1Inotify2(3) User Contributed Perl Documentation Inotify2(3)
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6 Linux::Inotify2 - scalable directory/file change notification
7
9 Callback Interface
10 use Linux::Inotify2;
11 # create a new object
13 my $inotify = new Linux::Inotify2
14 or die "unable to create new inotify object: $!";
15 # add watchers
17 $inotify->watch ("/etc/passwd", IN_ACCESS, sub {
18 my $e = shift;
19 my $name = $e->fullname;
20 print "$name was accessed\n" if $e->IN_ACCESS;
21 print "$name is no longer mounted\n" if $e->IN_UNMOUNT;
22 print "$name is gone\n" if $e->IN_IGNORED;
23 print "events for $name have been lost\n" if $e->IN_Q_OVERFLOW;
24 # cancel this watcher: remove no further events
26 $e->w->cancel;
27 });
28 # integration into AnyEvent (works with EV, Glib, Tk, POE...)
30 my $inotify_w = AE::io $inotify->fileno, 0, sub { $inotify->poll };
31 # manual event loop
33 $inotify->poll while 1;
34 Streaming Interface
36 use Linux::Inotify2;
37 # create a new object
39 my $inotify = new Linux::Inotify2
40 or die "Unable to create new inotify object: $!";
41 # create watch
43 $inotify->watch ("/etc/passwd", IN_ACCESS)
44 or die "watch creation failed";
45 while () {
47 my @events = $inotify->read;
48 printf "mask\t%d\n", $_->mask foreach @events;
49 }
50
52 This module implements an interface to the Linux 2.6.13 and later
53 Inotify file/directory change notification system.
54 It has a number of advantages over the Linux::Inotify module:
56 - it is portable (Linux::Inotify only works on x86)
58 - the equivalent of fullname works correctly
59 - it is better documented
60 - it has callback-style interface, which is better suited for
61 integration.
62 As for the inotify API itself - it is a very tricky, and somewhat
64 unreliable API. For a good overview of the challenges you might run
65 into, see this LWN article: <https://lwn.net/Articles/605128/>.
66 The Linux::Inotify2 Class
68 my $inotify = new Linux::Inotify2
69 Create a new notify object and return it. A notify object is kind
70 of a container that stores watches on file system names and is
71 responsible for handling event data.
72 On error, "undef" is returned and $! will be set accordingly. The
74 following errors are documented:
75 ENFILE The system limit on the total number of file descriptors has been reached.
77 EMFILE The user limit on the total number of inotify instances has been reached.
78 ENOMEM Insufficient kernel memory is available.
79 Example:
81 my $inotify = new Linux::Inotify2
83 or die "Unable to create new inotify object: $!";
84 $watch = $inotify->watch ($name, $mask[, $cb])
86 Add a new watcher to the given notifier. The watcher will create
87 events on the pathname $name as given in $mask, which can be any of
88 the following constants (all exported by default) ORed together.
89 "file" refers to any file system object in the watched object
91 (always a directory), that is files, directories, symlinks, device
92 nodes etc., while "object" refers to the object the watcher has
93 been set on itself:
94 IN_ACCESS object was accessed
96 IN_MODIFY object was modified
97 IN_ATTRIB object metadata changed
98 IN_CLOSE_WRITE writable fd to file / to object was closed
99 IN_CLOSE_NOWRITE readonly fd to file / to object closed
100 IN_OPEN object was opened
101 IN_MOVED_FROM file was moved from this object (directory)
102 IN_MOVED_TO file was moved to this object (directory)
103 IN_CREATE file was created in this object (directory)
104 IN_DELETE file was deleted from this object (directory)
105 IN_DELETE_SELF object itself was deleted
106 IN_MOVE_SELF object itself was moved
107 IN_ALL_EVENTS all of the above events
108 IN_ONESHOT only send event once
110 IN_ONLYDIR only watch the path if it is a directory
111 IN_DONT_FOLLOW don't follow a sym link (Linux 2.6.15+)
112 IN_EXCL_UNLINK don't create events for unlinked objects (Linux 2.6.36+)
113 IN_MASK_ADD not supported with the current version of this module
114 IN_CLOSE same as IN_CLOSE_WRITE | IN_CLOSE_NOWRITE
116 IN_MOVE same as IN_MOVED_FROM | IN_MOVED_TO
117 $cb is a perl code reference that, if given, is called for each
119 event. It receives a "Linux::Inotify2::Event" object.
120 The returned $watch object is of class "Linux::Inotify2::Watch".
122 On error, "undef" is returned and $! will be set accordingly. The
124 following errors are documented:
125 EBADF The given file descriptor is not valid.
127 EINVAL The given event mask contains no legal events.
128 ENOMEM Insufficient kernel memory was available.
129 ENOSPC The user limit on the total number of inotify watches was reached or the kernel failed to allocate a needed resource.
130 EACCESS Read access to the given file is not permitted.
131 Example, show when "/etc/passwd" gets accessed and/or modified
133 once:
134 $inotify->watch ("/etc/passwd", IN_ACCESS | IN_MODIFY, sub {
136 my $e = shift;
137 print "$e->{w}{name} was accessed\n" if $e->IN_ACCESS;
138 print "$e->{w}{name} was modified\n" if $e->IN_MODIFY;
139 print "$e->{w}{name} is no longer mounted\n" if $e->IN_UNMOUNT;
140 print "events for $e->{w}{name} have been lost\n" if $e->IN_Q_OVERFLOW;
141 $e->w->cancel;
143 });
144 $inotify->fileno
146 Returns the file descriptor for this notify object. When in non-
147 blocking mode, you are responsible for calling the "poll" method
148 when this file descriptor becomes ready for reading.
149 $inotify->blocking ($blocking)
151 Clears ($blocking true) or sets ($blocking false) the "O_NONBLOCK"
152 flag on the file descriptor.
153 $count = $inotify->poll
155 Reads events from the kernel and handles them. If the notify file
156 descriptor is blocking (the default), then this method waits for at
157 least one event. Otherwise it returns immediately when no pending
158 events could be read.
159 Returns the count of events that have been handled (which can be 0
161 in case events have been received but have been ignored or handled
162 internally).
163 Croaks when an error occurs.
165 @events = $inotify->read
167 Reads events from the kernel. Blocks when the file descriptor is in
168 blocking mode (default) until any event arrives. Returns list of
169 "Linux::Inotify2::Event" objects or empty list if none (non-
170 blocking mode or events got ignored).
171 Croaks on error.
173 Normally you shouldn't use this function, but instead use watcher
175 callbacks and call "->poll".
176 $inotify->on_overflow ($cb->($ev))
178 Sets the callback to be used for overflow handling (default:
179 "undef"): When "read" receives an event with "IN_Q_OVERFLOW" set,
180 it will invoke this callback with the event.
181 When the callback is "undef", then it broadcasts the event to all
183 registered watchers, i.e., "undef" is equivalent to:
184 sub { $inotify->broadcast ($_[0]) }
186 $inotify->broadcast ($ev)
188 Invokes all registered watcher callbacks and passes the given event
189 to them. Most useful in overflow handlers.
190 The Linux::Inotify2::Event Class
192 Objects of this class are handed as first argument to the watcher
193 callback. It has the following members and methods:
194 $event->w
196 $event->{w}
197 The watcher object for this event, if one is available. Generally,
198 you cna only rely on the value of this member inside watcher
199 callbacks.
200 $event->name
202 $event->{name}
203 The path of the file system object, relative to the watched name.
204 $event->fullname
206 Returns the "full" name of the relevant object, i.e. including the
207 "name" member of the watcher (if the watch object is on a directory
208 and a directory entry is affected), or simply the "name" member
209 itself when the object is the watch object itself.
210 This call requires "$event->{w}" to be valid, which is generally
212 only the case within watcher callbacks.
213 $event->mask
215 $event->{mask}
216 The received event mask. In addition to the events described for
217 "$inotify->watch", the following flags (exported by default) can be
218 set:
219 IN_ISDIR event object is a directory
221 IN_Q_OVERFLOW event queue overflowed
222 # when any of the following flags are set,
224 # then watchers for this event are automatically canceled
225 IN_UNMOUNT filesystem for watched object was unmounted
226 IN_IGNORED file was ignored/is gone (no more events are delivered)
227 IN_ONESHOT only one event was generated
228 IN_Q_OVERFLOW queue overflow - event might not be specific to a watcher
229 $event->IN_xxx
231 Returns a boolean that returns true if the event mask contains any
232 events specified by the mask. All of the "IN_xxx" constants can be
233 used as methods.
234 $event->cookie
236 $event->{cookie}
237 The event cookie to "synchronize two events". Normally zero, this
238 value is set when two events relating to the same file are
239 generated. As far as I know, this only happens for "IN_MOVED_FROM"
240 and "IN_MOVED_TO" events, to identify the old and new name of a
241 file.
242 Note that the inotify API makes it impossible to know whether there
244 will be a "IN_MOVED_TO" event - you might receive only one of the
245 events, and even if you receive both, there might be any number of
246 events in between. The best approach seems to be to implement a
247 small timeout after "IN_MOVED_FROM" to see if a matching
248 "IN_MOVED_TO" event will be received - 2ms seem to work relatively
249 well.
250 The Linux::Inotify2::Watch Class
252 Watcher objects are created by calling the "watch" method of a
253 notifier.
254 It has the following members and methods:
256 $watch->name
258 $watch->{name}
259 The name as specified in the "watch" call. For the object itself,
260 this is the empty string. For directory watches, this is the name
261 of the entry without leading path elements.
262 $watch->mask
264 $watch->{mask}
265 The mask as specified in the "watch" call.
266 $watch->cb ([new callback])
268 $watch->{cb}
269 The callback as specified in the "watch" call. Can optionally be
270 changed.
271 $watch->cancel
273 Cancels/removes this watcher. Future events, even if already queued
274 queued, will not be handled and resources will be freed.
275
277 AnyEvent, Linux::Inotify.
278
280 Marc Lehmann <schmorp@schmorp.de>
281 http://home.schmorp.de/
282perl v5.30.0 2019-07-26 Inotify2(3)