Fix hostname env.

Signed-off-by: Lantao Liu <lantaol@google.com>

pkg/os/os.go

@@ -43,6 +43,7 @@ type OS interface {
 	Mount(source string, target string, fstype string, flags uintptr, data string) error
 	Unmount(target string) error
 	LookupMount(path string) (mount.Info, error)
+	Hostname() (string, error)
 }
 
 // RealOS is used to dispatch the real system level operations.
@@ -134,3 +135,8 @@ func Unmount(target string) error {
 
 	return err
 }
+
+// Hostname will call os.Hostname to get the hostname of the host.
+func (RealOS) Hostname() (string, error) {
+	return os.Hostname()
+}

pkg/os/testing/fake_os.go

@@ -51,6 +51,7 @@ type FakeOS struct {
 	MountFn                func(source string, target string, fstype string, flags uintptr, data string) error
 	UnmountFn              func(target string) error
 	LookupMountFn          func(path string) (containerdmount.Info, error)
+	HostnameFn             func() (string, error)
 	calls                  []CalledDetail
 	errors                 map[string]error
 }
@@ -254,3 +255,16 @@ func (f *FakeOS) LookupMount(path string) (containerdmount.Info, error) {
 	}
 	return containerdmount.Info{}, nil
 }
+
+// Hostname is a fake call that invokes HostnameFn or just return nil.
+func (f *FakeOS) Hostname() (string, error) {
+	f.appendCalls("Hostname")
+	if err := f.getError("Hostname"); err != nil {
+		return "", err
+	}
+
+	if f.HostnameFn != nil {
+		return f.HostnameFn()
+	}
+	return "", nil
+}