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     kqueue_add_filteropts, kqueue_del_filteropts, kqfd_register, knote_fdclose, knlist_add,
     knlist_remove, knlist_remove_inevent, knlist_empty, knlist_init, knlist_destroy,
     knlist_clear, knlist_delete, KNOTE_LOCKED, KNOTE_UNLOCKED — event delivery subsystem


     #include <sys/event.h>

     kqueue_add_filteropts(int filt, struct filterops *filtops);

     kqueue_del_filteropts(int filt);

     kqfd_register(int fd, struct kevent *kev, struct thread *td, int waitok);

     knote_fdclose(struct thread *td, int fd);

     knlist_add(struct knlist *knl, struct knote *kn, int islocked);

     knlist_remove(struct knlist *knl, struct knote *kn, int islocked);

     knlist_remove_inevent(struct knlist *knl, struct knote *kn);

     knlist_empty(struct knlist *knl);

     knlist_init(struct knlist *knl, void *lock, void (*kl_lock)(void *),
         void (*kl_unlock)(void *), int (*kl_locked)(void *));

     knlist_destroy(struct knlist *knl);

     knlist_clear(struct knlist *knl, int islocked);

     knlist_delete(struct knlist *knl, struct thread *td, int islocked);

     KNOTE_LOCKED(struct knlist *knl, long hint);

     KNOTE_UNLOCKED(struct knlist *knl, long hint);


     The functions kqueue_add_filteropts() and kqueue_del_filteropts() allow for the addition and
     removal of a filter type.  The filter is statically defined by the EVFILT_* macros.  The
     function kqueue_add_filteropts() will make filt available.  The struct filterops has the
     following members:

     f_isfd    If f_isfd is set, ident in struct kevent is taken to be a file descriptor.  In
               this case, the knote passed into f_attach will have the kn_fp member initialized
               to the struct file * that represents the file descriptor.

     f_attach  The f_attach function will be called when attaching a knote to the object.  The
               method should call knlist_add() to add the knote to the list that was initialized
               with knlist_init().  The call to knlist_add() is only necessary if the object can
               have multiple knotes associated with it.  If there is no knlist to call
               knlist_add() with, the function f_attach must clear the KN_DETACHED bit of
               kn_status in the knote.  The function shall return 0 on success, or appropriate
               error for the failure.  During f_attach, it is valid to change the kn_fops pointer
               to a different pointer.  This will change the f_event and f_detach functions
               called when processing the knote.

     f_detach  The f_detach function will be called to detach the knote if the knote has not
               already been detached by a call to knlist_remove().

     f_event   The f_event function will be called to update the status of the knote.  If the
               function returns 0, it will be assumed that the object is not ready (or no longer
               ready) to be woken up.  The hint argument will be 0 when scanning knotes to see
               which are triggered.  Otherwise, the hint argument will be the value passed to
               either KNOTE_LOCKED or KNOTE_UNLOCKED.  The kn_data value should be updated as
               necessary to reflect the current value, such as number of bytes available for
               reading, or buffer space available for writing.  If the note needs to be removed,
               knlist_remove_inevent() must be called.  The function knlist_remove_inevent() will
               remove the note from the list, the f_detach function will not be called and the
               knote will not be returned as an event.

               Locks must not be acquired in f_event.  If a lock is required in f_event, it must
               be obtained in the kl_lock function of the knlist that the knote was added to.

     The function kqfd_register() will register the kevent on the kqueue file descriptor fd.  If
     it is safe to sleep, waitok should be set.

     The function knote_fdclose() is used to delete all knotes associated with fd.  Once
     returned, there will no longer be any knotes associated with the fd.  The knotes removed
     will never be returned from a kevent(2) call, so if userland uses the knote to track
     resources, they will be leaked.  The FILEDESC_LOCK() lock must be held over the call to
     knote_fdclose() so that file descriptors cannot be added or removed.

     The knlist_*() family of functions are for managing knotes associated with an object.  A
     knlist is not required, but is commonly used.  If used, the knlist must be initialized with
     the knlist_init() function.  If lock is NULL, an internal lock will be used and the
     remaining arguments will be ignored.  The kl_lock, kl_unlock and kl_locked functions will be
     used to manipulate a lock.  If the argument is NULL, default routines operating on struct
     mtx * will be used.  The knlist structure may be embedded into the object structure.  The
     lock will be held over calls to f_event.  If NULL is passed for the mutex, a private mutex
     will be used.  The function knlist_empty() requires that a lock be held.  The function
     knlist_clear() is used to remove all knotes associated with the list.  The islocked argument
     declares if lock has been acquired.  All knotes will be marked as detached, and EV_ONESHOT
     will be set so that the knote will be deleted after the next scan.  The knlist_destroy()
     function is used to destroy a knlist.  There must be no knotes associated with the knlist
     (knlist_empty() returns true) and no more knotes may be attached to the object.  A knlist
     may be emptied by calling knlist_clear().

     The macros KNOTE_LOCKED() and KNOTE_UNLOCKED() are used to notify knotes about events
     associated with the object.  It will iterate over all knotes on the list calling the f_event
     function associated with the knote.  The macro KNOTE_LOCKED() must be used if the lock
     associated with the knl passed in is held.  The function KNOTE_UNLOCKED() will acquire the
     lock before iterating over the list of knotes.


     The function kqueue_add_filteropts() will return zero on success, EINVAL in the case of an
     invalid filt, or EEXIST if the filter has already been installed.

     The function kqueue_del_filteropts() will return zero on success, EINVAL in the case of an
     invalid filt, or EBUSY if the filter is still in use.

     The function kqfd_register() will return zero on success, EBADF if the file descriptor is
     not a kqueue, or any of the possible values returned by kevent(2).


     kevent(2), kqueue(2)


     This manual page was written by John-Mark Gurney <>.