Add GetFileID function

fileinfo.go

@@ -9,22 +9,46 @@ import (
 //sys getFileInformationByHandleEx(h syscall.Handle, class uint32, buffer *byte, size uint32) (err error) = GetFileInformationByHandleEx
 //sys setFileInformationByHandle(h syscall.Handle, class uint32, buffer *byte, size uint32) (err error) = SetFileInformationByHandle
 
+const (
+	fileBasicInfo = 0
+	fileIDInfo    = 0x12
+)
+
+// FileBasicInfo contains file access time and file attributes information.
 type FileBasicInfo struct {
 	CreationTime, LastAccessTime, LastWriteTime, ChangeTime syscall.Filetime
 	FileAttributes                                          uintptr // includes padding
 }
 
+// GetFileBasicInfo retrieves times and attributes for a file.
 func GetFileBasicInfo(f *os.File) (*FileBasicInfo, error) {
 	bi := &FileBasicInfo{}
-	if err := getFileInformationByHandleEx(syscall.Handle(f.Fd()), 0, (*byte)(unsafe.Pointer(bi)), uint32(unsafe.Sizeof(*bi))); err != nil {
+	if err := getFileInformationByHandleEx(syscall.Handle(f.Fd()), fileBasicInfo, (*byte)(unsafe.Pointer(bi)), uint32(unsafe.Sizeof(*bi))); err != nil {
-		return nil, &os.PathError{"GetFileInformationByHandleEx", f.Name(), err}
+		return nil, &os.PathError{Op: "GetFileInformationByHandleEx", Path: f.Name(), Err: err}
 	}
 	return bi, nil
 }
 
+// SetFileBasicInfo sets times and attributes for a file.
 func SetFileBasicInfo(f *os.File, bi *FileBasicInfo) error {
-	if err := setFileInformationByHandle(syscall.Handle(f.Fd()), 0, (*byte)(unsafe.Pointer(bi)), uint32(unsafe.Sizeof(*bi))); err != nil {
+	if err := setFileInformationByHandle(syscall.Handle(f.Fd()), fileBasicInfo, (*byte)(unsafe.Pointer(bi)), uint32(unsafe.Sizeof(*bi))); err != nil {
-		return &os.PathError{"SetFileInformationByHandle", f.Name(), err}
+		return &os.PathError{Op: "SetFileInformationByHandle", Path: f.Name(), Err: err}
 	}
 	return nil
 }
+
+// FileIDInfo contains the volume serial number and file ID for a file. This pair should be
+// unique on a system.
+type FileIDInfo struct {
+	VolumeSerialNumber uint64
+	FileID             [16]byte
+}
+
+// GetFileID retrieves the unique (volume, file ID) pair for a file.
+func GetFileID(f *os.File) (*FileIDInfo, error) {
+	fileID := &FileIDInfo{}
+	if err := getFileInformationByHandleEx(syscall.Handle(f.Fd()), fileIDInfo, (*byte)(unsafe.Pointer(fileID)), uint32(unsafe.Sizeof(*fileID))); err != nil {
+		return nil, &os.PathError{Op: "GetFileInformationByHandleEx", Path: f.Name(), Err: err}
+	}
+	return fileID, nil
+}