The Driver of Character Device
实践字符设备驱动
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 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;
char kernel_buf[MYCDEV_SIZE] = "ok!";
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
#include <sys/types.h>
#include <sys/stat.h>
#include
#include
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;
}
</code></pre>
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；
