Linux::Inotify2 - scalable directory/file change notification
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;
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; }
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/.
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:
undef
$!
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: $!";
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.
$name
$mask
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.
$cb
Linux::Inotify2::Event
The returned $watch object is of class Linux::Inotify2::Watch.
$watch
Linux::Inotify2::Watch
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:
/etc/passwd
$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; $e->w->cancel; });
Returns the file descriptor for this notify object. When in non-blocking mode, you are responsible for calling the poll method when this file descriptor becomes ready for reading.
poll
Similar to fileno, but returns a perl file handle instead.
fileno
Clears ($blocking true) or sets ($blocking false) the O_NONBLOCK flag on the file descriptor.
O_NONBLOCK
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.
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.
->poll
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.
read
IN_Q_OVERFLOW
When the callback is undef, then it broadcasts the event to all registered watchers, i.e., undef is equivalent to:
sub { $inotify->broadcast ($_[0]) }
Invokes all registered watcher callbacks and passes the given event to them. Most useful in overflow handlers.
Objects of this class are handed as first argument to the watcher callback. It has the following members and methods:
The watcher object for this event, if one is available. Generally, you cna only rely on the value of this member inside watcher callbacks.
The path of the file system object, relative to the watched name.
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.
name
This call requires $event->{w} to be valid, which is generally only the case within watcher callbacks.
$event->{w}
The received event mask. In addition to the events described for $inotify->watch, the following flags (exported by default) can be set:
$inotify->watch
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
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.
IN_xxx
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.
IN_MOVED_FROM
IN_MOVED_TO
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.
Watcher objects are created by calling the watch method of a notifier.
watch
It has the following members and methods:
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.
The mask as specified in the watch call.
The callback as specified in the watch call. Can optionally be changed.
Cancels/removes this watcher. Future events, even if already queued queued, will not be handled and resources will be freed.
AnyEvent, Linux::Inotify.
Marc Lehmann <schmorp@schmorp.de> http://home.schmorp.de/
To install Linux::Inotify2, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Linux::Inotify2
CPAN shell
perl -MCPAN -e shell install Linux::Inotify2
For more information on module installation, please visit the detailed CPAN module installation guide.