The current mechanism for filtering events is to inspect the Op bitmask:

if event.Op&fsnotify.Create == fsnotify.Create {

In howeyc/fsnotify there is a WatchFlags method to filter operations. WatchFlags was removed in 10e1440 (v0.10.0) because:

• The implementation required a lot of extra bookkeeping while providing little benefit over filtering events as they were received.
• As @mstum reported, it wasn't working on Windows, which was due to the bookkeeping not being implemented for files within a directory watch: WatchFlags not supported on Windows? howeyc/fsnotify#93 (comment).
• There were no tests for WatchFlags.

@nightlyone pointed out that it still is desirable to specify filters so the kernel doesn't need to wakeup our thread/process for an event we'll just ignore.

Some research (API doc) reveal differences from one OS to the next:

• kqueue doesn't have a Create Op at all (NOTE_CREATE), much less a filter for it.
• Windows has a filter for FILE_NOTIFY_CHANGE_FILE_NAME that covers Create, Remove and Rename. An event does indicate which one of these it is, but some user-space filtering is still necessary.