class.c 添加中文注释（1）

/*
* class.c - basic device class management
*
* Copyright (c) 2002-3 Patrick Mochel
* Copyright (c) 2002-3 Open Source Development Labs
* Copyright (c) 2003-2004 Greg Kroah-Hartman
* Copyright (c) 2003-2004 IBM Corp.
*
* This file is released under the GPLv2
*
*/

#include <linux/device.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/kdev_t.h>
#include <linux/err.h>
#include <linux/slab.h>
#include "base.h"

#define to_class_attr(_attr) container_of(_attr, struct class_attribute, attr)
#define to_class(obj) container_of(obj, struct class, subsys.kobj)

static ssize_t
class_attr_show(struct kobject * kobj, struct attribute * attr, char * buf)
{
/* [cgw]: 找出包含这个attr的struct class_attribute *指针 */
struct class_attribute * class_attr = to_class_attr(attr);
/* [cgw]: 找出包含这个kobj的struct class *指针，struct class没有直接
* 包含kobj，通过subsys.kobj间接找到struct class *指针
*/
struct class * dc = to_class(kobj);
ssize_t ret = -EIO;
/* [cgw]: class_attr->show指针不为空 */
if (class_attr->show)
/* [cgw]: 调用class_attr->show这个方法 */
ret = class_attr->show(dc, buf);
return ret;
}

static ssize_t
class_attr_store(struct kobject * kobj, struct attribute * attr,
const char * buf, size_t count)
{
/* [cgw]: 找出包含这个attr的struct class_attribute *指针 */
struct class_attribute * class_attr = to_class_attr(attr);
/* [cgw]: 找出包含这个kobj的struct class *指针，struct class没有直接
* 包含kobj，通过subsys.kobj间接找到struct class *指针
*/
struct class * dc = to_class(kobj);
ssize_t ret = -EIO;

/* [cgw]: class_attr->store指针不为空 */
if (class_attr->store)
/* [cgw]: 调用class_attr->store这个方法 */
ret = class_attr->store(dc, buf, count);
return ret;
}

static void class_release(struct kobject * kobj)
{
/* [cgw]: 找出包含这个kobj的struct class *指针，struct class没有直接
* 包含kobj，通过subsys.kobj间接找到struct class *指针
*/
struct class *class = to_class(kobj);

pr_debug("class '%s': release.\n", class->name);

/* [cgw]: 释放这个类的方法class->class_release指针不为空 */
if (class->class_release)
/* [cgw]: 调用这个方法 */
class->class_release(class);
else
pr_debug("class '%s' does not have a release() function, "
"be careful\n", class->name);
}

static struct sysfs_ops class_sysfs_ops = {
.show    = class_attr_show,
.store    = class_attr_store,
};

static struct kobj_type ktype_class = {
.sysfs_ops    = &class_sysfs_ops,
.release    = class_release,
};

/* Hotplug events for classes go to the class_obj subsys */
static decl_subsys(class, &ktype_class, NULL);

int class_create_file(struct class * cls, const struct class_attribute * attr)
{
int error;
/* [cgw]: cls指针不为空 */
if (cls) {
/* [cgw]: 为cls->subsys.kobj对象创建一个属性文件 */
error = sysfs_create_file(&cls->subsys.kobj, &attr->attr);
} else
error = -EINVAL;
return error;
}

void class_remove_file(struct class * cls, const struct class_attribute * attr)
{
/* [cgw]: cls指针不为空 */
if (cls)
/* [cgw]: 删除cls->subsys.kobj这个对象的属性文件 */
sysfs_remove_file(&cls->subsys.kobj, &attr->attr);
}

static struct class *class_get(struct class *cls)
{
/* [cgw]: cls不为空 */
if (cls)
/* [cgw]: cls->subsys.kobj引用计数+1，并返回cls指针 */
return container_of(subsys_get(&cls->subsys), struct class, subsys);
return NULL;
}

static void class_put(struct class * cls)
{
/* [cgw]: cls指针不为空 */
if (cls)
/* [cgw]: 实际上是cls->subsys.kobj引用计数-1 */
subsys_put(&cls->subsys);
}

static int add_class_attrs(struct class * cls)
{
int i;
int error = 0;

/* [cgw]: cls->class_attrs指针不为空 */
if (cls->class_attrs) {
/* [cgw]: cls->class_attrs指向了一个struct class_attribute数组
* 历遍这个数组，并为这个数组里的每一个元素创建一个属性
* 文件
*/
for (i = 0; attr_name(cls->class_attrs[i]); i++) {
/* [cgw]: 为cls->subsys.kobj创建一个属性文件 */
error = class_create_file(cls,&cls->class_attrs[i]);
/* [cgw]: 创建失败 */
if (error)
goto Err;
}
}
Done:
return error;
Err:
/* [cgw]: 逐个删除cls->subsys.kobj对应的属性文件列表 */
while (--i >= 0)
class_remove_file(cls,&cls->class_attrs[i]);
goto Done;
}

static void remove_class_attrs(struct class * cls)
{
int i;

/* [cgw]: cls->class_attrs指针不为空 */
if (cls->class_attrs) {
/* [cgw]: cls->class_attrs指向了一个struct class_attribute数组
* 历遍这个数组，并删除这个数组里的每一个元素对应的属
* 性文件
*/
for (i = 0; attr_name(cls->class_attrs[i]); i++)
/* [cgw]: 删除cls->subsys.kobj对应的一个属性文件 */
class_remove_file(cls,&cls->class_attrs[i]);
}
}

int class_register(struct class * cls)
{
int error;

pr_debug("device class '%s': registering\n", cls->name);

/* [cgw]: 初始化children链表 */
INIT_LIST_HEAD(&cls->children);
/* [cgw]: 初始化devices链表 */
INIT_LIST_HEAD(&cls->devices);
/* [cgw]: 初始化interfaces链表 */
INIT_LIST_HEAD(&cls->interfaces);
/* [cgw]: 初始化kset */
kset_init(&cls->class_dirs);
/* [cgw]: 初始化一个互斥信号量 */
init_MUTEX(&cls->sem);
/* [cgw]: 设置kobj的名字和类的一样 */
error = kobject_set_name(&cls->subsys.kobj, "%s", cls->name);
/* [cgw]: 设置kobj的名字失败 */
if (error)
return error;
/* [cgw]: cls->subsys.kobj.kset指向class_subsys (kset)
* 实际上是分配了一个kset
*/
subsys_set_kset(cls, class_subsys);
/* [cgw]: 注册子系统，实际上是注册了kset */
error = subsystem_register(&cls->subsys);
/* [cgw]: 注册成功 */
if (!error) {
/* [cgw]: 添加类属性 */
error = add_class_attrs(class_get(cls));
/* [cgw]: cls->subsys.kobj 引用计数-1
* why ????
*/
class_put(cls);
}
return error;
}

void class_unregister(struct class * cls)
{
pr_debug("device class '%s': unregistering\n", cls->name);
/* [cgw]: 删除这个类的所有属性文件 */
remove_class_attrs(cls);
/* [cgw]: 注销这个子系统，cls->subsys.kobj */
subsystem_unregister(&cls->subsys);
}

static void class_create_release(struct class *cls)
{
pr_debug("%s called for %s\n", __FUNCTION__, cls->name);
/* [cgw]: 释放这个已分配的struct class *的内存空间 */
kfree(cls);
}

static void class_device_create_release(struct class_device *class_dev)
{
pr_debug("%s called for %s\n", __FUNCTION__, class_dev->class_id);
/* [cgw]: 释放这个已分配的struct class_device *内存空间 */
kfree(class_dev);
}

/* needed to allow these devices to have parent class devices */
static int class_device_create_uevent(struct class_device *class_dev,
char **envp, int num_envp,
char *buffer, int buffer_size)
{
pr_debug("%s called for %s\n", __FUNCTION__, class_dev->class_id);
return 0;
}

/**
* class_create - create a struct class structure
* @owner: pointer to the module that is to "own" this struct class
* @name: pointer to a string for the name of this class.
*
* This is used to create a struct class pointer that can then be used
* in calls to class_device_create().
*
* Note, the pointer created here is to be destroyed when finished by
* making a call to class_destroy().
*/
struct class *class_create(struct module *owner, const char *name)
{
struct class *cls;
int retval;

/* [cgw]: 分配sizeof(*cls)个字节的内存空间 */
cls = kzalloc(sizeof(*cls), GFP_KERNEL);
/* [cgw]: 分配失败 */
if (!cls) {
retval = -ENOMEM;
goto error;
}

/* [cgw]: 给这个类分配一个名字 */
cls->name = name;
/* [cgw]: 这个类属于哪个内核模块 */
cls->owner = owner;
/* [cgw]: 分配用于释放这个struct class类的回调
* 当一个设备从这个类中移除时调用
*/
cls->class_release = class_create_release;
/* [cgw]: 分配用于释放这个struct class_device类的回调
* 当这个类本身被移除时调用
*/
cls->release = class_device_create_release;
/* [cgw]: 注册这个类 */
retval = class_register(cls);
/* [cgw]: 注册失败 */
if (retval)
goto error;

return cls;

error:
/* [cgw]: 释放这个类 */
kfree(cls);
return ERR_PTR(retval);
}

/**
* class_destroy - destroys a struct class structure
* @cls: pointer to the struct class that is to be destroyed
*
* Note, the pointer to be destroyed must have been created with a call
* to class_create().
*/
void class_destroy(struct class *cls)
{
if ((cls == NULL) || (IS_ERR(cls)))
return;
/* [cgw]: 注销这个类cls，这个类必须是由class_create()
* 创建的
*/
class_unregister(cls);
}