lib/file: add Implemented constants

lib/file/preallocate_other.go

@@ -4,11 +4,19 @@ package file
 
 import "os"
 
+// PreallocateImplemented is a constant indicating whether the
+// implementation of Preallocate actually does anything.
+const PreallocateImplemented = false
+
 // PreAllocate the file for performance reasons
 func PreAllocate(size int64, out *os.File) error {
 	return nil
 }
 
+// SetSparseImplemented is a constant indicating whether the
+// implementation of SetSparse actually does anything.
+const SetSparseImplemented = false
+
 // SetSparse makes the file be a sparse file
 func SetSparse(out *os.File) error {
 	return nil

lib/file/preallocate_unix.go

@@ -18,6 +18,10 @@ var (
 	fallocFlagsIndex int32
 )
 
+// PreallocateImplemented is a constant indicating whether the
+// implementation of Preallocate actually does anything.
+const PreallocateImplemented = true
+
 // PreAllocate the file for performance reasons
 func PreAllocate(size int64, out *os.File) error {
 	if size <= 0 {
@@ -45,6 +49,10 @@ again:
 	return err
 }
 
+// SetSparseImplemented is a constant indicating whether the
+// implementation of SetSparse actually does anything.
+const SetSparseImplemented = false
+
 // SetSparse makes the file be a sparse file
 func SetSparse(out *os.File) error {
 	return nil

lib/file/preallocate_windows.go

@@ -32,6 +32,10 @@ type ioStatusBlock struct {
 	Status, Information uintptr
 }
 
+// PreallocateImplemented is a constant indicating whether the
+// implementation of Preallocate actually does anything.
+const PreallocateImplemented = true
+
 // PreAllocate the file for performance reasons
 func PreAllocate(size int64, out *os.File) error {
 	if size <= 0 {
@@ -82,6 +86,10 @@ const (
 	FSCTL_SET_SPARSE = 0x000900c4
 )
 
+// SetSparseImplemented is a constant indicating whether the
+// implementation of SetSparse actually does anything.
+const SetSparseImplemented = true
+
 // SetSparse makes the file be a sparse file
 func SetSparse(out *os.File) error {
 	err := syscall.DeviceIoControl(syscall.Handle(out.Fd()), FSCTL_SET_SPARSE, nil, 0, nil, 0, nil, nil)