var DefaultSysSpec = SysSpec{
	OS: "Linux",
	KernelSpec: KernelSpec{
		Versions: []string{`3\.[1-9][0-9].*`, `4\..*`},

		Required: []KernelConfig{
			{Name: "NAMESPACES"},
			{Name: "NET_NS"},
			{Name: "PID_NS"},
			{Name: "IPC_NS"},
			{Name: "UTS_NS"},
			{Name: "CGROUPS"},
			{Name: "CGROUP_CPUACCT"},
			{Name: "CGROUP_DEVICE"},
			{Name: "CGROUP_FREEZER"},
			{Name: "CGROUP_SCHED"},
			{Name: "CPUSETS"},
			{Name: "MEMCG"},
			{Name: "INET"},
			{Name: "EXT4_FS"},
			{Name: "PROC_FS"},
			{Name: "NETFILTER_XT_TARGET_REDIRECT", Aliases: []string{"IP_NF_TARGET_REDIRECT"}},
			{Name: "NETFILTER_XT_MATCH_COMMENT"},
		},
		Optional: []KernelConfig{
			{Name: "OVERLAY_FS", Aliases: []string{"OVERLAYFS_FS"}, Description: "Required for overlayfs."},
			{Name: "AUFS_FS", Description: "Required for aufs."},
			{Name: "BLK_DEV_DM", Description: "Required for devicemapper."},
		},
		Forbidden: []KernelConfig{},
	},
	Cgroups: []string{"cpu", "cpuacct", "cpuset", "devices", "freezer", "memory"},
	RuntimeSpec: RuntimeSpec{
		DockerSpec: &DockerSpec{
			Version: []string{`1\.(9|\d{2,})\..*`},

			GraphDriver: []string{"aufs", "overlay", "devicemapper"},
		},
	},
}

type CgroupsValidator struct{}

type DockerSpec struct {
	// Version is a group of regex matching supported docker versions.
	Version []string
	// GraphDriver is the graph drivers supported by kubelet.
	GraphDriver []string
}

type DockerValidator struct{}

type KernelConfig struct {
	// Name is the general name of the kernel configuration. It is used to
	// match kernel configuration.
	Name string
	// Aliases are aliases of the kernel configuration. Some configuration
	// has different names in different kernel version. Names of different
	// versions will be treated as aliases.
	Aliases []string
	// Description is the description of the kernel configuration, for example:
	//  * What is it used for?
	//  * Why is it needed?
	//  * Who needs it?
	Description string
}

type KernelSpec struct {
	// Versions define supported kernel version. It is a group of regexps.
	Versions []string
	// Required contains all kernel configurations required to be enabled
	// (built in or as module).
	Required []KernelConfig
	// Optional contains all kernel configurations are required for optional
	// features.
	Optional []KernelConfig
	// Forbidden contains all kernel configurations which areforbidden (disabled
	// or not set)
	Forbidden []KernelConfig
}

type KernelValidator struct {
	// contains filtered or unexported fields
}

type OSValidator struct{}

type RuntimeSpec struct {
	*DockerSpec
}

type SysSpec struct {
	// OS is the operating system of the SysSpec.
	OS string
	// KernelConfig defines the spec for kernel.
	KernelSpec KernelSpec
	// Cgroups is the required cgroups.
	Cgroups []string
	// RuntimeSpec defines the spec for runtime.
	RuntimeSpec RuntimeSpec
}

type Validator interface {
	// Name is the name of the validator.
	Name() string
	// Validate is the validate function.
	Validate(SysSpec) error
}