Method update

src/slave/containerizer/mesos/isolators/gpu/isolator.cpp:485–552

Future<Nothing> NvidiaGpuIsolatorProcess::update(
    const ContainerID& containerId,
    const Resources& resourceRequests,
    const google::protobuf::Map<string, Value::Scalar>& resourceLimits)
{
  if (containerId.has_parent()) {
    return Failure("Not supported for nested containers");
  }

  if (!infos.contains(containerId)) {
    return Failure("Unknown container");
  }

  Info* info = CHECK_NOTNULL(infos[containerId]);

  Option<double> gpus = resourceRequests.gpus();

  // Make sure that the `gpus` resource is not fractional.
  // We rely on scalar resources only having 3 digits of precision.
  if (static_cast<long long>(gpus.getOrElse(0.0) * 1000.0) % 1000 != 0) {
    return Failure("The 'gpus' resource must be an unsigned integer");
  }

  size_t requested =
    static_cast<size_t>(resourceRequests.gpus().getOrElse(0.0));

  // Update the GPU allocation to reflect the new total.
  if (requested > info->allocated.size()) {
    size_t additional = requested - info->allocated.size();

    return allocator.allocate(additional)
      .then(defer(PID<NvidiaGpuIsolatorProcess>(this),
                  &NvidiaGpuIsolatorProcess::_update,
                  containerId,
                  lambda::_1));
  } else if (requested < info->allocated.size()) {
    size_t fewer = info->allocated.size() - requested;

    set<Gpu> deallocated;

    for (size_t i = 0; i < fewer; i++) {
      const auto gpu = info->allocated.begin();

      cgroups::devices::Entry entry;
      entry.selector.type = Entry::Selector::Type::CHARACTER;
      entry.selector.major = gpu->major;
      entry.selector.minor = gpu->minor;
      entry.access.read = true;
      entry.access.write = true;
      entry.access.mknod = true;

      Try<Nothing> deny = cgroups::devices::deny(
          hierarchy, info->cgroup, entry);

      if (deny.isError()) {
        return Failure("Failed to deny cgroups access to GPU device"
                       " '" + stringify(entry) + "': " + deny.error());
      }