overlayfs/overlayfs_windows.go

//go:build windows && (amd64 || 386 || arm64)

package overlayfs

import (
	"os"
	"path/filepath"
	"runtime"
	"syscall"
	"unsafe"

	"github.com/aegistudio/go-winfsp"
	"github.com/aegistudio/go-winfsp/gofs"
)

// Check if winfsp is available on the system
func OverlayfsAvaible() bool {
	var dllName string
	switch runtime.GOARCH {
	case "386":
		dllName = "winfsp-x86.dll"
	case "amd64":
		dllName = "winfsp-x64.dll"
	case "arm64":
		dllName = "winfsp-a64.dll"
	default:
		return false
	}

	dll, _ := syscall.LoadDLL(dllName)
	if dll != nil {
		_ = dll.Release()
		return true
	}

	var keyReg syscall.Handle // HKLM\\Software\\WinFSP
	keyName, err := syscall.UTF16PtrFromString("Software\\WinFsp")
	if err != nil {
		return false
	} else if err := syscall.RegOpenKeyEx(syscall.HKEY_LOCAL_MACHINE, keyName, 0, syscall.KEY_READ|syscall.KEY_WOW64_32KEY, &keyReg); err != nil {
		return false
	}
	defer syscall.RegCloseKey(keyReg)
	valueName, err := syscall.UTF16PtrFromString("InstallDir")
	if err != nil {
		return false
	}
	var pathBuf [syscall.MAX_PATH]uint16
	var valueType, valueSize uint32
	valueSize = uint32(len(pathBuf)) * 2
	if err := syscall.RegQueryValueEx(keyReg, valueName, nil, &valueType, (*byte)(unsafe.Pointer(&pathBuf)), &valueSize); err != nil {
		return false
	} else if valueType != syscall.REG_SZ {
		return false
	}
	path := pathBuf[:int(valueSize/2)]
	if len(path) > 0 && path[len(path)-1] == 0 {
		path = path[:len(path)-1]
	}
	installPath := syscall.UTF16ToString(path)

	// Attempt to load the DLL that we have found.
	dll, err = syscall.LoadDLL(filepath.Join(installPath, "bin", dllName))
	if err != nil {
		return false
	}
	_ = dll.Release()
	return true
}

type winfspMerge struct{ *Overlayfs }

func (winfsp winfspMerge) OpenFile(name string, flag int, perm os.FileMode) (gofs.File, error) {
	return winfsp.Overlayfs.OpenFile(name, flag, perm)
}

func (fsp *Overlayfs) getWinfsp() (*winfsp.FileSystem, error) {
	if fssp, ok := fsp.ProcessInternal.(*winfsp.FileSystem); ok {
		return fssp, nil
	}
	return nil, ErrUnmounted
}

// Mount go-mergefs with winfsp
//
// This function supports drive letters (X:) or directories as mount points:
//
//   - Drive letters: Refer to the documentation of the DefineDosDevice Windows API to better understand how they are created.
//
//   - Directories: They can be used as mount points for disk based file systems. They cannot be used for network file systems. This is a limitation that Windows imposes on junctions.
func (overlay *Overlayfs) Mount() error {
	_, err := overlay.getWinfsp()
	if err != nil && err != ErrUnmounted {
		return err
	}

	// Clean folder path to mount
	if !filepath.IsAbs(overlay.Target) {
		if overlay.Target, err = filepath.Abs(overlay.Target); err != nil {
			return err
		}
	}

	overlay.ProcessInternal, err = winfsp.Mount(gofs.New(&winfspMerge{Overlayfs: overlay}), overlay.Target, winfsp.FileSystemName("go-mergefs"))
	return err
}

// Umount winfsp filesystem if mounted
func (overlay *Overlayfs) Unmount() error {
	fssp, err := overlay.getWinfsp()
	if err == nil && fssp != nil {
		fssp.Unmount()
		overlay.ProcessInternal = nil
	}
	return nil
}