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kobj - a kernel object system for FreeBSD
Methods are called using a dynamic method dispatching algorithm which is designed to allow new interfaces and classes to be introduced into the system at runtime. The method dispatch algorithm is designed to be both fast and robust and is only slightly more expensive than a direct function call, making kernel objects suitable for performance-critical algorithms.
Suitable uses for kernel objects are any algorithms which need some kind of polymorphism (i.e., many different objects which can be treated in a uniform way). The common behaviour of the objects is described by a suitable interface and each different type of object is implemented by a suitable class.
The simplest way to create a kernel object is to call
kobj_create ();
with a suitable class, malloc type and flags (see
malloc(9)
for a description of the malloc type and flags).
This will allocate memory for the object based on the object size
specified by the class and initialise it by zeroing the memory and
installing a pointer to the class' method dispatch table.
Objects created in this way should be freed by calling
kobj_delete (.);
Clients which would like to manage the allocation of memory
themselves should call
kobj_init ();
with a pointer to the memory for the object and the class which
implements it.
It is also possible to use
kobj_init ();
to change the class for an object.
This should be done with care as the classes must agree on the layout
of the object.
The device framework uses this feature to associate drivers with
devices.
The functions
kobj_class_compile (,);
kobj_class_compile_static ();
and
kobj_class_free ();
are used to process a class description to make method dispatching
efficient.
A client should not normally need to call these since a class
will automatically be compiled the first time it is used.
If a class is to be used before
malloc(9)
is initialised,
then
kobj_class_compile_static ();
should be called with the class and a pointer to a statically
allocated
Vt kobj_ops
structure before the class is used to initialise any objects.
To define a class, first define a simple array of
Vt kobj_method_t .
Each method which the class implements should be entered into the
table using the macro
KOBJMETHOD ();
which takes the name of the method (including its interface) and a
pointer to a function which implements it.
The table should be terminated with two zeros.
The macro
DEFINE_CLASS ();
can then be used to initialise a
Vt kobj_class_t
structure.
The size argument to
DEFINE_CLASS ();
specifies how much memory should be allocated for each object.
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Created 1996-2024 by Maxim Chirkov Добавить, Поддержать, Вебмастеру |