【runc 源码分析】runc init 流程分析

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NAME:
   docker-runc init - initialize the namespaces and launch the process (do not call it outside of runc)

USAGE:
   docker-runc init [arguments...]

Factory 接口

type Factory interface {
	// Creates a new container with the given id and starts the initial process inside it.
	Create(id string, config *configs.Config) (Container, error)

	// Load takes an ID for an existing container and returns the container information
	// from the state.  This presents a read only view of the container.
	Load(id string) (Container, error)

	// StartInitialization is an internal API to libcontainer used during the reexec of the
	// container.
	//
	// Errors:
	// Pipe connection error
	// System error
	StartInitialization() error

	// Type returns info string about factory type (e.g. lxc, libcontainer...)
	Type() string
}

一. runc init 分析

 

                                                                  网上的图片

  1.1 初始化iniit command

func init() {
	if len(os.Args) > 1 && os.Args[1] == "init" {
		runtime.GOMAXPROCS(1)
		runtime.LockOSThread()
	}
}

var initCommand = cli.Command{
	Name:  "init",
	Usage: `initialize the namespaces and launch the process (do not call it outside of runc)`,
	Action: func(context *cli.Context) error {
		factory, _ := libcontainer.New("")
		if err := factory.StartInitialization(); err != nil {
			// as the error is sent back to the parent there is no need to log
			// or write it to stderr because the parent process will handle this
			os.Exit(1)
		}
		panic("libcontainer: container init failed to exec")
	},
}

    1.1.1 New函数

      libcontainer.New函数初始化linuxFactory，实现了Factory接口

// New returns a linux based container factory based in the root directory and
// configures the factory with the provided option funcs.
func New(root string, options ...func(*LinuxFactory) error) (Factory, error) {
	if root != "" {
		if err := os.MkdirAll(root, 0700); err != nil {
			return nil, newGenericError(err, SystemError)
		}
	}
	l := &LinuxFactory{
		Root:      root,
		InitPath:  "/proc/self/exe",
		InitArgs:  []string{os.Args[0], "init"},
		Validator: validate.New(),
		CriuPath:  "criu",
	}
	Cgroupfs(l)
	for _, opt := range options {
		if opt == nil {
			continue
		}
		if err := opt(l); err != nil {
			return nil, err
		}
	}
	return l, nil
}

2. StartInitialization函数

     路径 libcontainer/factory_linux.go

// StartInitialization loads a container by opening the pipe fd from the parent to read the configuration and state
// This is a low level implementation detail of the reexec and should not be consumed externally
func (l *LinuxFactory) StartInitialization() (err error)