1.\" $OpenBSD: hook_establish.9,v 1.2 2001/07/28 00:09:24 mpech 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 July 27 2001 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 of such 35.Sh SYNOPSIS 36.Fd #include <sys/systm.h> 37.Ft void * 38.Fn hook_establish "struct hook_desc_head *head" "int tail" "void (*fn)(void *)" "void *arg" 39.Ft void 40.Fn hook_disestablish "struct hook_desc_head *head" "void *cookie" 41.Sh DESCRIPTION 42The 43.Fn hook_establish 44function adds 45.Fa fn 46to the list of hooks invoked by 47.Xr dohooks 9 . 48If 49.Fa tail 50is non-zero, the hook is added to the tail of the list 51denoted by the TAILQ_HEAD pointer 52.Fa head , 53otherwise to the front. 54The 55.Xr dohooks 9 56function will at its invocation call each hook from the front of this 57list. 58When invoked, the hook function 59.Fa fn 60will be passed 61.Fa arg 62as its only argument. 63.Pp 64The 65.Fn hook_disestablish 66function removes the hook described by the opaque pointer 67.Fa cookie 68from the list of hooks denoted by the TAILQ_HEAD pointer 69.Fa head . 70If 71.Fa cookie 72is invalid, the result of 73.Fn hook_disestablish 74is undefined. 75.Pp 76Both the startup- and shutdownhooks systems uses this API for their 77implementation. 78.Sh RETURN VALUES 79If successful, 80.Fn hook_establish 81returns an opaque pointer describing the newly established 82hook. 83Otherwise, it returns 84.Dv NULL . 85.Sh SEE ALSO 86.Xr dohooks 9 , 87.Xr doshutdownhooks 9 , 88.Xr dostartuphooks 9 , 89.Xr shutdownhook_establish 9 , 90.Xr startuphook_establish 9 91