minmax($res, "$mars/resource-$res/version-*", 0);
}

sub get_minmax_any {
  my ($res) = @_;
  return _get_minmax($res, "$mars/resource-$res/{log,version}-*", 0);
}

sub get_minmax_replays {
  my ($res) = @_;
  return _get_minmax($res, "$mars/resource-$res/replay-*", 1);
}

sub _parse_pos {
  my ($pos) = @_;
  $pos =~ m/(log-([0-9]+)-([^,]+),([0-9]+))/;
  return ($1, int($2), $3, int($4));
}

sub _get_prev_pos {
  my ($basedir, $nr, $host) = @_;
  my $path = sprintf("$basedir/version-%09d-$host", $nr);
  my $vers = get_link($path, 1);
  $vers =~ s/^.*://;
  return $vers;
}

sub _get_common_ancestor {
  # TODO: recursive formulation, improve efficiency
  my ($basedir, $pos1, $host1, $dep1, $pos2, $host2, $dep2) = @_;
  my ($p1, $nr1, $from1, $len1) = _parse_pos($pos1);
  my ($p2, $nr2, $from2, $len2) = _parse_pos($pos2);
  if ($p1 eq $p2) {
    # usually no split brain here (only if both path depths are non-zero)
    my $split = ($dep1 && $dep2);
    if (!$split) { # additionally check the corresponding version links
      my $path1 = sprintf("$basedir/version-%09d-$from1", $nr1);
      my $path2 = sprintf("$basedir/version-%09d-$from2", $nr2);
      if (my $vers1 = get_link($path1) and my $vers2 = get_link($path2)) {
	$split = 1 if $vers1 ne $vers2;
      }
    }
    return ($p1, $split);
  } elsif ($nr1 > $nr2) {
    # just flip arguments
    return _get_common_ancestor($basedir, $pos2, $host2, $dep2, $pos1, $host1, $dep1);
  } elsif ($nr1 < $nr2) {
    # recursively advance path depth
    my $vers2 = _get_prev_pos($basedir, $nr2, $host2);
    return ("", -1) if !$vers2;
    return _get_common_ancestor($basedir, $pos1, $host1, $dep1, $vers2, $host2, $dep2 + 1);
  } elsif ($from1 ne $from2) {
    # split brain is sure now, but continue computing the common split point
    my $vers1 = _get_prev_pos($basedir, $nr1, $host1);
    return ("", 1) if !$vers1;
    my $vers2 = _get_prev_pos($basedir, $nr2, $host2);
    return ("", 1) if !$vers2;
    my ($res, $split) = _get_common_ancestor($basedir, $vers1, $host1, $dep1 + 1, $vers2, $host2, $dep2 + 1);
    return ($res, 1);
  } elsif ($len1 < $len2) {
    # there may be no split brain (just incomplete replay) depending on path depth
    return ($p1, $dep1);
  } elsif ($len2 < $len1) {
    # dto symmetric
    return ($p2, $dep2);
  }
  lwarn "error in algorithm: $p1, $nr1, $from1, $len1 : $p2, $nr2, $from2, $len2\n";
  return ("", -1);
}

sub get_common_ancestor {
  my ($basedir, $host1, $host2) = @_;
  my $repl1 = get_link("$basedir/replay-$host1", 1);
  my $repl2 = get_link("$basedir/replay-$host2", 1);
  return _get_common_ancestor($basedir, $repl1, $host1, 0, $repl2, $host2, 0);
}

sub detect_splitbrain {
  my ($res, $do_report) = @_;
  my $basedir = "$mars/resource-$res";
  my $ok = 1;
  my @list = glob("$mars/resource-$res/replay-*");
  my @hosts = map { $_ =~ s:.*/replay-::; $_ } @list;
  foreach my $host1 (@hosts) {
    foreach my $host2 (@hosts) {
      next if $host1 ge $host2;
      my ($res, $split) = get_common_ancestor($basedir, $host1, $host2);
      if ($split) {
	$ok = 0;
	if ($do_report) {
	  lwarn "SPLIT BRAIN at '$res' detected: hostA = '$host1', hostB = '$host2'\n";
	} else {
	  return $ok;
	}
      }
    }
  }
  return $ok;
}

sub try_to_avoid_splitbrain {
  my ($cmd, $res) = @_;
  my ($min, $max) = get_minmax_versions($res);
  my @host_list = glob("$mars/resource-$res/replay-*");
  return if scalar(@host_list) < 2;
  my $vers_glob = sprintf("$mars/resource-$res/version-%09d-*", $max);
  for (;;) {
    my $ok = 1;
    my @versions = glob($vers_glob);
    my $first = get_link(shift @versions);
    while (@versions) {
      my $next = get_link(shift @versions);
      if ($next ne $first) {
	$ok = 0;
      }
    }
    last if $ok;
    lprint "trying to avoid split brain: logfile update not yet completed.\n";
    sleep_timeout();
  }
}

sub get_size {
  my $arg = shift || "";
  if (!($arg =~ m/^([0-9]+(?:\.[0-9]*)?)([kmgtp]?)$/i)) {
    ldie "size argument '$arg' must be a number, optionally followed by suffix k or m or g or t or p\n";
  }
  my $mod = $2 || "";
  $arg = $1;
  $_ = $mod;
 SWITCH: {
    /k/i and $arg *= 1024, last SWITCH;
    /m/i and $arg *= 1024 * 1024, last SWITCH;
    /g/i and $arg *= 1024 * 1024 * 1024, last SWITCH;
    /t/i and $arg *= 1024 * 1024 * 1024 * 1024, last SWITCH;
    /p/i and $arg *= 1024 * 1024 * 1024 * 1024 * 1024, last SWITCH;
  }
  ldie "size '$arg' is not a multiple of 4k\n" if ($arg % 4096) != 0;
  return $arg;
}

#
# Get actual primary node from links below actual-*/ subdirs
#
sub _get_actual_primary {
  my ($res) = @_;
  my @primary_links = glob("$mars/resource-$res/actual-*/is-primary");
  my $primary;
  foreach my $link (@primary_links) {
    if (my $val = get_link($link)) {
      $primary = ($link =~ qr%.*actual-([^/]+)/is-primary%)[0];
      last;
      # Note: if there are more than one 'is-primary' links (an insane state anyway),
      # the first 'is-primary' link is selected. Other links are ignored.
    }
  }
  return $primary;
}

sub _get_designated_primary {
  my ($res) = @_;
  return get_link("$mars/resource-$res/primary");
}

sub get_peers {
  my ($res) = @_;
  my @list = glob("$mars/resource-$res/data-*");
  return map { $_ =~ s:$mars/resource-$res/data-::; $_ } @list;
}

sub __conv_tv {
  my ($tv_sec, $tv_nsec) = @_;
  my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(int($tv_sec));
  return "$tv_sec.$tv_nsec" unless defined($sec);
  return sprintf("%04d-%02d-%02d %02d:%02d:%02d.%s", $year+1900, $mon + 1, $mday, $hour, $min, $sec, $tv_nsec);
}

sub _replace_timestamps {
  my ($txt) = @_;
  $txt =~ s:([0-9]{9,99})\.([0-9]{9}):__conv_tv($1,$2):ge;
  return $txt;
}

sub _get_text {
  my ($path, $regex, $do_print) = @_;
  open(IN, "<", $path) or return "";
  my $text = "";
  my $count = 0;
  while (my $line = <IN>) {
    # use regex e.g. for fetching only errors and warnings
    if (!$regex || $line =~ $regex) {
      $line = _replace_timestamps($line);
      $count++;
      if ($do_print) {
	print $line;
      } else {
	$text .= $line;
      }
    }
  }
  close(IN);
  return $count if $do_print;
  return $text;
}

sub get_error_text {
  my ($cmd, $res) = @_;
  my $text = _get_text("$mars/resource-$res/logstatus-$host.status", "m/^(err|warn)/i", 0);
  return $text;
}

##################################################################

# helpers

sub _trigger {
  system("(echo 2 > /proc/sys/mars/trigger) >/dev/null 2>&1");
}

sub _switch {
  my ($cmd, $res, $path, $on) = @_;
  my $src = $on ? "1" : "0";

  my $old = get_link($path);
  if ($old && $old eq $src) {
    lprint "${cmd} on resource $res is already activated\n" if $cmd;
    return;
  }
  set_link($src, $path);
  lprint "successfully started ${cmd} on resource $res\n" if $cmd;
}

sub _writable {
  my ($path, $on) = @_;
  my $oldmode = (lstat $path)[2] & 0700;
  my $newmode = $on ? $oldmode | 0200 : $oldmode & ~0200;
  lprint "chmod '$path' $oldmode $newmode";
  chmod($newmode, $path) == 1 or ldie "cannot chmod '$path'\n";
}

sub _get_ip {
  chomp (my @info = `/sbin/ip addr show dev eth0`);
  foreach (@info) {
    m#\sinet\s(\d+\.\d+\.\d+\.\d+)# && return $1;
  }
  return undef;
}

sub _fake_versionlink {
  my ($basedir, $log_nr, $primary) = @_;
  my $new_version = sprintf("$basedir/version-%09d-$host", $log_nr);
  my $pri_version = sprintf("$basedir/version-%09d-$primary", $log_nr);
  if ($primary eq $host) {
    ldie "Cannot fake my own version link '$new_version'\n";
  }
  my $pri_link = get_link($pri_version);
  if (!$pri_link) { # try any one else
    lwarn "cannot read symlink '$pri_version' -- trying a neighbor link instead\n";
    my $try_version = sprintf("$basedir/version-%09d-*", $log_nr);
    my @test = glob($try_version);
    my $test_version = shift @test;
    if ($test_version) {
      lwarn "trying substitute symlink '$test_version'\n";
      my $test_link = get_link($test_version);
      if ($test_link) {
	$pri_link = $test_link;
	lwarn "got value '$pri_link', hopefully this is right\n" if $pri_link;
      }
    }
  }
  if ($pri_link) {
    lprint "creating new version symlink '$new_version' -> '$pri_link'\n";
    set_link($pri_link, $new_version);
  } else {
    lwarn "cannot read symlink '$pri_version' -- cannot create faked versionlink '$pri_version'\n";
  }
}

sub _set_replaylink {
  my ($basedir, $log_nr, $primary, $msg) = @_;
  $msg = " -- THIS IS EXTREMELY RISKY -- any inconsistencies are on your own!" unless defined($msg);
  ldie "no designated primary defined\n" unless ($primary && $primary ne "(none)");
  my $rep_path = "$basedir/replay-$host";
  my $rep_val  = sprintf("log-%09d-$primary,0,0", $log_nr);
  lprint "creating new replaylink '$rep_path' -> '$rep_val'\n";
  set_link($rep_val, $rep_path);

  if ($log_nr > 1) {
    _fake_versionlink($basedir, $log_nr - 1, $primary);
  } else {
    my $initial;
    for (;;) {
      $initial = get_link("$basedir/version-000000001-$primary", 1);
      last if $initial;
      sleep_timeout();
    }
    set_link($initial, "$basedir/version-000000001-$host");
  }
  set_link("$log_nr$msg", "$basedir/skip-check-$host");
}

##################################################################

# commands

sub ignore_cmd {
  my ($cmd, $res) = @_;
  lprint "ignoring command '$cmd' on resource '$res'\n";
}

sub senseless_cmd {
  my ($cmd, $res) = @_;
  lprint "command '$cmd' makes no sense with MARS (ignoring on resource '$res')\n";
}

sub forbidden_cmd {
  my ($cmd, $res) = @_;
  ldie "command '$cmd' on resource '$res' cannot be used with MARS (migth affect too many hosts, lead to undesired consequences)\n";
}

sub nyi_cmd {
  my ($cmd, $res) = @_;
  ldie "command '$cmd'  on resource '$res' is not yet implemented\n";
}

sub is_module_loaded {
  open TEST, "lsmod | grep mars |";
  my $res = <TEST>;
  close TEST;
  return $res;
}

sub set_link_cmd {
  my $cmd = shift;
  for (;;) {
    my $src = shift || last;
    my $dst = shift || ldie "you did not supply a symlink destination for source '$src'\n";
    ldie "symlink target '$dst' is not an absolute path\n" unless $dst =~ m:^/:;
    check_userspace($dst);
    my $dir = `dirname "$dst"` or ldie "path '$dst' has no dirname\n";
    chomp $dir;
    ldie "directory '$dir' does not exist\n" unless -d $dir;
    set_link($src, $dst);
  }
}

sub _create_cluster {
  my ($cmd) = @_;
  system("mkdir $mars") unless -d $mars;
  my $old_uuid = get_link("$mars/uuid", 2);
  if ($cmd eq "create-cluster") {
    ldie "cluster was already created with uuid='$old_uuid'\n" if $old_uuid && !$force;
    my $uuid = `echo -n \$(hostname) \$(date)`;
    set_link($uuid, "$mars/uuid");
    finish_links(); # opportunity for errors => don't continue
  } elsif (!$old_uuid && !$force) {
    if ($user_version == 0.1) {
      my $uuid = `echo -n \$(hostname) \$(date)`;
      set_link($uuid, "$mars/uuid");
    }
    ldie "cluster has no uuid\n" if $user_version > 0.1;
  }
  system("mkdir $mars/ips") unless -d "$mars/ips";
  system("mkdir $mars/userspace") unless -d "$mars/userspace";
  system("mkdir $mars/defaults") unless -d "$mars/defaults";
  system("mkdir $mars/defaults-$host") unless -d "$mars/defaults-$host";
  system("mkdir $mars/todo-global") unless -d "$mars/todo-global";
  set_link($ip, "$mars/ips/ip-$host");
  set_link("1", "$mars/todo-global/deleted-$host");
}

sub create_cluster {
  my ($cmd, $peer) = @_;
  ldie "cluster is already created\n" if !$force && -d "$mars/ips";
  ldie "mars module is loaded, please unload first\n" if is_module_loaded();
  _create_cluster(@_);
}

sub join_cluster {
  my ($cmd, $peer) = @_;
  if (glob("$mars/resource-*") or glob("$mars/ips/*")) {
    ldie "Sorry, some resources already exist!\nThis is dangerous!\nIf you are sure that no resource clash is possible, re-invoke this command with '--force' option\n" unless $force;
  }
  ldie "mars module is loaded, please unload first\n" if is_module_loaded();
  lprint "joining cluster via rsync (peer='$peer')\n";
  # check connection
  system("ssh $peer uname -a") == 0 or ldie "oops, no connection to $peer ...\n";
  mkdir($mars) unless -d $mars;
  system("rsync --recursive --links --max-size=1 -v $peer:$mars/ $mars/") == 0 or ldie "cannot get remote symlink tree via rsync\n";
  _create_cluster(@_);
  finish_links();
  system("rsync --recursive --links -v $mars/ips/ $peer:$mars/ips/") == 0 or ldie "oops\n";
}

sub leave_cluster {
  my ($cmd) = @_;
  my $check = "/mars/resource-*/*-$host";
  ldie "I am member of some resources\n" if glob($check) && !$force;
  _create_delete("$mars/ips/$host");
}

sub create_res {
  my ($cmd, $res, $dev, $appear, $size_arg) = @_;
  my $create = ($cmd eq "create-resource");

  ldie "undefined device or size argument\n" unless $dev;
  $appear = $res if !$appear;
  check_id($appear) if $appear;

  my $resdir = "$mars/resource-$res";
  if ($create) {
    ldie "resource directory '$res' already exists; you may override this via --force\n" if (!$force && -d $resdir);
    ldie "resource directory '$res' has some contents -- remove by hand if you are sure that you really know what you are doing, or give --force.\n" if (!$force && glob("$resdir/*.status"));
    lprint "creating new resource '$res'\n";
  } else {
    if ( -e "$resdir/data-$host") {
      lwarn "resource '$res' has been already joined -- this is dangerous!\n";
      ldie "refusing dangerous operation\n" unless $force;
    } else {
      lprint "joining to existing resource '$res'\n";
    }
  }

  my $size = 0;
  if (-b $dev) {
    ldie "block device '$dev' must be an absolute path starting with '/'\n" unless $dev =~ m/^\//;
    use Fcntl 'SEEK_END', 'O_RDONLY', 'O_RDWR', 'O_EXCL';
    my $flags = O_RDWR | O_EXCL;
    if ($force) {
      $flags = O_RDONLY;
    }
    sysopen(TEST, $dev, $flags) or ldie "cannot open device '$dev' for exclusive rw access\n";
    $size = sysseek(TEST, 0, SEEK_END);
    close(TEST);
    lprint "block device '$dev': determined size = $size bytes\n";
    if ($size_arg) {
      my $new_size = get_size($size_arg);
      ldie "size argument '$size_arg' is smaller than device size '$size'\n" unless $new_size <= $size;
      lprint "reducing size from $size to $new_size\n";
      $size = $new_size;
    }
  } else {
    $size = get_size($dev);
    if ($size > 0) {
      $dev = "";
    } else {
      ldie "bad parameter '$dev': must be either a block device name, or size followed by k or m or g or t\n";
    }
  }

  ldie "implausible size $size" unless $size > 4096 * 16; # smaller floppies should not exist ;)

  my $primary;
  my $replay_nr = -1;
  if ($create) {
    mkdir($resdir);
    ldie "could not create resource '$res'\n" unless -d $resdir;
    set_link($size, "$resdir/size");
  } else { # join
    ldie "resource '$res' does not exist\n" unless -d $resdir;
    my $res_size = get_link("$mars/resource-$res/size");
    if ($size < $res_size) {
      lwarn "size of new device is only $size, but should be $res_size\n";
      ldie "refusing to join due to bad size\n" unless $force;
    } elsif ($size > $res_size) {
      lprint "Your physical device has size $size, which is larger than the logical resource size $res_size.\n";
      lprint "This does no harm, but you are wasting some space.\n";
    }
    $primary = _get_designated_primary($res);
    ldie "Sorry, joining is only possible if a designated primary exists.\n" if $primary eq "(none)";
    ldie "implausible state: I ($host) am already designated primary of resource '$res' which I just wanted to join\n" if $primary eq $host;
    ldie "my ip '$ip' is not registered -- please run 'join-cluster' first\n" unless -l "$mars/ips/ip-$host";
    my $replay = get_link("$resdir/replay-$primary");
    if ($replay =~ m/^log-([0-9]+)-/) {
      $replay_nr = $1;
    } else {
      ldie "cannot determine current logfile number.\n";
    }
  }

  # check for uniqeness of $appear
  if ($appear) {
    foreach my $old_dev (glob("$mars/resource-*/device-$host")) {
      $old_dev =~ m:/resource-([^/]+)/:;
      next unless defined($1);
      my $old_res = $1;
      next if $old_res eq $res;
      my $old_name = get_link($old_dev);
      if ($old_name eq $appear) {
	if ( -e "$mars/resource-$old_res/data-$host") {
	  ldie "device '/dev/mars/$old_name' is already present in joined resource '$old_res'\n";
	} else {
	  lwarn "device '/dev/mars/$old_name' is already present in another unjoined resource '$old_res' -- this does no harm, but may be confusing.\n";
	}
      }
    }
    # warn if devices are named differently throughout the cluster
    foreach my $old_dev (glob("$resdir/device-*")) {
      my $old_name = get_link($old_dev);
      if ($old_name ne $appear) {
	$old_dev =~ m:/device-(.+)$:;
	my $old_host = $1;
	lwarn "your name '/dev/mars/$appear' differs from '/dev/mars/$old_name' on host '$old_host'.";
	lwarn "this does no harm, but may be confusing.";
      }
    }
  }

  my $file = "$resdir/data-$host";
  if (!$dev) {
    lwarn "file '$file' already exists - reusing\n" if -e $file;
    lprint "setup sparse file '$file' with size $size\n";
    open(OUT, ">>", $file) or ldie "could not open '$file'\n";
    truncate(OUT, $size) or ldie "truncate to size $size failed\n";
    close OUT;
  } else {
    lprint "using existing device '$dev'\n";
    set_link($dev, $file);
  }

  if ($appear) {
    lprint "resource '$res' will appear as local device '/dev/mars/$appear'\n";
    set_link($appear, "$resdir/device-$host");
  }

  mkdir("$resdir/userspace") unless -d "$resdir/userspace";
  mkdir("$resdir/defaults") unless -d "$resdir/defaults";
  mkdir("$resdir/defaults-$host");
  mkdir("$resdir/local-$host");
  mkdir("$resdir/actual-$host");
  my $todo = "$resdir/todo-$host";
  mkdir($todo);
  set_link("1", "$todo/attach");
  set_link("1", "$todo/connect");
  set_link("1", "$todo/sync");
  set_link("1", "$todo/allow-replay");
  unlink("$resdir/syncstatus-$host");

  if ($create) {
    set_link($host, "$resdir/primary");
    set_link($size, "$resdir/syncstatus-$host");
    set_link("log-000000001-$host,0,0", "$resdir/replay-$host");
    system("touch $resdir/log-000000001-$host");
    set_link("00000000000000000000000000000000,log-000000001-$host,0:", "$resdir/version-000000001-$host");
    finish_links();
    lprint "successfully created resource '$res'\n";
  } else {
    _set_replaylink($resdir, $replay_nr, $primary, "");
    set_link("0", "$resdir/syncstatus-$host");
    finish_links();
    lprint "successfully joined resource '$res'\n";
  }
}

sub leave_res_phase0 {
  my ($cmd, $res) = @_;
  check_not_primary(@_);
  foreach my $tmp (glob("$mars/resource-$res/todo-$host/*")) {
    my $status = get_link($tmp, 2);
    ldie "switch '$tmp' is not off\n" if $status;
  }
  check_status($cmd, $res, "is-attached", 0, 0, 1);
  if (!$force) {
    foreach my $tmp (glob("$mars/resource-$res/actual-$host/{is-,logfile-}*")) {
      my $status = get_link($tmp);
      ldie "running status '$tmp' is not off\n" if $status;
    }
  }
}

sub leave_res_phase1 {
  my ($cmd, $res) = @_;
  _create_delete("$mars/resource-$res/replay-$host");
  _create_delete("$mars/resource-$res/data-$host");
  _create_delete("$mars/resource-$res/syncstatus-$host");
  _create_delete("$mars/resource-$res/device-$host");
  _create_delete("$mars/resource-$res/actsize-$host");
  foreach my $dir (glob("$mars/resource-$res/*-$host/")) {
    foreach my $tmp (glob("${dir}*")) {
      _create_delete($tmp);
    }
    _create_delete($dir);
  }
  finish_links();
}

# wait for deletions (avoid races with following commands)
sub leave_res_phase2 {
  my ($cmd, $res) = @_;
  _wait_delete();
  log_purge_res(@_);
}

sub logrotate_res {
  my ($cmd, $res) = @_;
  check_primary(@_);
  my @paths = glob("$mars/resource-$res/log-*-$host") or ldie "cannot find any logfiles\n";
  @paths = sort(@paths);
  my $last = pop(@paths);
  if (-z $last) {
    lprint "an empty logfile '$last' already exists, nothing to do.\n";
    return;
  }
  my $nr = $last;
  $nr =~ s/^.*log-([0-9]+)-.+$/$1/;
  my $next = sprintf("$mars/resource-$res/log-%09d-$host", $nr + 1);
  ldie "logfile '$next' already exists\n" if -e $next;
  system("touch $next");
}

sub _get_deletable_logfiles {
  my ($cmd, $res) = @_;
  my $min = -1;
  my $max = -1;
  my @log_paths = glob("$mars/resource-$res/log-*") or ldie "cannot find any logfiles\n";
  foreach my $path (@log_paths) {
    $path =~ m/\/log-([0-9]+)-/;
    my $nr = $1;
    $min = $nr if ($nr < $min || $min < 0);
    $max = $nr if ($nr > $max || $max < 0);
  }
  my @paths = glob("$mars/resource-$res/replay-*") or ldie "cannot find any replay symlinks\n";
  foreach my $path (@paths) {
    my $target = get_link($path);
    $target =~ m/^log-([0-9]+)/;
    my $nr = $1;
    $max = $nr if ($nr < $max || $max < 0);
  }
  lprint "min     deletable logfile number: $min\n";
  lprint "min non-deletable logfile number: $max\n";
  return ($min, $max);
}

my $delete_nr = -1;

sub _create_delete {
  my ($target) = @_;
  ldie "cannot delete: '$target' is no absolute path\n" unless $target =~ m:^/:;
  if ($delete_nr < 0) { # compute only upon first call
    my @paths = glob("$mars/todo-global/delete-*");
    foreach my $path (@paths) {
      $path =~ m/-([0-9]+)/;
      if (defined($1) && $1 > $delete_nr) {
	$delete_nr = $1;
      }
    }
    my @paths2 = glob("$mars/todo-global/deleted-*");
    foreach my $path (@paths2) {
      my $link = get_link($path, 1);
      $link =~ m/([0-9]+)/;
      if (defined($1) && $1 > $delete_nr) {
	$delete_nr = $1;
      }
    }
  }
  my $new = sprintf("$mars/todo-global/delete-%09d-$host", ++$delete_nr);
  lprint "create symlink $new -> $target\n";
  set_link($target, $new);
}

sub _wait_delete {
  for (;;) {
    my $deleted = get_link("$mars/todo-global/deleted-$host");
    last if $deleted >= $delete_nr;
    lprint "waiting for deletions to apply locally....\n";
    sleep_timeout();
  }
}

sub delete_file_cmd {
  my $cmd = shift;
  my $res = shift; # ignore this
  foreach my $path (@_) {
    check_userspace($path);
    _create_delete($path);
  }
}

sub logdelete_res {
  my ($cmd, $res) = @_;
  my @paths = glob("$mars/resource-$res/log-*") or ldie "cannot find any logfiles\n";
  @paths = sort(@paths);
  my ($min_deletable, $max_deletable) = _get_deletable_logfiles(@_);
  if ($min_deletable >= $max_deletable) {
    lprint "no logfiles are deletable.\n";
    return;
  }
  if ($cmd ne "log-delete-all") {
    $max_deletable = $min_deletable + 1; # delete only the first one
  }

  my $nr = 0;
  for (;;) {
    my $first = shift(@paths);
    last unless $first;
    $nr = $first;
    $nr =~ s/^.*log-([0-9]+)-.+$/$1/;
    next unless $nr < $max_deletable;

    lprint "chosen '$first' for deletion\n";

    _create_delete($first);
  }
  lprint "removing left-over version symlinks...\n";
  foreach my $versionlink (glob("$mars/resource-$res/version-*")) {
    my $nrv = $versionlink;
    $nrv =~ s/^.*\/version-([0-9]+)-.+$/$1/;
    # we need at least one more version link than logfiles for consistency checks
    next unless $nrv < $max_deletable - 1;
    _create_delete($versionlink);
  }
}

sub attach_res_phase0 {
  my ($cmd, $res) = @_;
  return if $force;
  my $detach = ($cmd eq "detach");
  if ($detach) {
    my $device_in_use = get_link("$mars/resource-$res/actual-$host/open-count", 1);
    if ($device_in_use) {
      my $name = get_link("$mars/resource-$res/device-$host");
      my $dev = "/dev/mars/$name";
      ldie "device '$dev' is in use\n";
    }
  }
}

sub attach_res_phase1 {
  my ($cmd, $res) = @_;
  my $detach = ($cmd eq "detach");
  my $path = "$mars/resource-$res/todo-$host/attach";
  _switch($cmd, $res, $path, !$detach);
}

sub attach_res_phase2 {
  my ($cmd, $res) = @_;
  my $detach = ($cmd eq "detach");
  check_status($cmd, $res, "is-attached", $detach ? 0 : 1, 1);
  if ($detach) {
    check_mars_device($cmd, $res, 1, 1);
    check_status($cmd, $res, "is-replaying", 0, 1);
    check_status($cmd, $res, "is-syncing", 0, 1);
  }
}

sub connect_global_res {
  my ($cmd, $res) = @_;
  my $disconnect = ($cmd =~ m/disconnect/);
  my @paths = glob("$mars/resource-$res/todo-*/");
  for my $path (@paths) {
    _switch($cmd, $res, "$path/connect", !$disconnect);
  }
}

sub connect_local_res {
  my ($cmd, $res) = @_;
  my $disconnect = ($cmd =~ m/disconnect/);
  my $path = "$mars/resource-$res/todo-$host/connect";
  _switch($cmd, $res, $path, !$disconnect);
}

sub pause_sync_global_res {
  my ($cmd, $res) = @_;
  my $pause = ($cmd =~ m/pause/);
  my @paths = glob("$mars/resource-$res/todo-*/");
  for my $path (@paths) {
    _switch($cmd, $res, "$path/sync", !$pause);
  }
}

sub pause_sync_local_res {
  my ($cmd, $res) = @_;
  my $pause = ($cmd =~ m/pause/);
  my $path = "$mars/resource-$res/todo-$host/sync";
  _switch($cmd, $res, $path, !$pause);
}

sub pause_replay_global_res {
  my ($cmd, $res) = @_;
  my $pause = ($cmd =~ m/pause/);
  my @paths = glob("$mars/resource-$res/todo-*/");
  for my $path (@paths) {
    _switch($cmd, $res, "$path/allow-replay", !$pause);
  }
}

sub pause_replay_local_res {
  my ($cmd, $res) = @_;
  my $pause = ($cmd =~ m/pause/);
  my $path = "$mars/resource-$res/todo-$host/allow-replay";
  _switch($cmd, $res, $path, !$pause);
}

sub up_res_phase0 {
  my ($cmd, $res) = @_;
  my $down = ($cmd eq "down");
  if ($down) {
    attach_res_phase0("detach", $res);
  } else {
    attach_res_phase0("attach", $res);
  }
}

sub up_res_phase1 {
  my ($cmd, $res) = @_;
  my $down = ($cmd eq "down");
  if ($down) {
    pause_replay_local_res("pause-replay-local", $res);
    pause_sync_local_res("pause-sync-local", $res);
    connect_local_res("disconnect", $res);
    attach_res_phase1("detach", $res);
  } else {
    attach_res_phase1("attach", $res);
    connect_local_res("connect", $res);
    pause_sync_local_res("resume-sync-local", $res);
    pause_replay_local_res("resume-replay-local", $res);
  }
}

sub up_res_phase2 {
  my ($cmd, $res) = @_;
  my $down = ($cmd eq "down");
  if ($down) {
    attach_res_phase2("detach", $res);
  } else {
    attach_res_phase2("attach", $res);
  }
}

sub set_replay_res {
  my ($cmd, $res, $new_nr) = @_;
  if (!$new_nr || $new_nr <= 0) {
    ldie "you must supply a numeric logfile number as third argument.\n";
  }
  check_not_primary(@_);
  check_todo($cmd, $res, "allow-replay", 0, 0);
  my $replaylink = "$mars/resource-$res/replay-$host";
  my $old_val = get_link($replaylink);
  my $old_nr = $old_val;
  $old_nr =~ s/log-([0-9]+)-.*/$1/;
  ldie "old log number '$old_nr' is wrong\n" unless $old_nr > 0;
  if ($new_nr > $old_nr) {
    lwarn "you try to skip logfile numbers from $old_nr to $new_nr, are you sure?\n";
    ldie "you would need --force if you really know what you are doing.\n" unless $force;
  }
  my $primary = _get_designated_primary($res);
  _set_replaylink("$mars/resource-$res", $new_nr, $primary);
}

sub fake_local_res {
  my ($cmd, $res) = @_;
  my $path = "$mars/resource-$res/todo-$host/sync";
  _switch($cmd, $res, $path, 0);
  #check_status($res, "copy-syncstatus-$host", 0);
  my $size = get_link("$mars/resource-$res/size");
  my $target = "$mars/resource-$res/syncstatus-$host";
  set_link($size, $target);
}

sub _primary_res {
  my ($res, $new, $old) = @_;
  my $pri = "$mars/resource-$res/primary";
  set_link($new, $pri);
  lprint "designated primary changed from '$old' to '$new'\n";
}

# check whether primary/secondary switching is possible at all
sub primary_phase0 {
  my ($cmd, $res) = @_;
  ldie "cannot switch primary: mars kernel module is not loaded\n" unless ($cmd eq "secondary" || -d "/proc/sys/mars");
  if ($force) {
    lwarn "You can do a '$cmd --force' only in DISCONNECTED state.\n";
    check_todo($cmd, $res, "connect", 0, 0);
  }
  if ($cmd eq "primary") {
    check_sync_finished($res, $host);
    check_todo($cmd, $res, "attach", 1, 0);
    check_todo($cmd, $res, "connect", 1, 0) if !$force;
    check_todo($cmd, $res, "allow-replay", 1, 0);
  }
  my $old = _get_designated_primary($res);
  return if ($old eq $host and $cmd eq "primary");
  return if $old eq "(none)";
  my $open_count_path = "$mars/resource-$res/actual-$old/open-count";
  my $device_in_use = get_link($open_count_path, 1);
  if ($device_in_use) {
    my $name = get_link("$mars/resource-$res/device-$old", 1) || "unknown";
    lwarn "device '/dev/mars/$name' for resource '$res' is $device_in_use times in use on primary host '$old'\n";
    ldie "first you must umount/close the device (on host '$old')\n" unless $force;
    lwarn "First you SHOULD umount/close the device (on host '$old'), but you ignore this recommendation by giving the --force option.\n";
    if (is_link_recent($open_count_path)) {
      lwarn "You are forcing a SPLIT BRAIN via --force right now. Do you know that this is an ERRONEOUS state? Do you really know what you are doing?\n";
    } else {
      lwarn "You may produce a SPLIT BRAIN via --force because the peer host '$old' is currently not reachable.\n";
    }
  }
  lprint "all preconditions OK for resource '$res'\n";
}

# when necessary, switch to secondary (intermediately)
sub primary_phase1 {
  my ($cmd, $res) = @_;
  return if ($force and $cmd eq "primary");
  my $old = _get_designated_primary($res);
  return if ($old eq $host and $cmd eq "primary");
  return if ($old ne $host and $cmd eq "secondary");
  my $new = "(none)";
  return if $old eq $new;
  _primary_res($res, $new, $old);
}

# when necessary, wait
sub primary_phase2 {
  my ($cmd, $res) = @_;
  return if $force;
  return unless $cmd eq "primary";
  check_primary_gone($res);
  my $ok = detect_splitbrain($res);
  try_to_avoid_splitbrain(@_) if $ok;
}

# when necessary, switch to primary
sub primary_phase3 {
  my ($cmd, $res) = @_;
  return unless $cmd eq "primary";
  my $old = _get_designated_primary($res);
  my $new = $host;
  _primary_res($res, $new, $old);
}

# wait for device to appear / disappear
sub primary_phase4 {
  my ($cmd, $res) = @_;
  if($cmd eq "secondary") {
    check_mars_device($cmd, $res, 1, 1);
    return;
  }
  my $ok = detect_splitbrain($res, 1);
  if (!$ok) {
    lwarn "Sorry, in split brain situations I can only set the _designated_\n";
    lwarn "primary, but I cannot _guarantee_ that becoming the\n";
    lwarn "the actual primary is possible.\n";
    lwarn "You SHOULD resolve the split brain ASAP (e.g. by leave-resource\n";
    lwarn "or invalidate etc).\n";
    return;
  }
  check_mars_device($cmd, $res, 1, 0);
}

sub wait_umount_res {
  my ($cmd, $res) = @_;
  while (1) {
    my $sum = 0;
    foreach my $path (glob("$mars/resource-$res/actual-*/open-count")) {
      $sum += get_link($path);
    }
    last if !$sum;
    lprint "device for resource '$res' is $sum times in use somewhere\n";
    sleep_timeout(3);
  }
  lprint "OK, device for resource '$res' is not in use.\n";
}

sub invalidate_res_phase0 {
  my ($cmd, $res) = @_;
  check_not_primary(@_);
  my $primary = _get_designated_primary($res);
  ldie "for operation '$cmd', some other designated primary must exist (currently there is none)\n" if $primary eq "(none)";
}

sub invalidate_res_phase1 {
  my ($cmd, $res) = @_;
  _switch($cmd, $res, "$mars/resource-$res/todo-$host/sync", 0);
  _switch($cmd, $res, "$mars/resource-$res/todo-$host/allow-replay", 0);
}

sub invalidate_res_phase2 {
  my ($cmd, $res) = @_;
  if (!$force) {
    check_status($cmd, $res, "is-syncing", 0, 1);
    check_status($cmd, $res, "is-replaying", 0, 1);
  }
}

sub invalidate_res_phase3 {
  my ($cmd, $res) = @_;
  my $dst = "$mars/resource-$res/syncstatus-$host";
  my $primary = _get_designated_primary($res);
  ldie "Cannot execute 'invalidate' because noone is designated as primary.\n" if (!$primary || $primary eq "(none)");
  my $replay = get_link("$mars/resource-$res/replay-$primary");
  $replay =~ m/^log-([0-9]+)-/ or ldie "replay link '$replay' is not parsable\n";
  my $replay_nr = $1;
  set_link("0", $dst);
  finish_links(); # opportunity for errors => don't continue
  _set_replaylink("$mars/resource-$res", $replay_nr, $primary, "");
  _switch($cmd, $res, "$mars/resource-$res/todo-$host/allow-replay", 1);
  _switch($cmd, $res, "$mars/resource-$res/todo-$host/sync", 1);
}

sub resize_res {
  my ($cmd, $res, $size_arg) = @_;
  my $new_size = 0;
  if ($size_arg) {
    $new_size = get_size($size_arg);
    ldie "optional size argument '$new_size' must be numeric and positive\n" unless scalar($new_size) > 0;
    lprint "new size: $new_size bytes\n";
  }
  check_primary(@_);
  my @actsizes = glob("$mars/resource-$res/actsize-*");
  ldie "resource $res has no actsize-* symlinks\n" unless @actsizes;
  my $lnk = "$mars/resource-$res/size";
  my $old_size = get_link($lnk);
  my $min_size = 0;
  foreach my $actsize (@actsizes) {
    my $this_size = get_link($actsize);
    if (!$min_size || $this_size < $min_size) {
      $min_size = $this_size;
    }
  }
  lprint "old_size=$old_size\n";
  lprint "min_size=$min_size\n";
  $new_size = $min_size if !$new_size;
  lprint "new_size=$new_size\n";
  ldie "new size $new_size is higher than the minimum size of all volumes $min_size" if $new_size > $min_size; # no override with --force possible
  # for now, disallow decreasing until some bugs are fixed
  ldie "only increases of the size are possible!\n" if $new_size < $old_size;
  ldie "only increases of the size are possible without --force\n" if $new_size <= $old_size && !$force;
  foreach my $switch (glob("$mars/resource-$res/todo-*/sync")) {
    my $this_switch = get_link($switch);
    ldie "sync on '$switch' is switched on -- use marsadm pause-sync to stop\n" unless !$this_switch;
  }
  my @syncsizes = glob("$mars/resource-$res/syncstatus-$host");
  foreach my $syncsize (@syncsizes) {
    my $this_size = get_link($syncsize);
    ldie "sync on $syncsize has not yet finished: $this_size != $old_size (DANGEROUS FIX: if you know what you are doing, marsadm fake-sync can 'fix' it -- but this may need a full-sync afterwards)\n" unless $this_size == $old_size;
  }
  foreach my $syncsize (@syncsizes) {
    my $this_size = get_link($syncsize);
    set_link($new_size, $syncsize);
  }
  set_link($new_size, $lnk);
}

sub role_cmd {
  my ($cmd, $res) = @_;
  my $primary = _get_actual_primary($res) || '(none)';
  my $todo_primary = _get_designated_primary($res);
  my $msg = "I am actually ";
  $msg .= ($primary eq $host) ? "primary" : "secondary";
  if ($primary eq $todo_primary) {
    $msg .= " and $primary is primary" if ($primary ne $host);
  }
  elsif ($primary ne $todo_primary) {
    $todo_primary = "I" if ($todo_primary eq $host);
    $msg .= " and $todo_primary should be primary";
  }
  lprint $msg . "\n";
}

sub mars_state_cmd {
  my ($cmd, $res) = @_;
  my $primary = _get_actual_primary($res) || '(none)';
  my $todo_primary = _get_designated_primary($res);

  if ($primary eq $host) {
    lprint "is_primary\n";
    return;
  }
  elsif ($todo_primary eq $host) {
    lprint "becoming_primary\n";
    return;
  }

  # secondary without ambitions to become primary

  my $size = get_link("$mars/resource-$res/size");
  my $syncstatus = get_link("$mars/resource-$res/syncstatus-$host");
  if ($syncstatus != $size) {
    lprint "secondary inconsistent ($syncstatus bytes of $size)\n";
    return;
  }

  if ($primary eq "(none)") {
    my $min = 0;
    foreach my $path (glob("$mars/resource-$res/log-*")) {
      my $nr = $path;
      $nr =~ s:^.*[a-z]+-([0-9]+)(-[^/]*)?$:$1:;
      if ($nr > $min) {
	$primary = $path;
	$primary =~ s:^.*/[a-z]+-[0-9]+-([^/]*)$:$1:;
	$min = $nr;
      }
    }
  }
  my $primary_replay = get_link("$mars/resource-$res/replay-$primary");
  my $host_replay = get_link("$mars/resource-$res/replay-$host");
  if ($primary_replay eq $host_replay) {
    lprint "secondary uptodate\n";
    return;
  }
  lprint "secondary outdated ($host_replay instead of $primary_replay)\n";
}

sub cat_cmd {
  my $cmd = shift;
  foreach my $path (@_) {
    _get_text($path, undef, 1);
  }
}

sub mars_info_cmd {
  my ($cmd, $res) = @_;
  my $info = "$mars/resource-$res/logstatus-$host.status";
  cat_cmd($cmd, $info);
}

sub show_cmd {
  my ($cmd, $res) = @_;
  $res = "*" if !$res || $res eq "all";
  my $glob = "$mars/{ips/ip-$host,alive-$host,emergency-$host,rest-space-$host,resource-$res/{device,primary,size,actsize-$host,syncstatus-$host,replay-$host,actual-$host/*,todo-$host/*}}";
  foreach my $link (glob($glob)) {
    next unless -l $link;
    my $res = get_link($link);
    my $short = $link;
    $short =~ s:^$mars/::;
    lprint "$short=$res\n";
  }
}

sub show_errors_cmd {
  my ($cmd, $res) = @_;
  my $text = get_error_text(@_);
  if ($text) {
    lprint $text;
    ldie "resource $res has some (old) problems.\n";
  } else {
    lprint "no errors/warnings are reported.\n";
  }
}

sub helplist {
  my $temp;
  $temp = shift;
  lprint "ERROR: $temp" if ($temp);
  lprint "
marsadm [<global_option>] <command> [<resource>] [<option>]

<global_option> =
  --force             : skip safety checks
                        use only when you know what you are doing!
  --timeout=<seconds> : leave safety checks after timeout with an error
                        instead of waiting forever

<command> =
  cluster    : create-cluster join-cluster leave-cluster
  resource   : create-resource join-resource leave-resource
               primary secondary invalidate
               up down
  replication: connect disconnect connect-local disconnect-local
  replay     : pause-replay resume-replay pause-replay-local resume-replay-local
  sync       : pause-sync resume-sync pause-sync-local resume-sync-local fake-sync
  logfile    : log-rotate log-delete log-delete-all
  device     : attach detach
  internal   : help version

<resource> = name of resource or \"all\" for all resources

<option>   = special by command
  \n";
  exit 0;
}

sub version {
	lprint "$0 $Id\n";
	#lprint "my IP is $ip\n";
	exit 0;
} 

##################################################################
my %cmd_table =
  (
   # new keywords
   "create-cluster"     => \&create_cluster,
   "join-cluster"       => \&join_cluster,
   "leave-cluster"      => \&leave_cluster,
   "create-resource"   => \&create_res,
   "join-resource"     => \&create_res,
   "leave-resource"    => [
			   "check preconditions", \&leave_res_phase0,
			   "switch state",        \&leave_res_phase1,
			   "wait for deletions",  \&leave_res_phase2,
			  ],
   "log-rotate"        => \&logrotate_res,
   "log-delete"        => \&logdelete_res,
   "log-delete-all"    => \&logdelete_res,
   "fake-sync"         => \&fake_local_res,
   "set-link"          => \&set_link_cmd,
   "delete-file"       => \&delete_file_cmd,
   "cat"               => \&cat_cmd,
   "show"              => \&show_cmd,
   "show-errors"       => \&show_errors_cmd,
   "show-state"        => \&mars_state_cmd,
   "mars-state"        => \&mars_state_cmd, # deprecated
   "show-info"         => \&mars_info_cmd,
   "mars-info"         => \&mars_info_cmd, # deprecated
   "pause-replay-local"  => \&pause_replay_local_res,
   "pause-replay-global" => \&pause_replay_global_res,
   "pause-replay"        => \&pause_replay_local_res,
   "resume-replay-local" => \&pause_replay_local_res,
   "resume-replay-global"=> \&pause_replay_global_res,
   "resume-replay"       => \&pause_replay_local_res,
   "set-replay"          => \&set_replay_res,
   "wait-umount"         => \&wait_umount_res,
   "wait-cluster"        => \&wait_cluster,
   "wait-resource"       => \&wait_cluster,

   # compatible keywords (or their derivatives)
   "attach"            => [
			   "check preconditions", \&attach_res_phase0,
			   "switch state",        \&attach_res_phase1,
			   "wait for effect",     \&attach_res_phase2,
			  ],
   "detach"            => [
			   "check preconditions", \&attach_res_phase0,
			   "switch state",        \&attach_res_phase1,
			   "wait for effect",     \&attach_res_phase2,
			  ],
   "connect-local"     => \&connect_local_res,
   "connect-global"    => \&connect_global_res,
   "connect"           => \&connect_local_res,
   "disconnect-local"  => \&connect_local_res,
   "disconnect-global" => \&connect_global_res,
   "disconnect"        => \&connect_local_res,
   "syncer"            => \&ignore_cmd,
   "up"                => [
			   "check preconditions", \&up_res_phase0,
			   "switch state",        \&up_res_phase1,
			   "wait for effect",     \&up_res_phase2,
			  ],
   "down"              => [
			   "check preconditions", \&up_res_phase0,
			   "switch state",        \&up_res_phase1,
			   "wait for effect",     \&up_res_phase2,
			  ],
   "primary"           => [
			   "check preconditions", \&primary_phase0,
			   "leave primary state", \&primary_phase1,
			   "wait when necessary", \&primary_phase2,
			   "switch to primary",   \&primary_phase3,
			   "wait for device",     \&primary_phase4,
			  ],
   "secondary"         => [
			   "check preconditions", \&primary_phase0,
			   "leave primary state", \&primary_phase1,
                           "wait for effect", \&primary_phase4,
			  ],
   "invalidate"        => [
			   "check preconditions", \&invalidate_res_phase0,
			   "stop old replay",     \&invalidate_res_phase1,
			   "wait for replay off", \&invalidate_res_phase2,
			   "force symlinks",      \&invalidate_res_phase3,
			  ],
   "invalidate-remote" => \&forbidden_cmd,
   "resize"            => \&resize_res,
   "create-md"         => \&senseless_cmd,
   "get-gi"            => \&ignore_cmd,
   "show-gi"           => \&ignore_cmd,
   "dump-md"           => \&senseless_cmd,
   "outdate"           => \&ignore_cmd,
   "adjust"            => \&ignore_cmd,
   "wait-connect"      => \&wait_cluster,
   "role"              => \&role_cmd,
   "state"             => \&role_cmd,
   "cstate"            => \&nyi_cmd,
   "dstate"            => \&nyi_cmd,
   "status"            => \&nyi_cmd,
   "dump"              => \&senseless_cmd,
   "verify"            => \&forbidden_cmd,
   "pause-sync-local"  => \&pause_sync_local_res,
   "pause-sync-global" => \&pause_sync_global_res,
   "pause-sync"        => \&pause_sync_local_res,
   "resume-sync-local" => \&pause_sync_local_res,
   "resume-sync-global"=> \&pause_sync_global_res,
   "resume-sync"       => \&pause_sync_local_res,
   "new-current-uuid"  => \&senseless_cmd,
   "hidden-commands"   => \&ignore_cmd,
  );

my @args;

foreach my $arg (@ARGV) {
  if ($arg eq "--force" || $arg eq "-f") {
    $force++;
    next;
  } elsif ($arg eq "--verbose" || $arg eq "-v") {
    $verbose++;
    next;
  } elsif ($arg =~ s/--timeout\s*=\s*([0-9]+)/$1/) {
    $timeout = $arg;
    next;
  } elsif ($arg =~ s/--host\s*=\s*([-_A-Za-z0-9]+)/$1/) {
    ldie "host '$arg' does not exist in /mars/ips/ip-*\n" unless -l "/mars/ips/ip-$arg";
    if ($arg ne $host) {
      lprint "ATTENTION: acting as if I were host '$arg'\n";
      lwarn "some commands require local knowledge not available here.\n";
      lwarn "thus something may fail or go wrong - use this at your risk!\n";
      $host = $arg;
    }
    next;
  }
  if ($arg =~ s/^force-//) {
    $force++;
  }
  push @args, $arg;
}

my $cmd = shift @args || helplist "command argument is missing\n";

$notify = "(cmd: $cmd)" unless $cmd eq "version";

if ($cmd =~ m/^help$/ || $cmd =~ m/^h$/) {
  helplist;
}

if ($cmd =~ m/^version$/ || $cmd =~ m/^v$/) {      
  version;
}

ldie "only root may use this tool\n" if $< != 0 && $cmd !~ m/^cat$/; # getpid() seems to be missing in perlfunc
helplist "unknown command $cmd\n" if !exists $cmd_table{$cmd};
if (!(-d $mars) && $cmd !~ m/(create|join)-cluster|cat/) {
  ldie "The $mars directory does not exist.\n";
}

my $res = "";
if ($cmd eq "show") {
  $res = shift @args;
} elsif (!($cmd =~ m/^(create|leave|wait)-cluster|cat|[a-z]+-file|set-[a-z]+$/)) {
  $res = shift @args || helplist "resource argument is missing\n";
  check_id($res);
}


lwarn "Using FORCE option -- hopefully you know what you are doing!\n" if $force;

my %checked_res;

sub do_one_res {
  my $func = shift;
  my ($cmd, $res) = @_;
  if (!$checked_res{"$cmd$res"}) {
    $res = check_res($res) unless $cmd =~ m/^(join|create|leave|wait)-cluster|create-resource|show|cat|[a-z]+-file|set-link$/;
    check_res_member($res) unless $cmd =~ m/^(join|create)-(cluster|resource)|(leave|wait)-cluster|show|cat|[a-z]+-file|set-link$/;
    detect_splitbrain($res, 1);
    $checked_res{"$cmd$res"} = 1;
  }
  &{$func}(@_);
}

my %skip_res;

sub do_all_res {
  my $func = shift;
  my $cmd = shift;
  my $res = shift || "all";
  if ($res eq "all" && $cmd !~ m/show|cat|cluster|set-link|delete-file/) {
    ldie "For safety reasons, --force is only allowed on explicitly named resources. Combination of 'all' with --force is disallowed!\n" if $force;
    ldie "Cannot combine command '$cmd' with 'all' existing resources - you must explicitly name a single new resource\n" if $cmd =~ m/create|join/;
    my $any_success = 0;
    my $any_member = 0;
    foreach $res (glob("$mars/resource-*")) {
      next unless -e "$res/data-$host";
      $any_member++;
      $res =~ s/^.*\/resource-(.*)$/$1/;
      next if defined($skip_res{$res});
      lprint "--------- resource $res\n";
      eval {
	do_one_res($func, $cmd, $res, @_);
	1;
      } and $any_success = 1 or $skip_res{$res} = 1;
    }
    if (!$any_success) {
      if (!$any_member) {
	lprint "I am not member of any resource\n";
	return 1;
      }
      ldie "all resources have errors\n";
    }
    return !$any_success;
  } else {
    return do_one_res($func, $cmd, $res, @_);
  }
}

my $func = $cmd_table{$cmd};
ldie "unknown command '$cmd'\n" unless $func;

if (ref($func) eq "ARRAY") {
  my @list = @$func;
  while (@list) {
    my $headline = shift @list;
    my $memb_func = shift @list;
    lprint "---------------------------- $headline:\n";
    my $status = do_all_res($memb_func, $cmd, $res, @args);
    last if (defined($status) && $status);
    finish_links();
  }
} elsif (ref($func) eq "CODE") {
  do_all_res($func, $cmd, $res, @args);
} else {
  ldie "internal error: command table is wrong for '$cmd'";
}

finish_links();

exit($error_count);