The
kfilter_register() function adds a new kernel event filter (kfilter) to the system, for use by callers of
kqueue(2) and
kevent(2).
name is the name of the new filter (which must not already exist), and
filtops is a pointer to a
filterops structure which describes the filter operations. Both
name and
filtops will be copied to an internal data structure, and a new filter number will be allocated. If
retfilter is not
NULL, then the new filter number will be returned in the address pointed at by
retfilter.
The
kfilter_unregister() function removes a kfilter named
name that was previously registered with
kfilter_register(). If a filter with the same
name is later reregistered with
kfilter_register(), it will get a different filter number (i.e., filter numbers are not recycled). It is not possible to unregister the system filters (i.e., those that start with “EVFILT_” and are documented in
kqueue(2)).
The
filterops structure is defined as follows:
struct filterops {
int f_isfd; /* true if ident == filedescriptor */
int (*f_attach)(struct knote *kn);
/* called when knote is ADDed */
void (*f_detach)(struct knote *kn);
/* called when knote is DELETEd */
int (*f_event)(struct knote *kn, long hint);
/* called when event is triggered */
};
If the filter operation is for a file descriptor,
f_isfd should be non-zero, otherwise it should be zero. This controls where the
kqueue(2) system stores the knotes for an object.