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本帖最后由 寒小咸 于 2016-9-29 14:50 编辑
概述
Kobject是linux设备驱动模型的基础，也是设备模型中抽象的一部分。如果想了解设备驱动模型就需要明白Kobject的构成或原理。linux内核为了兼容各种形形色色的设备，就需要对各种设备的共性进行抽象，抽象出一个基类，其余的设备只需要继承此基类就可以了。而此基类就是kobject，但是C语言没有面向对象语法，这时候就需要将此基类(Kobject)嵌入到具体的结构体中，从而就可以访问控制此设备的操作。通常驱动程序员很少使用到kobject结构及其相关接口，而是使用封装之后的更高层的接口函数。
Kobject结构体struct kobject {
const char *name;
struct list_head entry;
struct kobject *parent;
struct kset *kset;
struct kobj_type *ktype;
struct kernfs_node *sd;
struct kref kref;
#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
struct delayed_work release;
#endif
unsigned int state_initialized:1;
unsigned int state_in_sysfs:1;
unsigned int state_add_uevent_sent:1;
unsigned int state_remove_uevent_sent:1;
unsigned int uevent_suppress:1;
};
entry: 用来将一系列的内核对象kobject连接成链表
parent: 用来指向该内核对象的上层节点，从而可以实现内核对象的层次化结构
kset: 用来执行内核对象所属的kset。kset对象用来容纳一系列同类型的kobject
ktype: 用来定义该内核对象的sys文件系统的相关操作函数和属性。
sd: 用来表示该内核对象在sys文件系统中的目录项实例
kref: 其核心是原子操作变量，用来表示该内核对象的引用计数。
state_initialized: 用来表示该内核对象的初始化状态，1表示已经初始化，0表示未初始化。
state_in_sysfs: 用来表示该内核对象是否在sys中已经存在。
state_add_uevent_sent: 用来表示该内核对象是否向用户空间发送了ADD uevent事件
state_remove_uevent_sent:用来表示该内核对象是否向用户空间发送了Remove uevent事件
uevent_suppress: 用来表示该内核对象状态发生改变时，时候向用户空间发送uevent事件，1表示不发送。
kobject数据结构通常的用法就是嵌入到某一个对象的数据结构中，比如struct device结构struct device {
struct device *parent;
struct device_private *p;
struct kobject kobj;
const char *init_name; /* initial name of the device */
const struct device_type *type;
Kobject相关操作函数
kobject相关的操作函数一般驱动程序员是不会直接操作的。
1. kobject_initvoid kobject_init(struct kobject *kobj, struct kobj_type *ktype)
{
char *err_str;
if (!kobj) { //合法性检测
err_str = "invalid kobject pointer!";
goto error;
}
if (!ktype) { //kobject结构必须设置相应的属性
err_str = "must have a ktype to be initialized properly!\n";
goto error;
}
if (kobj->state_initialized) { //如果已经初始化，在打印log
/* do not error out as sometimes we can recover */
printk(KERN_ERR "kobject (%p): tried to init an initialized "
"object, something is seriously wrong.\n", kobj);
dump_stack();
}
kobject_init_internal(kobj);
kobj->ktype = ktype;
return;
error:
printk(KERN_ERR "kobject (%p): %s\n", kobj, err_str);
dump_stack();
}
static void kobject_init_internal(struct kobject *kobj)
{
if (!kobj)
return;
kref_init(&kobj->kref); //原子变量初始化
INIT_LIST_HEAD(&kobj->entry); //初始化链表
kobj->state_in_sysfs = 0; //没有出现在sys目录中
kobj->state_add_uevent_sent = 0;
kobj->state_remove_uevent_sent = 0;
kobj->state_initialized = 1; //已经初始化
}
2. kobject_set_name: 用于设置kobject中的name成员int kobject_set_name(struct kobject *kobj, const char *fmt, ...)
{
va_list vargs;
int retval;
va_start(vargs, fmt);
retval = kobject_set_name_vargs(kobj, fmt, vargs);
va_end(vargs);
return retval;
}
int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
va_list vargs)
{
const char *old_name = kobj->name;
char *s;
if (kobj->name && !fmt) //名字存在返回
return 0;
kobj->name = kvasprintf(GFP_KERNEL, fmt, vargs);
if (!kobj->name) {
kobj->name = old_name;
return -ENOMEM;
}
/* ewww... some of these buggers have '/' in the name ... */
while ((s = strchr(kobj->name, '/'))) //除掉name中存在“/”
s[0] = '!';
kfree(old_name);
return 0;
}
3. kobject_get（增加kobject的引用计数）/**
* kobject_get - increment refcount for object.
* @kobj: object.
*/
struct kobject *kobject_get(struct kobject *kobj)
{
if (kobj)
kref_get(&kobj->kref); //原子加1操作
return kobj;
}
4. kobject_put（减少kobject的引用计数）/**
* kobject_put - decrement refcount for object.
* @kobj: object.
*
* Decrement the refcount, and if 0, call kobject_cleanup().
*/
void kobject_put(struct kobject *kobj)
{
if (kobj) {
if (!kobj->state_initialized) //如果没有初始化,调用put函数，打印log
WARN(1, KERN_WARNING "kobject: '%s' (%p): is not "
"initialized, yet kobject_put() is being "
"called.\n", kobject_name(kobj), kobj);
kref_put(&kobj->kref, kobject_release);
}
}
5. kobject_add(增加一个kobject到sys目录下)int kobject_add(struct kobject *kobj, struct kobject *parent,
const char *fmt, ...)
{
va_list args;
int retval;
if (!kobj)
return -EINVAL;
if (!kobj->state_initialized) { //没有初始化的kobject，返回错误
printk(KERN_ERR "kobject '%s' (%p): tried to add an "
"uninitialized object, something is seriously wrong.\n",
kobject_name(kobj), kobj);
dump_stack();
return -EINVAL;
}
va_start(args, fmt);
retval = kobject_add_varg(kobj, parent, fmt, args); //核心的实现代码
va_end(args);
return retval;
}
static int kobject_add_varg(struct kobject *kobj, struct kobject *parent,
const char *fmt, va_list vargs)
{
int retval;
retval = kobject_set_name_vargs(kobj, fmt, vargs); //设置kobject的name
if (retval) {
printk(KERN_ERR "kobject: can not set name properly!\n");
return retval;
}
kobj->parent = parent; //设置parent成员
return kobject_add_internal(kobj); //调用此函数进行进一步add操作
}
static int kobject_add_internal(struct kobject *kobj)
{
int error = 0;
struct kobject *parent;
if (!kobj)
return -ENOENT;
if (!kobj->name || !kobj->name[0]) { //尝试注册一个name为空的kobject
WARN(1, "kobject: (%p): attempted to be registered with empty "
"name!\n", kobj);
return -EINVAL;
}
parent = kobject_get(kobj->parent); //kobj的parent的引用计数加1，返回parent
/* join kset if set, use it as parent if we do not already have one */
if (kobj->kset) {
if (!parent) //在kset存在的前提下，如果kobj的parent节点为NULL，就将kobj的kset中的kobj设置为kobj的parent
parent = kobject_get(&kobj->kset->kobj);
kobj_kset_join(kobj); //添加kobj到kset的list链表中
kobj->parent = parent; //设置kobj的parent
}
pr_debug("kobject: '%s' (%p): %s: parent: '%s', set: '%s'\n",
kobject_name(kobj), kobj, __func__,
parent ? kobject_name(parent) : "<NULL>",
kobj->kset ? kobject_name(&kobj->kset->kobj) : "<NULL>");
error = create_dir(kobj); //在sys下创建目录
if (error) {
kobj_kset_leave(kobj);
kobject_put(parent);
kobj->parent = NULL;
/* be noisy on error issues */
if (error == -EEXIST)
WARN(1, "%s failed for %s with "
"-EEXIST, don't try to register things with "
"the same name in the same directory.\n",
__func__, kobject_name(kobj));
else
WARN(1, "%s failed for %s (error: %d parent: %s)\n",
__func__, kobject_name(kobj), error,
parent ? kobject_name(parent) : "'none'");
} else
kobj->state_in_sysfs = 1; //设置state_in_sysfs为1，代表obj已经初始化在sys中
return error;
}
下来大概看看create_dir的过程，也就是创建目录的过程。
static int create_dir(struct kobject *kobj)
{
const struct kobj_ns_type_operations *ops;
int error;
error = sysfs_create_dir_ns(kobj, kobject_namespace(kobj)); //为kobject创建目录
if (error)
return error;
error = populate_dir(kobj); //填充kobj的属性
if (error) {
sysfs_remove_dir(kobj);
return error;
}
/*
* @kobj->sd may be deleted by an ancestor going away. Hold an
* extra reference so that it stays until @kobj is gone.
*/
sysfs_get(kobj->sd); //kobj->sd引用计数加1
/*
* If @kobj has ns_ops, its children need to be filtered based on
* their namespace tags. Enable namespace support on @kobj->sd.
*/
ops = kobj_child_ns_ops(kobj); //namespace的知识
if (ops) {
BUG_ON(ops->type <= KOBJ_NS_TYPE_NONE);
BUG_ON(ops->type >= KOBJ_NS_TYPES);
BUG_ON(!kobj_ns_type_registered(ops->type));
sysfs_enable_ns(kobj->sd);
}
return 0;
}
主要是分析下sysfs_create_dir_ns函数的执行流程。
/**
* sysfs_create_dir_ns - create a directory for an object with a namespace tag
* @kobj: object we're creating directory for
* @ns: the namespace tag to use
*/
int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
{
struct kernfs_node *parent, *kn;
BUG_ON(!kobj); //如果执行到这里，kobj为NULL,就会panic
if (kobj->parent)
parent = kobj->parent->sd; //如果存在parent就在父目录下创建
else
parent = sysfs_root_kn; //如果不存在parent,就在sys目录下创建
if (!parent)
return -ENOENT;
kn = kernfs_create_dir_ns(parent, kobject_name(kobj), //正真的创建函数，不是此节的重点，不再分析。
S_IRWXU | S_IRUGO | S_IXUGO, kobj, ns);
if (IS_ERR(kn)) {
if (PTR_ERR(kn) == -EEXIST)
sysfs_warn_dup(parent, kobject_name(kobj));
return PTR_ERR(kn);
}
kobj->sd = kn;
return 0;
}
6. kobject_init_and_add(kobject_init函数和kobject_add函数的合并)
7. kobject_create(动态分析一个kobject)struct kobject *kobject_create(void)
{
struct kobject *kobj;
kobj = kzalloc(sizeof(*kobj), GFP_KERNEL); //分配一个kobject结构
if (!kobj)
return NULL;
kobject_init(kobj, &dynamic_kobj_ktype); //初始化kobject，kobj_type会在后面说到
return kobj;
}
8. kobject_create_and_add(动态创建一个kobject然后注册到sys文件系统中，也就是kobject_create和kobject_add的结合体)
9. kobject_del(从sys删除对应的kobj)void kobject_del(struct kobject *kobj)
{
struct kernfs_node *sd;
if (!kobj)
return; //如果不存在，直接返回。
sd = kobj->sd;
sysfs_remove_dir(kobj); //从sys目录下删除kobj
sysfs_put(sd); //sd的引用技术减去1
kobj->state_in_sysfs = 0; //表示没有在sys中初始化
kobj_kset_leave(kobj); //如果存在于kset中，从kset中删除
kobject_put(kobj->parent); //parent引用计数减1
kobj->parent = NULL;
}
举例
在sys目录下创建一个123_test的文件夹。#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/sysfs.h>
#include <linux/init.h>
static struct kobject *kobj;
static int kobject_test_init(void)
{
kobj = kobject_create_and_add("123_test", NULL);
return 0;
}
static void kobject_test_exit(void)
{
kobject_del(kobj);
}
module_init(kobject_test_init);
module_exit(kobject_test_exit);
MODULE_LICENSE("GPL v2");
root@test:/sys # ls -l
drwxr-xr-x root root 2012-01-02 09:31 123_test
drwxr-xr-x root root 2012-01-02 07:13 bcm-dhd
drwxr-xr-x root root 2012-01-02 05:02 block
drwxr-xr-x root root 2012-01-02 05:02 bus
drwxr-xr-x root root 2012-01-02 05:02 class
....
接着在123_test目录下创建456_test目录，修改代码如下：#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/sysfs.h>
#include <linux/init.h>
static struct kobject *kobj;
static struct kobject *ckobj;
static int kobject_test_init(void)
{
kobj = kobject_create_and_add("123_test", NULL);
ckobj = kobject_create_and_add("456_test", kobj);
return 0;
}
static void kobject_test_exit(void)
{
kobject_del(ckobj);
kobject_del(kobj);
}
module_init(kobject_test_init);
module_exit(kobject_test_exit);
MODULE_LICENSE("GPL v2");
测试结果如下：
root@test:/sys/123_test # ls
456_test
而目前456_test目录下是不存在任何文件的，那是因为我们没有添加该obj的属性，此测试case将在下解完善。 | 
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发表于 2016-9-29 14:43:34
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