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NAME |
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Linux::Inotify2 - scalable directory/file change notification |
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|
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SYNOPSIS |
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Callback Interface |
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use Linux::Inotify2; |
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|
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# create a new object |
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my $inotify = new Linux::Inotify2 |
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or die "unable to create new inotify object: $!"; |
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|
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# add watchers |
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$inotify->watch ("/etc/passwd", IN_ACCESS, sub { |
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my $e = shift; |
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my $name = $e->fullname; |
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print "$name was accessed\n" if $e->IN_ACCESS; |
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print "$name is no longer mounted\n" if $e->IN_UNMOUNT; |
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print "$name is gone\n" if $e->IN_IGNORED; |
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print "events for $name have been lost\n" if $e->IN_Q_OVERFLOW; |
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|
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# cancel this watcher: remove no further events |
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$e->w->cancel; |
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}); |
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|
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# integration into AnyEvent (works with EV, Glib, Tk, POE...) |
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my $inotify_w = AE::io $inotify->fileno, 0, sub { $inotify->poll }; |
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|
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# manual event loop |
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$inotify->poll while 1; |
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|
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Streaming Interface |
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use Linux::Inotify2; |
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|
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# create a new object |
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my $inotify = new Linux::Inotify2 |
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or die "Unable to create new inotify object: $!"; |
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|
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# create watch |
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$inotify->watch ("/etc/passwd", IN_ACCESS) |
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or die "watch creation failed"; |
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|
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while () { |
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my @events = $inotify->read; |
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printf "mask\t%d\n", $_->mask foreach @events; |
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} |
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|
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DESCRIPTION |
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This module implements an interface to the Linux 2.6.13 and later |
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Inotify file/directory change notification system. |
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|
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It has a number of advantages over the Linux::Inotify module: |
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|
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- it is portable (Linux::Inotify only works on x86) |
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- the equivalent of fullname works correctly |
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- it is better documented |
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- it has callback-style interface, which is better suited for |
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integration. |
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|
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As for the inotify API itself - it is a very tricky, and somewhat |
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unreliable API. For a good overview of the challenges you might run |
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into, see this LWN article: <https://lwn.net/Articles/605128/>. |
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|
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The Linux::Inotify2 Class |
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my $inotify = new Linux::Inotify2 |
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Create a new notify object and return it. A notify object is kind of |
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a container that stores watches on file system names and is |
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responsible for handling event data. |
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|
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On error, "undef" is returned and $! will be set accordingly. The |
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following errors are documented: |
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|
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ENFILE The system limit on the total number of file descriptors has been reached. |
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EMFILE The user limit on the total number of inotify instances has been reached. |
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ENOMEM Insufficient kernel memory is available. |
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|
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Example: |
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|
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my $inotify = new Linux::Inotify2 |
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or die "Unable to create new inotify object: $!"; |
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|
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$watch = $inotify->watch ($name, $mask[, $cb]) |
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Add a new watcher to the given notifier. The watcher will create |
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events on the pathname $name as given in $mask, which can be any of |
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the following constants (all exported by default) ORed together. |
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Constants unavailable on your system will evaluate to 0. |
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|
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"file" refers to any file system object in the watched object |
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(always a directory), that is files, directories, symlinks, device |
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nodes etc., while "object" refers to the object the watcher has been |
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set on itself: |
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|
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IN_ACCESS object was accessed |
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IN_MODIFY object was modified |
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IN_ATTRIB object metadata changed |
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IN_CLOSE_WRITE writable fd to file / to object was closed |
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IN_CLOSE_NOWRITE readonly fd to file / to object closed |
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IN_OPEN object was opened |
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IN_MOVED_FROM file was moved from this object (directory) |
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IN_MOVED_TO file was moved to this object (directory) |
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IN_CREATE file was created in this object (directory) |
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IN_DELETE file was deleted from this object (directory) |
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IN_DELETE_SELF object itself was deleted |
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IN_MOVE_SELF object itself was moved |
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IN_ALL_EVENTS all of the above events |
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|
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IN_ONESHOT only send event once |
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IN_ONLYDIR only watch the path if it is a directory |
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IN_DONT_FOLLOW don't follow a sym link (Linux 2.6.15+) |
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IN_EXCL_UNLINK don't create events for unlinked objects (Linux 2.6.36+) |
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IN_MASK_ADD not supported with the current version of this module |
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|
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IN_CLOSE same as IN_CLOSE_WRITE | IN_CLOSE_NOWRITE |
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IN_MOVE same as IN_MOVED_FROM | IN_MOVED_TO |
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|
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$cb is a perl code reference that, if given, is called for each |
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event. It receives a "Linux::Inotify2::Event" object. |
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|
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The returned $watch object is of class "Linux::Inotify2::Watch". |
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|
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On error, "undef" is returned and $! will be set accordingly. The |
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following errors are documented: |
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|
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EBADF The given file descriptor is not valid. |
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EINVAL The given event mask contains no legal events. |
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ENOMEM Insufficient kernel memory was available. |
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ENOSPC The user limit on the total number of inotify watches was reached or the kernel failed to allocate a needed resource. |
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EACCESS Read access to the given file is not permitted. |
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|
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Example, show when "/etc/passwd" gets accessed and/or modified once: |
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|
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$inotify->watch ("/etc/passwd", IN_ACCESS | IN_MODIFY, sub { |
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my $e = shift; |
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print "$e->{w}{name} was accessed\n" if $e->IN_ACCESS; |
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print "$e->{w}{name} was modified\n" if $e->IN_MODIFY; |
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print "$e->{w}{name} is no longer mounted\n" if $e->IN_UNMOUNT; |
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print "events for $e->{w}{name} have been lost\n" if $e->IN_Q_OVERFLOW; |
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|
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$e->w->cancel; |
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}); |
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|
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$inotify->fileno |
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Returns the file descriptor for this notify object. When in |
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non-blocking mode, you are responsible for calling the "poll" method |
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when this file descriptor becomes ready for reading. |
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|
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$inotify->fh |
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Similar to "fileno", but returns a perl file handle instead. |
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|
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$inotify->blocking ($blocking) |
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Clears ($blocking true) or sets ($blocking false) the "O_NONBLOCK" |
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flag on the file descriptor. |
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|
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$count = $inotify->poll |
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Reads events from the kernel and handles them. If the notify file |
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descriptor is blocking (the default), then this method waits for at |
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least one event. Otherwise it returns immediately when no pending |
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events could be read. |
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|
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Returns the count of events that have been handled (which can be 0 |
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in case events have been received but have been ignored or handled |
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internally). |
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|
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Croaks when an error occurs. |
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|
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@events = $inotify->read |
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Reads events from the kernel. Blocks when the file descriptor is in |
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blocking mode (default) until any event arrives. Returns list of |
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"Linux::Inotify2::Event" objects or empty list if none (non-blocking |
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mode or events got ignored). |
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|
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Croaks on error. |
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|
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Normally you shouldn't use this function, but instead use watcher |
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callbacks and call "->poll". |
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|
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$inotify->on_overflow ($cb->($ev)) |
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Sets the callback to be used for overflow handling (default: |
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"undef"): When "read" receives an event with "IN_Q_OVERFLOW" set, it |
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will invoke this callback with the event. |
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|
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When the callback is "undef", then it broadcasts the event to all |
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registered watchers, i.e., "undef" is equivalent to: |
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|
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sub { $inotify->broadcast ($_[0]) } |
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|
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$inotify->broadcast ($ev) |
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Invokes all registered watcher callbacks and passes the given event |
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to them. Most useful in overflow handlers. |
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|
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The Linux::Inotify2::Event Class |
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Objects of this class are handed as first argument to the watcher |
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callback. It has the following members and methods: |
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|
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$event->w |
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$event->{w} |
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The watcher object for this event, if one is available. Generally, |
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you cna only rely on the value of this member inside watcher |
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callbacks. |
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|
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$event->name |
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$event->{name} |
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The path of the file system object, relative to the watched name. |
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|
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$event->fullname |
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Returns the "full" name of the relevant object, i.e. including the |
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"name" member of the watcher (if the watch object is on a directory |
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and a directory entry is affected), or simply the "name" member |
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itself when the object is the watch object itself. |
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|
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This call requires "$event->{w}" to be valid, which is generally |
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only the case within watcher callbacks. |
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|
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$event->mask |
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$event->{mask} |
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The received event mask. In addition to the events described for |
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"$inotify->watch", the following flags (exported by default) can be |
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set: |
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|
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IN_ISDIR event object is a directory |
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IN_Q_OVERFLOW event queue overflowed |
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|
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# when any of the following flags are set, |
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# then watchers for this event are automatically canceled |
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IN_UNMOUNT filesystem for watched object was unmounted |
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IN_IGNORED file was ignored/is gone (no more events are delivered) |
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IN_ONESHOT only one event was generated |
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IN_Q_OVERFLOW queue overflow - event might not be specific to a watcher |
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|
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$event->IN_xxx |
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Returns a boolean that returns true if the event mask contains any |
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events specified by the mask. All of the "IN_xxx" constants can be |
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used as methods. |
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|
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$event->cookie |
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$event->{cookie} |
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The event cookie to "synchronize two events". Normally zero, this |
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value is set when two events relating to the same file are |
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generated. As far as I know, this only happens for "IN_MOVED_FROM" |
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and "IN_MOVED_TO" events, to identify the old and new name of a |
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file. |
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|
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Note that the inotify API makes it impossible to know whether there |
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will be a "IN_MOVED_TO" event - you might receive only one of the |
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events, and even if you receive both, there might be any number of |
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events in between. The best approach seems to be to implement a |
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small timeout after "IN_MOVED_FROM" to see if a matching |
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"IN_MOVED_TO" event will be received - 2ms seem to work relatively |
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well. |
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|
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The Linux::Inotify2::Watch Class |
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Watcher objects are created by calling the "watch" method of a notifier. |
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|
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It has the following members and methods: |
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|
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$watch->name |
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$watch->{name} |
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The name as specified in the "watch" call. For the object itself, |
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this is the empty string. For directory watches, this is the name of |
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the entry without leading path elements. |
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|
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$watch->mask |
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$watch->{mask} |
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The mask as specified in the "watch" call. |
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|
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$watch->cb ([new callback]) |
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$watch->{cb} |
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The callback as specified in the "watch" call. Can optionally be |
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changed. |
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|
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$watch->cancel |
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Cancels/removes this watcher. Future events, even if already queued |
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queued, will not be handled and resources will be freed. |
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|
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SEE ALSO |
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AnyEvent, Linux::Inotify. |
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|
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AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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|
