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http://wanderer-zjhit.blogbus.com/logs/149965638.html
注：样例结合/sysfs探索2阅读，效果较好
简单分析：
1 本样例主要测试kobject结构，kobject对应sysfs文件系统中的一个目录，该目录对应一个具体的事物。
2 首先通过example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);将该结构加入 到/sys/kernel目录下[kernel_kobj为kernel子系统的kobject结构]，形成层次结构，并且在父目录下建立该子目录[kobject->sd指向该kobject所在的目录节点]。
3 通过retval = sysfs_create_group(example_kobj, &attr_group)将事物的3个特色属性与其对应的kobject绑定起来,将该文件操作接口和sysfs系统结合起来。使得可以通过kobj_attribute中的show何store进行实际的内核读写操作，该函数实际上在父目录下新建3个文件，结构用sysfs_dirent表示。且sysfs_dirent->s_attr.attr=相应属性结构，据此可获得读写该文件的方法。
4 每个struct attribute结构对应kobject目录下一个文件，文件的读写方法由kobj_attribute中的show和store指定，kobj_attribute是kobject属性导出的接口
struct attribute{
const char *name;
struct module* owner;
mode_t mode;
}
struct kobj_attribute{
struct attribute attr;
ssize_t (*show)(struct kobject* kobj,struct kobj_attribute* attr,char* buf);
ssize_t (*store)(struct kobject* kobj,struct kobj_attribute* attr,const char* buf,size_t count);
}
5当使用结束时，调用kobject_put（example_kobj）删除该kobject结构，及其对应的目录和文件。
扩展：实际上对于不同子系统有不同的属性和属性操作函数
比如：在genhd.h文件中，磁盘属性操作结构为，disk_attribute是磁盘属性导出的接口：
struct disk_attribute{
struct attribute attr;
ssize_t (* show)(struct gendisk*,char*);
ssize_t (* store)(struct gendisk*,const char*,size_t);//新内核中该函数取消，磁盘属性只有只读操作
}
在device.h文件中，外设属性操作结构为，device_attribute是外设属性导出的接口：
struct device_attribute{
struct attribute attr;
ssize_t (* show)(struct device*dev,struct device_attribute*attr,char* buf);
ssize_t (*store)(struct device *dev,struct device_attribute*attr,const char*buf,size_t count);
}
源代码如下：
/*
* Sample kobject implementation
*
* Copyright (C) 2004-2007 Greg Kroah-Hartman <[email protected]>
* Copyright (C) 2007 Novell Inc.
*
* Released under the GPL version 2 only.
*
*/
#include <linux/kobject.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/module.h>
#include <linux/init.h>
/*
* This module shows how to create a simple subdirectory in sysfs called
* /sys/kernel/kobject-example In that directory, 3 files are created:
* "foo", "baz", and "bar". If an integer is written to these files, it can be
* later read out of it.
*/
static int foo;
static int baz;
static int bar;
/*
* The "foo" file where a static variable is read from and written to.
*/
static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr,
char *buf)
{
return sprintf(buf, "%d\n", foo);
}
static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count)
{
sscanf(buf, "%du", &foo);
return count;
}
static struct kobj_attribute foo_attribute =
__ATTR(foo, 0666, foo_show, foo_store);
/*
* More complex function where we determine which variable is being accessed by
* looking at the attribute for the "baz" and "bar" files.
*/
static ssize_t b_show(struct kobject *kobj, struct kobj_attribute *attr,
char *buf)
{
int var;
if (strcmp(attr->attr.name, "baz") == 0)
var = baz;
else
var = bar;
return sprintf(buf, "%d\n", var);
}
static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count)
{
int var;
sscanf(buf, "%du", &var);
if (strcmp(attr->attr.name, "baz") == 0)
baz = var;
else
bar = var;
return count;
}
static struct kobj_attribute baz_attribute =
__ATTR(baz, 0666, b_show, b_store);
static struct kobj_attribute bar_attribute =
__ATTR(bar, 0666, b_show, b_store);
/*
* Create a group of attributes so that we can create and destroy them all
* at once.
*/
static struct attribute *attrs[] = {
&foo_attribute.attr,
&baz_attribute.attr,
&bar_attribute.attr,
NULL, /* need to NULL terminate the list of attributes */
};
/*
* An unnamed attribute group will put all of the attributes directly in
* the kobject directory. If we specify a name, a subdirectory will be
* created for the attributes with the directory being the name of the
* attribute group.
*/
static struct attribute_group attr_group = {
.attrs = attrs,
};
static struct kobject *example_kobj;
static int __init example_init(void)
{
int retval;
/*
* Create a simple kobject with the name of "kobject_example",
* located under /sys/kernel/
*
* As this is a simple directory, no uevent will be sent to
* userspace. That is why this function should not be used for
* any type of dynamic kobjects, where the name and number are
* not known ahead of time.
*/
example_kobj = kobject_create_and_add("kobject_example", kernel_kobj);
if (!example_kobj)
return -ENOMEM;
/* Create the files associated with this kobject */
retval = sysfs_create_group(example_kobj, &attr_group);
if (retval)
kobject_put(example_kobj);
return retval;
}
static void __exit example_exit(void)
{
kobject_put(example_kobj);
}
module_init(example_init);
module_exit(example_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Greg Kroah-Hartman <[email protected]>");