1.\" -*- nroff -*- 2.\" 3.\" Copyright (c) 2000 Doug Rabson 4.\" 5.\" All rights reserved. 6.\" 7.\" This program is free software. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 19.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 20.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 21.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 22.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 23.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 27.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28.\" 29.\" $FreeBSD: src/share/man/man9/kobj.9,v 1.16 2005/06/28 20:15:18 hmp Exp $ 30.\" $DragonFly: src/share/man/man9/kobj.9,v 1.5 2007/12/13 20:51:37 swildner Exp $ 31.\" 32.Dd April 4, 2000 33.Dt KOBJ 9 34.Os 35.Sh NAME 36.Nm kobj 37.Nd a kernel object system for DragonFly 38.Sh SYNOPSIS 39.In sys/param.h 40.In sys/kobj.h 41.Ft kobj_t 42.Fn kobj_create "kobj_class_t cls" "struct malloc_type *mtype" "int mflags" 43.Ft void 44.Fn kobj_init "kobj_t obj" "kobj_class_t cls" 45.Ft void 46.Fn kobj_delete "kobj_t obj" "struct malloc_type *mtype" 47.Fn DEFINE_CLASS name "kobj_method_t *methods" "size_t size" 48.Sh DESCRIPTION 49The kernel object system implements an object-oriented programming 50system in the 51.Dx 52kernel. 53The system is based around the concepts of interfaces, which are 54descriptions of sets of methods; classes, which are lists of functions 55implementing certain methods from those interfaces; and objects, 56which combine a class with a structure in memory. 57.Pp 58Methods are called using a dynamic method dispatching algorithm which 59is designed to allow new interfaces and classes to be introduced into 60the system at runtime. 61The method dispatch algorithm is designed to be both fast and robust 62and is only slightly more expensive than a direct function call, 63making kernel objects suitable for performance-critical algorithms. 64.Pp 65Suitable uses for kernel objects are any algorithms which need some 66kind of polymorphism (i.e., many different objects which can be treated 67in a uniform way). 68The common behaviour of the objects is described by a suitable 69interface and each different type of object is implemented by a 70suitable class. 71.Pp 72The simplest way to create a kernel object is to call 73.Fn kobj_create 74with a suitable class, malloc type and flags (see 75.Xr kmalloc 9 76for a description of the malloc type and flags). 77This will allocate memory for the object based on the object size 78specified by the class and initialise it by zeroing the memory and 79installing a pointer to the class' method dispatch table. 80Objects created in this way should be freed by calling 81.Fn kobj_delete . 82.Pp 83Clients which would like to manage the allocation of memory 84themselves should call 85.Fn kobj_init 86with a pointer to the memory for the object and the class which 87implements it. 88It is also possible to use 89.Fn kobj_init 90to change the class for an object. 91This should be done with care as the classes must agree on the layout 92of the object. 93The device framework uses this feature to associate drivers with 94devices. 95.Pp 96To define a class, first define a simple array of 97.Vt kobj_method_t . 98Each method which the class implements should be entered into the 99table using the macro 100.Fn KOBJMETHOD 101which takes the name of the method (including its interface) and a 102pointer to a function which implements it. 103The table should be terminated with two zeros. 104The macro 105.Fn DEFINE_CLASS 106can then be used to initialise a 107.Vt kobj_class_t 108structure. 109The size argument to 110.Fn DEFINE_CLASS 111specifies how much memory should be allocated for each object. 112.Sh HISTORY 113Some of the concepts for this interface appeared in the device 114framework used for the alpha port of 115.Fx 3.0 116and more widely in 117.Fx 4.0 . 118.Sh AUTHORS 119This manual page was written by 120.An Doug Rabson . 121