Linux字符驱动

gadfly0217

Normal 0 7.8 磅 0 2 false false false MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:普通表格; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;}

第一步：分配设备号

（1）dev_t结构

【结构】                                                               相关文件

dev_t：无符号32位数                                           <linux/types.h>

前12位是主设备号，后20位是次设备号。

 

索引：typedef __kernel_dev_t             dev_t;       /* 把__kernel_dev_t 定义到dev_t */

typedef __u32 __kernel_dev_t;                /* 把__u32定义成 __kernel_dev_t */

#ifndef __u32                                           /* 把 unsigned int定义成__u32 */

         #define __u32 unsigned int

#endif

【宏】                                      相关文件

MAJOR (dev_t dev)                            <linux/kdev_t.h>

MINOR (dev_t dev)

MKDEV(int major, int minor);

 

#define MAJOR(dev)     ((unsigned int) ((dev) >> MINORBITS))   /*右移20位，以0填补*/

#define MINOR(dev)     ((unsigned int) ((dev) & MINORMASK))  /*屏蔽高12位*/

#define MINORBITS     20

#define MINORMASK   ((1U << MINORBITS) - 1)              /* 000FFFFF */

#define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi))

 

（2）静态分配设备号

【函数】register_chrdev_region                  

extern int register_chrdev_region(dev_t, unsigned, const char *);       <linux/fs.h>

 

【原型】：

/**

 * 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)

{

       struct char_device_struct *cd;

       dev_t to = from + count;

       dev_t n, next;

 

       for (n = from; n < to; n = next) {

              next = MKDEV(MAJOR(n)+1, 0);

              if (next > to)

                     next = to;

              cd = __register_chrdev_region(MAJOR(n), MINOR(n),

                            next - n, name);

              if (IS_ERR(cd))

                     goto fail;

       }

       return 0;

fail:

       to = n;

       for (n = from; n < to; n = next) {

              next = MKDEV(MAJOR(n)+1, 0);

              kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));

       }

       return PTR_ERR(cd);

}

int register_chrdev_region(dev_t first, unsigned count, const char *name)

这里, first 是你要分配的起始设备编号. first 的次编号部分常常是 0, 但是没有要求是那个效果. count 是你请求的连续设备编号的总数. 注意, 如果 count 太大, 你要求的范围可能溢出到下一个次编号; 但是只要你要求的编号范围可用, 一切都仍然会正确工作. 最后, name 是应当连接到这个编号范围的设备的名子; 它会出现在 /proc/devices 和 sysfs 中.

【例子】：

 int result;

 dev_t devno = MAKEDEV (globalmem_major , 0)

 result = register_chrdev_region (devno, 1, “globalmem”)

 

(3) 动态分配设备号

【函数】 alloc_chrdev_region

【原型】

extern int alloc_chrdev_region(dev_t *, unsigned, unsigned, const char *);     <linux/fs.h>

/**                                                              <fs/char_dev.c>

 * 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)

{

       struct char_device_struct *cd;

       cd = __register_chrdev_region(0, baseminor, count, name);

       if (IS_ERR(cd))

              return PTR_ERR(cd);

       *dev = MKDEV(cd->major, cd->baseminor);

       return 0;

【例子】：

int result;

dev_t devno;

result = alloc_chardev_region (&devno,0,1,”globalmem”)

 

（4）释放设备号

【函数】 unregister_chrdev_region

【原型】

extern void unregister_chrdev_region(dev_t, unsigned);

/**

 * unregister_chrdev_region() - return a range of device numbers

 * @from: the first in the range of numbers to unregister

 * @count: the number of device numbers to unregister

 *

 * This function will unregister a range of @count device numbers,

 * starting with @from.  The caller should normally be the one who

 * allocated those numbers in the first place...

 */

void unregister_chrdev_region(dev_t from, unsigned count)

{

       dev_t to = from + count;

       dev_t n, next;

 

       for (n = from; n < to; n = next) {

              next = MKDEV(MAJOR(n)+1, 0);

              if (next > to)

                     next = to;

              kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));

       }

}

【例子】

 Unregister_chrdev_region (MKDEV(globalmem_major,0),1);