int
kqueue(
void
)
int
kevent(
int kq
, const struct kevent *changelist
, size_t nchanges
, struct kevent *eventlist
, size_t nevents
, const struct timespec *timeout
)
EV_SET(
&kev
, ident
, filter
, flags
, fflags
, data
, udata
)
)
provides a generic method of notifying the user when an event
happens or a condition holds, based on the results of small
pieces of kernel code termed filters.
A kevent is identified by the (ident, filter) pair; there may only
be one unique kevent per kqueue.
The filter is executed upon the initial registration of a kevent in order to detect whether a preexisting condition is present, and is also executed whenever an event is passed to the filter for evaluation. If the filter determines that the condition should be reported, then the kevent is placed on the kqueue for the user to retrieve.
The filter is also run when the user attempts to retrieve the kevent from the kqueue. If the filter indicates that the condition that triggered the event no longer holds, the kevent is removed from the kqueue and is not returned.
Multiple events which trigger the filter do not result in multiple
kevents being placed on the kqueue; instead, the filter will aggregate
the events into a single struct kevent.
Calling
close()
on a file descriptor will remove any kevents that reference the descriptor.
kqueue()
creates a new kernel event queue and returns a descriptor.
The queue is not inherited by a child created with
fork(2).
kevent()
is used to register events with the queue, and return any pending
events to the user.
changelist
is a pointer to an array of
kevent
structures, as defined in
<sys/event.h
>.
All changes contained in the
changelist
are applied before any pending events are read from the queue.
nchanges
gives the size of
changelist
.
eventlist
is a pointer to an array of kevent structures.
nevents
determines the size of
eventlist
.
If
timeout
is a
non-NULL
pointer, it specifies a maximum interval to wait
for an event, which will be interpreted as a struct timespec.
If
timeout
is a
NULL
pointer,
kevent()
waits indefinitely.
To effect a poll, the
timeout
argument should be
non-NULL
,
pointing to a zero-valued
timespec
structure.
The same array may be used for the
changelist
and
eventlist
.
EV_SET()
is a macro which is provided for ease of initializing a
kevent structure.
The
kevent
structure is defined as:
struct kevent {
uintptr_t ident; /* identifier for this event */
uint32_t filter; /* filter for event */
uint32_t flags; /* action flags for kqueue */
uint32_t fflags; /* filter flag value */
int64_t data; /* filter data value */
intptr_t udata; /* opaque user data identifier */
};
The fields of
struct
kevent
are:
The flags field can contain the following values:
)
to return the event if it is triggered.
)
will not return it.
The filter itself is not disabled.
As a third-party filter is referenced by a well-known name instead
of a statically assigned number, two
ioctl(2)s
are supported on the file descriptor returned by
kqueue()
to map a filter name to a filter number, and vice-versa (passing
arguments in a structure described below):
The following structure is used to pass arguments in and out of the ioctl(2):
struct kfilter_mapping {
char *name; /* name to lookup or return */
size_t len; /* length of name */
uint32_t filter; /* filter to lookup or return */
};
Arguments may be passed to and from the filter via the fflags and data fields in the kevent structure.
The predefined system filters are:
)
return when there is an incoming connection pending.
data
contains the size of the listen backlog (i.e., the number of
connections ready to be accepted with
accept(2).)
Other socket descriptors return when there is data to be read,
subject to the
SO_RCVLOWAT
value of the socket buffer.
This may be overridden with a per-filter low water mark at the
time the filter is added by setting the
NOTE_LOWAT
flag in
fflags,
and specifying the new low water mark in
data.
On return,
data
contains the number of bytes in the socket buffer.
If the read direction of the socket has shutdown, then the filter also sets EV_EOF in flags, and returns the socket error (if any) in fflags. It is possible for EOF to be returned (indicating the connection is gone) while there is still data pending in the socket buffer.
When the last writer disconnects, the filter will set EV_EOF in flags. This may be cleared by passing in EV_CLEAR, at which point the filter will resume waiting for data to become available before returning.
For sockets, the low water mark and socket error handling is identical to the EVFILT_READ case.
)
was called on the file referenced by the descriptor.
On return, fflags contains the events which triggered the filter.
).
)
calls.
The parent process will return with NOTE_TRACK set in the
fflags
field, while the child process will return with NOTE_CHILD set in
fflags
and the parent PID in
data.
On return, fflags contains the events which triggered the filter.
)
and
sigaction(
)
facilities, and has a lower precedence.
The filter will record
all attempts to deliver a signal to a process, even if the signal has
been marked as SIG_IGN.
Event notification happens after normal signal delivery processing.
data
returns the number of times the signal has occurred since the last call to
kevent(
).
This filter automatically sets the EV_CLEAR flag internally.
).
This filter automatically sets the EV_CLEAR flag internally.
)
creates a new kernel event queue and returns a file descriptor.
If there was an error creating the kernel event queue, a value of -1 is
returned and errno set.
kevent()
returns the number of events placed in the
eventlist
,
up to the value given by
nevents
.
If an error occurs while processing an element of the
changelist
and there is enough room in the
eventlist
,
then the event will be placed in the
eventlist
with
EV_ERROR
set in
flags
and the system error in
data.
Otherwise,
-1
will be returned, and
errno
will be set to indicate the error condition.
If the time limit expires, then
kevent()
returns 0.
)
function fails if:
ENOMEM
]
EMFILE
]
ENFILE
]
The
kevent()
function fails if:
EACCES
]
EFAULT
]
EBADF
]
EINTR
]
EINVAL
]
ENOENT
]
ENOMEM
]
ESRCH
]
)
and
kevent(
)
functions first appeared in
FreeBSD4.1,
and then in
NetBSD2.0.
)
system and this manual page were written by
Jonathan Lemon <jlemon@FreeBSD.org>