Do not suppress Chmod on non-existent file

Currently fsnorify suppresses a Chmod event if the file does not exist
when event is received.

This prevents a possibility of fsnotify user to detect a situation
when an opened file is removed. In such case the Linux kernel sends
IN_ATTRIB event, as described in inotify(7) man page:

> IN_ATTRIB (*)
>        Metadata  changed—for example, permissions (e.g., chmod(2)),
>        timestamps (e.g., utimensat(2)), extended attributes  (setx‐
>        attr(2)), link count (since Linux 2.6.25; e.g., for the tar‐
>        get of link(2) and for unlink(2)), and user/group ID  (e.g.,
>        chown(2)).

To fix:
 * Modify the code to only suppress MODIFY and CREATE events.
 * Add a test case to verify Chmod event is delivered.

While at it, fix the comment in ignoreLinux() to use the up-to-date
terminology (event ops).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

inotify.go

@@ -303,12 +303,12 @@ func (e *Event) ignoreLinux(mask uint32) bool {
 		return true
 	}
 
-	// If the event is not a DELETE or RENAME, the file must exist.
-	// Otherwise the event is ignored.
-	// *Note*: this was put in place because it was seen that a MODIFY
-	// event was sent after the DELETE. This ignores that MODIFY and
-	// assumes a DELETE will come or has come if the file doesn't exist.
-	if !(e.Op&Remove == Remove || e.Op&Rename == Rename) {
+	// If the event is Create or Write, the file must exist, or the
+	// event will be suppressed.
+	// *Note*: this was put in place because it was seen that a Write
+	// event was sent after the Remove. This ignores the Write and
+	// assumes a Remove will come or has come if the file doesn't exist.
+	if e.Op&Create == Create || e.Op&Write == Write {
 		_, statErr := os.Lstat(e.Name)
 		return os.IsNotExist(statErr)
 	}

inotify_test.go

@@ -447,3 +447,52 @@ func TestInotifyOverflow(t *testing.T) {
 			numDirs*numFiles, creates)
 	}
 }
+
+func TestInotifyDeleteOpenedFile(t *testing.T) {
+	testDir := tempMkdir(t)
+	defer os.RemoveAll(testDir)
+
+	testFile := filepath.Join(testDir, "testfile")
+
+	// create and open a file
+	fd, err := os.Create(testFile)
+	if err != nil {
+		t.Fatalf("Create failed: %v", err)
+	}
+	defer fd.Close()
+
+	w, err := NewWatcher()
+	if err != nil {
+		t.Fatalf("Failed to create watcher: %v", err)
+	}
+	defer w.Close()
+
+	err = w.Add(testFile)
+	if err != nil {
+		t.Fatalf("Failed to add watch for %s: %v", testFile, err)
+	}
+
+	checkEvent := func(exp Op) {
+		select {
+		case event := <-w.Events:
+			t.Logf("Event received: %s", event.Op)
+			if event.Op != exp {
+				t.Fatalf("Event expected: %s, got: %s", exp, event.Op)
+			}
+		case <-time.After(100 * time.Millisecond):
+			t.Fatalf("Expected %s event not received", exp)
+		}
+	}
+
+	// Remove the (opened) file, check Chmod event (notifying
+	// about file link count change) is received
+	err = os.Remove(testFile)
+	if err != nil {
+		t.Fatalf("Failed to remove file: %s", err)
+	}
+	checkEvent(Chmod)
+
+	// Close the file, check Remove event is received
+	fd.Close()
+	checkEvent(Remove)
+}