wclayer: Work around Windows bug when expanding sandbox size

This change works around a bug in Windows where a sandbox VHDX that has
been resized cannot be successfully mounted. This is due to a failure in
the path that resizes the NTFS volume inside the VHDX during the sandbox
mount process. To work around this, manually expand the volume in the
wclayer package just after making the call to expand the VHDX.

This change hurts the performance of the resize operation on affected
Windows hosts (19H1 and prerelease versions of Vb) and should be
reverted once the Windows bug has been fixed and is widely deployed.

internal/wclayer/expandscratchsize.go

@@ -1,7 +1,13 @@
 package wclayer
 
 import (
+	"os"
+	"path/filepath"
+	"syscall"
+	"unsafe"
+
 	"github.com/Microsoft/hcsshim/internal/hcserror"
+	"github.com/Microsoft/hcsshim/osversion"
 	"github.com/sirupsen/logrus"
 )
 
@@ -26,5 +32,114 @@ func ExpandScratchSize(path string, size uint64) (err error) {
 	if err != nil {
 		return hcserror.New(err, title+" - failed", "")
 	}
+
+	// Manually expand the volume now in order to work around bugs in 19H1 and
+	// prerelease versions of Vb. Remove once this is fixed in Windows.
+	if build := osversion.Get().Build; build >= osversion.Win19H1 && build < 19020 {
+		err = expandSandboxVolume(path)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+type virtualStorageType struct {
+	DeviceID uint32
+	VendorID [16]byte
+}
+
+type openVersion2 struct {
+	GetInfoOnly    int32    // bool but 4-byte aligned
+	ReadOnly       int32    // bool but 4-byte aligned
+	ResiliencyGUID [16]byte // GUID
+}
+
+type openVirtualDiskParameters struct {
+	Version  uint32 // Must always be set to 2
+	Version2 openVersion2
+}
+
+func attachVhd(path string) (syscall.Handle, error) {
+	var (
+		defaultType virtualStorageType
+		handle      syscall.Handle
+	)
+	parameters := openVirtualDiskParameters{Version: 2}
+	err := openVirtualDisk(
+		&defaultType,
+		path,
+		0,
+		0,
+		&parameters,
+		&handle)
+	if err != nil {
+		return 0, &os.PathError{Op: "OpenVirtualDisk", Path: path, Err: err}
+	}
+	err = attachVirtualDisk(handle, 0, 0, 0, 0, 0)
+	if err != nil {
+		syscall.Close(handle)
+		return 0, &os.PathError{Op: "AttachVirtualDisk", Path: path, Err: err}
+	}
+	return handle, nil
+}
+
+func expandSandboxVolume(path string) error {
+	// Mount the sandbox VHD temporarily.
+	vhdPath := filepath.Join(path, "sandbox.vhdx")
+	vhd, err := attachVhd(vhdPath)
+	if err != nil {
+		return &os.PathError{Op: "OpenVirtualDisk", Path: vhdPath, Err: err}
+	}
+	defer syscall.Close(vhd)
+
+	// Open the volume.
+	volumePath, err := GetLayerMountPath(path)
+	if err != nil {
+		return err
+	}
+	if volumePath[len(volumePath)-1] == '\\' {
+		volumePath = volumePath[:len(volumePath)-1]
+	}
+	volume, err := os.OpenFile(volumePath, os.O_RDWR, 0)
+	if err != nil {
+		return err
+	}
+	defer volume.Close()
+
+	// Get the volume's underlying partition size in NTFS clusters.
+	var (
+		partitionSize int64
+		bytes         uint32
+	)
+	const _IOCTL_DISK_GET_LENGTH_INFO = 0x0007405C
+	err = syscall.DeviceIoControl(syscall.Handle(volume.Fd()), _IOCTL_DISK_GET_LENGTH_INFO, nil, 0, (*byte)(unsafe.Pointer(&partitionSize)), 8, &bytes, nil)
+	if err != nil {
+		return &os.PathError{Op: "IOCTL_DISK_GET_LENGTH_INFO", Path: volume.Name(), Err: err}
+	}
+	const (
+		clusterSize = 4096
+		sectorSize  = 512
+	)
+	targetClusters := partitionSize / clusterSize
+
+	// Get the volume's current size in NTFS clusters.
+	var volumeSize int64
+	err = getDiskFreeSpaceEx(volume.Name()+"\\", nil, &volumeSize, nil)
+	if err != nil {
+		return &os.PathError{Op: "GetDiskFreeSpaceEx", Path: volume.Name(), Err: err}
+	}
+	volumeClusters := volumeSize / clusterSize
+
+	// Only resize the volume if there is space to grow, otherwise this will
+	// fail with invalid parameter. NTFS reserves one cluster.
+	if volumeClusters+1 < targetClusters {
+		targetSectors := targetClusters * (clusterSize / sectorSize)
+		const _FSCTL_EXTEND_VOLUME = 0x000900F0
+		err = syscall.DeviceIoControl(syscall.Handle(volume.Fd()), _FSCTL_EXTEND_VOLUME, (*byte)(unsafe.Pointer(&targetSectors)), 8, nil, 0, &bytes, nil)
+		if err != nil {
+			return &os.PathError{Op: "FSCTL_EXTEND_VOLUME", Path: volume.Name(), Err: err}
+		}
+	}
 	return nil
 }

internal/wclayer/wclayer.go

@@ -24,4 +24,9 @@ import "github.com/Microsoft/hcsshim/internal/guid"
 
 //sys grantVmAccess(vmid string, filepath string) (hr error) = vmcompute.GrantVmAccess?
 
+//sys openVirtualDisk(virtualStorageType *virtualStorageType, path string, virtualDiskAccessMask uint32, flags uint32, parameters *openVirtualDiskParameters, handle *syscall.Handle) (err error) [failretval != 0] = virtdisk.OpenVirtualDisk
+//sys attachVirtualDisk(handle syscall.Handle, sd uintptr, flags uint32, providerFlags uint32, params uintptr, overlapped uintptr) (err error) [failretval != 0] = virtdisk.AttachVirtualDisk
+
+//sys getDiskFreeSpaceEx(directoryName string, freeBytesAvailableToCaller *int64, totalNumberOfBytes *int64, totalNumberOfFreeBytes *int64) (err error) = GetDiskFreeSpaceExW
+
 type _guid = guid.GUID