gpu: add log messages for not found cards

Let a user know the plugin can't find any Intel GPU if that's
the case. It might be cumbersome to realize that the plugin runs
on a host which doesn't have any Intel GPUs.

Also make the code less nested for better readability.

cmd/gpu_plugin/gpu_plugin.go

@@ -85,15 +85,23 @@ func (dp *devicePlugin) scan() (dpapi.DeviceTree, error) {
 
 	devTree := dpapi.NewDeviceTree()
 	for _, f := range files {
-		if dp.gpuDeviceReg.MatchString(f.Name()) {
+		var nodes []pluginapi.DeviceSpec
+
+		if !dp.gpuDeviceReg.MatchString(f.Name()) {
+			debug.Print("Not compatible device", f.Name())
+			continue
+		}
+
 		dat, err := ioutil.ReadFile(path.Join(dp.sysfsDir, f.Name(), "device/vendor"))
 		if err != nil {
 			fmt.Println("WARNING: Skipping. Can't read vendor file: ", err)
 			continue
 		}
 
-			if strings.TrimSpace(string(dat)) == vendorString {
-				var nodes []pluginapi.DeviceSpec
+		if strings.TrimSpace(string(dat)) != vendorString {
+			debug.Print("Non-Intel GPU", f.Name())
+			continue
+		}
 
 		drmFiles, err := ioutil.ReadDir(path.Join(dp.sysfsDir, f.Name(), "device/drm"))
 		if err != nil {
@@ -130,8 +138,6 @@ func (dp *devicePlugin) scan() (dpapi.DeviceTree, error) {
 			}
 		}
 	}
-		}
-	}
 
 	return devTree, nil
 }

cmd/gpu_plugin/gpu_plugin_test.go

@@ -79,6 +79,20 @@ func TestScan(t *testing.T) {
 			expectedDevs: 1,
 			expectedErr:  false,
 		},
+		{
+			sysfsdirs: []string{"card0/device/drm/card0"},
+			sysfsfiles: map[string][]byte{
+				"card0/device/vendor": []byte("0xbeef"),
+			},
+			devfsdirs:    []string{"card0"},
+			expectedDevs: 0,
+			expectedErr:  false,
+		},
+		{
+			sysfsdirs:    []string{"non_gpu_card"},
+			expectedDevs: 0,
+			expectedErr:  false,
+		},
 	}
 
 	testPlugin := newDevicePlugin(sysfs, devfs, 1)