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25 .\" $FreeBSD: src/lib/libc/sys/kqueue.2,v 1.1.2.16 2002/07/02 21:05:08 mp Exp $
33 .Nd kernel event notification mechanism
43 .Fn kevent "int kq" "const struct kevent *changelist" "int nchanges" "struct kevent *eventlist" "int nevents" "const struct timespec *timeout"
44 .Fn EV_SET "&kev" ident filter flags fflags data udata
47 provides a generic method of notifying the user when an event
48 happens or a condition holds, based on the results of small
49 pieces of kernel code termed filters.
50 A kevent is identified by the (ident, filter) pair; there may only
51 be one unique kevent per kqueue.
53 The filter is executed upon the initial registration of a kevent
54 in order to detect whether a preexisting condition is present, and is also
55 executed whenever an event is passed to the filter for evaluation.
56 If the filter determines that the condition should be reported,
57 then the kevent is placed on the kqueue for the user to retrieve.
59 The filter is also run when the user attempts to retrieve the kevent
61 If the filter indicates that the condition that triggered
62 the event no longer holds, the kevent is removed from the kqueue and
65 Multiple events which trigger the filter do not result in multiple
66 kevents being placed on the kqueue; instead, the filter will aggregate
67 the events into a single struct kevent.
70 on a file descriptor will remove any kevents that reference the descriptor.
73 creates a new kernel event queue and returns a descriptor.
74 The queue is not inherited by a child created with
80 flag, then the descriptor table is shared,
81 which will allow sharing of the kqueue between two processes.
84 is used to register events with the queue, and return any pending
87 is a pointer to an array of
89 structures, as defined in
91 All changes contained in the
93 are applied before any pending events are read from the queue.
98 is a pointer to an array of kevent structures.
100 determines the size of
104 is a non-NULL pointer, it specifies a maximum interval to wait
105 for an event, which will be interpreted as a struct timespec. If
109 waits indefinitely. To effect a poll, the
111 argument should be non-NULL, pointing to a zero-valued
113 structure. The same array may be used for the
119 is a macro which is provided for ease of initializing a
124 structure is defined as:
127 uintptr_t ident; /* identifier for this event */
128 short filter; /* filter for event */
129 u_short flags; /* action flags for kqueue */
130 u_int fflags; /* filter flag value */
131 intptr_t data; /* filter data value */
132 void *udata; /* opaque user data identifier */
139 .Bl -tag -width XXXfilter
141 Value used to identify this event.
142 The exact interpretation is determined by the attached filter,
143 but often is a file descriptor.
145 Identifies the kernel filter used to process this event. The pre-defined
146 system filters are described below.
148 Actions to perform on the event.
150 Filter-specific flags.
152 Filter-specific data value.
154 Opaque user-defined value passed through the kernel unchanged.
159 field can contain the following values:
160 .Bl -tag -width XXXEV_ONESHOT
162 Adds the event to the kqueue. Re-adding an existing event
163 will modify the parameters of the original event, and not result
164 in a duplicate entry. Adding an event automatically enables it,
165 unless overridden by the EV_DISABLE flag.
169 to return the event if it is triggered.
173 will not return it. The filter itself is not disabled.
175 Removes the event from the kqueue. Events which are attached to
176 file descriptors are automatically deleted on the last close of
179 Causes the event to return only the first occurrence of the filter
180 being triggered. After the user retrieves the event from the kqueue,
183 After the event is retrieved by the user, its state is reset.
184 This is useful for filters which report state transitions
185 instead of the current state. Note that some filters may automatically
186 set this flag internally.
188 Filters may set this flag to indicate filter-specific EOF condition.
195 The predefined system filters are listed below.
196 Arguments may be passed to and from the filter via the
200 fields in the kevent structure.
201 .Bl -tag -width EVFILT_SIGNAL
203 Takes a descriptor as the identifier, and returns whenever
204 there is data available to read.
205 The behavior of the filter is slightly different depending
206 on the descriptor type.
210 Sockets which have previously been passed to
212 return when there is an incoming connection pending.
214 contains the size of the listen backlog.
216 Other socket descriptors return when there is data to be read,
219 value of the socket buffer.
220 This may be overridden with a per-filter low water mark at the
221 time the filter is added by setting the
225 and specifying the new low water mark in
229 contains the number of bytes in the socket buffer.
231 If the read direction of the socket has shutdown, then the filter
234 and returns the socket error (if any) in
236 It is possible for EOF to be returned (indicating the connection is gone)
237 while there is still data pending in the socket buffer.
239 Returns when the file pointer is not at the end of file.
241 contains the offset from current position to end of file,
244 Returns when the there is data to read;
246 contains the number of bytes available.
248 When the last writer disconnects, the filter will set EV_EOF in
250 This may be cleared by passing in EV_CLEAR, at which point the
251 filter will resume waiting for data to become available before
255 Takes a descriptor as the identifier, and returns whenever
256 it is possible to write to the descriptor. For sockets, pipes
259 will contain the amount of space remaining in the write buffer.
260 The filter will set EV_EOF when the reader disconnects, and for
261 the fifo case, this may be cleared by use of EV_CLEAR.
262 Note that this filter is not supported for vnodes.
264 For sockets, the low water mark and socket error handling is
265 identical to the EVFILT_READ case.
267 The sigevent portion of the AIO request is filled in, with
268 .Va sigev_notify_kqueue
269 containing the descriptor of the kqueue that the event should
272 containing the udata value, and
275 When the aio_* function is called, the event will be registered
276 with the specified kqueue, and the
280 returned by the aio_* function.
281 The filter returns under the same conditions as aio_error.
283 Alternatively, a kevent structure may be initialized, with
285 containing the descriptor of the kqueue, and the
286 address of the kevent structure placed in the
288 field of the AIO request. However, this approach will not work on
289 architectures with 64-bit pointers, and should be considered depreciated.
291 Takes a file descriptor as the identifier and the events to watch for in
293 and returns when one or more of the requested events occurs on the descriptor.
294 The events to monitor are:
295 .Bl -tag -width XXNOTE_RENAME
298 was called on the file referenced by the descriptor.
300 A write occurred on the file referenced by the descriptor.
302 The file referenced by the descriptor was extended.
304 The file referenced by the descriptor had its attributes changed.
306 The link count on the file changed.
308 The file referenced by the descriptor was renamed.
310 Access to the file was revoked via
312 or the underlying fileystem was unmounted.
317 contains the events which triggered the filter.
319 Takes the process ID to monitor as the identifier and the events to watch for
322 and returns when the process performs one or more of the requested events.
323 If a process can normally see another process, it can attach an event to it.
324 The events to monitor are:
325 .Bl -tag -width XXNOTE_TRACKERR
327 The process has exited.
329 The process has called
332 The process has executed a new process via
336 Follow a process across
338 calls. The parent process will return with NOTE_TRACK set in the
340 field, while the child process will return with NOTE_CHILD set in
342 and the parent PID in
345 This flag is returned if the system was unable to attach an event to
346 the child process, usually due to resource limitations.
351 contains the events which triggered the filter.
353 Takes the signal number to monitor as the identifier and returns
354 when the given signal is delivered to the process.
355 This coexists with the
359 facilities, and has a lower precedence. The filter will record
360 all attempts to deliver a signal to a process, even if the signal has
361 been marked as SIG_IGN. Event notification happens after normal
362 signal delivery processing.
364 returns the number of times the signal has occurred since the last call to
366 This filter automatically sets the EV_CLEAR flag internally.
368 Establishes an arbitrary timer identified by
372 specifies the timeout period in milliseconds.
373 The timer will be periodic unless EV_ONESHOT is specified.
376 contains the number of times the timeout has expired since the last call to
378 This filter automatically sets the EV_CLEAR flag internally.
382 creates a new kernel event queue and returns a file descriptor.
383 If there was an error creating the kernel event queue, a value of -1 is
384 returned and errno set.
387 returns the number of events placed in the
389 up to the value given by
391 If an error occurs while processing an element of the
393 and there is enough room in the
395 then the event will be placed in the
401 and the system error in
405 will be returned, and
407 will be set to indicate the error condition.
408 If the time limit expires, then
417 The kernel failed to allocate enough memory for the kernel queue.
419 The per-process descriptor table is full.
421 The system file table is full.
429 The process does not have permission to register a filter.
431 There was an error reading or writing the
435 The specified descriptor is invalid.
437 A signal was delivered before the timeout expired and before any
438 events were placed on the kqueue for return.
440 The specified time limit or filter is invalid.
442 The event could not be found to be modified or deleted.
444 No memory was available to register the event.
446 The specified process to attach to does not exist.
463 functions first appeared in
468 system and this manual page were written by
469 .An Jonathan Lemon Aq jlemon@FreeBSD.org .
471 It is currently not possible to watch a
473 that resides on anything but