1. cdev是linux用来管理字符设备的结构体，其在内核中采用数组结构设计，这样系统中有多少个主设备号就约定了数组大小，此设备号采用链表管理，同一主设备号下可以有多个子设备。设备即文件，上层应用要访问设备，必须通过文件，cdev中包含file_operations结构体，该结构体就是驱动的文件操作集合。

（根据于说得）

2. cdev定义在include/linux/cdev.h中，如下。具体实现在fs/char_dev.c中。

#include 
     
      #include 
      
       #include 
       
        struct file_operations;struct inode;struct module;struct cdev {struct kobject kobj;struct module *owner;const struct file_operations *ops;struct list_head list;dev_t dev;unsigned int count;};void cdev_init(struct cdev *, const struct file_operations *); struct cdev *cdev_alloc(void);void cdev_put(struct cdev *p);int cdev_add(struct cdev *, dev_t, unsigned);void cdev_del(struct cdev *);void cd_forget(struct inode *);extern struct backing_dev_info directly_mappable_cdev_bdi;
       
      
     

//fs/char_dev.c/*** cdev_add() - add a char device to the system* @p: the cdev structure for the device* @dev: the first device number for which this device is responsible* @count: the number of consecutive minor numbers corresponding to this * device** cdev_add() adds the device represented by @p to the system, making it* live immediately. A negative error code is returned on failure. */int cdev_add(struct cdev *p, dev_t dev, unsigned count){p->dev = dev;p->count = count;return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);}

3. cdev函数

>>cdev定义有两种方式，struct cdev cdev；另外一种struct cdev *cdev; cdev=cdev_alloc();

一种静态声明定义，另一种动态分配。

>>cdev通过函数cdev_init()初始化，主要工作就是将file_operations和cdev关联起来。file_operations是字符驱动需要实现的主要内容。

>>cdev通过cdev_add()实现cdev的注册，所谓注册就是将cdev根据设备号（dev_t）添加到cdev数组（cdev_map）中供系统管理。

>>cdev通过cdev_del()将cdev从cdev_map中移除。

4. 设备号

申请设备号用如下两个函数：

alloc_chrdev_region() --自动分配设备号

register_chrdev_region() --分配已设定的设备号

/*** register_chrdev_region() - register a range of device numbers* @from: the first in the desired range of device numbers; must include* the major number.* @count: the number of consecutive device numbers required* @name: the name of the device or driver.** Return value is zero on success, a negative error code on failure.*/int register_chrdev_region(dev_t from, unsigned count, const char *name);/*** alloc_chrdev_region() - register a range of char device numbers* @dev: output parameter for first assigned number* @baseminor: first of the requested range of minor numbers* @count: the number of minor numbers required* @name: the name of the associated device or driver** Allocates a range of char device numbers. The major number will be* chosen dynamically, and returned (along with the first minor number)* in @dev. Returns zero or a negative error code.*/int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,const char *name);

5. more

参考：

http://www.embedu.org/Column/Column552.htm

http://blog.chinaunix.net/uid-24517893-id-161446.html