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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

     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

     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

     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 ⟨⟩.