kobject: remove old, outdated documentation.
As we are replacing the documentation, it's easier to do this in a two stage pass, delete the old file and add the new one. Cc: Kay Sievers <kay.sievers@vrfy.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Greg Kroah-Hartman
parent
af5ca3f4ec
commit
5008743dc7
@ -1,289 +0,0 @@
|
||||
The kobject Infrastructure
|
||||
|
||||
Patrick Mochel <mochel@osdl.org>
|
||||
|
||||
Updated: 3 June 2003
|
||||
|
||||
|
||||
Copyright (c) 2003 Patrick Mochel
|
||||
Copyright (c) 2003 Open Source Development Labs
|
||||
|
||||
|
||||
0. Introduction
|
||||
|
||||
The kobject infrastructure performs basic object management that larger
|
||||
data structures and subsystems can leverage, rather than reimplement
|
||||
similar functionality. This functionality primarily concerns:
|
||||
|
||||
- Object reference counting.
|
||||
- Maintaining lists (sets) of objects.
|
||||
- Object set locking.
|
||||
- Userspace representation.
|
||||
|
||||
The infrastructure consists of a number of object types to support
|
||||
this functionality. Their programming interfaces are described below
|
||||
in detail, and briefly here:
|
||||
|
||||
- kobjects a simple object.
|
||||
- kset a set of objects of a certain type.
|
||||
- ktype a set of helpers for objects of a common type.
|
||||
|
||||
|
||||
The kobject infrastructure maintains a close relationship with the
|
||||
sysfs filesystem. Each kobject that is registered with the kobject
|
||||
core receives a directory in sysfs. Attributes about the kobject can
|
||||
then be exported. Please see Documentation/filesystems/sysfs.txt for
|
||||
more information.
|
||||
|
||||
The kobject infrastructure provides a flexible programming interface,
|
||||
and allows kobjects and ksets to be used without being registered
|
||||
(i.e. with no sysfs representation). This is also described later.
|
||||
|
||||
|
||||
1. kobjects
|
||||
|
||||
1.1 Description
|
||||
|
||||
|
||||
struct kobject is a simple data type that provides a foundation for
|
||||
more complex object types. It provides a set of basic fields that
|
||||
almost all complex data types share. kobjects are intended to be
|
||||
embedded in larger data structures and replace fields they duplicate.
|
||||
|
||||
1.2 Definition
|
||||
|
||||
struct kobject {
|
||||
const char * k_name;
|
||||
struct kref kref;
|
||||
struct list_head entry;
|
||||
struct kobject * parent;
|
||||
struct kset * kset;
|
||||
struct kobj_type * ktype;
|
||||
struct sysfs_dirent * sd;
|
||||
wait_queue_head_t poll;
|
||||
};
|
||||
|
||||
void kobject_init(struct kobject *);
|
||||
int kobject_add(struct kobject *);
|
||||
int kobject_register(struct kobject *);
|
||||
|
||||
void kobject_del(struct kobject *);
|
||||
void kobject_unregister(struct kobject *);
|
||||
|
||||
struct kobject * kobject_get(struct kobject *);
|
||||
void kobject_put(struct kobject *);
|
||||
|
||||
|
||||
1.3 kobject Programming Interface
|
||||
|
||||
kobjects may be dynamically added and removed from the kobject core
|
||||
using kobject_register() and kobject_unregister(). Registration
|
||||
includes inserting the kobject in the list of its dominant kset and
|
||||
creating a directory for it in sysfs.
|
||||
|
||||
Alternatively, one may use a kobject without adding it to its kset's list
|
||||
or exporting it via sysfs, by simply calling kobject_init(). An
|
||||
initialized kobject may later be added to the object hierarchy by
|
||||
calling kobject_add(). An initialized kobject may be used for
|
||||
reference counting.
|
||||
|
||||
Note: calling kobject_init() then kobject_add() is functionally
|
||||
equivalent to calling kobject_register().
|
||||
|
||||
When a kobject is unregistered, it is removed from its kset's list,
|
||||
removed from the sysfs filesystem, and its reference count is decremented.
|
||||
List and sysfs removal happen in kobject_del(), and may be called
|
||||
manually. kobject_put() decrements the reference count, and may also
|
||||
be called manually.
|
||||
|
||||
A kobject's reference count may be incremented with kobject_get(),
|
||||
which returns a valid reference to a kobject; and decremented with
|
||||
kobject_put(). An object's reference count may only be incremented if
|
||||
it is already positive.
|
||||
|
||||
When a kobject's reference count reaches 0, the method struct
|
||||
kobj_type::release() (which the kobject's kset points to) is called.
|
||||
This allows any memory allocated for the object to be freed.
|
||||
|
||||
|
||||
NOTE!!!
|
||||
|
||||
It is _imperative_ that you supply a destructor for dynamically
|
||||
allocated kobjects to free them if you are using kobject reference
|
||||
counts. The reference count controls the lifetime of the object.
|
||||
If it goes to 0, then it is assumed that the object will
|
||||
be freed and cannot be used.
|
||||
|
||||
More importantly, you must free the object there, and not immediately
|
||||
after an unregister call. If someone else is referencing the object
|
||||
(e.g. through a sysfs file), they will obtain a reference to the
|
||||
object, assume it's valid and operate on it. If the object is
|
||||
unregistered and freed in the meantime, the operation will then
|
||||
reference freed memory and go boom.
|
||||
|
||||
This can be prevented, in the simplest case, by defining a release
|
||||
method and freeing the object from there only. Note that this will not
|
||||
secure reference count/object management models that use a dual
|
||||
reference count or do other wacky things with the reference count
|
||||
(like the networking layer).
|
||||
|
||||
|
||||
1.4 sysfs
|
||||
|
||||
Each kobject receives a directory in sysfs. This directory is created
|
||||
under the kobject's parent directory.
|
||||
|
||||
If a kobject does not have a parent when it is registered, its parent
|
||||
becomes its dominant kset.
|
||||
|
||||
If a kobject does not have a parent nor a dominant kset, its directory
|
||||
is created at the top-level of the sysfs partition.
|
||||
|
||||
|
||||
|
||||
2. ksets
|
||||
|
||||
2.1 Description
|
||||
|
||||
A kset is a set of kobjects that are embedded in the same type.
|
||||
|
||||
|
||||
struct kset {
|
||||
struct kobj_type * ktype;
|
||||
struct list_head list;
|
||||
struct kobject kobj;
|
||||
struct kset_uevent_ops * uevent_ops;
|
||||
};
|
||||
|
||||
|
||||
void kset_init(struct kset * k);
|
||||
int kset_add(struct kset * k);
|
||||
int kset_register(struct kset * k);
|
||||
void kset_unregister(struct kset * k);
|
||||
|
||||
struct kset * kset_get(struct kset * k);
|
||||
void kset_put(struct kset * k);
|
||||
|
||||
struct kobject * kset_find_obj(struct kset *, char *);
|
||||
|
||||
|
||||
The type that the kobjects are embedded in is described by the ktype
|
||||
pointer.
|
||||
|
||||
A kset contains a kobject itself, meaning that it may be registered in
|
||||
the kobject hierarchy and exported via sysfs. More importantly, the
|
||||
kset may be embedded in a larger data type, and may be part of another
|
||||
kset (of that object type).
|
||||
|
||||
For example, a block device is an object (struct gendisk) that is
|
||||
contained in a set of block devices. It may also contain a set of
|
||||
partitions (struct hd_struct) that have been found on the device. The
|
||||
following code snippet illustrates how to express this properly.
|
||||
|
||||
struct gendisk * disk;
|
||||
...
|
||||
disk->kset.kobj.kset = &block_kset;
|
||||
disk->kset.ktype = &partition_ktype;
|
||||
kset_register(&disk->kset);
|
||||
|
||||
- The kset that the disk's embedded object belongs to is the
|
||||
block_kset, and is pointed to by disk->kset.kobj.kset.
|
||||
|
||||
- The type of objects on the disk's _subordinate_ list are partitions,
|
||||
and is set in disk->kset.ktype.
|
||||
|
||||
- The kset is then registered, which handles initializing and adding
|
||||
the embedded kobject to the hierarchy.
|
||||
|
||||
|
||||
2.2 kset Programming Interface
|
||||
|
||||
All kset functions, except kset_find_obj(), eventually forward the
|
||||
calls to their embedded kobjects after performing kset-specific
|
||||
operations. ksets offer a similar programming model to kobjects: they
|
||||
may be used after they are initialized, without registering them in
|
||||
the hierarchy.
|
||||
|
||||
kset_find_obj() may be used to locate a kobject with a particular
|
||||
name. The kobject, if found, is returned.
|
||||
|
||||
There are also some helper functions which names point to the formerly
|
||||
existing "struct subsystem", whose functions have been taken over by
|
||||
ksets.
|
||||
|
||||
|
||||
decl_subsys(name,type,uevent_ops)
|
||||
|
||||
Declares a kset named '<name>_subsys' of type <type> with
|
||||
uevent_ops <uevent_ops>. For example,
|
||||
|
||||
decl_subsys(devices, &ktype_device, &device_uevent_ops);
|
||||
|
||||
is equivalent to doing:
|
||||
|
||||
struct kset devices_subsys = {
|
||||
.ktype = &ktype_devices,
|
||||
.uevent_ops = &device_uevent_ops,
|
||||
};
|
||||
kobject_set_name(&devices_subsys, name);
|
||||
|
||||
The objects that are registered with a subsystem that use the
|
||||
subsystem's default list must have their kset ptr set properly. These
|
||||
objects may have embedded kobjects or ksets. The
|
||||
following helper makes setting the kset easier:
|
||||
|
||||
|
||||
kobj_set_kset_s(obj,subsys)
|
||||
|
||||
- Assumes that obj->kobj exists, and is a struct kobject.
|
||||
- Sets the kset of that kobject to the kset <subsys>.
|
||||
|
||||
int subsystem_register(struct kset *s);
|
||||
void subsystem_unregister(struct kset *s);
|
||||
|
||||
These are just wrappers around the respective kset_* functions.
|
||||
|
||||
2.3 sysfs
|
||||
|
||||
ksets are represented in sysfs when their embedded kobjects are
|
||||
registered. They follow the same rules of parenting, with one
|
||||
exception. If a kset does not have a parent, nor is its embedded
|
||||
kobject part of another kset, the kset's parent becomes its dominant
|
||||
subsystem.
|
||||
|
||||
If the kset does not have a parent, its directory is created at the
|
||||
sysfs root. This should only happen when the kset registered is
|
||||
embedded in a subsystem itself.
|
||||
|
||||
|
||||
3. struct ktype
|
||||
|
||||
3.1. Description
|
||||
|
||||
struct kobj_type {
|
||||
void (*release)(struct kobject *);
|
||||
struct sysfs_ops * sysfs_ops;
|
||||
struct attribute ** default_attrs;
|
||||
};
|
||||
|
||||
|
||||
Object types require specific functions for converting between the
|
||||
generic object and the more complex type. struct kobj_type provides
|
||||
the object-specific fields, which include:
|
||||
|
||||
- release: Called when the kobject's reference count reaches 0. This
|
||||
should convert the object to the more complex type and free it.
|
||||
|
||||
- sysfs_ops: Provides conversion functions for sysfs access. Please
|
||||
see the sysfs documentation for more information.
|
||||
|
||||
- default_attrs: Default attributes to be exported via sysfs when the
|
||||
object is registered.Note that the last attribute has to be
|
||||
initialized to NULL ! You can find a complete implementation
|
||||
in block/genhd.c
|
||||
|
||||
|
||||
Instances of struct kobj_type are not registered; only referenced by
|
||||
the kset. A kobj_type may be referenced by an arbitrary number of
|
||||
ksets, as there may be disparate sets of identical objects.
|
||||
|
||||
Loading…
Reference in New Issue
Block a user