device: add GetHostPath() to generic device

`GetHostPath()` method returns the device path in the host, this way the
runtime can get the device information for updating the sandbox's device
cgroup.

Signed-off-by: Julio Montes <julio.montes@intel.com>
Signed-off-by: Peng Tao <bergwolf@hyper.sh>

src/runtime/virtcontainers/device/api/interface.go

@@ -56,6 +56,9 @@ type Device interface {
 	// GetMajorMinor returns major and minor numbers
 	GetMajorMinor() (int64, int64)
 
+	// GetHostPath return the device path in the host
+	GetHostPath() string
+
 	// GetDeviceInfo returns device specific data used for hotplugging by hypervisor
 	// Caller could cast the return value to device specific struct
 	// e.g. Block device returns *config.BlockDrive,

src/runtime/virtcontainers/device/drivers/generic.go

@@ -68,6 +68,14 @@ func (device *GenericDevice) GetMajorMinor() (int64, int64) {
 	return device.DeviceInfo.Major, device.DeviceInfo.Minor
 }
 
+// GetHostPath return the device path in the host
+func (device *GenericDevice) GetHostPath() string {
+	if device.DeviceInfo != nil {
+		return device.DeviceInfo.HostPath
+	}
+	return ""
+}
+
 // Reference adds one reference to device
 func (device *GenericDevice) Reference() uint {
 	if device.RefCount != intMax {

src/runtime/virtcontainers/device/drivers/generic_test.go

@@ -8,6 +8,7 @@ package drivers
 import (
 	"testing"
 
+	"github.com/kata-containers/runtime/virtcontainers/device/config"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -42,3 +43,15 @@ func TestBumpAttachCount(t *testing.T) {
 		}
 	}
 }
+
+func TestGetHostPath(t *testing.T) {
+	assert := assert.New(t)
+	dev := &GenericDevice{}
+	assert.Empty(dev.GetHostPath())
+
+	expectedHostPath := "/dev/null"
+	dev.DeviceInfo = &config.DeviceInfo{
+		HostPath: expectedHostPath,
+	}
+	assert.Equal(expectedHostPath, dev.GetHostPath())
+}