channel: Check for channel type in kernel cmdline options

agent.go

@@ -156,6 +156,22 @@ var collatedTrace = false
 // if true, coredump when an internal error occurs or a fatal signal is received
 var crashOnError = false
 
+// commType is used to denote the communication channel type used.
+type commType int
+
+const (
+	// virtio-serial channel
+	serialCh commType = iota
+
+	// vsock channel
+	vsockCh
+
+	// channel type not passed explicitly
+	unknownCh
+)
+
+var commCh = unknownCh
+
 // This is the list of file descriptors we can properly close after the process
 // has been started. When the new process is exec(), those file descriptors are
 // duplicated and it is our responsibility to close them since we have opened

channel.go

@@ -50,24 +50,29 @@ func newChannel(ctx context.Context) (channel, error) {
 	defer span.Finish()
 
 	var serialErr error
-	var serialPath string
 	var vsockErr error
-	var vSockSupported bool
+	var ch channel
 
 	for i := 0; i < channelExistMaxTries; i++ {
-		// check vsock path
-		if _, err := os.Stat(vSockDevPath); err == nil {
-			if vSockSupported, vsockErr = isAFVSockSupportedFunc(); vSockSupported && vsockErr == nil {
-				span.SetTag("channel-type", "vsock")
-				return &vSockChannel{}, nil
+		switch commCh {
+		case serialCh:
+			if ch, serialErr = checkForSerialChannel(ctx); serialErr == nil && ch.(*serialChannel) != nil {
+				return ch, nil
+			}
+		case vsockCh:
+			if ch, vsockErr = checkForVsockChannel(ctx); vsockErr == nil && ch.(*vSockChannel) != nil {
+				return ch, nil
 			}
-		}
 
-		// Check serial port path
-		if serialPath, serialErr = findVirtualSerialPath(serialChannelName); serialErr == nil {
-			span.SetTag("channel-type", "serial")
-			span.SetTag("serial-path", serialPath)
-			return &serialChannel{serialPath: serialPath}, nil
+		case unknownCh:
+			// If we have not been explicitly passed if vsock is used or not, maybe due to
+			// an older runtime, try to check for vsock support.
+			if ch, vsockErr = checkForVsockChannel(ctx); vsockErr == nil && ch.(*vSockChannel) != nil {
+				return ch, nil
+			}
+			if ch, serialErr = checkForSerialChannel(ctx); serialErr == nil && ch.(*serialChannel) != nil {
+				return ch, nil
+			}
 		}
 
 		time.Sleep(channelExistWaitTime)
@@ -84,6 +89,41 @@ func newChannel(ctx context.Context) (channel, error) {
 	return nil, fmt.Errorf("Neither vsocks nor serial ports were found")
 }
 
+func checkForSerialChannel(ctx context.Context) (*serialChannel, error) {
+	span, _ := trace(ctx, "channel", "checkForSerialChannel")
+	defer span.Finish()
+
+	// Check serial port path
+	serialPath, serialErr := findVirtualSerialPath(serialChannelName)
+	if serialErr == nil {
+		span.SetTag("channel-type", "serial")
+		span.SetTag("serial-path", serialPath)
+		agentLog.Debug("Serial channel type detected")
+		return &serialChannel{serialPath: serialPath}, nil
+	}
+
+	return nil, serialErr
+}
+
+func checkForVsockChannel(ctx context.Context) (*vSockChannel, error) {
+	span, _ := trace(ctx, "channel", "checkForVsockChannel")
+	defer span.Finish()
+
+	// check vsock path
+	if _, err := os.Stat(vSockDevPath); err != nil {
+		return nil, err
+	}
+
+	vSockSupported, vsockErr := isAFVSockSupportedFunc()
+	if vSockSupported && vsockErr == nil {
+		span.SetTag("channel-type", "vsock")
+		agentLog.Debug("Vsock channel type detected")
+		return &vSockChannel{}, nil
+	}
+
+	return nil, fmt.Errorf("Vsock not found : %s", vsockErr)
+}
+
 type vSockChannel struct {
 }
 
@@ -228,23 +268,51 @@ func (c *serialChannel) teardown() error {
 	return c.serialConn.Close()
 }
 
+// isAFVSockSupported checks if vsock channel is used by the runtime
+// by checking for devices under the vhost-vsock driver path.
+// It returns true if a device is found for the vhost-vsock driver.
 func isAFVSockSupported() (bool, error) {
-	fd, err := unix.Socket(unix.AF_VSOCK, unix.SOCK_STREAM, 0)
-	if err != nil {
-		// This case is valid. It means AF_VSOCK is not a supported
-		// domain on this system.
-		if err == unix.EAFNOSUPPORT {
-			return false, nil
-		}
+	// Driver path for virtio-vsock
+	sysVsockPath := "/sys/bus/virtio/drivers/vmw_vsock_virtio_transport/"
+
+	files, err := ioutil.ReadDir(sysVsockPath)
 
+	// This should not happen for a hypervisor with vsock driver
+	if err != nil {
 		return false, err
 	}
 
-	if err := unix.Close(fd); err != nil {
-		return true, err
+	// standard driver files that should be ignored
+	driverFiles := []string{"bind", "uevent", "unbind"}
+
+	for _, file := range files {
+		for _, f := range driverFiles {
+			if file.Name() == f {
+				continue
+			}
+		}
+
+		fPath := filepath.Join(sysVsockPath, file.Name())
+		fInfo, err := os.Lstat(fPath)
+		if err != nil {
+			return false, err
+		}
+
+		if fInfo.Mode()&os.ModeSymlink == 0 {
+			continue
+		}
+
+		link, err := os.Readlink(fPath)
+		if err != nil {
+			return false, err
+		}
+
+		if strings.Contains(link, "devices") {
+			return true, nil
+		}
 	}
 
-	return true, nil
+	return false, nil
 }
 
 func findVirtualSerialPath(serialName string) (string, error) {

config.go

@@ -8,6 +8,7 @@ package main
 
 import (
 	"io/ioutil"
+	"strconv"
 	"strings"
 
 	"github.com/sirupsen/logrus"
@@ -20,6 +21,7 @@ const (
 	logLevelFlag       = optionPrefix + "log"
 	devModeFlag        = optionPrefix + "devmode"
 	traceModeFlag      = optionPrefix + "trace"
+	useVsockFlag       = optionPrefix + "use_vsock"
 	kernelCmdlineFile  = "/proc/cmdline"
 	traceValueIsolated = "isolated"
 	traceValueCollated = "collated"
@@ -102,6 +104,18 @@ func (c *agentConfig) parseCmdlineOption(option string) error {
 		case traceValueCollated:
 			enableTracing(true)
 		}
+	case useVsockFlag:
+		flag, err := strconv.ParseBool(split[valuePosition])
+		if err != nil {
+			return err
+		}
+		if flag {
+			agentLog.Debug("Param passed to use vsock channel")
+			commCh = vsockCh
+		} else {
+			agentLog.Debug("Param passed to NOT use vsock channel")
+			commCh = serialCh
+		}
 	default:
 		if strings.HasPrefix(split[optionPosition], optionPrefix) {
 			return grpcStatus.Errorf(codes.NotFound, "Unknown option %s", split[optionPosition])

config_test.go

@@ -285,3 +285,46 @@ func TestEnableTracing(t *testing.T) {
 		}
 	}
 }
+
+func TestParseCmdlineOptionWrongOptionVsock(t *testing.T) {
+	t.Skip()
+	assert := assert.New(t)
+
+	a := &agentConfig{}
+
+	wrongOption := "use_vsockkk=true"
+
+	err := a.parseCmdlineOption(wrongOption)
+	assert.Errorf(err, "Parsing should fail because wrong option %q", wrongOption)
+}
+
+func TestParseCmdlineOptionsVsock(t *testing.T) {
+	assert := assert.New(t)
+
+	a := &agentConfig{}
+
+	type testData struct {
+		val            string
+		shouldErr      bool
+		expectedCommCh commType
+	}
+
+	data := []testData{
+		{"true", false, vsockCh},
+		{"false", false, serialCh},
+		{"blah", true, unknownCh},
+	}
+
+	for _, d := range data {
+		commCh = unknownCh
+		option := useVsockFlag + "=" + d.val
+
+		err := a.parseCmdlineOption(option)
+		if d.shouldErr {
+			assert.Error(err)
+		} else {
+			assert.NoError(err)
+		}
+		assert.Equal(commCh, d.expectedCommCh)
+	}
+}