fix golint errors for pkg/kubelet/dockershim

Signed-off-by: zvier <zvier20@gmail.com>

pkg/kubelet/dockershim/docker_checkpoint.go

@@ -34,11 +34,13 @@ const (
 	schemaVersion        = "v1"
 )
 
-type DockershimCheckpoint interface {
+// ContainerCheckpoint provides the interface for process container's checkpoint data
+type ContainerCheckpoint interface {
 	checkpointmanager.Checkpoint
 	GetData() (string, string, string, []*PortMapping, bool)
 }
 
+// Protocol is the type of port mapping protocol
 type Protocol string
 
 // PortMapping is the port mapping configurations of a sandbox.
@@ -73,7 +75,8 @@ type PodSandboxCheckpoint struct {
 	Checksum checksum.Checksum `json:"checksum"`
 }
 
-func NewPodSandboxCheckpoint(namespace, name string, data *CheckpointData) DockershimCheckpoint {
+// NewPodSandboxCheckpoint inits a PodSandboxCheckpoint with the given args
+func NewPodSandboxCheckpoint(namespace, name string, data *CheckpointData) ContainerCheckpoint {
 	return &PodSandboxCheckpoint{
 		Version:   schemaVersion,
 		Namespace: namespace,
@@ -82,19 +85,24 @@ func NewPodSandboxCheckpoint(namespace, name string, data *CheckpointData) Docke
 	}
 }
 
+// MarshalCheckpoint encodes the PodSandboxCheckpoint instance to a json object
 func (cp *PodSandboxCheckpoint) MarshalCheckpoint() ([]byte, error) {
 	cp.Checksum = checksum.New(*cp.Data)
 	return json.Marshal(*cp)
 }
 
+// UnmarshalCheckpoint decodes the blob data to the PodSandboxCheckpoint instance
 func (cp *PodSandboxCheckpoint) UnmarshalCheckpoint(blob []byte) error {
 	return json.Unmarshal(blob, cp)
 }
 
+// VerifyChecksum verifies whether the PodSandboxCheckpoint's data checksum is
+// the same as calculated checksum
 func (cp *PodSandboxCheckpoint) VerifyChecksum() error {
 	return cp.Checksum.Verify(*cp.Data)
 }
 
+// GetData gets the PodSandboxCheckpoint's version and some net information
 func (cp *PodSandboxCheckpoint) GetData() (string, string, string, []*PortMapping, bool) {
 	return cp.Version, cp.Name, cp.Namespace, cp.Data.PortMappings, cp.Data.HostNetwork
 }