132 lines
4.7 KiB
Groff
132 lines
4.7 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" Copyright (c) 2000 Doug Rabson
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.\"
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.\" All rights reserved.
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.\"
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.\" This program is free software.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd April 4, 2000
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.Dt KOBJ 9
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.Os FreeBSD
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.Sh NAME
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.Nm kobj
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.Nd a kernel object system for FreeBSD
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.Sh SYNOPSIS
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.Fd #include <sys/param.h>
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.Fd #include <sys/kobj.h>
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.Ft void
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.Fn kobj_class_compile "kobj_class_t cls"
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.Ft void
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.Fn kobj_class_free "kobj_class_t cls"
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.Ft kobj_t
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.Fn kobj_create "kobj_class_t cls" "struct malloc_type *mtype" "int mflags"
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.Ft void
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.Fn kobj_init "kobj_t obj" "kobj_class_t cls"
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.Ft void
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.Fn kobj_delete "kobj_t obj" "struct malloc_type *mtype"
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.Fn DEFINE_CLASS "name" "methods" "size"
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.Sh DESCRIPTION
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.Pp
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The kernel object system implements an object-oriented programming
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system in the FreeBSD kernel.
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The system is based around the concepts of interfaces, which are
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descriptions of sets of methods, classes which are lists of functions
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implementing certain methods from those interfaces and objects
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which combine a class with a structure in memory.
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.Pp
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Methods are called using a dynamic method dispatching algorithm which
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is designed to allow new interfaces and classes to be introduced into
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the system at runtime.
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The method dispatch algorithm is designed to be both fast and robust
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and is only slightly more expensive than a direct function call,
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making kernel objects suitable for performance-critical algorithms.
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.Pp
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Suitable uses for kernel objects are any algorithms which need some
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kind of polymorphism (i.e. many different objects which can be treated
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in a uniform way).
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The common behaviour of the objects is described by a suitable
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interface and each different type of object is implemented by a
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suitable class.
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.Pp
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The simplest way to create a kernel object is to call
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.Fn kobj_create
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with a suitable class, malloc type and flags (see
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.Xr malloc 9
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for a description of the malloc type and flags).
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This will allocate memory for the object based on the object size
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specified by the class and initialise it be zeroing the memory and
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installing a pointer to the class' method dispatch table.
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Objects created in this way should be freed by calling
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.Fn kobj_free .
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.Pp
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Clients which would like to manage the allocation of memory
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themselves should call
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.Fn kobj_init
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with a pointer to the memory for the object and the class which
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implements it.
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It is also possible to use
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.Fn kobj_init
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to change the class for an object.
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This should be done with care as the classes must agree on the layout
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of the object.
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The device framework uses this feature to associate drivers with
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devices.
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.Pp
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The functions
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.Fn kobj_class_compile
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and
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.Fn kobj_class_free
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are used to process a class description to make method despatching
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efficient.
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A client should not normally need to call these since a class
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will automatically be compiled the first time it is used.
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.Pp
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To define a class, first define a simple array of
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.Dv kobj_method_t .
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Each method which the class implements should be entered into the
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table using the macro
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.Fn KOBJMETHOD
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which takes the name of the method (including its interface) and a
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pointer to a function which implements it.
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The table should be terminated with two zeros.
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The macro
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.Fn DEFINE_CLASS
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can then be used to initialise a
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.Dv kobj_class_t
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structure.
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The size argument to
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.Fn DEFINE_CLASS
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specifies how much memory should be allocated for each object.
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.Sh HISTORY
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Some of the concepts for this interface appeared in the device
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framework used for the alpha port of
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.Fx 3.0
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and more widely in
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.Fx 4.0 .
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.Sh AUTHORS
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This man page was written by
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.An Doug Rabson .
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