NAME
    Linux::Inotify2 - scalable directory/file change notification

SYNOPSIS
  Callback Interface
     use Linux::Inotify2;

     # create a new object
     my $inotify = new Linux::Inotify2
        or die "unable to create new inotify object: $!";
 
     # add watchers
     $inotify->watch ("/etc/passwd", IN_ACCESS, sub {
        my $e = shift;
        my $name = $e->fullname;
        print "$name was accessed\n" if $e->IN_ACCESS;
        print "$name is no longer mounted\n" if $e->IN_UNMOUNT;
        print "$name is gone\n" if $e->IN_IGNORED;
        print "events for $name have been lost\n" if $e->IN_Q_OVERFLOW;
 
        # cancel this watcher: remove no further events
        $e->w->cancel;
     });

     # integration into AnyEvent (works with EV, Glib, Tk, POE...)
     my $inotify_w = AE::io $inotify->fileno, 0, sub { $inotify->poll };

     # manual event loop
     $inotify->poll while 1;

  Streaming Interface
     use Linux::Inotify2;

     # create a new object
     my $inotify = new Linux::Inotify2
        or die "Unable to create new inotify object: $!";

     # create watch
     $inotify->watch ("/etc/passwd", IN_ACCESS)
        or die "watch creation failed";

     while () {
       my @events = $inotify->read;
       printf "mask\t%d\n", $_->mask foreach @events;
     }

DESCRIPTION
    This module implements an interface to the Linux 2.6.13 and later
    Inotify file/directory change notification system.

    It has a number of advantages over the Linux::Inotify module:

       - it is portable (Linux::Inotify only works on x86)
       - the equivalent of fullname works correctly
       - it is better documented
       - it has callback-style interface, which is better suited for
         integration.

    As for the inotify API itself - it is a very tricky, and somewhat
    unreliable API. For a good overview of the challenges you might run
    into, see this LWN article: <https://lwn.net/Articles/605128/>.

  The Linux::Inotify2 Class
    my $inotify = new Linux::Inotify2
        Create a new notify object and return it. A notify object is kind of
        a container that stores watches on file system names and is
        responsible for handling event data.

        On error, "undef" is returned and $! will be set accordingly. The
        following errors are documented:

         ENFILE   The system limit on the total number of file descriptors has been reached.
         EMFILE   The user limit on the total number of inotify instances has been reached.
         ENOMEM   Insufficient kernel memory is available.

        Example:

           my $inotify = new Linux::Inotify2
              or die "Unable to create new inotify object: $!";

    $watch = $inotify->watch ($name, $mask[, $cb])
        Add a new watcher to the given notifier. The watcher will create
        events on the pathname $name as given in $mask, which can be any of
        the following constants (all exported by default) ORed together.
        Constants unavailable on your system will evaluate to 0.

        "file" refers to any file system object in the watched object
        (always a directory), that is files, directories, symlinks, device
        nodes etc., while "object" refers to the object the watcher has been
        set on itself:

         IN_ACCESS            object was accessed
         IN_MODIFY            object was modified
         IN_ATTRIB            object metadata changed
         IN_CLOSE_WRITE       writable fd to file / to object was closed
         IN_CLOSE_NOWRITE     readonly fd to file / to object closed
         IN_OPEN              object was opened
         IN_MOVED_FROM        file was moved from this object (directory)
         IN_MOVED_TO          file was moved to this object (directory)
         IN_CREATE            file was created in this object (directory)
         IN_DELETE            file was deleted from this object (directory)
         IN_DELETE_SELF       object itself was deleted
         IN_MOVE_SELF         object itself was moved
         IN_ALL_EVENTS        all of the above events

         IN_ONESHOT           only send event once
         IN_ONLYDIR           only watch the path if it is a directory
         IN_DONT_FOLLOW       don't follow a sym link (Linux 2.6.15+)
         IN_EXCL_UNLINK       don't create events for unlinked objects (Linux 2.6.36+)
         IN_MASK_ADD          not supported with the current version of this module

         IN_CLOSE             same as IN_CLOSE_WRITE | IN_CLOSE_NOWRITE
         IN_MOVE              same as IN_MOVED_FROM | IN_MOVED_TO

        $cb is a perl code reference that, if given, is called for each
        event. It receives a "Linux::Inotify2::Event" object.

        The returned $watch object is of class "Linux::Inotify2::Watch".

        On error, "undef" is returned and $! will be set accordingly. The
        following errors are documented:

         EBADF    The given file descriptor is not valid.
         EINVAL   The given event mask contains no legal events.
         ENOMEM   Insufficient kernel memory was available.
         ENOSPC   The user limit on the total number of inotify watches was reached or the kernel failed to allocate a needed resource.
         EACCESS  Read access to the given file is not permitted.

        Example, show when "/etc/passwd" gets accessed and/or modified once:

           $inotify->watch ("/etc/passwd", IN_ACCESS | IN_MODIFY, sub {
              my $e = shift;
              print "$e->{w}{name} was accessed\n" if $e->IN_ACCESS;
              print "$e->{w}{name} was modified\n" if $e->IN_MODIFY;
              print "$e->{w}{name} is no longer mounted\n" if $e->IN_UNMOUNT;
              print "events for $e->{w}{name} have been lost\n" if $e->IN_Q_OVERFLOW;

              $e->w->cancel;
           });

    $inotify->fileno
        Returns the file descriptor for this notify object. When in
        non-blocking mode, you are responsible for calling the "poll" method
        when this file descriptor becomes ready for reading.

    $inotify->blocking ($blocking)
        Clears ($blocking true) or sets ($blocking false) the "O_NONBLOCK"
        flag on the file descriptor.

    $count = $inotify->poll
        Reads events from the kernel and handles them. If the notify file
        descriptor is blocking (the default), then this method waits for at
        least one event. Otherwise it returns immediately when no pending
        events could be read.

        Returns the count of events that have been handled (which can be 0
        in case events have been received but have been ignored or handled
        internally).

        Croaks when an error occurs.

    @events = $inotify->read
        Reads events from the kernel. Blocks when the file descriptor is in
        blocking mode (default) until any event arrives. Returns list of
        "Linux::Inotify2::Event" objects or empty list if none (non-blocking
        mode or events got ignored).

        Croaks on error.

        Normally you shouldn't use this function, but instead use watcher
        callbacks and call "->poll".

    $inotify->on_overflow ($cb->($ev))
        Sets the callback to be used for overflow handling (default:
        "undef"): When "read" receives an event with "IN_Q_OVERFLOW" set, it
        will invoke this callback with the event.

        When the callback is "undef", then it broadcasts the event to all
        registered watchers, i.e., "undef" is equivalent to:

           sub { $inotify->broadcast ($_[0]) }

    $inotify->broadcast ($ev)
        Invokes all registered watcher callbacks and passes the given event
        to them. Most useful in overflow handlers.

  The Linux::Inotify2::Event Class
    Objects of this class are handed as first argument to the watcher
    callback. It has the following members and methods:

    $event->w
    $event->{w}
        The watcher object for this event, if one is available. Generally,
        you cna only rely on the value of this member inside watcher
        callbacks.

    $event->name
    $event->{name}
        The path of the file system object, relative to the watched name.

    $event->fullname
        Returns the "full" name of the relevant object, i.e. including the
        "name" member of the watcher (if the watch object is on a directory
        and a directory entry is affected), or simply the "name" member
        itself when the object is the watch object itself.

        This call requires "$event->{w}" to be valid, which is generally
        only the case within watcher callbacks.

    $event->mask
    $event->{mask}
        The received event mask. In addition to the events described for
        "$inotify->watch", the following flags (exported by default) can be
        set:

         IN_ISDIR             event object is a directory
         IN_Q_OVERFLOW        event queue overflowed

         # when any of the following flags are set,
         # then watchers for this event are automatically canceled
         IN_UNMOUNT           filesystem for watched object was unmounted
         IN_IGNORED           file was ignored/is gone (no more events are delivered)
         IN_ONESHOT           only one event was generated
         IN_Q_OVERFLOW        queue overflow - event might not be specific to a watcher

    $event->IN_xxx
        Returns a boolean that returns true if the event mask contains any
        events specified by the mask. All of the "IN_xxx" constants can be
        used as methods.

    $event->cookie
    $event->{cookie}
        The event cookie to "synchronize two events". Normally zero, this
        value is set when two events relating to the same file are
        generated. As far as I know, this only happens for "IN_MOVED_FROM"
        and "IN_MOVED_TO" events, to identify the old and new name of a
        file.

        Note that the inotify API makes it impossible to know whether there
        will be a "IN_MOVED_TO" event - you might receive only one of the
        events, and even if you receive both, there might be any number of
        events in between. The best approach seems to be to implement a
        small timeout after "IN_MOVED_FROM" to see if a matching
        "IN_MOVED_TO" event will be received - 2ms seem to work relatively
        well.

  The Linux::Inotify2::Watch Class
    Watcher objects are created by calling the "watch" method of a notifier.

    It has the following members and methods:

    $watch->name
    $watch->{name}
        The name as specified in the "watch" call. For the object itself,
        this is the empty string. For directory watches, this is the name of
        the entry without leading path elements.

    $watch->mask
    $watch->{mask}
        The mask as specified in the "watch" call.

    $watch->cb ([new callback])
    $watch->{cb}
        The callback as specified in the "watch" call. Can optionally be
        changed.

    $watch->cancel
        Cancels/removes this watcher. Future events, even if already queued
        queued, will not be handled and resources will be freed.

SEE ALSO
    AnyEvent, Linux::Inotify.

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/