Message-ID: <20070727134110.53053188@gondolin.boeblingen.de.ibm.com>
Date:	Fri, 27 Jul 2007 13:41:10 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Greg KH <gregkh@...e.de>
Cc:	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix kobject documentation

<Removed Patrick's e-mail address as it bounces>

Update kobject documentation:

- Update structure definitions.
- Remove documentation of removed struct subsystem.

(First shot, uevent_ops probably need some documentation as well.)

Signed-off-by: Cornelia Huck <cornelia.huck@...ibm.com>

---
 Documentation/kobject.txt |  178 +++++++++++++++-------------------------------
 1 file changed, 59 insertions(+), 119 deletions(-)

--- linux-2.6.orig/Documentation/kobject.txt
+++ linux-2.6/Documentation/kobject.txt
@@ -27,7 +27,6 @@ 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. 
-- subsystem	a controlling object for a number of ksets.
 
 
 The kobject infrastructure maintains a close relationship with the
@@ -54,13 +53,15 @@ embedded in larger data structures and r
 1.2 Definition
 
 struct kobject {
+	const char		* k_name;
 	char			name[KOBJ_NAME_LEN];
-	atomic_t		refcount;
+	struct kref		kref;
 	struct list_head	entry;
 	struct kobject		* parent;
 	struct kset		* kset;
 	struct kobj_type	* ktype;
-	struct dentry		* dentry;
+	struct sysfs_dirent	* sd;
+	wait_queue_head_t	poll;
 };
 
 void kobject_init(struct kobject *);
@@ -137,8 +138,7 @@ If a kobject does not have a parent when
 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. This should only
-happen for kobjects that are embedded in a struct subsystem. 
+is created at the top-level of the sysfs partition.
 
 
 
@@ -150,10 +150,10 @@ A kset is a set of kobjects that are emb
 
 
 struct kset {
-	struct subsystem	* subsys;
 	struct kobj_type	* ktype;
 	struct list_head	list;
 	struct kobject		kobj;
+	struct kset_uevent_ops	* uevent_ops;
 };
 
 
@@ -169,8 +169,7 @@ struct kobject * kset_find_obj(struct ks
 
 
 The type that the kobjects are embedded in is described by the ktype
-pointer. The subsystem that the kobject belongs to is pointed to by the
-subsys pointer. 
+pointer.
 
 A kset contains a kobject itself, meaning that it may be registered in
 the kobject hierarchy and exported via sysfs. More importantly, the
@@ -209,6 +208,58 @@ 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 = {
+     .kobj = {
+	   .name = "devices",
+     },
+     .ktype = &ktype_devices,
+     .uevent_ops = &device_uevent_ops,
+};
+
+
+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 helpers make 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>.
+
+
+kset_set_kset_s(obj,subsys)
+
+- Assumes that obj->kset exists, and is a struct kset.
+- Sets the kset of the embedded kobject to the kset <subsys>.
+
+subsys_set_kset(obj,subsys)
+
+- Assumes obj->subsys exists, and is a struct subsystem.
+- Sets obj->subsys.kset.kobj.kset to the subsystem's embedded kset.
+
+void subsystem_init(struct kset *s);
+int subsystem_register(struct kset *s);
+void subsystem_unregister(struct kset *s);
+struct kset *subsys_get(struct kset *s);
+void kset_put(struct kset *s);
+
+These are just wrappers around the respective kset_* functions.
 
 2.3 sysfs
 
@@ -254,114 +305,3 @@ Instances of struct kobj_type are not re
 the kset. A kobj_type may be referenced by an arbitrary number of
 ksets, as there may be disparate sets of identical objects. 
 
-
-
-4. subsystems
-
-4.1 Description
-
-A subsystem represents a significant entity of code that maintains an
-arbitrary number of sets of objects of various types. Since the number
-of ksets and the type of objects they contain are variable, a
-generic representation of a subsystem is minimal. 
-
-
-struct subsystem {
-	struct kset		kset;
-	struct rw_semaphore	rwsem;
-};
-
-int subsystem_register(struct subsystem *);
-void subsystem_unregister(struct subsystem *);
-
-struct subsystem * subsys_get(struct subsystem * s);
-void subsys_put(struct subsystem * s);
-
-
-A subsystem contains an embedded kset so:
-
-- It can be represented in the object hierarchy via the kset's
-  embedded kobject. 
-
-- It can maintain a default list of objects of one type. 
-
-Additional ksets may attach to the subsystem simply by referencing the
-subsystem before they are registered. (This one-way reference means
-that there is no way to determine the ksets that are attached to the
-subsystem.) 
-
-All ksets that are attached to a subsystem share the subsystem's R/W
-semaphore. 
-
-
-4.2 subsystem Programming Interface.
-
-The subsystem programming interface is simple and does not offer the
-flexibility that the kset and kobject programming interfaces do. They
-may be registered and unregistered, as well as reference counted. Each
-call forwards the calls to their embedded ksets (which forward the
-calls to their embedded kobjects).
-
-
-4.3 Helpers
-
-A number of macros are available to make dealing with subsystems and
-their embedded objects easier. 
-
-
-decl_subsys(name,type)
-
-Declares a subsystem named '<name>_subsys', with an embedded kset of
-type <type>. For example, 
-
-decl_subsys(devices,&ktype_devices);
-
-is equivalent to doing:
-
-struct subsystem device_subsys = {
-       .kset = {
-	     .kobj = {
-		   .name = "devices",
-	     },
-	     .ktype = &ktype_devices,
-	}
-}; 
-
-
-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, ksets, or other subsystems. The
-following helpers make 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 subsystem's embedded kset.
-
-
-kset_set_kset_s(obj,subsys)
-
-- Assumes that obj->kset exists, and is a struct kset.
-- Sets the kset of the embedded kobject to the subsystem's 
-  embedded kset. 
-
-subsys_set_kset(obj,subsys)
-
-- Assumes obj->subsys exists, and is a struct subsystem.
-- Sets obj->subsys.kset.kobj.kset to the subsystem's embedded kset.
-
-
-4.4 sysfs
-
-subsystems are represented in sysfs via their embedded kobjects. They
-follow the same rules as previously mentioned with no exceptions. They
-typically receive a top-level directory in sysfs, except when their
-embedded kobject is part of another kset, or the parent of the
-embedded kobject is explicitly set. 
-
-Note that the subsystem's embedded kset must be 'attached' to the
-subsystem itself in order to use its rwsem. This is done after
-kset_add() has been called. (Not before, because kset_add() uses its
-subsystem for a default parent if it doesn't already have one).
-
-
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