Adding VHD library with simple function, updating mksyscall

Adds the basic structs for VHD function calls and includes one simple wrapper for VHDX creation.
This includes the updated version of mksyscall_windows.go, which previously assumed any api that doesn't end in "W" must not be unicode, and encodes the strings incorrectly. This hard-codes for unicode support and generates the syscalls from there.

vhd/vhd.go

@@ -0,0 +1,82 @@
+// +build windows
+
+package vhd
+
+import "syscall"
+
+//go:generate go run mksyscall_windows.go -output zvhd.go vhd.go
+
+//sys createVirtualDisk(virtualStorageType *virtualStorageType, path string, virtualDiskAccessMask uint32, securityDescriptor *uintptr, flags uint32, providerSpecificFlags uint32, parameters *createVirtualDiskParameters, o *syscall.Overlapped, handle *syscall.Handle) (err error) [failretval != 0] = VirtDisk.CreateVirtualDisk
+
+type virtualStorageType struct {
+	DeviceID uint32
+	VendorID [16]byte
+}
+
+const virtualDiskAccessNONE uint32 = 0
+const virtualDiskAccessATTACHRO uint32 = 65536
+const virtualDiskAccessATTACHRW uint32 = 131072
+const virtualDiskAccessDETACH uint32 = 262144
+const virtualDiskAccessGETINFO uint32 = 524288
+const virtualDiskAccessCREATE uint32 = 1048576
+const virtualDiskAccessMETAOPS uint32 = 2097152
+const virtualDiskAccessREAD uint32 = 851968
+const virtualDiskAccessALL uint32 = 4128768
+const virtualDiskAccessWRITABLE uint32 = 3276800
+
+const createVirtualDiskFlagNone uint32 = 0
+const createVirtualDiskFlagFullPhysicalAllocation uint32 = 1
+const createVirtualDiskFlagPreventWritesToSourceDisk uint32 = 2
+const createVirtualDiskFlagDoNotCopyMetadataFromParent uint32 = 4
+
+type version2 struct {
+	UniqueID                 [16]byte // GUID
+	MaximumSize              uint64
+	BlockSizeInBytes         uint32
+	SectorSizeInBytes        uint32
+	ParentPath               *uint16 // string
+	SourcePath               *uint16 // string
+	OpenFlags                uint32
+	ParentVirtualStorageType virtualStorageType
+	SourceVirtualStorageType virtualStorageType
+	ResiliencyGUID           [16]byte // GUID
+}
+
+type createVirtualDiskParameters struct {
+	Version  uint32 // Must always be set to 2
+	Version2 version2
+}
+
+// CreateVhdx will create a simple vhdx file at the given path using default values.
+func CreateVhdx(path string, maxSizeInGb, blockSizeInMb uint32) error {
+	var defaultType virtualStorageType
+
+	parameters := createVirtualDiskParameters{
+		Version: 2,
+		Version2: version2{
+			MaximumSize:      uint64(maxSizeInGb) * 1024 * 1024 * 1024,
+			BlockSizeInBytes: blockSizeInMb * 1024 * 1024,
+		},
+	}
+
+	var handle syscall.Handle
+
+	if err := createVirtualDisk(
+		&defaultType,
+		path,
+		virtualDiskAccessNONE,
+		nil,
+		createVirtualDiskFlagNone,
+		0,
+		&parameters,
+		nil,
+		&handle); err != nil {
+		return err
+	}
+
+	if err := syscall.CloseHandle(handle); err != nil {
+		return err
+	}
+
+	return nil
+}