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.Dd November 14, 2011 30.Dt KOBJ 9 31.Os 32.Sh NAME 33.Nm kobj 34.Nd a kernel object system for FreeBSD 35.Sh SYNOPSIS 36.In sys/param.h 37.In sys/kobj.h 38.Ft void 39.Fn kobj_class_compile "kobj_class_t cls" 40.Ft void 41.Fn kobj_class_compile_static "kobj_class_t cls" "kobj_ops_t ops" 42.Ft void 43.Fn kobj_class_free "kobj_class_t cls" 44.Ft kobj_t 45.Fn kobj_create "kobj_class_t cls" "struct malloc_type *mtype" "int mflags" 46.Ft void 47.Fn kobj_init "kobj_t obj" "kobj_class_t cls" 48.Ft void 49.Fn kobj_init_static "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 91or 92.Fn kobj_init_static 93with a pointer to the memory for the object and the class which 94implements it. 95It is also possible to use 96.Fn kobj_init 97and 98.Fn kobj_init_static 99to change the class for an object. 100This should be done with care as the classes must agree on the layout 101of the object. 102The device framework uses this feature to associate drivers with 103devices. 104.Pp 105The functions 106.Fn kobj_class_compile , 107.Fn kobj_class_compile_static 108and 109.Fn kobj_class_free 110are used to process a class description to make method dispatching 111efficient. 112A client should not normally need to call these since a class 113will automatically be compiled the first time it is used. 114If a class is to be used before 115.Xr malloc 9 116and 117.Xr mutex 9 118are initialised, 119then 120.Fn kobj_class_compile_static 121should be called with the class and a pointer to a statically 122allocated 123.Vt kobj_ops 124structure before the class is used to initialise any objects. 125In that case, also 126.Fn kobj_init_static 127should be used instead of 128.Fn kobj_init . 129.Pp 130To define a class, first define a simple array of 131.Vt kobj_method_t . 132Each method which the class implements should be entered into the 133table using the macro 134.Fn KOBJMETHOD 135which takes the name of the method (including its interface) and a 136pointer to a function which implements it. 137The table should be terminated with two zeros. 138The macro 139.Fn DEFINE_CLASS 140can then be used to initialise a 141.Vt kobj_class_t 142structure. 143The size argument to 144.Fn DEFINE_CLASS 145specifies how much memory should be allocated for each object. 146.Sh HISTORY 147Some of the concepts for this interface appeared in the device 148framework used for the alpha port of 149.Fx 3.0 150and more widely in 151.Fx 4.0 . 152.Sh AUTHORS 153This manual page was written by 154.An Doug Rabson . 155