Use bind filer for mounts

The bind filter supports bind-like mounts and volume mounts. It also
allows us to have read-only mounts.

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

mount/mount_windows.go

@@ -36,8 +36,16 @@ var (
 
 // Mount to the provided target.
 func (m *Mount) mount(target string) error {
+	readOnly := false
+	for _, option := range m.Options {
+		if option == "ro" {
+			readOnly = true
+			break
+		}
+	}
+
 	if m.Type == "bind" {
-		if err := m.bindMount(target); err != nil {
+		if err := ApplyFileBinding(target, m.Source, readOnly); err != nil {
 			return fmt.Errorf("failed to bind-mount to %s: %w", target, err)
 		}
 		return nil
@@ -81,12 +89,12 @@ func (m *Mount) mount(target string) error {
 		return fmt.Errorf("failed to get volume path for layer %s: %w", m.Source, err)
 	}
 
-	if err = setVolumeMountPoint(target, volume); err != nil {
+	if err = ApplyFileBinding(target, volume, readOnly); err != nil {
 		return fmt.Errorf("failed to set volume mount path for layer %s: %w", m.Source, err)
 	}
 	defer func() {
 		if err != nil {
-			deleteVolumeMountPoint(target)
+			RemoveFileBinding(target)
 		}
 	}()
 
@@ -120,50 +128,60 @@ func (m *Mount) GetParentPaths() ([]string, error) {
 
 // Unmount the mount at the provided path
 func Unmount(mount string, flags int) error {
+	var err error
 	mount = filepath.Clean(mount)
-
-	// Helpfully, both reparse points and symlinks look like links to Go
-	// Less-helpfully, ReadLink cannot return \\?\Volume{GUID} for a volume mount,
-	// and ends up returning the directory we gave it for some reason.
-	if mountTarget, err := os.Readlink(mount); err != nil {
-		// Not a mount point.
-		// This isn't an error, per the EINVAL handling in the Linux version
-		return nil
-	} else if mount != filepath.Clean(mountTarget) {
-		// Directory symlink
-		if err := bindUnmount(mount); err != nil {
-			return fmt.Errorf("failed to bind-unmount from %s: %w", mount, err)
-		}
-		return nil
-	}
-
-	layerPathb, err := os.ReadFile(mount + ":" + sourceStreamName)
-
+	// This should expand paths like ADMINI~1 and PROGRA~1 to long names.
+	mount, err = getFinalPath(mount)
 	if err != nil {
-		return fmt.Errorf("failed to retrieve source for layer %s: %w", mount, err)
+		return fmt.Errorf("fetching real path: %w", err)
 	}
-
-	layerPath := string(layerPathb)
-
-	if err := deleteVolumeMountPoint(mount); err != nil {
-		return fmt.Errorf("failed failed to release volume mount path for layer %s: %w", mount, err)
+	mounts, err := GetBindMappings(mount)
+	if err != nil {
+		return fmt.Errorf("fetching bind mappings: %w", err)
 	}
-
-	var (
-		home, layerID = filepath.Split(layerPath)
-		di            = hcsshim.DriverInfo{
-			HomeDir: home,
+	found := false
+	for _, mnt := range mounts {
+		if mnt.MountPoint == mount {
+			found = true
+			break
 		}
-	)
-
-	if err := hcsshim.UnprepareLayer(di, layerID); err != nil {
-		return fmt.Errorf("failed to unprepare layer %s: %w", mount, err)
+	}
+	if !found {
+		// not a mount point
+		return nil
 	}
 
-	if err := hcsshim.DeactivateLayer(di, layerID); err != nil {
-		return fmt.Errorf("failed to deactivate layer %s: %w", mount, err)
+	adsFile := mount + ":" + sourceStreamName
+	var layerPath string
+
+	if _, err := os.Lstat(adsFile); err == nil {
+		layerPathb, err := os.ReadFile(mount + ":" + sourceStreamName)
+		if err != nil {
+			return fmt.Errorf("failed to retrieve source for layer %s: %w", mount, err)
+		}
+		layerPath = string(layerPathb)
 	}
 
+	if err := RemoveFileBinding(mount); err != nil {
+		return fmt.Errorf("removing mount: %w", err)
+	}
+
+	if layerPath != "" {
+		var (
+			home, layerID = filepath.Split(layerPath)
+			di            = hcsshim.DriverInfo{
+				HomeDir: home,
+			}
+		)
+
+		if err := hcsshim.UnprepareLayer(di, layerID); err != nil {
+			return fmt.Errorf("failed to unprepare layer %s: %w", mount, err)
+		}
+
+		if err := hcsshim.DeactivateLayer(di, layerID); err != nil {
+			return fmt.Errorf("failed to deactivate layer %s: %w", mount, err)
+		}
+	}
 	return nil
 }
 
@@ -183,21 +201,13 @@ func UnmountRecursive(mount string, flags int) error {
 }
 
 func (m *Mount) bindMount(target string) error {
+	readOnly := false
 	for _, option := range m.Options {
 		if option == "ro" {
-			return fmt.Errorf("read-only bind mount: %w", ErrNotImplementOnWindows)
+			readOnly = true
+			break
 		}
 	}
 
-	if err := os.Remove(target); err != nil {
-		return err
-	}
-
-	// TODO: We don't honour the Read-Only flag.
-	// It's possible that Windows simply lacks this.
-	return os.Symlink(m.Source, target)
-}
-
-func bindUnmount(target string) error {
-	return os.Remove(target)
+	return ApplyFileBinding(target, m.Source, readOnly)
 }