docker run源码分析（二）之Docker daemon--container start

Bertha 。 2022-04-18 05:53 479阅读 0赞

### **上一篇咱们简单的分析了docker run命令在Docker daemon中的create实现，接下来咱们开始start的分析。源码基于Docker-ce17.09** ###

### **1、daemon端对container start的处理，即[ r.postContainersStart() ][r.postContainersStart_]函数。** ###

### **1.1、流程：** ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2dvb3NlX2ZsZXNo_size_16_color_FFFFFF_t_70][]

### **1.2、源码：[postContainerStart(）][r.postContainersStart_]函数** ###

func (s *containerRouter) postContainersStart(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
    
    	version := httputils.VersionFromContext(ctx)
    	//获取hostConfig配置信息
    	var hostConfig *container.HostConfig
    	// A non-nil json object is at least 7 characters.
    	//非nil 的json对象至少为7个字符。一系列检查
    	if r.ContentLength > 7 || r.ContentLength == -1 {
    		if versions.GreaterThanOrEqualTo(version, "1.24") {
    			return bodyOnStartError{}
    		}
    		if err := httputils.CheckForJSON(r); err != nil {
    			return err
    		}
    		c, err := s.decoder.DecodeHostConfig(r.Body)
    		if err != nil {
    			return err
    		}
    		hostConfig = c
    	}
    	//解析form表单
    	if err := httputils.ParseForm(r); err != nil {
    		return err
    	}
    	//获得与键关联的值
    	checkpoint := r.Form.Get("checkpoint")
    	checkpointDir := r.Form.Get("checkpoint-dir")
    	//调用ContainerStart进一步启动容器，下面详细分析
    	if err := s.backend.ContainerStart(vars["name"], hostConfig, checkpoint, checkpointDir); err != nil {
    		return err
    	}
    
    	w.WriteHeader(http.StatusNoContent)
    	return nil
    }

### **1.3、源码：[ backend.ContainerStart（）][backend.ContainerStart]函数 和  [ContainerStart（）][ContainerStart]函数** ###

// ContainerStart starts a container.
    func (daemon *Daemon) ContainerStart(name string, hostConfig *containertypes.HostConfig, checkpoint string, checkpointDir string) error {
    	if checkpoint != "" && !daemon.HasExperimental() {
    		return validationError{errors.New("checkpoint is only supported in experimental mode")}
    	}
    	//可以根据全容器ID、容器名、容器ID前缀获取容器对象
    	container, err := daemon.GetContainer(name)
    	if err != nil {
    		return err
    	}
    
    	//调用containerStart进一步启动容器，下面详细分析
    	if err := daemon.containerStart(container, checkpoint, checkpointDir, true); err != nil {
    		return err
    	}
    	return nil
    }

### **下面的containerStart()  没看懂，再补充** ###

// containerStart prepares the container to run by setting up everything the
    // container needs, such as storage and networking, as well as links
    // between containers. The container is left waiting for a signal to
    // begin running.
    func (daemon *Daemon) containerStart(container *container.Container, checkpoint string, checkpointDir string, resetRestartManager bool) (err error) {
    	start := time.Now()
    	container.Lock()
    	defer container.Unlock()
    
    	if resetRestartManager && container.Running { // skip this check if already in restarting step and resetRestartManager==false
    		return nil
    	}
    
    	if container.RemovalInProgress || container.Dead {
    		return stateConflictError{errors.New("container is marked for removal and cannot be started")}
    	}
    
    	// if we encounter an error during start we need to ensure that any other
    	// setup has been cleaned up properly
    	defer func() {
    		if err != nil {
    			container.SetError(err)
    			// if no one else has set it, make sure we don't leave it at zero
    			if container.ExitCode() == 0 {
    				container.SetExitCode(128)
    			}
    			if err := container.CheckpointTo(daemon.containersReplica); err != nil {
    				logrus.Errorf("%s: failed saving state on start failure: %v", container.ID, err)
    			}
    			container.Reset(false)
    
    			daemon.Cleanup(container)
    			// if containers AutoRemove flag is set, remove it after clean up
    			if container.HostConfig.AutoRemove {
    				container.Unlock()
    				if err := daemon.ContainerRm(container.ID, &types.ContainerRmConfig{ForceRemove: true, RemoveVolume: true}); err != nil {
    					logrus.Errorf("can't remove container %s: %v", container.ID, err)
    				}
    				container.Lock()
    			}
    		}
    	}()
    
    	if err := daemon.conditionalMountOnStart(container); err != nil {
    		return err
    	}
    
    	if err := daemon.initializeNetworking(container); err != nil {
    		return err
    	}
    
    	spec, err := daemon.createSpec(container)
    	if err != nil {
    		return systemError{err}
    	}
    
    	createOptions, err := daemon.getLibcontainerdCreateOptions(container)
    	if err != nil {
    		return err
    	}
    
    	if resetRestartManager {
    		container.ResetRestartManager(true)
    	}
    
    	if checkpointDir == "" {
    		checkpointDir = container.CheckpointDir()
    	}
    
    	if daemon.saveApparmorConfig(container); err != nil {
    		return err
    	}
    
    	if err := daemon.containerd.Create(container.ID, checkpoint, checkpointDir, *spec, container.InitializeStdio, createOptions...); err != nil {
    		return translateContainerdStartErr(container.Path, container.SetExitCode, err)
    
    	}
    
    	containerActions.WithValues("start").UpdateSince(start)
    
    	return nil
    }

### **1.4、[daemon.containerd.Create()][daemon.containerd.Create]中的Create是在client 接口里面，client提供对容器功能的访问。**下面分析Create（）函数 ，[位置][Link 1]。 ###

func (clnt *client) Create(containerID string, checkpoint string, checkpointDir string, spec specs.Spec, attachStdio StdioCallback, options ...CreateOption) (err error) {
    	clnt.lock(containerID)
    	defer clnt.unlock(containerID)
    
    	if _, err := clnt.getContainer(containerID); err == nil {
    		return fmt.Errorf("Container %s is already active", containerID)
    	}
    
    	uid, gid, err := getRootIDs(spec)
    	if err != nil {
    		return err
    	}
    	dir, err := clnt.prepareBundleDir(uid, gid)
    	if err != nil {
    		return err
    	}
    	//生成一个libcontainerd.container对象
    	container := clnt.newContainer(filepath.Join(dir, containerID), options...)
    	if err := container.clean(); err != nil {
    		return err
    	}
    
    	defer func() {
    		if err != nil {
    			container.clean()
    			clnt.deleteContainer(containerID)
    		}
    	}()
    	//创建目录
    	if err := idtools.MkdirAllAndChown(container.dir, 0700, idtools.IDPair{uid, gid}); err != nil && !os.IsExist(err) {
    		return err
    	}
    	//生成文件config.json
    	f, err := os.Create(filepath.Join(container.dir, configFilename))
    	if err != nil {
    		return err
    	}
    	defer f.Close()
    	if err := json.NewEncoder(f).Encode(spec); err != nil {
    		return err
    	}
    	//调用container.start()进一步启动container
    	return container.start(&spec, checkpoint, checkpointDir, attachStdio)
    }

### **1.5、分析：[container.start()][container.start]。** ###

**该函数主要功能是发送CreateContainerRequest RPC请求给 docker-containerd。（不明白）**

func (ctr *container) start(spec *specs.Spec, checkpoint, checkpointDir string, attachStdio StdioCallback) (err error) {
    	ctx, cancel := context.WithCancel(context.Background())
    	defer cancel()
    	ready := make(chan struct{})
    
    	fifoCtx, cancel := context.WithCancel(context.Background())
    	defer func() {
    		if err != nil {
    			cancel()
    		}
    	}()
    
    	iopipe, err := ctr.openFifos(fifoCtx, spec.Process.Terminal)
    	if err != nil {
    		return err
    	}
    
    	var stdinOnce sync.Once
    
    	// we need to delay stdin closure after container start or else "stdin close"
    	// event will be rejected by containerd.
    	// stdin closure happens in attachStdio
    	stdin := iopipe.Stdin
    	iopipe.Stdin = ioutils.NewWriteCloserWrapper(stdin, func() error {
    		var err error
    		stdinOnce.Do(func() { // on error from attach we don't know if stdin was already closed
    			err = stdin.Close()
    			go func() {
    				select {
    				case <-ready:
    				case <-ctx.Done():
    				}
    				select {
    				case <-ready:
    					if err := ctr.sendCloseStdin(); err != nil {
    						logrus.Warnf("failed to close stdin: %+v", err)
    					}
    				default:
    				}
    			}()
    		})
    		return err
    	})
    	//CreateContainerRequest对象，应该是保存一些容器信息给libcontainer start时使用
    	r := &containerd.CreateContainerRequest{
    		Id:            ctr.containerID,
    		BundlePath:    ctr.dir,
    		Stdin:         ctr.fifo(unix.Stdin),
    		Stdout:        ctr.fifo(unix.Stdout),
    		Stderr:        ctr.fifo(unix.Stderr),
    		Checkpoint:    checkpoint,
    		CheckpointDir: checkpointDir,
    		// check to see if we are running in ramdisk to disable pivot root
    		NoPivotRoot: os.Getenv("DOCKER_RAMDISK") != "",
    		Runtime:     ctr.runtime,
    		RuntimeArgs: ctr.runtimeArgs,
    	}
    	ctr.client.appendContainer(ctr)
    
    	if err := attachStdio(*iopipe); err != nil {
    		ctr.closeFifos(iopipe)
    		return err
    	}
    	//发送CreateContainerRequest RPC请求给docker containerd（不懂）
    	resp, err := ctr.client.remote.apiClient.CreateContainer(context.Background(), r)
    	if err != nil {
    		ctr.closeFifos(iopipe)
    		return err
    	}
    	ctr.systemPid = systemPid(resp.Container)
    	close(ready)
    
    	return ctr.client.backend.StateChanged(ctr.containerID, StateInfo{
    		CommonStateInfo: CommonStateInfo{
    			State: StateStart,
    			Pid:   ctr.systemPid,
    		}})
    
    }

### **参考：** ###

** [https://guanjunjian.github.io/2017/09/28/study-5-docker-5-postContainersStart/][https_guanjunjian.github.io_2017_09_28_study-5-docker-5-postContainersStart]**

**       《Docker源码分析》**

**        百度网盘：链接: https://pan.baidu.com/s/1m5AqgfZKvPRu2BcmWz-WxA 提取码: wjrj**

[r.postContainersStart_]: https://github.com/docker/docker-ce/blob/17.09/components/engine/api/server/router/container/container_routes.go#L130
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2dvb3NlX2ZsZXNo_size_16_color_FFFFFF_t_70]: /images/20220418/54ed921d01154f0691362f858cf28302.png
[backend.ContainerStart]: https://github.com/docker/docker-ce/blob/17.09/components/engine/api/server/router/container/backend.go#L43:2
[ContainerStart]: https://github.com/docker/docker-ce/blob/17.09/components/engine/daemon/start.go#L15
[daemon.containerd.Create]: https://github.com/moby/moby/blob/HEAD/libcontainerd/types.go#L71:2
[Link 1]: https://github.com/docker/docker-ce/blob/17.09/components/engine/libcontainerd/client_unix.go#L45
[container.start]: https://github.com/docker/docker-ce/blob/17.09/components/engine/libcontainerd/container_unix.go#L89:23
[https_guanjunjian.github.io_2017_09_28_study-5-docker-5-postContainersStart]: https://guanjunjian.github.io/2017/09/28/study-5-docker-5-postContainersStart/