virtcontainers: introducing HybridVSock type

This new socket type is currently supported only by the firecracker hypervisor.
For more details about its internal implementation see:
https://github.com/firecracker-microvm/firecracker/blob/master/docs/vsock.md

Signed-off-by: Julio Montes <[email protected]>

virtcontainers/hypervisor.go

@@ -104,6 +104,10 @@ const (
 
 	// memoryDevice is memory device type
 	memoryDev
+
+	// hybridVirtioVsockDev is a hybrid virtio-vsock device supported
+	// only on certain hypervisors, like firecracker.
+	hybridVirtioVsockDev
 )
 
 type memoryDevice struct {

virtcontainers/kata_agent.go

@@ -342,6 +342,8 @@ func (k *kataAgent) agentURL() (string, error) {
 		return s.HostPath, nil
 	case kataVSOCK:
 		return s.String(), nil
+	case types.HybridVSock:
+		return s.String(), nil
 	default:
 		return "", fmt.Errorf("Invalid socket type")
 	}
@@ -398,6 +400,11 @@ func (k *kataAgent) configure(h hypervisor, id, sharePath string, builtin bool,
 			return err
 		}
 		k.vmSocket = s
+	case types.HybridVSock:
+		err = h.addDevice(s, hybridVirtioVsockDev)
+		if err != nil {
+			return err
+		}
 	default:
 		return vcTypes.ErrInvalidConfigType
 	}

virtcontainers/types/sandbox.go

@@ -29,6 +29,8 @@ const (
 	StateStopped StateString = "stopped"
 )
 
+const HybridVSockScheme = "hvsock"
+
 // SandboxState is a sandbox state structure
 type SandboxState struct {
 	State StateString `json:"state"`
@@ -161,6 +163,21 @@ func (v *Volumes) String() string {
 	return strings.Join(volSlice, " ")
 }
 
+// HybridVSock defines a hybrid vsocket to communicate between
+// the host and any process inside the VM.
+// This is a virtio-vsock implementation based on AF_VSOCK on the
+// guest side and multiple AF_UNIX sockets on the host side.
+// This kind of socket is not supported in all hypervisors.
+// Firecracker supports it.
+type HybridVSock struct {
+	UdsPath string
+	Port    uint32
+}
+
+func (s *HybridVSock) String() string {
+	return fmt.Sprintf("%s://%s:%d", HybridVSockScheme, s.UdsPath, s.Port)
+}
+
 // Socket defines a socket to communicate between
 // the host and any process inside the VM.
 type Socket struct {