1.\" $OpenBSD: hook_establish.9,v 1.12 2015/12/12 11:26:32 mpi Exp $ 2.\" 3.\" Copyright (c) 2001 Niklas Hallqvist. 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. The name of the author may not be used to endorse or promote products 15.\" derived from this software without specific prior written permission 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27.\" 28.Dd $Mdocdate: December 12 2015 $ 29.Dt HOOK_ESTABLISH 9 30.Os 31.Sh NAME 32.Nm hook_establish , 33.Nm hook_disestablish 34.Nd add or remove a hook from a specified list 35.Sh SYNOPSIS 36.In sys/types.h 37.In sys/systm.h 38.Ft void * 39.Fn hook_establish "struct hook_desc_head *head" "int tail" "void (*fn)(void *)" "void *arg" 40.Ft void 41.Fn hook_disestablish "struct hook_desc_head *head" "void *cookie" 42.Sh DESCRIPTION 43The 44.Fn hook_establish 45function adds 46.Fa fn 47to the list of hooks invoked by 48.Xr dohooks 9 . 49If 50.Fa tail 51is non-zero, the hook is added to the tail of the list 52denoted by the TAILQ_HEAD pointer 53.Fa head , 54otherwise to the front. 55The 56.Xr dohooks 9 57function will at its invocation call each hook from the front of this 58list. 59When invoked, the hook function 60.Fa fn 61will be passed 62.Fa arg 63as its only argument. 64.Pp 65The 66.Fn hook_disestablish 67function removes the hook described by the opaque pointer 68.Fa cookie 69from the list of hooks denoted by the TAILQ_HEAD pointer 70.Fa head . 71If 72.Fa cookie 73is invalid, the result of 74.Fn hook_disestablish 75is undefined. 76.Pp 77The startup and mountroot systems use this API for their 78implementation. 79.Sh RETURN VALUES 80If successful, 81.Fn hook_establish 82returns an opaque pointer describing the newly established 83hook. 84Otherwise, it returns 85.Dv NULL . 86.Sh SEE ALSO 87.Xr dohooks 9 , 88.Xr dostartuphooks 9 , 89.Xr startuphook_establish 9 90