Revert "Pass disk handle for computestorage.FormatWritableLayerVhd on…

… RS5 (microsoft#1204)"

This reverts commit aaf5db9.

We'd added a change to FormatWritableLayerVhd to help the caller work around
a breaking change in the OS, but this would actually cause a breaking change
in our wrapper of it if the caller was already working around the issue
themselves. To avoid this scenario, revert the commit that added the
"friendly" behavior.

Signed-off-by: Daniel Canter <dcanter@microsoft.com>

computestorage/format.go

@@ -4,40 +4,12 @@ package computestorage
 
 import (
 	"context"
-	"os"
-	"syscall"
 
-	"github.com/Microsoft/go-winio/vhd"
 	"github.com/Microsoft/hcsshim/internal/oc"
-	"github.com/Microsoft/hcsshim/osversion"
 	"github.com/pkg/errors"
 	"golang.org/x/sys/windows"
 )
 
-func openDisk(path string) (windows.Handle, error) {
-	u16, err := windows.UTF16PtrFromString(path)
-	if err != nil {
-		return 0, err
-	}
-	h, err := windows.CreateFile(
-		u16,
-		windows.GENERIC_READ|windows.GENERIC_WRITE,
-		windows.FILE_SHARE_READ|windows.FILE_SHARE_WRITE,
-		nil,
-		windows.OPEN_EXISTING,
-		windows.FILE_ATTRIBUTE_NORMAL|windows.FILE_FLAG_NO_BUFFERING,
-		0,
-	)
-	if err != nil {
-		return 0, &os.PathError{
-			Op:   "CreateFile",
-			Path: path,
-			Err:  err,
-		}
-	}
-	return h, nil
-}
-
 // FormatWritableLayerVhd formats a virtual disk for use as a writable container layer.
 //
 // If the VHD is not mounted it will be temporarily mounted.
@@ -47,31 +19,9 @@ func FormatWritableLayerVhd(ctx context.Context, vhdHandle windows.Handle) (err
 	defer span.End()
 	defer func() { oc.SetSpanStatus(span, err) }()
 
-	h := vhdHandle
-	// On RS5 HcsFormatWritableLayerVhd expects to receive a disk handle instead of a vhd handle.
-	if osversion.Build() < osversion.V19H1 {
-		if err := vhd.AttachVirtualDisk(syscall.Handle(vhdHandle), vhd.AttachVirtualDiskFlagNone, &vhd.AttachVirtualDiskParameters{Version: 1}); err != nil {
-			return err
-		}
-		defer func() {
-			if detachErr := vhd.DetachVirtualDisk(syscall.Handle(vhdHandle)); err == nil && detachErr != nil {
-				err = detachErr
-			}
-		}()
-		diskPath, err := vhd.GetVirtualDiskPhysicalPath(syscall.Handle(vhdHandle))
-		if err != nil {
-			return err
-		}
-		diskHandle, err := openDisk(diskPath)
-		if err != nil {
-			return err
-		}
-		defer windows.CloseHandle(diskHandle) // nolint: errcheck
-		h = diskHandle
-	}
-	err = hcsFormatWritableLayerVhd(h)
+	err = hcsFormatWritableLayerVhd(vhdHandle)
 	if err != nil {
 		return errors.Wrap(err, "failed to format writable layer vhd")
 	}
-	return
+	return nil
 }