bug:fix fd doesn't close in time

[ningmingxiao]

I add some sleep

	s := l.config.SpecState
	s.Pid = unix.Getpid()
	s.Status = specs.StateCreated
	if err := l.config.Config.Hooks.Run(configs.StartContainer, s); err != nil {
		return err
	}
	time.Sleep(time.Second*30)

and find io.ReadAll(execFifo) will hang 30s.

func readFromExecFifo(execFifo io.Reader) error {
	data, err := io.ReadAll(execFifo)
	if err != nil {
		return err
	}
	if len(data) <= 0 {
		return errors.New("cannot start an already running container")
	}
	return nil
}

[ningmingxiao]

Is it a bug or a special design? run c start will hang until begin to run system.Exec. Can you review my pr thank you. @kolyshkin @cyphar

[kolyshkin]

I don't think it's a bug. If you look at the code, you'll see that the parent process uses handleFifoResult to read all data from the fifo and (once it's closed from the other side) remove it.

Now, the presence of exec.fifo file is used to distinguish between the created and the running state, as you can see in (*container).RefreshState function.

[kolyshkin]

Obviously, we don't have any tests to check if the container state is reported correctly for the case when the startContainer hook is still running (which is what this PR essentially breaks).

If you have some time, feel free to write such a test @ningmingxiao

[ningmingxiao]

Is it necessary to call "unix.Close(fd)" before to run startcontainer hook?