Tutorial: ladang - inotify Made Easy

You are only 6 steps away to fully utilize ladang. In this tutorial we will monitor a directory for all possible inotify events.

Step One

Import the module.

import ladang

Step Two

Instantiate ladang.Ladang() object.

inotify = ladang.Ladang() # This call is for blocking get_event()

or

inotify = ladang.Ladang(ladang.NONBLOCK|ladang.CLOEXEC) # This call for non-blocking get_event()

Step Three

Next we register a file or a directory which we are interested to monitor and event which we wish the kernel to notify us. By default all events will be reported.

inotify.watch('/path/to/mydir', ladang.IN_ALL_EVENTS)

The bit mask ladang.IN_ALL_EVENTS indicates we are interested in all events. There are many other masks available which can be bitwise ORed. See Inotify event mask constants for other possible values.

Step Four

If any of the events we are interested in occur, inotify will put it into an event queue. All we have to do is fetch the occured events from the queue. First create a file in /path/to/mydir so that there is a filesystem event happen. Execute from the shell:

$ touch /path/to/mydir/myfile

Then we can pull the events from the queue by doing:

events = inotify.get_event()

If there is no inotify event, inotify.get_event() returns an empty tuple. Else we can do this to print out the events:

for event in events:
    print("Watch description: %d" % evt['wd'])
    print("Mask: %d" % evt['mask'])
    print("Mask descr: %s => %s" % ladang.INOTIFY_MASKS[evt['mask']])
    print("Cookie: %d" % evt['cookie'])
    print("Name: %s" % evt['name'].strip("\0"))

A word of cautious, if you are employing a multithreaded strategy, it is important to employ a proper locking. This is because internally, the watched file descriptor will be shared across all thread.

Step Five

When you are no longer interested to monitor any event, just do:

inotify.unwatch('/path/to/dir')

Step Six

And when you’re done, simply call the inotify.close() method to close the controlling inotify file descriptor.

inotify.close(notify_fd)