1 .\" Copyright (c) 2000 Jonathan Lemon
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
9 .\" 2. Redistributions in binary form must reproduce the above copyright
10 .\" notice, this list of conditions and the following disclaimer in the
11 .\" documentation and/or other materials provided with the distribution.
13 .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND
14 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 .\" $FreeBSD: src/lib/libc/sys/kqueue.2,v 1.1.2.16 2002/07/02 21:05:08 mp Exp $
26 .\" $DragonFly: src/lib/libc/sys/kqueue.2,v 1.7 2008/05/02 02:05:04 swildner Exp $
34 .Nd kernel event notification mechanism
44 .Fn kevent "int kq" "const struct kevent *changelist" "int nchanges" "struct kevent *eventlist" "int nevents" "const struct timespec *timeout"
45 .Fn EV_SET "&kev" ident filter flags fflags data udata
48 provides a generic method of notifying the user when an event
49 happens or a condition holds, based on the results of small
50 pieces of kernel code termed filters.
51 A kevent is identified by the (ident, filter) pair; there may only
52 be one unique kevent per kqueue.
54 The filter is executed upon the initial registration of a kevent
55 in order to detect whether a preexisting condition is present, and is also
56 executed whenever an event is passed to the filter for evaluation.
57 If the filter determines that the condition should be reported,
58 then the kevent is placed on the kqueue for the user to retrieve.
60 The filter is also run when the user attempts to retrieve the kevent
62 If the filter indicates that the condition that triggered
63 the event no longer holds, the kevent is removed from the kqueue and
66 Multiple events which trigger the filter do not result in multiple
67 kevents being placed on the kqueue; instead, the filter will aggregate
68 the events into a single struct kevent.
71 on a file descriptor will remove any kevents that reference the descriptor.
74 creates a new kernel event queue and returns a descriptor.
75 The queue is not inherited by a child created with
81 flag, then the descriptor table is shared,
82 which will allow sharing of the kqueue between two processes.
85 is used to register events with the queue, and return any pending
88 is a pointer to an array of
90 structures, as defined in
92 All changes contained in the
94 are applied before any pending events are read from the queue.
99 is a pointer to an array of kevent structures.
101 determines the size of
105 is a non-NULL pointer, it specifies a maximum interval to wait
106 for an event, which will be interpreted as a struct timespec.
112 To effect a poll, the
114 argument should be non-NULL, pointing to a zero-valued
117 The same array may be used for the
123 is a macro which is provided for ease of initializing a
128 structure is defined as:
131 uintptr_t ident; /* identifier for this event */
132 short filter; /* filter for event */
133 u_short flags; /* action flags for kqueue */
134 u_int fflags; /* filter flag value */
135 intptr_t data; /* filter data value */
136 void *udata; /* opaque user data identifier */
143 .Bl -tag -width XXXfilter
145 Value used to identify this event.
146 The exact interpretation is determined by the attached filter,
147 but often is a file descriptor.
149 Identifies the kernel filter used to process this event.
150 The pre-defined system filters are described below.
152 Actions to perform on the event.
154 Filter-specific flags.
156 Filter-specific data value.
158 Opaque user-defined value passed through the kernel unchanged.
163 field can contain the following values:
164 .Bl -tag -width ".Dv EV_ONESHOT"
166 Adds the event to the kqueue.
167 Re-adding an existing event will modify the parameters of the original
168 event, and not result in a duplicate entry.
169 Adding an event automatically enables it, unless overridden by the
175 to return the event if it is triggered.
180 The filter itself is not disabled.
182 Removes the event from the kqueue.
183 Events which are attached to file descriptors are automatically
184 deleted on the last close of the descriptor.
186 Causes the event to return only the first occurrence of the filter
188 After the user retrieves the event from the kqueue, it is deleted.
190 After the event is retrieved by the user, its state is reset.
191 This is useful for filters which report state transitions
192 instead of the current state.
193 Note that some filters may automatically set this flag internally.
195 Filters may set this flag to indicate filter-specific EOF condition.
202 The predefined system filters are listed below.
203 Arguments may be passed to and from the filter via the
207 fields in the kevent structure.
208 .Bl -tag -width ".Dv EVFILT_SIGNAL"
210 Takes a descriptor as the identifier, and returns whenever
211 there is data available to read.
212 The behavior of the filter is slightly different depending
213 on the descriptor type.
216 Sockets which have previously been passed to
218 return when there is an incoming connection pending.
220 contains the size of the listen backlog.
222 Other socket descriptors return when there is data to be read,
225 value of the socket buffer.
226 This may be overridden with a per-filter low water mark at the
227 time the filter is added by setting the
231 and specifying the new low water mark in
235 contains the number of bytes in the socket buffer.
237 If the read direction of the socket has shutdown, then the filter also sets
241 and returns the socket error (if any) in
243 It is possible for EOF to be returned (indicating the connection is gone)
244 while there is still data pending in the socket buffer.
246 Returns when the file pointer is not at the end of file.
248 contains the offset from current position to end of file,
251 Returns when the there is data to read;
253 contains the number of bytes available.
255 When the last writer disconnects, the filter will set
259 This may be cleared by passing in
261 at which point the filter will resume waiting for data to become
262 available before returning.
265 Takes a descriptor as the identifier, and returns whenever
266 it is possible to write to the descriptor.
267 For sockets, pipes and fifos,
269 will contain the amount of space remaining in the write buffer.
272 when the reader disconnects, and for the fifo case, this may be cleared
275 Note that this filter is not supported for vnodes.
277 For sockets, the low water mark and socket error handling is
282 The sigevent portion of the AIO request is filled in, with
283 .Va sigev_notify_kqueue
284 containing the descriptor of the kqueue that the event should
287 containing the udata value, and
291 When the aio_* function is called, the event will be registered
292 with the specified kqueue, and the
296 returned by the aio_* function.
297 The filter returns under the same conditions as aio_error.
299 Alternatively, a kevent structure may be initialized, with
301 containing the descriptor of the kqueue, and the
302 address of the kevent structure placed in the
304 field of the AIO request.
305 However, this approach will not work on architectures with 64-bit
306 pointers, and should be considered deprecated.
308 Takes a file descriptor as the identifier and the events to watch for in
310 and returns when one or more of the requested events occurs on the descriptor.
311 The events to monitor are:
312 .Bl -tag -width ".Dv NOTE_RENAME"
315 was called on the file referenced by the descriptor.
317 A write occurred on the file referenced by the descriptor.
319 The file referenced by the descriptor was extended.
321 The file referenced by the descriptor had its attributes changed.
323 The link count on the file changed.
325 The file referenced by the descriptor was renamed.
327 Access to the file was revoked via
329 or the underlying fileystem was unmounted.
334 contains the events which triggered the filter.
336 Takes the process ID to monitor as the identifier and the events to watch for
339 and returns when the process performs one or more of the requested events.
340 If a process can normally see another process, it can attach an event to it.
341 The events to monitor are:
342 .Bl -tag -width ".Dv NOTE_TRACKERR"
344 The process has exited.
346 The process has called
349 The process has executed a new process via
353 Follow a process across
356 The parent process will return with
360 field, while the child process will return with
364 and the parent PID in
367 This flag is returned if the system was unable to attach an event to
368 the child process, usually due to resource limitations.
373 contains the events which triggered the filter.
375 Takes the signal number to monitor as the identifier and returns
376 when the given signal is delivered to the process.
377 This coexists with the
381 facilities, and has a lower precedence.
382 The filter will record all attempts to deliver a signal to a process,
383 even if the signal has been marked as
385 Event notification happens after normal signal delivery processing.
387 returns the number of times the signal has occurred since the last call to
389 This filter automatically sets the
393 Establishes an arbitrary timer identified by
397 specifies the timeout period in milliseconds.
398 The timer will be periodic unless
403 contains the number of times the timeout has expired since the last call to
405 This filter automatically sets the
411 creates a new kernel event queue and returns a file descriptor.
412 If there was an error creating the kernel event queue, a value of -1 is
418 returns the number of events placed in the
420 up to the value given by
422 If an error occurs while processing an element of the
424 and there is enough room in the
426 then the event will be placed in the
432 and the system error in
436 will be returned, and
438 will be set to indicate the error condition.
439 If the time limit expires, then
448 The kernel failed to allocate enough memory for the kernel queue.
450 The per-process descriptor table is full.
452 The system file table is full.
460 The process does not have permission to register a filter.
462 There was an error reading or writing the
466 The specified descriptor is invalid.
468 A signal was delivered before the timeout expired and before any
469 events were placed on the kqueue for return.
471 The specified time limit or filter is invalid.
473 The event could not be found to be modified or deleted.
475 No memory was available to register the event.
477 The specified process to attach to does not exist.
494 functions first appeared in
499 system and this manual page were written by
500 .An Jonathan Lemon Aq jlemon@FreeBSD.org .
502 It is currently not possible to watch a
504 that resides on anything but a