virtcontainers: implement function to cold plug vsocks

`appendVSockPCI` function can be used to cold plug vocks, vhost file descriptor
holds the context ID and it's inherit by QEMU process, ID must be unique and
disable-modern prevents qemu from relying on fast MMIO.

Signed-off-by: Julio Montes <julio.montes@intel.com>

virtcontainers/qemu.go

@@ -62,6 +62,10 @@ type qemu struct {
 	state QemuState
 
 	arch qemuArch
+
+	// fds is a list of file descriptors inherited by QEMU process
+	// they'll be closed once QEMU process is running
+	fds []*os.File
 }
 
 const (
@@ -497,6 +501,14 @@ func (q *qemu) startSandbox() error {
 		q.Logger().WithField("default-kernel-parameters", formatted).Debug()
 	}
 
+	defer func() {
+		for _, fd := range q.fds {
+			if err := fd.Close(); err != nil {
+				q.Logger().WithError(err).Error("After launching Qemu")
+			}
+		}
+	}()
+
 	strErr, err := govmmQemu.LaunchQemu(q.qemuConfig, newQMPLogger())
 	if err != nil {
 		return fmt.Errorf("%s", strErr)
@@ -956,6 +968,9 @@ func (q *qemu) addDevice(devInfo interface{}, devType deviceType) error {
 		q.qemuConfig.Devices = q.arch.append9PVolume(q.qemuConfig.Devices, v)
 	case Socket:
 		q.qemuConfig.Devices = q.arch.appendSocket(q.qemuConfig.Devices, v)
+	case kataVSOCK:
+		q.fds = append(q.fds, v.vhostFd)
+		q.qemuConfig.Devices = q.arch.appendVSockPCI(q.qemuConfig.Devices, v)
 	case Endpoint:
 		q.qemuConfig.Devices = q.arch.appendNetwork(q.qemuConfig.Devices, v)
 	case deviceDrivers.Drive:

virtcontainers/qemu_arch_base.go

@@ -68,6 +68,9 @@ type qemuArch interface {
 	// appendSocket appends a socket to devices
 	appendSocket(devices []govmmQemu.Device, socket Socket) []govmmQemu.Device
 
+	// appendVSockPCI appends a vsock PCI to devices
+	appendVSockPCI(devices []govmmQemu.Device, vsock kataVSOCK) []govmmQemu.Device
+
 	// appendNetwork appends a endpoint device to devices
 	appendNetwork(devices []govmmQemu.Device, endpoint Endpoint) []govmmQemu.Device
 
@@ -389,6 +392,20 @@ func (q *qemuArchBase) appendSocket(devices []govmmQemu.Device, socket Socket) [
 	return devices
 }
 
+func (q *qemuArchBase) appendVSockPCI(devices []govmmQemu.Device, vsock kataVSOCK) []govmmQemu.Device {
+	devices = append(devices,
+		govmmQemu.VSOCKDevice{
+			ID:            fmt.Sprintf("vsock-%d", vsock.contextID),
+			ContextID:     vsock.contextID,
+			VHostFD:       vsock.vhostFd,
+			DisableModern: q.nestedRun,
+		},
+	)
+
+	return devices
+
+}
+
 func networkModelToQemuType(model NetInterworkingModel) govmmQemu.NetDeviceType {
 	switch model {
 	case NetXConnectBridgedModel:

virtcontainers/qemu_test.go

@@ -246,6 +246,28 @@ func TestQemuAddDeviceSerialPortDev(t *testing.T) {
 	testQemuAddDevice(t, socket, serialPortDev, expectedOut)
 }
 
+func TestQemuAddDeviceKataVSOCK(t *testing.T) {
+	contextID := uint32(3)
+	port := uint32(1024)
+	vHostFD := os.NewFile(1, "vsock")
+
+	expectedOut := []govmmQemu.Device{
+		govmmQemu.VSOCKDevice{
+			ID:        fmt.Sprintf("vsock-%d", contextID),
+			ContextID: contextID,
+			VHostFD:   vHostFD,
+		},
+	}
+
+	vsock := kataVSOCK{
+		contextID: contextID,
+		port:      port,
+		vhostFd:   vHostFD,
+	}
+
+	testQemuAddDevice(t, vsock, vSockPCIDev, expectedOut)
+}
+
 func TestQemuGetSandboxConsole(t *testing.T) {
 	q := &qemu{}
 	sandboxID := "testSandboxID"