runc 的一段代码

github 源码

// CreateCgroupPath creates cgroupv2 path, enabling all the supported controllers.
func CreateCgroupPath(path string, c *configs.Cgroup) (Err error) {
	if !strings.HasPrefix(path, UnifiedMountpoint) {
		return fmt.Errorf("invalid cgroup path %s", path)
	}

	content, err := supportedControllers()
	if err != nil {
		return err
	}

	const (
		cgTypeFile  = "cgroup.type"
		cgStCtlFile = "cgroup.subtree_control"
	)
	ctrs := strings.Fields(content)
	res := "+" + strings.Join(ctrs, " +")

	elements := strings.Split(path, "/")
	elements = elements[3:]
	current := "/sys/fs"
	for i, e := range elements {
		current = filepath.Join(current, e)
		if i > 0 {
			if err := os.Mkdir(current, 0o755); err != nil {
				if !os.IsExist(err) {
					return err
				}
			} else {
				// If the directory was created, be sure it is not left around on errors.
				current := current
				defer func() {
					if Err != nil {
						os.Remove(current)
					}
				}()
			}
			cgType, _ := cgroups.ReadFile(current, cgTypeFile)
			cgType = strings.TrimSpace(cgType)
			switch cgType {
			// If the cgroup is in an invalid mode (usually this means there's an internal
			// process in the cgroup tree, because we created a cgroup under an
			// already-populated-by-other-processes cgroup), then we have to error out if
			// the user requested controllers which are not thread-aware. However, if all
			// the controllers requested are thread-aware we can simply put the cgroup into
			// threaded mode.
			case "domain invalid":
				if containsDomainController(c.Resources) {
					return fmt.Errorf("cannot enter cgroupv2 %q with domain controllers -- it is in an invalid state", current)
				} else {
					// Not entirely correct (in theory we'd always want to be a domain --
					// since that means we're a properly delegated cgroup subtree) but in
					// this case there's not much we can do and it's better than giving an
					// error.
					_ = cgroups.WriteFile(current, cgTypeFile, "threaded")
				}
			// If the cgroup is in (threaded) or (domain threaded) mode, we can only use thread-aware controllers
			// (and you cannot usually take a cgroup out of threaded mode).
			case "domain threaded":
				fallthrough
			case "threaded":
				if containsDomainController(c.Resources) {
					return fmt.Errorf("cannot enter cgroupv2 %q with domain controllers -- it is in %s mode", current, cgType)
				}
			}
		}
		// enable all supported controllers
		if i < len(elements)-1 {
			if err := cgroups.WriteFile(current, cgStCtlFile, res); err != nil {
				// try write one by one
				allCtrs := strings.Split(res, " ")
				for _, ctr := range allCtrs {
					_ = cgroups.WriteFile(current, cgStCtlFile, ctr)
				}
			}
			// Some controllers might not be enabled when rootless or containerized,
			// but we don't catch the error here. (Caught in setXXX() functions.)
		}
	}

	return nil
}

switch​中代码一些要点记录

fallthrough​关键字是干嘛的

一句话：执行下一个 case​中的语句，并且不执行 case 中的检测。如果没有其他逻辑代码在当前 case​执行，应该直接合并两个 case​.

*要点*：

1. golang `case`​块默认有一个`break`​语句，一般代码里也是直接不写的，也就是执行完之后会跳出`switch`​。区别与其他的一些语言，所以有了 `fallthrough`​。

2. 执行到下一个`case`​是**不进行条件检查**的。

3. 因为要执行到下一个`case`​，所以不能出现在最后一个`case`​块。

cgroup.type​是什么

文档地址

​cgroup​的两种类型

1. ​domain​

   一个 cgroup 组创建出来，默认是 domain​类型的。进程的所有线程属于一个 cgroup​，并对资源进行管理。

2. ​threaded​

   ​echo threaded > cgroup.type​ ，转换成 thraeded​类型操作是单向的。

   ​thread​类型用于管理进程的不同线程。

   1. 父节点必须是 （thread）domain ​或者 thread​类型的
   2. 如果父节点是 non threaded​类型，不能开启 domain​类型的 controllers​. root​节点除外。

3. ​thread domain​

   一组 threaded subtree​的根节点。

   ​A(thread domain) -> B(threaded) ->C(threaded)​。 当 cgroup​子树变成 thread​类型的时候，父节点就会被更改为 domain thread​。

4. ​domain invalid​

   不能 populate​以及不能开启 controllers​的状态。

​populated​

每一个非根节点的 cgroup​都有一个 cgroup.event​文件。其中记录着 populated​字段。标识 当前 cgroup 的 sub-hierarchy​有没有活动的进程（0 没有 ；1 有）。

cat cgroup.events 

populated 0
frozen 0

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