一直在学习linux下设备驱动程序的编写，但是一直都是挑最简单的做。比如写makefile文件，设备号的分配，都是以最简单的形式来应付。静态实现设备号的分配有很多缺点，容易引起设备号冲突等。经过几天的突击终于实现了设备号的动态分配，现在来和大家分享以下（附有字符驱动源码）。
如下所示是简单字符驱动程序(baovar.c):
#include
#include
#include
#include
#include
#include
#include"baovar.h"
MODULE_LICENSE("GPL");
static int MAJOR_NUM=0;//主设备号
ssize_t bao_read (struct file*,char*,size_t,loff_t*);
ssize_t bao_write (struct file*,const char*,size_t,loff_t*);
int bao_ioctl(struct inode *inode,struct file*filp,unsigned int cmd,unsigned long args);
int bao_open(struct inode *inode,struct file *filp);
int bao_release(struct inode *inode,struct file *filp);
//初始化file_operations
struct file_operations bao_fops=
{
read:bao_read,
write:bao_write,
ioctl:bao_ioctl,
open:bao_open,
release:bao_release,
owner:THIS_MODULE,
};
static int bao_var=0;//baovar设备的全局变量
static int bao_count=0;
static struct semaphore sem;
static spinlock_t spin=SPIN_LOCK_UNLOCKED;
int __init bao_init(void)
{
int ret;
//注册设备驱动
ret=register_chrdev(MAJOR_NUM,"baovar",&bao_fops);
if(ret<0)
{
printk("baovar register failure\n");
return ret;
}
else
{
printk("baovar register success\n");
init_MUTEX(&sem);
}
if(MAJOR_NUM==0)
MAJOR_NUM=ret;
return 0;
}
void __exit bao_exit(void)
{
int ret;
//注销设备驱动
ret=unregister_chrdev(MAJOR_NUM,"baovar");
if(ret)
{
printk("baovar unregister failure\n");
}
else
{
printk("baovar unregister success\n");
}
}
int bao_open(struct inode *inode,struct file *filp)
{
//获得自旋锁
spin_lock(&spin);
//临界资源访问
if(bao_count)
{
spin_unlock(&spin);
return -EBUSY;
}
printk("baoopen\n");
bao_count++;
//释放自旋锁
spin_unlock(&spin);
return 0;
}
int bao_release(struct inode *inode,struct file *filp)
{
bao_count--;
printk("close->bao\n");
return 0;
}
ssize_t bao_read(struct file*filp,char *buf,size_t len,loff_t *off)
{
//获得信号量
if(down_interruptible(&sem))
{
return -ERESTARTSYS;
}
//将baovar从内核空间复制到用户空间
if(__copy_to_user(buf,&bao_var,sizeof(int)))
{
up(&sem);
return -EFAULT;
}
up(&sem);
return sizeof(int);
}
ssize_t bao_write(struct file*filp,const char *buf,size_t len,loff_t *off)
{
//获得信号量
if(down_interruptible(&sem))
{
return -ERESTARTSYS;
}
//将数据从用户空间复制到内核空间
if(__copy_from_user(&bao_var,buf,sizeof(int)))
{
up(&sem);
return -EFAULT;
}
//释放信号量
up(&sem);
return sizeof(int);
}
int bao_ioctl(struct inode *inode,struct file*filp,unsigned int cmd,unsigned long args)
{
if(_IOC_TYPE(cmd)!=BAO_IOCTL){return -EINVAL;}
if(_IOC_NR(cmd)>BAO_IOCTL_MAXNR){return -EINVAL;}
int ret;
switch(cmd)
{
case IOCTL_READ:
return __put_user(bao_var, (int *) args);
case IOCTL_WRITE:
{ret = __get_user(bao_var, (int *) args);
if (ret)
return ret;
printk("bao_var = %d\n", bao_var);
break; }
default:printk("error\n");
}
return 1;
}
module_init(bao_init);
module_exit(bao_exit);
以下是头文件(baovar.h):
#include
#define BAO_IOCTL 't'
#define IOCTL_READ _IOR(BAO_IOCTL, 0, int)
#define IOCTL_WRITE _IOW(BAO_IOCTL, 1, int)
#define BAO_IOCTL_MAXNR 1
使MAJOR_NUM=0可以实现系统动态分配设备号，从255开始，从大到小搜索，直到找到未被使用的号。
使用的makefile文件如下：
CC=gcc
MODCFLAGS := -Wall -DMODULE -D__KERNEL__ -DLINUX -I/usr/src/linux-2.4/include
baovar.o :baovar.c
$(CC) $(MODCFLAGS) -c baovar.c
clean:
rm -f *.o
下面重点介绍shell文件的编写（脚本文件）：
1.bao_load.sh文件
#!/bin/bash
#bao.sh
module="baovar"
device="baovar"
mode="664"
# Group: since distributions do it differently, look for wheel or use staff
if grep '^staff:' /etc/group > /dev/null; then
group="staff"
else
group="wheel"
fi
# invoke insmod with all arguments we got
# and use a pathname, as newer modutils don't look in . by default
/sbin/insmod ./$module.o $* || exit 1
cat /proc/devices
major=`cat /proc/devices | awk "" {print }"`
# Remove stale nodes and replace them, then give gid and perms
# Usually the script is shorter, it's simple that has several devices in it.
rm -f /dev/${device}
mknod /dev/${device} c $major 0
chgrp $group /dev/${device}
chmod $mode /dev/${device}
echo "finish"
2.bao_unload.sh文件
#!/bin/sh
module="baovar"
device="baovar"
# invoke rmmod with all arguments we got
/sbin/rmmod $module $* || exit 1
# Remove stale nodes
rm -f /dev/${device}
echo "finish"
把这些文件放在同一文件夹下：
加载驱动：
在终端中输入：make
：sh bao_load.sh
现在就可以使用字符驱动程序了
卸载驱动：sh bao-unload.sh
