Allow a custom event mask to be specified for use with the Linux inotify observer

[exarkun]

If I want to use watchdog as a Python library and I want to receive events other than the ones that watchmedo is interested, I have to jump through a bunch of hoops to get an InotifyObserver which will set or clear values in the event mask given to inotify_c.Inotify.

I want to be able to supply my own mask to InotifyObserver so that I can receive these other events without monkey-patching the watchdog implementation.

An example of an acceptable interface would be:

InotifyObserver(event_mask=my_integer_mask)

Another example that might provide better flexibility would be:

InotifyObserver(emitter_class=MyInotifyEmitterClass)

coupled with the necessary changes to InotifyBuffer so that it passes through an event mask argument, eg

InotifyBuffer(path, recursive, event_mask=my_integer_mask)

with event_mask being passed on to the inotify_c.Inotify instance it creates.

Note that the emitter_class parameter is a generalization of an idea already present in the code (generate_full_events - which is essentially just a parameter to control the behavior of the emitter and the observer doesn't otherwise need to know anything about it).

[MPalarya]

+1
We encountered this need over at Redis.
Our options for a workaround are not amazing -
patching / reimplementing or overriding non trivial core classes such as the InotifyBuffer..
We even considered switching to the polling observer

[BoboTiG]

The feature was done in #989. I'll cut a new release "quite soon" :)