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Linux內核簡化版kset-example.c解析

/**********************************************
* Author: [email protected]
* File name: kset_sample.c
* Description: kset example
* Date: 2011-12-10
*********************************************/
#include <linux/kobject.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/init.h>
/*
* 將要創建的文件foo對應的kobj.
*/
struct foo_obj {
struct kobject kobj;
int foo;
int baz;
int bar;
};
/* 通過域成員返回結構體的指針 */
#define to_foo_obj(x) container_of(x, struct foo_obj, kobj)
/* 屬性 */
struct foo_attribute {
struct attribute attr;
ssize_t (*show)(struct foo_obj *foo, struct foo_attribute *attr, char *buf);
ssize_t (*store)(struct foo_obj *foo, struct foo_attribute *attr, const char *buf, size_t count);
};
#define to_foo_attr(x) container_of(x, struct foo_attribute, attr)
/*
* 屬性foo信息顯示函數 (涉及文件目錄foo/)
*/
static ssize_t foo_attr_show(struct kobject *kobj,
struct attribute *attr,
char *buf)
{
struct foo_attribute *attribute;
struct foo_obj *foo;
attribute = to_foo_attr(attr);
foo = to_foo_obj(kobj);
if (!attribute->show)
return -EIO;
return attribute->show(foo, attribute, buf);
}
/*
* 屬性foo存儲函數(涉及文件目錄foo/) (when a value is written to a file.)
*/
static ssize_t foo_attr_store(struct kobject *kobj,
struct attribute *attr,
const char *buf, size_t len)
{
struct foo_attribute *attribute;
struct foo_obj *foo;
attribute = to_foo_attr(attr);
foo = to_foo_obj(kobj);
if (!attribute->store)
return -EIO;
return attribute->store(foo, attribute, buf, len);
}
/*
* foo的show/store列表
*/
static const struct sysfs_ops foo_sysfs_ops = {
.show = foo_attr_show,
.store = foo_attr_store,
};
/*
* The release function for our object. This is REQUIRED by the kernel to
* have. We free the memory held in our object here.
*/
static void foo_release(struct kobject *kobj)
{
struct foo_obj *foo;
foo = to_foo_obj(kobj);
kfree(foo);
}
/*
* 當需要從foo文件中讀取信息時，調用此函數
*/
static ssize_t foo_show(struct foo_obj *foo_obj, struct foo_attribute *attr,
char *buf)
{
return sprintf(buf, "%d\n", foo_obj->foo);
}
/*
* 當往foo文件寫入信息時，調用此函數
*/
static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
const char *buf, size_t count)
{
sscanf(buf, "%du", &foo_obj->foo);
return count;
}
static struct foo_attribute foo_attribute =
__ATTR(foo, 0666, foo_show, foo_store);
/*
* foo_ktype的屬性列表
*/
static struct attribute *foo_default_attrs[] = {
&foo_attribute.attr,
NULL, /* need to NULL terminate the list of attributes */
};
/*
* 定義kobj_type結構體
* 指定sysfs_ops,release函數, 屬性列表foo_default_attrs
*/
static struct kobj_type foo_ktype = {
.sysfs_ops = &foo_sysfs_ops,
.release = foo_release,
.default_attrs = foo_default_attrs,
};
static struct kset *example_kset;
static struct foo_obj *foo_obj;
static struct foo_obj *create_foo_obj(const char *name)
{
struct foo_obj *foo;
int retval;
/* allocate the memory for the whole object */
foo = kzalloc(sizeof(*foo), GFP_KERNEL);
if (!foo)
return NULL;
foo->kobj.kset = example_kset;
/*
* 初始化kobject數據結結構foo->lobj,
* 即在foo->kobj的層次組織kset中創建個名為name的文件foo/foo
* 成功返回0
*/
retval = kobject_init_and_add(&foo->kobj, &foo_ktype, NULL, "%s", name);
if (retval) {
/* 減小kobj的引用計數 */
kobject_put(&foo->kobj);
return NULL;
}
/*
* 發送 KOBJ_ADD / KOBJ_REMOVE 等事件
* We are always responsible for sending the uevent that the kobject
* was added to the system.
*/
kobject_uevent(&foo->kobj, KOBJ_ADD);
return foo;
}
static void destroy_foo_obj(struct foo_obj *foo)
{
/* 減小kobj的引用計數 */
kobject_put(&foo->kobj);
}
static int __init example_init(void)
{
/*
* 動態地在kernel_kobj所對應的目錄/sys/kernel/下創建一個目錄kset_example
* 並返回kset_example對應的kset
*/
example_kset = kset_create_and_add("kset_example", NULL, kernel_kobj);
if (!example_kset)
return -ENOMEM;
foo_obj = create_foo_obj("foo");
if (!foo_obj)
goto foo_error;
return 0;
foo_error:
return -EINVAL;
}
static void __exit example_exit(void)
{
destroy_foo_obj(foo_obj);
kset_unregister(example_kset);
}
module_init(example_init);
module_exit(example_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("lewiyon <[email protected]>");