1.核心結構體定義：

struct cdev

?{

struct kobject kobj;?? ??? ??// 每個 cdev 都是一個 kobject

struct module *owner;?? ???// 指向實現驅動的模塊
const struct file_operations *ops;?? // 操縱這個字符設備文件的方法
??struct list_head list;?? ??? // 與 cdev 對應的字符設備文件的 inode->i_devices 的鏈表頭
??dev_t dev;?? ??? ??? ??????? // 起始設備編號
??unsigned int count;?? ??? // 設備范圍號大小

};

2.兩種定義初始化方式：靜態的（在stack中生成對象）和動態的（在heap中生成對象）。

靜態內存定義初始化：
struct cdev my_cdev;//變量在stack中
cdev_init(&my_cdev, &fops);
my_cdev.owner = THIS_MODULE;

動態內存定義初始化：
struct cdev *ptr_my_cdev = cdev_alloc();//變量在heap中
ptr_my_cdev?->ops = &fops;
ptr_my_cdev?->owner = THIS_MODULE;

錯誤的定義初始化方式：

struct cdev *ptr_my_cdev?= cdev_alloc();//變量在heap中

cdev_init(ptr_my_cdev?, &fops);

ptr_my_cdev?->owner = THIS_MODULE;

錯誤原因分析：

相關函數源碼如下：

struct cdev *cdev_alloc(void)
{
struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
if (p)?

{
INIT_LIST_HEAD(&p->list);
kobject_init(&p->kobj, &ktype_cdev_dynamic);//ktype_cdev_dynamic用于指示cdev對象的產生方式是heap，銷毀時要釋放之。
}
return p;
}

void cdev_init(struct cdev *cdev, const struct file_operations *fops)
{
memset(cdev, 0, sizeof *cdev);
INIT_LIST_HEAD(&cdev->list);
kobject_init(&cdev->kobj, &ktype_cdev_default);//ktype_cdev_default用于指示cdev對象的產生方式是stack，銷毀時不需要釋放之。
cdev->ops = fops;
}

static void cdev_default_release(struct kobject *kobj)
{
struct cdev *p = container_of(kobj, struct cdev, kobj);
cdev_purge(p);
}


static void cdev_dynamic_release(struct kobject *kobj)
{
struct cdev *p = container_of(kobj, struct cdev, kobj);
cdev_purge(p);
kfree(p);//ktype_cdev_dynamic的特別之處
}


static struct kobj_type ktype_cdev_default = {
.release = cdev_default_release,
};


static struct kobj_type ktype_cdev_dynamic = {
.release = cdev_dynamic_release,
};

4.另類的定義初始化方式：

struct cdev my_cdev;//變量在stack中

struct cdev *ptr_my_cdev?= &my_cdev;

cdev_init(ptr_my_cdev?, &fops);

ptr_my_cdev?->owner = THIS_MODULE;

總結

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