mount: add virtio-fs mount driver

Mounting a virtio-fs filesystem is similar to 9pfs.

Fixes: #440
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

device.go

@@ -25,6 +25,7 @@ import (
 
 const (
 	driver9pType        = "9p"
+	driverVirtioFSType  = "virtio-fs"
 	driverBlkType       = "blk"
 	driverMmioBlkType   = "mmioblk"
 	driverSCSIType      = "scsi"

mount.go

@@ -22,6 +22,7 @@ import (
 
 const (
 	type9pFs       = "9p"
+	typeVirtioFS   = "virtio_fs"
 	typeTmpFs      = "tmpfs"
 	devPrefix      = "/dev/"
 	timeoutHotplug = 3
@@ -98,7 +99,7 @@ func mount(source, destination, fsType string, flags int, options string) error
 
 	var err error
 	switch fsType {
-	case type9pFs:
+	case type9pFs, typeVirtioFS:
 		if err = createDestinationDir(destination); err != nil {
 			return err
 		}
@@ -191,6 +192,7 @@ type storageHandler func(storage pb.Storage, s *sandbox) (string, error)
 // storageHandlerList lists the supported drivers.
 var storageHandlerList = map[string]storageHandler{
 	driver9pType:        virtio9pStorageHandler,
+	driverVirtioFSType:  virtioFSStorageHandler,
 	driverBlkType:       virtioBlkStorageHandler,
 	driverMmioBlkType:   virtioMmioBlkStorageHandler,
 	driverSCSIType:      virtioSCSIStorageHandler,
@@ -223,6 +225,11 @@ func virtioMmioBlkStorageHandler(storage pb.Storage, s *sandbox) (string, error)
 	return commonStorageHandler(storage)
 }
 
+// virtioFSStorageHandler handles the storage for virtio-fs.
+func virtioFSStorageHandler(storage pb.Storage, s *sandbox) (string, error) {
+	return commonStorageHandler(storage)
+}
+
 // virtioBlkStorageHandler handles the storage for blk driver.
 func virtioBlkStorageHandler(storage pb.Storage, s *sandbox) (string, error) {
 	// Get the device node path based on the PCI address provided