Replace config.Privatefs with config.RootPropagation

Right now config.Privatefs is a boolean which determines if / is applied
with propagation flag syscall.MS_PRIVATE | syscall.MS_REC or not.

Soon we want to represent other propagation states like private, [r]slave,
and [r]shared. So either we can introduce more boolean variable or keep
track of propagation flags in an integer variable. Keeping an integer
variable is more versatile and can allow various kind of propagation flags
to be specified. So replace Privatefs with RootPropagation which is an
integer.

Note, this will require changes in docker. Instead of setting Privatefs
to true, they will need to set.

config.RootPropagation = syscall.MS_PRIVATE | syscall.MS_REC
 
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

libcontainer/configs/config.go

@@ -92,8 +92,8 @@ type Config struct {
 	// bind mounts are writtable.
 	Readonlyfs bool `json:"readonlyfs"`
 
-	// Privatefs will mount the container's rootfs as private where mount points from the parent will not propogate
-	Privatefs bool `json:"privatefs"`
+	// Specifies the mount propagation flags to be applied to /.
+	RootPropagation int `json:"rootPropagation"`
 
 	// Mounts specify additional source and destination paths that will be mounted inside the container's
 	// rootfs and mount namespace if specified

libcontainer/rootfs_linux.go

@@ -422,8 +422,8 @@ func mknodDevice(dest string, node *configs.Device) error {
 
 func prepareRoot(config *configs.Config) error {
 	flag := syscall.MS_SLAVE | syscall.MS_REC
-	if config.Privatefs {
-		flag = syscall.MS_PRIVATE | syscall.MS_REC
+	if config.RootPropagation != 0 {
+		flag = config.RootPropagation
 	}
 	if err := syscall.Mount("", "/", "", uintptr(flag), ""); err != nil {
 		return err

spec.go

@@ -329,11 +329,11 @@ func createLibcontainerConfig(cgroupName string, spec *specs.LinuxSpec, rspec *s
 		rootfsPath = filepath.Join(cwd, rootfsPath)
 	}
 	config := &configs.Config{
-		Rootfs:       rootfsPath,
-		Capabilities: spec.Linux.Capabilities,
-		Readonlyfs:   spec.Root.Readonly,
-		Hostname:     spec.Hostname,
-		Privatefs:    true,
+		Rootfs:          rootfsPath,
+		Capabilities:    spec.Linux.Capabilities,
+		Readonlyfs:      spec.Root.Readonly,
+		Hostname:        spec.Hostname,
+		RootPropagation: syscall.MS_PRIVATE | syscall.MS_REC,
 	}
 	for _, ns := range rspec.Linux.Namespaces {
 		t, exists := namespaceMapping[ns.Type]