[ViewVC] Contents of: cvs/cvsroot/Linux-Inotify2/README

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.

        "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/

Revision:	1.11
Committed:	Thu Oct 25 01:19:37 2018 UTC (5 years, 8 months ago) by root
Branch:	MAIN
CVS Tags:	rel-2_0, rel-2_1
Changes since 1.10:	+51 -19 lines
Log Message:	2.0
#	Content
1	NAME
2	Linux::Inotify2 - scalable directory/file change notification
3
4	SYNOPSIS
5	Callback Interface
6	use Linux::Inotify2;
7
8	# create a new object
9	my $inotify = new Linux::Inotify2
10	or die "unable to create new inotify object: $!";
11
12	# add watchers
13	$inotify->watch ("/etc/passwd", IN_ACCESS, sub {
14	my $e = shift;
15	my $name = $e->fullname;
16	print "$name was accessed\n" if $e->IN_ACCESS;
17	print "$name is no longer mounted\n" if $e->IN_UNMOUNT;
18	print "$name is gone\n" if $e->IN_IGNORED;
19	print "events for $name have been lost\n" if $e->IN_Q_OVERFLOW;
20
21	# cancel this watcher: remove no further events
22	$e->w->cancel;
23	});
24
25	# integration into AnyEvent (works with EV, Glib, Tk, POE...)
26	my $inotify_w = AE::io $inotify->fileno, 0, sub { $inotify->poll };
27
28	# manual event loop
29	$inotify->poll while 1;
30
31	Streaming Interface
32	use Linux::Inotify2;
33
34	# create a new object
35	my $inotify = new Linux::Inotify2
36	or die "Unable to create new inotify object: $!";
37
38	# create watch
39	$inotify->watch ("/etc/passwd", IN_ACCESS)
40	or die "watch creation failed";
41
42	while () {
43	my @events = $inotify->read;
44	printf "mask\t%d\n", $_->mask foreach @events;
45	}
46
47	DESCRIPTION
48	This module implements an interface to the Linux 2.6.13 and later
49	Inotify file/directory change notification system.
50
51	It has a number of advantages over the Linux::Inotify module:
52
53	- it is portable (Linux::Inotify only works on x86)
54	- the equivalent of fullname works correctly
55	- it is better documented
56	- it has callback-style interface, which is better suited for
57	integration.
58
59	As for the inotify API itself - it is a very tricky, and somewhat
60	unreliable API. For a good overview of the challenges you might run
61	into, see this LWN article: <https://lwn.net/Articles/605128/>.
62
63	The Linux::Inotify2 Class
64	my $inotify = new Linux::Inotify2
65	Create a new notify object and return it. A notify object is kind of
66	a container that stores watches on file system names and is
67	responsible for handling event data.
68
69	On error, "undef" is returned and $! will be set accordingly. The
70	following errors are documented:
71
72	ENFILE The system limit on the total number of file descriptors has been reached.
73	EMFILE The user limit on the total number of inotify instances has been reached.
74	ENOMEM Insufficient kernel memory is available.
75
76	Example:
77
78	my $inotify = new Linux::Inotify2
79	or die "Unable to create new inotify object: $!";
80
81	$watch = $inotify->watch ($name, $mask[, $cb])
82	Add a new watcher to the given notifier. The watcher will create
83	events on the pathname $name as given in $mask, which can be any of
84	the following constants (all exported by default) ORed together.
85
86	"file" refers to any file system object in the watched object
87	(always a directory), that is files, directories, symlinks, device
88	nodes etc., while "object" refers to the object the watcher has been
89	set on itself:
90
91	IN_ACCESS object was accessed
92	IN_MODIFY object was modified
93	IN_ATTRIB object metadata changed
94	IN_CLOSE_WRITE writable fd to file / to object was closed
95	IN_CLOSE_NOWRITE readonly fd to file / to object closed
96	IN_OPEN object was opened
97	IN_MOVED_FROM file was moved from this object (directory)
98	IN_MOVED_TO file was moved to this object (directory)
99	IN_CREATE file was created in this object (directory)
100	IN_DELETE file was deleted from this object (directory)
101	IN_DELETE_SELF object itself was deleted
102	IN_MOVE_SELF object itself was moved
103	IN_ALL_EVENTS all of the above events
104
105	IN_ONESHOT only send event once
106	IN_ONLYDIR only watch the path if it is a directory
107	IN_DONT_FOLLOW don't follow a sym link (Linux 2.6.15+)
108	IN_EXCL_UNLINK don't create events for unlinked objects (Linux 2.6.36+)
109	IN_MASK_ADD not supported with the current version of this module
110
111	IN_CLOSE same as IN_CLOSE_WRITE \| IN_CLOSE_NOWRITE
112	IN_MOVE same as IN_MOVED_FROM \| IN_MOVED_TO
113
114	$cb is a perl code reference that, if given, is called for each
115	event. It receives a "Linux::Inotify2::Event" object.
116
117	The returned $watch object is of class "Linux::Inotify2::Watch".
118
119	On error, "undef" is returned and $! will be set accordingly. The
120	following errors are documented:
121
122	EBADF The given file descriptor is not valid.
123	EINVAL The given event mask contains no legal events.
124	ENOMEM Insufficient kernel memory was available.
125	ENOSPC The user limit on the total number of inotify watches was reached or the kernel failed to allocate a needed resource.
126	EACCESS Read access to the given file is not permitted.
127
128	Example, show when "/etc/passwd" gets accessed and/or modified once:
129
130	$inotify->watch ("/etc/passwd", IN_ACCESS \| IN_MODIFY, sub {
131	my $e = shift;
132	print "$e->{w}{name} was accessed\n" if $e->IN_ACCESS;
133	print "$e->{w}{name} was modified\n" if $e->IN_MODIFY;
134	print "$e->{w}{name} is no longer mounted\n" if $e->IN_UNMOUNT;
135	print "events for $e->{w}{name} have been lost\n" if $e->IN_Q_OVERFLOW;
136
137	$e->w->cancel;
138	});
139
140	$inotify->fileno
141	Returns the file descriptor for this notify object. When in
142	non-blocking mode, you are responsible for calling the "poll" method
143	when this file descriptor becomes ready for reading.
144
145	$inotify->blocking ($blocking)
146	Clears ($blocking true) or sets ($blocking false) the "O_NONBLOCK"
147	flag on the file descriptor.
148
149	$count = $inotify->poll
150	Reads events from the kernel and handles them. If the notify file
151	descriptor is blocking (the default), then this method waits for at
152	least one event. Otherwise it returns immediately when no pending
153	events could be read.
154
155	Returns the count of events that have been handled (which can be 0
156	in case events have been received but have been ignored or handled
157	internally).
158
159	Croaks when an error occurs.
160
161	@events = $inotify->read
162	Reads events from the kernel. Blocks when the file descriptor is in
163	blocking mode (default) until any event arrives. Returns list of
164	"Linux::Inotify2::Event" objects or empty list if none (non-blocking
165	mode or events got ignored).
166
167	Croaks on error.
168
169	Normally you shouldn't use this function, but instead use watcher
170	callbacks and call "->poll".
171
172	$inotify->on_overflow ($cb->($ev))
173	Sets the callback to be used for overflow handling (default:
174	"undef"): When "read" receives an event with "IN_Q_OVERFLOW" set, it
175	will invoke this callback with the event.
176
177	When the callback is "undef", then it broadcasts the event to all
178	registered watchers, i.e., "undef" is equivalent to:
179
180	sub { $inotify->broadcast ($_[0]) }
181
182	$inotify->broadcast ($ev)
183	Invokes all registered watcher callbacks and passes the given event
184	to them. Most useful in overflow handlers.
185
186	The Linux::Inotify2::Event Class
187	Objects of this class are handed as first argument to the watcher
188	callback. It has the following members and methods:
189
190	$event->w
191	$event->{w}
192	The watcher object for this event, if one is available. Generally,
193	you cna only rely on the value of this member inside watcher
194	callbacks.
195
196	$event->name
197	$event->{name}
198	The path of the file system object, relative to the watched name.
199
200	$event->fullname
201	Returns the "full" name of the relevant object, i.e. including the
202	"name" member of the watcher (if the watch object is on a directory
203	and a directory entry is affected), or simply the "name" member
204	itself when the object is the watch object itself.
205
206	This call requires "$event->{w}" to be valid, which is generally
207	only the case within watcher callbacks.
208
209	$event->mask
210	$event->{mask}
211	The received event mask. In addition to the events described for
212	"$inotify->watch", the following flags (exported by default) can be
213	set:
214
215	IN_ISDIR event object is a directory
216	IN_Q_OVERFLOW event queue overflowed
217
218	# when any of the following flags are set,
219	# then watchers for this event are automatically canceled
220	IN_UNMOUNT filesystem for watched object was unmounted
221	IN_IGNORED file was ignored/is gone (no more events are delivered)
222	IN_ONESHOT only one event was generated
223	IN_Q_OVERFLOW queue overflow - event might not be specific to a watcher
224
225	$event->IN_xxx
226	Returns a boolean that returns true if the event mask contains any
227	events specified by the mask. All of the "IN_xxx" constants can be
228	used as methods.
229
230	$event->cookie
231	$event->{cookie}
232	The event cookie to "synchronize two events". Normally zero, this
233	value is set when two events relating to the same file are
234	generated. As far as I know, this only happens for "IN_MOVED_FROM"
235	and "IN_MOVED_TO" events, to identify the old and new name of a
236	file.
237
238	Note that the inotify API makes it impossible to know whether there
239	will be a "IN_MOVED_TO" event - you might receive only one of the
240	events, and even if you receive both, there might be any number of
241	events in between. The best approach seems to be to implement a
242	small timeout after "IN_MOVED_FROM" to see if a matching
243	"IN_MOVED_TO" event will be received - 2ms seem to work relatively
244	well.
245
246	The Linux::Inotify2::Watch Class
247	Watcher objects are created by calling the "watch" method of a notifier.
248
249	It has the following members and methods:
250
251	$watch->name
252	$watch->{name}
253	The name as specified in the "watch" call. For the object itself,
254	this is the empty string. For directory watches, this is the name of
255	the entry without leading path elements.
256
257	$watch->mask
258	$watch->{mask}
259	The mask as specified in the "watch" call.
260
261	$watch->cb ([new callback])
262	$watch->{cb}
263	The callback as specified in the "watch" call. Can optionally be
264	changed.
265
266	$watch->cancel
267	Cancels/removes this watcher. Future events, even if already queued
268	queued, will not be handled and resources will be freed.
269
270	SEE ALSO
271	AnyEvent, Linux::Inotify.
272
273	AUTHOR
274	Marc Lehmann <schmorp@schmorp.de>
275	http://home.schmorp.de/
276