NAME
hook_establish,
hook_disestablish —
add or remove a hook from a specified
list
SYNOPSIS
#include
<sys/types.h>
#include <sys/systm.h>
void *
hook_establish(struct
hook_desc_head *head, int
tail, void (*fn)(void
*), void *arg);
void
hook_disestablish(struct
hook_desc_head *head,
void *cookie);
DESCRIPTION
The
hook_establish()
function adds fn to the list of hooks invoked by
dohooks(9). If tail is non-zero, the hook is
added to the tail of the list denoted by the TAILQ_HEAD pointer
head, otherwise to the front. The
dohooks(9) function will at its invocation call each hook from the
front of this list. When invoked, the hook function fn
will be passed arg as its only argument.
The
hook_disestablish()
function removes the hook described by the opaque pointer
cookie from the list of hooks denoted by the
TAILQ_HEAD pointer head. If
cookie is invalid, the result of
hook_disestablish() is undefined.
The startup and mountroot systems use this API for their implementation.
RETURN VALUES
If successful, hook_establish() returns an
opaque pointer describing the newly established hook. Otherwise, it returns
NULL.