Function sdNotifyBarrier

notify_socket.go:178–230

sdNotifyBarrier performs synchronization with systemd by means of the sd_notify_barrier protocol.

(client *net.UnixConn)

// sdNotifyBarrier performs synchronization with systemd by means of the sd_notify_barrier protocol.
func sdNotifyBarrier(client *net.UnixConn) (retErr error) {
	// Create a pipe for communicating with systemd daemon.
	pipeR, pipeW, err := os.Pipe()
	if err != nil {
		return err
	}
	defer func() {
		if retErr != nil {
			pipeW.Close()
			pipeR.Close()
		}
	}()

	// Get the FD for the unix socket file to be able to use sendmsg.
	clientFd, err := client.File()
	if err != nil {
		return err
	}

	// Send the write end of the pipe along with a BARRIER=1 message.
	fdRights := unix.UnixRights(int(pipeW.Fd()))
	err = linux.Sendmsg(int(clientFd.Fd()), []byte("BARRIER=1"), fdRights, nil, 0)
	if err != nil {
		return err
	}

	// Close our copy of pipeW.
	err = pipeW.Close()
	if err != nil {
		return err
	}

	// Expect the read end of the pipe to be closed after 30 seconds.
	err = pipeR.SetReadDeadline(time.Now().Add(30 * time.Second))
	if err != nil {
		return nil
	}

	// Read a single byte expecting EOF.
	var buf [1]byte
	n, err := pipeR.Read(buf[:])
	if n != 0 || err == nil {
		return errUnexpectedRead
	} else if errors.Is(err, os.ErrDeadlineExceeded) {
		// Probably the other end doesn't support the sd_notify_barrier protocol.
		logrus.Warn("Timeout after waiting 30s for barrier. Ignored.")
		return nil
	} else if err == io.EOF { //nolint:errorlint // https://github.com/polyfloyd/go-errorlint/issues/49
		return nil
	} else {
		return err
	}
}