Function cgroup

src/linux/cgroups.cpp:1785–1821

Helper for finding the cgroup of the specified pid for the specified subsystem.

// Helper for finding the cgroup of the specified pid for the
// specified subsystem.
Result<string> cgroup(pid_t pid, const string& subsystem)
{
  // Determine cgroup for hierarchy with the subsystem attached.
  string path = path::join("/proc", stringify(pid), "cgroup");

  Try<string> read = os::read(path);

  if (read.isError()) {
    return Error("Failed to read " + path + ": " + read.error());
  }

  // Now determine the cgroup by parsing each line of the output which
  // should be of the form "N:subsystems:cgroup" where 'N' is the
  // hierarchy number and 'subsystems' are the attached subsystems and
  // 'cgroup' is the relative path to the cgroup from the hierarchy
  // path.
  Option<string> cgroup = None();

  foreach (const string& line, strings::tokenize(read.get(), "\n")) {
    vector<string> tokens = strings::tokenize(line, ":");

    // The second field is empty for cgroups v2 hierarchy.
    if (tokens.size() == 2) {
      continue;
    } else if (tokens.size() != 3) {
      return Error("Unexpected format in " + path);
    }

    foreach (const string& token, strings::tokenize(tokens[1], ",")) {
      if (subsystem == token) {
        cgroup = tokens[2];
      }
    }
  }

  return cgroup;
}

} // namespace internal {