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d7ecd801ed
curthread-accessing part of mtx_{,un}lock(9) when using a r210623-style
curthread implementation on sparc64, crashing the kernel in its early
cycles as PCPU isn't set up, yet (and can't be set up as OFW is one of the
things we need for that, which leads to a chicken-and-egg problem). What
happens is that due to the fact that the idea of r210623 actually is to
allow the compiler to cache invocations of curthread, it factors out
obtaining curthread needed for both mtx_lock(9) and mtx_unlock(9) to
before the branch based on kobj_mutex_inited when compiling the kernel
without the debugging options. So change kobj_class_compile_static(9)
to just never acquire kobj_mtx, effectively restricting it to its
documented use, and add a kobj_init_static(9) for initializing objects
using a class compiled with the former and that also avoids using mutex(9)
(and malloc(9)). Also assert in both of these functions that they are
used in their intended way only.
While at it, inline kobj_register_method() and kobj_unregister_method()
as there wasn't much point for factoring them out in the first place
and so that a reader of the code has to figure out the locking for
fewer functions missing a KOBJ_ASSERT.
Tested on powerpc{,64} by andreast.
Reviewed by: nwhitehorn (earlier version), jhb
MFC after: 3 days
157 lines
5.3 KiB
Groff
157 lines
5.3 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 November 14, 2011
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.Dt KOBJ 9
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.Os
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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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.In sys/param.h
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.In 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_compile_static "kobj_class_t cls" "kobj_ops_t ops"
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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_init_static "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 "kobj_method_t *methods" "size_t size"
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.Sh DESCRIPTION
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The kernel object system implements an object-oriented programming
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system in the
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.Fx
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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 by 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_delete .
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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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or
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.Fn kobj_init_static
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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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and
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.Fn kobj_init_static
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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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.Fn kobj_class_compile_static
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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 dispatching
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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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If a class is to be used before
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.Xr malloc 9
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and
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.Xr mutex 9
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are initialised,
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then
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.Fn kobj_class_compile_static
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should be called with the class and a pointer to a statically
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allocated
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.Vt kobj_ops
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structure before the class is used to initialise any objects.
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In that case, also
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.Fn kobj_init_static
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should be used instead of
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.Fn kobj_init .
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.Pp
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To define a class, first define a simple array of
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.Vt 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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.Vt 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 manual page was written by
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.An Doug Rabson .
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