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36 .Nd a kernel object system for FreeBSD
41 .Fn kobj_class_compile "kobj_class_t cls"
43 .Fn kobj_class_compile_static "kobj_class_t cls" "kobj_ops_t ops"
45 .Fn kobj_class_free "kobj_class_t cls"
47 .Fn kobj_create "kobj_class_t cls" "struct malloc_type *mtype" "int mflags"
49 .Fn kobj_init "kobj_t obj" "kobj_class_t cls"
51 .Fn kobj_delete "kobj_t obj" "struct malloc_type *mtype"
52 .Fn DEFINE_CLASS name "kobj_method_t *methods" "size_t size"
54 The kernel object system implements an object-oriented programming
58 The system is based around the concepts of interfaces, which are
59 descriptions of sets of methods; classes, which are lists of functions
60 implementing certain methods from those interfaces; and objects,
61 which combine a class with a structure in memory.
63 Methods are called using a dynamic method dispatching algorithm which
64 is designed to allow new interfaces and classes to be introduced into
65 the system at runtime.
66 The method dispatch algorithm is designed to be both fast and robust
67 and is only slightly more expensive than a direct function call,
68 making kernel objects suitable for performance-critical algorithms.
70 Suitable uses for kernel objects are any algorithms which need some
71 kind of polymorphism (i.e., many different objects which can be treated
73 The common behaviour of the objects is described by a suitable
74 interface and each different type of object is implemented by a
77 The simplest way to create a kernel object is to call
79 with a suitable class, malloc type and flags (see
81 for a description of the malloc type and flags).
82 This will allocate memory for the object based on the object size
83 specified by the class and initialise it by zeroing the memory and
84 installing a pointer to the class' method dispatch table.
85 Objects created in this way should be freed by calling
88 Clients which would like to manage the allocation of memory
89 themselves should call
91 with a pointer to the memory for the object and the class which
93 It is also possible to use
95 to change the class for an object.
96 This should be done with care as the classes must agree on the layout
98 The device framework uses this feature to associate drivers with
102 .Fn kobj_class_compile ,
103 .Fn kobj_class_compile_static
106 are used to process a class description to make method dispatching
108 A client should not normally need to call these since a class
109 will automatically be compiled the first time it is used.
110 If a class is to be used before
114 .Fn kobj_class_compile_static
115 should be called with the class and a pointer to a statically
118 structure before the class is used to initialise any objects.
120 To define a class, first define a simple array of
122 Each method which the class implements should be entered into the
123 table using the macro
125 which takes the name of the method (including its interface) and a
126 pointer to a function which implements it.
127 The table should be terminated with two zeros.
130 can then be used to initialise a
135 specifies how much memory should be allocated for each object.
137 Some of the concepts for this interface appeared in the device
138 framework used for the alpha port of
143 This manual page was written by