Function childMain

src/posix/subprocess.hpp:216–310

The main entry of the child process. NOTE: This function has to be async signal safe.

//
// NOTE: This function has to be async signal safe.
inline int childMain(
    const std::string& path,
    char** argv,
    char** envp,
    const InputFileDescriptors& stdinfds,
    const OutputFileDescriptors& stdoutfds,
    const OutputFileDescriptors& stderrfds,
    const std::vector<int_fd>& whitelist_fds,
    bool blocking,
    int pipes[2],
    const std::vector<Subprocess::ChildHook>& child_hooks)
{
  // Close parent's end of the pipes.
  if (stdinfds.write.isSome()) {
    ::close(stdinfds.write.get());
  }
  if (stdoutfds.read.isSome()) {
    ::close(stdoutfds.read.get());
  }
  if (stderrfds.read.isSome()) {
    ::close(stderrfds.read.get());
  }

  // Currently we will block the child's execution of the new process
  // until all the parent hooks (if any) have executed.
  if (blocking) {
    ::close(pipes[1]);
  }

  // Redirect I/O for stdin/stdout/stderr.
  while (::dup2(stdinfds.read, STDIN_FILENO) == -1 && errno == EINTR);
  while (::dup2(stdoutfds.write, STDOUT_FILENO) == -1 && errno == EINTR);
  while (::dup2(stderrfds.write, STDERR_FILENO) == -1 && errno == EINTR);

  // Close the copies. We need to make sure that we do not close the
  // file descriptor assigned to stdin/stdout/stderr in case the
  // parent has closed stdin/stdout/stderr when calling this
  // function (in that case, a dup'ed file descriptor may have the
  // same file descriptor number as stdin/stdout/stderr).
  //
  // We also need to ensure that we don't "double close" any file
  // descriptors in the case where one of stdinfds.read,
  // stdoutfds.write, or stdoutfds.write are equal.
  if (stdinfds.read != STDIN_FILENO &&
      stdinfds.read != STDOUT_FILENO &&
      stdinfds.read != STDERR_FILENO) {
    ::close(stdinfds.read);
  }
  if (stdoutfds.write != STDIN_FILENO &&
      stdoutfds.write != STDOUT_FILENO &&
      stdoutfds.write != STDERR_FILENO &&
      stdoutfds.write != stdinfds.read) {
    ::close(stdoutfds.write);
  }
  if (stderrfds.write != STDIN_FILENO &&
      stderrfds.write != STDOUT_FILENO &&
      stderrfds.write != STDERR_FILENO &&
      stderrfds.write != stdinfds.read &&