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.\" $FreeBSD$ 30.\" 31.Dd April 4, 2000 32.Dt KOBJ 9 33.Os 34.Sh NAME 35.Nm kobj 36.Nd a kernel object system for FreeBSD 37.Sh SYNOPSIS 38.In sys/param.h 39.In sys/kobj.h 40.Ft void 41.Fn kobj_class_compile "kobj_class_t cls" 42.Ft void 43.Fn kobj_class_compile_static "kobj_class_t cls" "kobj_ops_t ops" 44.Ft void 45.Fn kobj_class_free "kobj_class_t cls" 46.Ft kobj_t 47.Fn kobj_create "kobj_class_t cls" "struct malloc_type *mtype" "int mflags" 48.Ft void 49.Fn kobj_init "kobj_t obj" "kobj_class_t cls" 50.Ft void 51.Fn kobj_delete "kobj_t obj" "struct malloc_type *mtype" 52.Fn DEFINE_CLASS name "kobj_method_t *methods" "size_t size" 53.Sh DESCRIPTION 54The kernel object system implements an object-oriented programming 55system in the 56.Fx 57kernel. 58The system is based around the concepts of interfaces, which are 59descriptions of sets of methods; classes, which are lists of functions 60implementing certain methods from those interfaces; and objects, 61which combine a class with a structure in memory. 62.Pp 63Methods are called using a dynamic method dispatching algorithm which 64is designed to allow new interfaces and classes to be introduced into 65the system at runtime. 66The method dispatch algorithm is designed to be both fast and robust 67and is only slightly more expensive than a direct function call, 68making kernel objects suitable for performance-critical algorithms. 69.Pp 70Suitable uses for kernel objects are any algorithms which need some 71kind of polymorphism (i.e., many different objects which can be treated 72in a uniform way). 73The common behaviour of the objects is described by a suitable 74interface and each different type of object is implemented by a 75suitable class. 76.Pp 77The simplest way to create a kernel object is to call 78.Fn kobj_create 79with a suitable class, malloc type and flags (see 80.Xr malloc 9 81for a description of the malloc type and flags). 82This will allocate memory for the object based on the object size 83specified by the class and initialise it by zeroing the memory and 84installing a pointer to the class' method dispatch table. 85Objects created in this way should be freed by calling 86.Fn kobj_delete . 87.Pp 88Clients which would like to manage the allocation of memory 89themselves should call 90.Fn kobj_init 91with a pointer to the memory for the object and the class which 92implements it. 93It is also possible to use 94.Fn kobj_init 95to change the class for an object. 96This should be done with care as the classes must agree on the layout 97of the object. 98The device framework uses this feature to associate drivers with 99devices. 100.Pp 101The functions 102.Fn kobj_class_compile , 103.Fn kobj_class_compile_static 104and 105.Fn kobj_class_free 106are used to process a class description to make method dispatching 107efficient. 108A client should not normally need to call these since a class 109will automatically be compiled the first time it is used. 110If a class is to be used before 111.Xr malloc 9 112is initialised, 113then 114.Fn kobj_class_compile_static 115should be called with the class and a pointer to a statically 116allocated 117.Vt kobj_ops 118structure before the class is used to initialise any objects. 119.Pp 120To define a class, first define a simple array of 121.Vt kobj_method_t . 122Each method which the class implements should be entered into the 123table using the macro 124.Fn KOBJMETHOD 125which takes the name of the method (including its interface) and a 126pointer to a function which implements it. 127The table should be terminated with two zeros. 128The macro 129.Fn DEFINE_CLASS 130can then be used to initialise a 131.Vt kobj_class_t 132structure. 133The size argument to 134.Fn DEFINE_CLASS 135specifies how much memory should be allocated for each object. 136.Sh HISTORY 137Some of the concepts for this interface appeared in the device 138framework used for the alpha port of 139.Fx 3.0 140and more widely in 141.Fx 4.0 . 142.Sh AUTHORS 143This manual page was written by 144.An Doug Rabson . 145