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[原创]什么是runC？
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发表于: 2022-1-11 11:19
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容器运行时，Container runtime是指管理和运行容器的工具，当前的容器工具很多，比如docker，rkt等，但是如果每个容器工具都使用自己的运行时，那么就不利于容器灵雨的发展，因此，一些容器厂商就一起制定了容器镜像格式和容器运行时的标准，即Open Container Initiative(OCI)。
OCI Bundle是指满足OCI标准的一系列文件，这些文件包含了运行容器所需要的所有数据，它们存放在一个共同的目录，该目录包含以下两项：
这是runC主要的代码逻辑，其中libcontainer其实就是早期docker的一大基础，为了适应OCI格式进行了二次的封装。
以runc create 为例子，其对应的主要操作如下：
contianer对应的一些数据结构如下，这里创建了一个接口，里面包括了一个容器需要的所有的操作：
在linux平台上，对该接口进行了一些包裹，生成了linux 平台的一些专用接口：
还有一个重要的接口Factory:
其中也有对应Linux 平台的一个实现：
Linux Factory中的create的具体实现其实就是创建一个LinuxContainer（这正和我们之前所说的Linux下的container接口相对应）:
可以看到，首先加载配置config，然后使用loadFactory创建相关的LinuxFactory，最终调用了factory.Create(id, config)，然后由factory.Create(id, config)返回一个LinuxContainer。其中LoadFactory十分关键，他在最后调用了libcontainer.New()函数来返回LinuxContainer，在该New函数里面其设置了InitPath（InitPath非常重要）：
在LinuxFactory的Create过程中InitPath和InitArgs被传递给linuxContainer。在知道是如何创建出一个linuxContainer之后，我们把目光返回到startContainer，该函数最后生成了runner结构体，然后调用了其run方法，参数为spec.Process，这里的spec.Process其实就是当初config.json里面的进程信息。
在run方法中，一方面通过newProcess以config.json为模板创建了libcontainer.Process结构体，与进程相关的limt和Capabilities等设置都在此时完成，另一方面主要根据action做了三种操作：
Process结构体，其中大部分的内容都来自config.json文件：
start方法：
可以看到，start方法，主要是创建了一个fifo管道（这个管道主要用于阻塞，后面会用到），然后调用了start方法。
该方法第一步首先返回了一个initProcess结构体，这个结构体实现了 parentProcess接口，该结构体由linuxContainer的newInitProcess函数创建。
接口如下：
在整个的newParentProcess函数过程中，首先创了一对sock和一对pipe管道，然后用这一对sock中的childsock和childpipe创建了一个cmd模板，该模板中执行的命令正好就是之前的InitPath中设置的路径（"/proc/self/exe",和 "init"，这其实表示会执行runC本身，参数就是init），sock和pipe其实是为了实现cmd和父进程直接的数据通信，它们被放入到cmd.ExtraFiles中，同时相关的文件描述符被放入到环境变量里面，接下来是对进程是否是初始化进程进行判断，如果不是，则调用newSetnsProcess，来返回一个setnsProcess结构体，该结构体同样实现了parentProcess接口，newSetnsProcess主要是用来在已有容器中创建一个新的进程。
接下来执行includeExecFifo()方法，其就是打开之前创建的exec.fifo文件，并存入到cmd.ExtraFiles和环境变量中，最后调用最关键的函数newInitProcess来创建Init结构体：
在该函数中首先设置standard环境变量，然后从config.json里面读取需要新建的namespaces，并将这些数据进行存储，然后创建initProcess结构体，中间的shouldSendMountSources不用特别关心，它其实是为了挂载一些目录所设置的。到此为止，parentProcess结构体就基本设置完成了。
在start方法中接下来调用了parentProcess的start()函数，这里其实是initProcess结构体实现的start函数。在该start函数中会启动之前设置的/proc/self/exe进程，参数为init，然后给父进程设置了cgroup，之后通过sock把信息传输给子进程，这里最关键的其实是启动了runC init这样一个子进程，因为创建的容器可能具备新的namespaces，因此，通过子进程执行runC init的时候可以很方便的通过setns()完成命名空间的切换，同时setns其实是不运行在多线程条件下使用的，但是go runtime就是多线程的，因此必须在go runtime之前设置命名空间，因此使用cgo在go runtime启动之前使用c代码设置命名空间。
在cgo中，首先利用环境变量拿到了pipe（可以看到之前父进程在环境变量里面进程了设置），然后以netlink msg的格式读取父进程发送的config配置信息，接着同样执行了创建sock组的操作，这是为了使得它和孙进程之间可以相互通信，接着以状态机的形式用clone创建出符合config.json中设置的命名空间的进程，然后本来的子进程就exit(0)销毁。、
接着回到create中，在执行init进程之后对其进行了cgroup的限制，这也方便在接下来的过程中防止子进程通过cgroup进行逃逸，接着父进程发送bootstrapData数据到init进程，之后create拿到init创建的子进程的pid，然后通过pipe管拿到子进程打开的fd进行保存，在进行一系列的设置之后通过sendConfig发送config.json中的要执行的进程的信息，接下来就是容器初始化和执行config.json中设置的进程了，具体的过程可以参考standard_init_linux.go中linuxStandardInit的Init函数，到此为止一个容器的大致启动过程就基本分析结束了。
参考链接：
https://segmentfault.com/a/1190000017576314#item-1
https://github.com/opencontainers/runc
type BaseContainer interface {
// Returns the ID of the container
ID() string
// Returns the current status of the container.
Status() (Status, error)
// State returns the current container's state information.
State() (*State, error)
// OCIState returns the current container's state information.
OCIState() (*specs.State, error)
// Returns the current config of the container.
Config() configs.Config
// Returns the PIDs inside this container. The PIDs are in the namespace of the calling process.
//
// Some of the returned PIDs may no longer refer to processes in the Container, unless
// the Container state is PAUSED in which case every PID in the slice is valid.
Processes() ([]int, error)
// Returns statistics for the container.
Stats() (*Stats, error)
// Set resources of container as configured
//
// We can use this to change resources when containers are running.
//
Set(config configs.Config) error
// Start a process inside the container. Returns error if process fails to
// start. You can track process lifecycle with passed Process structure.
Start(process *Process) (err error)
// Run immediately starts the process inside the container. Returns error if process
// fails to start. It does not block waiting for the exec fifo after start returns but
// opens the fifo after start returns.
Run(process *Process) (err error)
// Destroys the container, if its in a valid state, after killing any
// remaining running processes.
//
// Any event registrations are removed before the container is destroyed.
// No error is returned if the container is already destroyed.
//
// Running containers must first be stopped using Signal(..).
// Paused containers must first be resumed using Resume(..).
Destroy() error
// Signal sends the provided signal code to the container's initial process.
//
// If all is specified the signal is sent to all processes in the container
// including the initial process.
Signal(s os.Signal, all bool) error
// Exec signals the container to exec the users process at the end of the init.
Exec() error
}type BaseContainer interface {
// Returns the ID of the container
ID() string
// Returns the current status of the container.
Status() (Status, error)
// State returns the current container's state information.
State() (*State, error)
// OCIState returns the current container's state information.
OCIState() (*specs.State, error)
// Returns the current config of the container.
Config() configs.Config
// Returns the PIDs inside this container. The PIDs are in the namespace of the calling process.
//
// Some of the returned PIDs may no longer refer to processes in the Container, unless
// the Container state is PAUSED in which case every PID in the slice is valid.
Processes() ([]int, error)
// Returns statistics for the container.
Stats() (*Stats, error)
// Set resources of container as configured
//
// We can use this to change resources when containers are running.
//
Set(config configs.Config) error
// Start a process inside the container. Returns error if process fails to
// start. You can track process lifecycle with passed Process structure.
Start(process *Process) (err error)
// Run immediately starts the process inside the container. Returns error if process
// fails to start. It does not block waiting for the exec fifo after start returns but
// opens the fifo after start returns.
Run(process *Process) (err error)
// Destroys the container, if its in a valid state, after killing any
// remaining running processes.
//
// Any event registrations are removed before the container is destroyed.
// No error is returned if the container is already destroyed.
//
// Running containers must first be stopped using Signal(..).
// Paused containers must first be resumed using Resume(..).
Destroy() error
// Signal sends the provided signal code to the container's initial process.
//
// If all is specified the signal is sent to all processes in the container
// including the initial process.
Signal(s os.Signal, all bool) error
// Exec signals the container to exec the users process at the end of the init.
Exec() error
}// Container is a libcontainer container object.
//
// Each container is thread-safe within the same process. Since a container can
// be destroyed by a separate process, any function may return that the container
// was not found.
type Container interface {
BaseContainer
// Methods below here are platform specific
// Checkpoint checkpoints the running container's state to disk using the criu(8) utility.
Checkpoint(criuOpts *CriuOpts) error
// Restore restores the checkpointed container to a running state using the criu(8) utility.
Restore(process *Process, criuOpts *CriuOpts) error
// If the Container state is RUNNING or CREATED, sets the Container state to PAUSING and pauses
// the execution of any user processes. Asynchronously, when the container finished being paused the
// state is changed to PAUSED.
// If the Container state is PAUSED, do nothing.
Pause() error
// If the Container state is PAUSED, resumes the execution of any user processes in the
// Container before setting the Container state to RUNNING.
// If the Container state is RUNNING, do nothing.
Resume() error
// NotifyOOM returns a read-only channel signaling when the container receives an OOM notification.
NotifyOOM() (<-chan struct{}, error)
// NotifyMemoryPressure returns a read-only channel signaling when the container reaches a given pressure level
NotifyMemoryPressure(level PressureLevel) (<-chan struct{}, error)
}// Container is a libcontainer container object.
//
// Each container is thread-safe within the same process. Since a container can
// be destroyed by a separate process, any function may return that the container
// was not found.
type Container interface {
BaseContainer
// Methods below here are platform specific
// Checkpoint checkpoints the running container's state to disk using the criu(8) utility.
Checkpoint(criuOpts *CriuOpts) error
// Restore restores the checkpointed container to a running state using the criu(8) utility.
Restore(process *Process, criuOpts *CriuOpts) error
// If the Container state is RUNNING or CREATED, sets the Container state to PAUSING and pauses
// the execution of any user processes. Asynchronously, when the container finished being paused the
// state is changed to PAUSED.
// If the Container state is PAUSED, do nothing.
Pause() error
// If the Container state is PAUSED, resumes the execution of any user processes in the
// Container before setting the Container state to RUNNING.
// If the Container state is RUNNING, do nothing.
Resume() error
// NotifyOOM returns a read-only channel signaling when the container receives an OOM notification.
NotifyOOM() (<-chan struct{}, error)
// NotifyMemoryPressure returns a read-only channel signaling when the container reaches a given pressure level
NotifyMemoryPressure(level PressureLevel) (<-chan struct{}, error)
}type Factory interface {
// Creates a new container with the given id and starts the initial process inside it.
// id must be a string containing only letters, digits and underscores and must contain
// between 1 and 1024 characters, inclusive.
//
// The id must not already be in use by an existing container. Containers created using
// a factory with the same path (and filesystem) must have distinct ids.
//
// Returns the new container with a running process.
//
// On error, any partially created container parts are cleaned up (the operation is atomic).
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.
StartInitialization() error
// Type returns info string about factory type (e.g. lxc, libcontainer...)
Type() string
}type Factory interface {
// Creates a new container with the given id and starts the initial process inside it.
// id must be a string containing only letters, digits and underscores and must contain
// between 1 and 1024 characters, inclusive.
//
// The id must not already be in use by an existing container. Containers created using
// a factory with the same path (and filesystem) must have distinct ids.
//
// Returns the new container with a running process.
//
// On error, any partially created container parts are cleaned up (the operation is atomic).
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.
StartInitialization() error
// Type returns info string about factory type (e.g. lxc, libcontainer...)
Type() string
}// LinuxFactory implements the default factory interface for linux based systems.
type LinuxFactory struct {
// Root directory for the factory to store state.
Root string
// InitPath is the path for calling the init responsibilities for spawning
// a container.
InitPath string
// InitArgs are arguments for calling the init responsibilities for spawning
// a container.
InitArgs []string
// CriuPath is the path to the criu binary used for checkpoint and restore of
// containers.
CriuPath string
// New{u,g}idmapPath is the path to the binaries used for mapping with
// rootless containers.
NewuidmapPath string
NewgidmapPath string
// Validator provides validation to container configurations.
Validator validate.Validator
// NewIntelRdtManager returns an initialized Intel RDT manager for a single container.
NewIntelRdtManager func(config *configs.Config, id string, path string) intelrdt.Manager
}// LinuxFactory implements the default factory interface for linux based systems.
type LinuxFactory struct {
// Root directory for the factory to store state.
Root string
// InitPath is the path for calling the init responsibilities for spawning
// a container.
InitPath string
// InitArgs are arguments for calling the init responsibilities for spawning
// a container.
InitArgs []string
// CriuPath is the path to the criu binary used for checkpoint and restore of
// containers.
CriuPath string
// New{u,g}idmapPath is the path to the binaries used for mapping with
// rootless containers.
NewuidmapPath string
NewgidmapPath string
// Validator provides validation to container configurations.
Validator validate.Validator
// NewIntelRdtManager returns an initialized Intel RDT manager for a single container.
NewIntelRdtManager func(config *configs.Config, id string, path string) intelrdt.Manager
}type linuxContainer struct {
id string
root string
config *configs.Config
cgroupManager cgroups.Manager
intelRdtManager intelrdt.Manager
initPath string
initArgs []string
initProcess parentProcess
initProcessStartTime uint64
criuPath string
newuidmapPath string
newgidmapPath string
m sync.Mutex
criuVersion int
state containerState
created time.Time
fifo *os.File
}type linuxContainer struct {
id string
root string
config *configs.Config
cgroupManager cgroups.Manager
intelRdtManager intelrdt.Manager
initPath string
initArgs []string
initProcess parentProcess
initProcessStartTime uint64
criuPath string
newuidmapPath string
newgidmapPath string
m sync.Mutex
criuVersion int
state containerState
created time.Time
fifo *os.File
}func createContainer(context *cli.Context, id string, spec *specs.Spec) (libcontainer.Container, error) {
rootlessCg, err := shouldUseRootlessCgroupManager(context)
if err != nil {
return nil, err
}
config, err := specconv.CreateLibcontainerConfig(&specconv.CreateOpts{
CgroupName: id,
UseSystemdCgroup: context.GlobalBool("systemd-cgroup"),
NoPivotRoot: context.Bool("no-pivot"),
NoNewKeyring: context.Bool("no-new-keyring"),
Spec: spec,
RootlessEUID: os.Geteuid() != 0,
RootlessCgroups: rootlessCg,
})
if err != nil {
return nil, err
}
factory, err := loadFactory(context)
if err != nil {
return nil, err
}
return factory.Create(id, config)
}func createContainer(context *cli.Context, id string, spec *specs.Spec) (libcontainer.Container, error) {
rootlessCg, err := shouldUseRootlessCgroupManager(context)
if err != nil {
return nil, err
}
config, err := specconv.CreateLibcontainerConfig(&specconv.CreateOpts{
CgroupName: id,
UseSystemdCgroup: context.GlobalBool("systemd-cgroup"),
NoPivotRoot: context.Bool("no-pivot"),
NoNewKeyring: context.Bool("no-new-keyring"),
Spec: spec,
RootlessEUID: os.Geteuid() != 0,
RootlessCgroups: rootlessCg,
})
if err != nil {
return nil, err
}
factory, err := loadFactory(context)
if err != nil {
return nil, err
}
return factory.Create(id, config)
}// 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, 0o700); err != nil {
return nil, err
}
}
l := &LinuxFactory{
Root: root,
InitPath: "/proc/self/exe",
InitArgs: []string{os.Args[0], "init"},
Validator: validate.New(),
CriuPath: "criu",
}
for _, opt := range options {
if opt == nil {
continue
}
if err := opt(l); err != nil {
return nil, err
}
}
return l, nil
}// 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, 0o700); err != nil {
return nil, err
}
}
l := &LinuxFactory{
Root: root,
InitPath: "/proc/self/exe",
InitArgs: []string{os.Args[0], "init"},
Validator: validate.New(),
CriuPath: "criu",
}
for _, opt := range options {
if opt == nil {
continue
}
if err := opt(l); err != nil {
return nil, err
}
}
return l, nil
}switch r.action {case CT_ACT_CREATE: err = r.container.Start(process)
case CT_ACT_RESTORE: err = r.container.Restore(process, r.criuOpts)
case CT_ACT_RUN: err = r.container.Run(process)
default: panic("Unknown action")
}switch r.action {case CT_ACT_CREATE: err = r.container.Start(process)
case CT_ACT_RESTORE: err = r.container.Restore(process, r.criuOpts)
case CT_ACT_RUN: err = r.container.Run(process)
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