change the user of the Process to a reference

The type of `user` becomes `string` instead of platform aware
structure, so the Spec becomes a platform-independent structure.

It makes we can parse the config.json as a Spec before knowing
the os, and allows we move the linux related *.go to linux/.

Signed-off-by: Lai Jiangshan <[email protected]>

Author: laijs

config.go

@@ -21,8 +21,8 @@ type Spec struct {
 type Process struct {
 	// Terminal creates an interactive terminal for the container.
 	Terminal bool `json:"terminal"`
-	// User specifies user information for the process.
-	User User `json:"user"`
+	// User is a unique descriptive identifier which refers to the User in the runtime.json which specifies user information for the process.
+	User string `json:"user"`
 	// Args specifies the binary and arguments for the application to execute.
 	Args []string `json:"args"`
 	// Env populates the process environment for the process.

config_linux.go

@@ -15,11 +15,15 @@ type Linux struct {
 	Capabilities []string `json:"capabilities"`
 	// RootfsPropagation is the rootfs mount propagation mode for the container.
 	RootfsPropagation string `json:"rootfsPropagation"`
+	// Users is the search table for the User for the Process
+	Users []User `json:"users"`
 }
 
 // User specifies linux specific user and group information for the container's
-// main process.
+// main process or the other later entry processes.
 type User struct {
+	// Name is identifier referenced from the Process
+	Name string `json:"name"`
 	// UID is the user id.
 	UID int32 `json:"uid"`
 	// GID is the group id.