Inotify2(3pm)

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->fh
    Similar to "fileno", but returns a perl file handle instead.

$inotify->blocking ($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/