Add ResolvePath tests

Add required computestorage APIs to allow for running tests of
`ResolvePath`.

Signed-off-by: Hamza El-Saawy <[email protected]>

internal/computestorage/computestorage.go

@@ -0,0 +1,48 @@
+//go:build windows
+
+package computestorage
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/windows"
+
+	"github.com/Microsoft/go-winio/internal/interop"
+)
+
+//go:generate go run github.com/Microsoft/go-winio/tools/mkwinsyscall -output zsyscall_windows.go computestorage.go
+
+// https://learn.microsoft.com/en-us/virtualization/api/hcs/reference/hcsformatwritablelayervhd
+//
+//sys hcsFormatWritableLayerVhd(handle windows.Handle) (hr error) = computestorage.HcsFormatWritableLayerVhd?
+
+// FormatWritableLayerVhd formats a virtual disk for use as a writable container layer.
+//
+// If the VHD is not mounted it will be temporarily mounted.
+//
+// NOTE: This API had a breaking change in the operating system after Windows Server 2019.
+// On ws2019 the API expects to get passed a file handle from CreateFile for the vhd that
+// the caller wants to format. On > ws2019, its expected that the caller passes a vhd handle
+// that can be obtained from the virtdisk APIs.
+func FormatWritableLayerVhd(vhdHandle windows.Handle) (err error) {
+	err = hcsFormatWritableLayerVhd(vhdHandle)
+	if err != nil {
+		return fmt.Errorf("failed to format writable layer vhd: %w", err)
+	}
+	return nil
+}
+
+// https://learn.microsoft.com/en-us/virtualization/api/hcs/reference/hcsgetlayervhdmountpath
+//
+//sys hcsGetLayerVhdMountPath(vhdHandle windows.Handle, mountPath **uint16) (hr error) = computestorage.HcsGetLayerVhdMountPath?
+
+// GetLayerVhdMountPath returns the volume path for a virtual disk of a writable container layer.
+func GetLayerVhdMountPath(vhdHandle windows.Handle) (path string, err error) {
+	var mountPath *uint16
+	err = hcsGetLayerVhdMountPath(vhdHandle, &mountPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to get vhd mount path: %w", err)
+	}
+	path = interop.ConvertAndFreeCoTaskMemString(mountPath)
+	return path, nil
+}

internal/computestorage/doc.go

@@ -0,0 +1 @@
+package computestorage

internal/interop/doc.go

@@ -0,0 +1 @@
+package interop

internal/interop/interop.go

@@ -0,0 +1,25 @@
+//go:build windows
+
+package interop
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+//go:generate go run github.com/Microsoft/go-winio/tools/mkwinsyscall -output zsyscall_windows.go interop.go
+
+//sys coTaskMemFree(buffer unsafe.Pointer) = api_ms_win_core_com_l1_1_0.CoTaskMemFree
+
+func ConvertAndFreeCoTaskMemString(buffer *uint16) string {
+	str := syscall.UTF16ToString((*[1 << 29]uint16)(unsafe.Pointer(buffer))[:])
+	coTaskMemFree(unsafe.Pointer(buffer))
+	return str
+}
+
+func Win32FromHresult(hr uintptr) syscall.Errno {
+	if hr&0x1fff0000 == 0x00070000 {
+		return syscall.Errno(hr & 0xffff)
+	}
+	return syscall.Errno(hr)
+}

pkg/fs/resolve.go

@@ -20,28 +20,9 @@ import (
 // It is intended to address short-comings of [filepath.EvalSymlinks], which does not work
 // well on Windows.
 func ResolvePath(path string) (string, error) {
-	// We are not able to use builtin Go functionality for opening a directory path:
-	//   - os.Open on a directory returns a os.File where Fd() is a search handle from FindFirstFile.
-	//   - syscall.Open does not provide a way to specify FILE_FLAG_BACKUP_SEMANTICS, which is needed to
-	//     open a directory.
-	//
-	// We could use os.Open if the path is a file, but it's easier to just use the same code for both.
-	// Therefore, we call windows.CreateFile directly.
-	h, err := fs.CreateFile(
-		path,
-		fs.FILE_ANY_ACCESS, // access
-		fs.FILE_SHARE_READ|fs.FILE_SHARE_WRITE|fs.FILE_SHARE_DELETE,
-		nil, // security attributes
-		fs.OPEN_EXISTING,
-		fs.FILE_FLAG_BACKUP_SEMANTICS, // Needed to open a directory handle.
-		fs.NullHandle,                 // template file
-	)
+	h, err := openMetadata(path)
 	if err != nil {
-		return "", &os.PathError{
-			Op:   "CreateFile",
-			Path: path,
-			Err:  err,
-		}
+		return "", err
 	}
 	defer windows.CloseHandle(h) //nolint:errcheck
 
@@ -126,3 +107,33 @@ func ResolvePath(path string) (string, error) {
 	}
 	return rPath, err
 }
+
+// openMetadata takes a path, opens it with only meta-data access, and returns the resulting handle.
+// It works for both file and directory paths.
+func openMetadata(path string) (windows.Handle, error) {
+	// We are not able to use builtin Go functionality for opening a directory path:
+	//   - os.Open on a directory returns a os.File where Fd() is a search handle from FindFirstFile.
+	//   - syscall.Open does not provide a way to specify FILE_FLAG_BACKUP_SEMANTICS, which is needed to
+	//     open a directory.
+	//
+	// We could use os.Open if the path is a file, but it's easier to just use the same code for both.
+	// Therefore, we call windows.CreateFile directly.
+	h, err := fs.CreateFile(
+		path,
+		fs.FILE_ANY_ACCESS,
+		fs.FILE_SHARE_READ|fs.FILE_SHARE_WRITE|fs.FILE_SHARE_DELETE,
+		nil, // security attributes
+		fs.OPEN_EXISTING,
+		fs.FILE_FLAG_BACKUP_SEMANTICS, // Needed to open a directory handle.
+		fs.NullHandle,
+	)
+
+	if err != nil {
+		return 0, &os.PathError{
+			Op:   "CreateFile",
+			Path: path,
+			Err:  err,
+		}
+	}
+	return h, nil
+}