a5c6347ff0
This makes things more efficient (we don't need to use an SSH master connection, and we only start a single remote process) and gets rid of locking issues (the remote nix-store process will keep inputs and outputs locked as long as they're needed). It also makes it more or less secure to connect directly to the root account on the build machine, using a forced command (e.g. ‘command="nix-store --serve --write"’). This bypasses the Nix daemon and is therefore more efficient. Also, don't call nix-store to import the output paths.
278 lines
9.1 KiB
Perl
Executable file
278 lines
9.1 KiB
Perl
Executable file
#! @perl@ -w @perlFlags@
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use Fcntl qw(:DEFAULT :flock);
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use English '-no_match_vars';
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use IO::Handle;
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use Nix::Config;
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use Nix::SSH;
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use Nix::CopyClosure;
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use Nix::Store;
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no warnings('once');
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# General operation:
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#
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# Try to find a free machine of type $neededSystem. We do this as
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# follows:
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# - We acquire an exclusive lock on $currentLoad/main-lock.
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# - For each machine $machine of type $neededSystem and for each $slot
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# less than the maximum load for that machine, we try to get an
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# exclusive lock on $currentLoad/$machine-$slot (without blocking).
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# If we get such a lock, we send "accept" to the caller. Otherwise,
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# we send "postpone" and exit.
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# - We release the exclusive lock on $currentLoad/main-lock.
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# - We perform the build on $neededSystem.
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# - We release the exclusive lock on $currentLoad/$machine-$slot.
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#
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# The nice thing about this scheme is that if we die prematurely, the
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# locks are released automatically.
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# Make sure that we don't get any SSH passphrase or host key popups -
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# if there is any problem it should fail, not do something
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# interactive.
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$ENV{"DISPLAY"} = "";
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$ENV{"SSH_ASKPASS"} = "";
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sub sendReply {
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my $reply = shift;
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print STDERR "# $reply\n";
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}
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sub all { $_ || return 0 for @_; 1 }
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# Initialisation.
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my $loadIncreased = 0;
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my ($localSystem, $maxSilentTime, $printBuildTrace, $buildTimeout) = @ARGV;
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my $currentLoad = $ENV{"NIX_CURRENT_LOAD"};
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my $conf = $ENV{"NIX_REMOTE_SYSTEMS"};
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sub openSlotLock {
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my ($machine, $slot) = @_;
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my $slotLockFn = "$currentLoad/" . (join '+', @{$machine->{systemTypes}}) . "-" . $machine->{hostName} . "-$slot";
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my $slotLock = new IO::Handle;
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sysopen $slotLock, "$slotLockFn", O_RDWR|O_CREAT, 0600 or die;
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return $slotLock;
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}
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# Read the list of machines.
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my @machines;
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if (defined $conf && -e $conf) {
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open CONF, "<$conf" or die;
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while (<CONF>) {
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chomp;
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s/\#.*$//g;
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next if /^\s*$/;
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my @tokens = split /\s/, $_;
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my @supportedFeatures = split(/,/, $tokens[5] || "");
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my @mandatoryFeatures = split(/,/, $tokens[6] || "");
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push @machines,
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{ hostName => $tokens[0]
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, systemTypes => [ split(/,/, $tokens[1]) ]
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, sshKeys => $tokens[2]
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, maxJobs => int($tokens[3])
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, speedFactor => 1.0 * (defined $tokens[4] ? int($tokens[4]) : 1)
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, supportedFeatures => [ @supportedFeatures, @mandatoryFeatures ]
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, mandatoryFeatures => [ @mandatoryFeatures ]
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, enabled => 1
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};
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}
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close CONF;
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}
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# Wait for the calling process to ask us whether we can build some derivation.
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my ($drvPath, $hostName, $slotLock);
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my ($from, $to);
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REQ: while (1) {
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$_ = <STDIN> || exit 0;
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(my $amWilling, my $neededSystem, $drvPath, my $requiredFeatures) = split;
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my @requiredFeatures = split /,/, $requiredFeatures;
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my $canBuildLocally = $amWilling && ($localSystem eq $neededSystem);
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if (!defined $currentLoad) {
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sendReply "decline";
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next;
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}
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# Acquire the exclusive lock on $currentLoad/main-lock.
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mkdir $currentLoad, 0777 or die unless -d $currentLoad;
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my $mainLock = "$currentLoad/main-lock";
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sysopen MAINLOCK, "$mainLock", O_RDWR|O_CREAT, 0600 or die;
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flock(MAINLOCK, LOCK_EX) or die;
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while (1) {
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# Find all machine that can execute this build, i.e., that
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# support builds for the given platform and features, and are
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# not at their job limit.
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my $rightType = 0;
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my @available = ();
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LOOP: foreach my $cur (@machines) {
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if ($cur->{enabled}
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&& (grep { $neededSystem eq $_ } @{$cur->{systemTypes}})
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&& all(map { my $f = $_; 0 != grep { $f eq $_ } @{$cur->{supportedFeatures}} } (@requiredFeatures, @mandatoryFeatures))
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&& all(map { my $f = $_; 0 != grep { $f eq $_ } @requiredFeatures } @{$cur->{mandatoryFeatures}})
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)
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{
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$rightType = 1;
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# We have a machine of the right type. Determine the load on
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# the machine.
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my $slot = 0;
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my $load = 0;
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my $free;
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while ($slot < $cur->{maxJobs}) {
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my $slotLock = openSlotLock($cur, $slot);
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if (flock($slotLock, LOCK_EX | LOCK_NB)) {
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$free = $slot unless defined $free;
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flock($slotLock, LOCK_UN) or die;
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} else {
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$load++;
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}
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close $slotLock;
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$slot++;
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}
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push @available, { machine => $cur, load => $load, free => $free }
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if $load < $cur->{maxJobs};
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}
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}
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if (defined $ENV{NIX_DEBUG_HOOK}) {
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print STDERR "load on " . $_->{machine}->{hostName} . " = " . $_->{load} . "\n"
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foreach @available;
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}
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# Didn't find any available machine? Then decline or postpone.
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if (scalar @available == 0) {
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# Postpone if we have a machine of the right type, except
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# if the local system can and wants to do the build.
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if ($rightType && !$canBuildLocally) {
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sendReply "postpone";
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} else {
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sendReply "decline";
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}
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close MAINLOCK;
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next REQ;
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}
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# Prioritise the available machines as follows:
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# - First by load divided by speed factor, rounded to the nearest
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# integer. This causes fast machines to be preferred over slow
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# machines with similar loads.
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# - Then by speed factor.
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# - Finally by load.
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sub lf { my $x = shift; return int($x->{load} / $x->{machine}->{speedFactor} + 0.4999); }
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@available = sort
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{ lf($a) <=> lf($b)
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|| $b->{machine}->{speedFactor} <=> $a->{machine}->{speedFactor}
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|| $a->{load} <=> $b->{load}
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} @available;
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# Select the best available machine and lock a free slot.
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my $selected = $available[0];
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my $machine = $selected->{machine};
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$slotLock = openSlotLock($machine, $selected->{free});
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flock($slotLock, LOCK_EX | LOCK_NB) or die;
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utime undef, undef, $slotLock;
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close MAINLOCK;
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# Connect to the selected machine.
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@sshOpts = ("-i", $machine->{sshKeys}, "-x");
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$hostName = $machine->{hostName};
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eval {
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($from, $to) = connectToRemoteNix($hostName, \@sshOpts);
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# FIXME: check if builds are inhibited.
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};
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last REQ unless $@;
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print STDERR "$@";
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warn "unable to open SSH connection to `$hostName', trying other available machines...\n";
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$from = undef;
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$to = undef;
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$machine->{enabled} = 0;
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}
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}
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# Tell Nix we've accepted the build.
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sendReply "accept";
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my @inputs = split /\s/, readline(STDIN);
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my @outputs = split /\s/, readline(STDIN);
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print STDERR "@ build-remote $drvPath $hostName\n" if $printBuildTrace;
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my $maybeSign = "";
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$maybeSign = "--sign" if -e "$Nix::Config::confDir/signing-key.sec";
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# Copy the derivation and its dependencies to the build machine. This
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# is guarded by an exclusive lock per machine to prevent multiple
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# build-remote instances from copying to a machine simultaneously.
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# That's undesirable because we may end up with N instances uploading
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# the same missing path simultaneously, causing the effective network
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# bandwidth and target disk speed to be divided by N.
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my $uploadLock = "$currentLoad/$hostName.upload-lock";
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sysopen UPLOADLOCK, "$uploadLock", O_RDWR|O_CREAT, 0600 or die;
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eval {
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local $SIG{ALRM} = sub { die "alarm\n" };
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# Don't wait forever, so that a process that gets stuck while
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# holding the lock doesn't block everybody else indefinitely.
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# It's safe to continue after a timeout, just (potentially)
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# inefficient.
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alarm 15 * 60;
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flock(UPLOADLOCK, LOCK_EX);
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alarm 0;
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};
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if ($@) {
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die unless $@ eq "alarm\n";
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print STDERR "somebody is hogging $uploadLock, continuing...\n";
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unlink $uploadLock;
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}
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Nix::CopyClosure::copyToOpen($from, $to, $hostName, [ $drvPath, @inputs ], "", "", 0, 0, $maybeSign ne "", "");
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close UPLOADLOCK;
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# Perform the build.
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print STDERR "building `$drvPath' on `$hostName'\n";
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writeInt(6, $to) or die; # == cmdBuildPaths
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writeStrings([$drvPath], $to);
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writeInt($maxSilentTime, $to);
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writeInt($buildTimeout, $to);
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my $res = readInt($from);
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if ($res != 0) {
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# Note that if we get exit code 100 from `nix-store -r', it
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# denotes a permanent build failure (as opposed to an SSH problem
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# or a temporary Nix problem). We propagate this to the caller to
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# allow it to distinguish between transient and permanent
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# failures.
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print STDERR "build of `$drvPath' on `$hostName' failed with exit code $res\n";
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exit $res;
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}
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# Copy the output from the build machine.
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my @outputs2 = grep { !isValidPath($_) } @outputs;
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if (scalar @outputs2 > 0) {
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writeInt(5, $to) or die; # == cmdExportPaths
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writeStrings(\@outputs2, $to);
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$ENV{'NIX_HELD_LOCKS'} = "@outputs2"; # FIXME: ugly
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importPaths(fileno($from));
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}
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