实践字符设备驱动

October 7th, 2014 by JasonLe's Tech Leave a reply »

我们都知道在linux里面存在块设备与字符设备。我们这里是设计的字符驱动,在不久,我会加入支持阻塞的功能。

我们可以通过查看cat /proc/device查看已注册的设备

[lzz@localhost device_character]$ cat /proc/devices
Character devices:
  1 mem
  4 /dev/vc/0
  4 tty
  4 ttyS
  5 /dev/tty
  5 /dev/console
  5 /dev/ptmx
  7 vcs
 10 misc
 13 input
 14 sound
 21 sg
 29 fb
 99 ppdev
116 alsa
128 ptm
136 pts
162 raw
180 usb
188 ttyUSB
189 usb_device
202 cpu/msr
203 cpu/cpuid
226 drm
250 hidraw
251 usbmon
252 bsg
253 watchdog
254 rtc

Block devices:
259 blkext
  8 sd
  9 md
 11 sr
 65 sd
 66 sd
 67 sd
 68 sd
 69 sd
 70 sd
 71 sd
128 sd
129 sd
130 sd
131 sd
132 sd
133 sd
134 sd
135 sd
253 device-mapper
254 mdp

我们选取一个231作为我们字符设备号,别的不废话,上代码.

字符设备驱动程序:

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <asm/io.h>
#include <linux/mman.h>
#include <linux/uaccess.h>

MODULE_AUTHOR("lzz");
MODULE_LICENSE("GPL");

#define MYCDEV_MAJOR 231 /*the predefined mycdev's major devno*/
#define MYCDEV_SIZE 100

static char kernel_buf[MYCDEV_SIZE];

static int mycdev_open(struct inode *inode, struct file *fp)
{
 return 0;
}

static int mycdev_release(struct inode *inode, struct file *fp)
{
 return 0;
}

static ssize_t mycdev_read(struct file *fp, char __user *buf, size_t size, loff_t *pos)
{

 unsigned long p = *pos;
 unsigned int count = size;
// int i;

 if(p >= MYCDEV_SIZE)
 return -1;
 if(count > MYCDEV_SIZE)
 count = MYCDEV_SIZE - p;

 if (copy_to_user(buf, kernel_buf, count) != 0) 
 {
 printk("read error!\n");
 return -1;
 }

 printk("lzz's reader: %d bytes was read...\n", count);
 return count;

}

static ssize_t mycdev_write(struct file *fp, const char __user *buf, size_t size, loff_t *pos)
{
 unsigned long p = *pos;
 unsigned int count = size;
 int ret =0;

 if(copy_from_user(kernel_buf+p,buf,count))
 ret = -EFAULT;
 else
 {
 *pos+=count;
 ret = count;
 printk("lzz's write: %d bytes was wroten...\n", count);
 }
 return ret;
}

/*filling the mycdev's file operation interface in the struct file_operations*/
static const struct file_operations mycdev_fops =
{
 .owner = THIS_MODULE,
 .read = mycdev_read,
 .write = mycdev_write,
 .open = mycdev_open,
 .release = mycdev_release,
};

/*module loading function*/
static int __init mycdev_init(void)
{
 int ret;

 printk("mycdev module is staring..\n");

 ret=register_chrdev(MYCDEV_MAJOR,"lzz_cdev",&mycdev_fops);
 if(ret<0)
 {
 printk("register failed..\n");
 return 0;
 }
 else
 {
 printk("register success..\n");
 } 

 return 0;
}

/*module unloading function*/
static void __exit mycdev_exit(void)
{
 printk("mycdev module is leaving..\n");
 unregister_chrdev(MYCDEV_MAJOR,"lzz_cdev");
}

module_init(mycdev_init);
module_exit(mycdev_exit);

Makefile文件:

obj-m:= map_driver.o

CURRENT_PATH:=$(shell pwd)

LINUX_KERNEL:=$(shell uname -r)

LINUX_KERNEL_PATH:=/lib/modules/$(LINUX_KERNEL)/build

all:
 make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) modules

clean:
 make -C $(LINUX_KERNEL_PATH) M=$(CURRENT_PATH) clean

用户态测试程序:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>

int main()
{
 int testdev;
 int i, ret;
 char buf[100]="test lzz's cdev ok!";
 char buff[100];

 testdev = open("/dev/mycdev", O_RDWR);

 if (-1 == testdev) {
 printf("cannot open file.\n");
 exit(1);
 }

 write(testdev,buf,sizeof(buf)-1);

 if ((ret = read(testdev, buff, sizeof(buff)-1)) < 0) {
 printf("read error!\n");
 exit(1);
 }

 printf("%s\n", buff);

 close(testdev);

 return 0;
}

使用方法:
1.make编译map_driver.c文件,并插入到内核;
2.通过cat /proc/devices 查看系统中未使用的字符设备主设备号,比如当前231未使用;
3.创建设备文件结点:sudo mknod /dev/mycdev c 231 0;具体使用方法通过man mknod命令查看;
4.修改设备文件权限:sudo chmod 777 /dev/mycdev;(可选)
5.以上成功完成后,编译本用户态测试程序;运行该程序查看结果;
6.通过dmesg查看日志信息;

Screenshot from 2014-10-07 22:10:11