daemon/graphdriver/windows: use go-winio.GetFileSystemType()

go-winio now defines this function, so we can consume that.

Note that there's a difference between the old implementation and the original
one (added in 1cb9e9b44e). The old implementation
had special handling for win32 error codes, which was removed in the go-winio
implementation in 0966e1ad56

As `go-winio.GetFileSystemType()` calls `filepath.VolumeName(path)` internally,
this patch also removes the `string(home[0])`, which is redundant, and could
potentially panic if an empty string would be passed.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/graphdriver/windows/windows.go

@@ -16,12 +16,11 @@ import (
 	"strconv"
 	"strings"
 	"sync"
-	"syscall"
 	"time"
-	"unsafe"
 
 	winio "github.com/Microsoft/go-winio"
 	"github.com/Microsoft/go-winio/backuptar"
+	winiofs "github.com/Microsoft/go-winio/pkg/fs"
 	"github.com/Microsoft/go-winio/vhd"
 	"github.com/Microsoft/hcsshim"
 	"github.com/Microsoft/hcsshim/osversion"
@@ -99,7 +98,7 @@ type Driver struct {
 func InitFilter(home string, options []string, _ idtools.IdentityMapping) (graphdriver.Driver, error) {
 	logrus.Debugf("WindowsGraphDriver InitFilter at %s", home)
 
-	fsType, err := getFileSystemType(string(home[0]))
+	fsType, err := winiofs.GetFileSystemType(home)
 	if err != nil {
 		return nil, err
 	}
@@ -136,37 +135,6 @@ func InitFilter(home string, options []string, _ idtools.IdentityMapping) (graph
 	return d, nil
 }
 
-// win32FromHresult is a helper function to get the win32 error code from an HRESULT
-func win32FromHresult(hr uintptr) uintptr {
-	if hr&0x1fff0000 == 0x00070000 {
-		return hr & 0xffff
-	}
-	return hr
-}
-
-// getFileSystemType obtains the type of a file system through GetVolumeInformation
-// https://msdn.microsoft.com/en-us/library/windows/desktop/aa364993(v=vs.85).aspx
-func getFileSystemType(drive string) (fsType string, hr error) {
-	var (
-		modkernel32              = windows.NewLazySystemDLL("kernel32.dll")
-		procGetVolumeInformation = modkernel32.NewProc("GetVolumeInformationW")
-		buf                      = make([]uint16, 255)
-		size                     = windows.MAX_PATH + 1
-	)
-	if len(drive) != 1 {
-		hr = errors.New("getFileSystemType must be called with a drive letter")
-		return
-	}
-	drive += `:\`
-	n := uintptr(unsafe.Pointer(nil))
-	r0, _, _ := syscall.Syscall9(procGetVolumeInformation.Addr(), 8, uintptr(unsafe.Pointer(windows.StringToUTF16Ptr(drive))), n, n, n, n, n, uintptr(unsafe.Pointer(&buf[0])), uintptr(size), 0)
-	if int32(r0) < 0 {
-		hr = syscall.Errno(win32FromHresult(r0))
-	}
-	fsType = windows.UTF16ToString(buf)
-	return
-}
-
 // String returns the string representation of a driver. This should match
 // the name the graph driver has been registered with.
 func (d *Driver) String() string {

vendor/github.com/Microsoft/go-winio/pkg/fs/fs_windows.go

@@ -0,0 +1,31 @@
+package fs
+
+import (
+	"errors"
+	"path/filepath"
+
+	"golang.org/x/sys/windows"
+)
+
+var (
+	// ErrInvalidPath is returned when the location of a file path doesn't begin with a driver letter.
+	ErrInvalidPath = errors.New("the path provided to GetFileSystemType must start with a drive letter")
+)
+
+// GetFileSystemType obtains the type of a file system through GetVolumeInformation.
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa364993(v=vs.85).aspx
+func GetFileSystemType(path string) (fsType string, err error) {
+	drive := filepath.VolumeName(path)
+	if len(drive) != 2 {
+		return "", ErrInvalidPath
+	}
+
+	var (
+		buf  = make([]uint16, 255)
+		size = uint32(windows.MAX_PATH + 1)
+	)
+	drive += `\`
+	err = windows.GetVolumeInformation(windows.StringToUTF16Ptr(drive), nil, 0, nil, nil, nil, &buf[0], size)
+	fsType = windows.UTF16ToString(buf)
+	return
+}

vendor/modules.txt

@@ -24,6 +24,7 @@ github.com/Microsoft/go-winio
 github.com/Microsoft/go-winio/backuptar
 github.com/Microsoft/go-winio/pkg/etw
 github.com/Microsoft/go-winio/pkg/etwlogrus
+github.com/Microsoft/go-winio/pkg/fs
 github.com/Microsoft/go-winio/pkg/guid
 github.com/Microsoft/go-winio/pkg/security
 github.com/Microsoft/go-winio/vhd