|
|
代码(代码来自《驱动开发详解》,为了测试，小有修改)：
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#define GLOBALMEM_SIZE 0x1000
#define MEM_CLEAR 0x01
#define GLOBALMEM_MAJOR 240
static int globalmem_major = GLOBALMEM_MAJOR;
/*globalmem 设备结构体*/
struct globalmem_dev {
struct cdev cdev; /*cdev 结构体*/
unsigned char mem [GLOBALMEM_SIZE]; /*全局内存*/
};
/*设备结构体指针*/
struct globalmem_dev *globalmem_devp;
struct globalmem_dev dev; /*设备结构体实例*/
/*文件打开函数*/
int globalmem_open (struct inode *inode, struct file *filp)
{
/*将设备结构体指针赋值给文件私有数据指针*/
filp->private_data = globalmem_devp;
return 0;
}
/*文件释放函数*/
int globalmem_release (struct inode *inode, struct file *filp)
{
return 0;
}
/*读函数*/
static ssize_t globalmem_read (struct file *filp, char __user *buf, size_t size, loff_t *ppos)
{
unsigned long p = *ppos;
unsigned int count = size;
printk (KERN_INFO "count is: %d and *ppos is: %ld\n", count, *ppos);
int ret = 0;
struct globalmem_dev *dev = filp->private_data; /*获得设备结构指针*/
/*分析和获取有效的读长度*/
if (p >= GLOBALMEM_SIZE) { /*要读的偏移位置越界*/
printk (KERN_INFO "p is %ld\n", p);
return count ? -ENXIO : 0;
}
if (count > GLOBALMEM_SIZE - p) { /*要读的字节数太大*/
count = GLOBALMEM_SIZE - p;
printk (KERN_INFO "COUNT IS %d\n", count);
}
/*内核空间->用户空间 */
printk (KERN_INFO "right to copy_to_user()?\n");
if (copy_to_user (buf, (void *)(dev->mem + p), count)) {
ret = -EFAULT;
} else {
*ppos += count;
ret = count;
printk (KERN_INFO "read %d bytes(s) from %ld\n", count, p);
}
return ret;
}
/*写函数*/
static ssize_t globalmem_write (struct file *filp, const char __user *buf, size_t size, loff_t *ppos)
{
unsigned long p = *ppos;
unsigned int count = size;
int ret = 0;
struct globalmem_dev *dev = filp->private_data; /*获得设备结构指针*/
/*分析和获取有效的写长度*/
if (p >= GLOBALMEM_SIZE) /*要写的偏移位置越界*/
return count ? -ENXIO : 0;
if (count > GLOBALMEM_SIZE - p) /*要写的字节数太多*/
count = GLOBALMEM_SIZE - p; /*把剩余的空间都写完*/
/*用户空间->内核空间*/
if (copy_from_user (dev->mem + p, buf, count))
ret = -EFAULT;
else {
*ppos += count;
ret = count;
printk (KERN_INFO "written %d bytes(s) from %ld\n", count, p);
}
return ret;
}
/* seek() 函数*/
static loff_t globalmem_llseek (struct file *filp, loff_t offset, int orig)
{
loff_t ret;
switch (orig) {
case 0:
if (offset < 0) {
ret = -EINVAL;
break;
}
if ((unsigned int)offset > GLOBALMEM_SIZE) { /*偏移越界*/
ret = -EINVAL;
break;
}
filp->f_pos = (unsigned int)offset; /*从文件头偏移*/
ret = filp->f_pos;
break;
case 1:
if ((filp->f_pos + offset) > GLOBALMEM_SIZE) { /*偏移越界*/
ret = -EINVAL;
break;
}
if ((filp->f_pos + offset) < 0) {
ret = -EINVAL;
break;
}
filp->f_pos += offset;
ret = filp->f_pos;
break;
default:
ret = -EINVAL;
}
return ret;
}
/*ioctl() 设备控制函数*/
static int globalmem_ioctl (struct inode *inodep, struct file *filp, unsigned int cmd, unsigned long arg)
{
struct globalmem_dev *dev = filp->private_data; /*获得设备结构指针*/
switch (cmd) {
case MEM_CLEAR:
/*清全局内存*/
memset (dev->mem, 0, GLOBALMEM_SIZE);
printk (KERN_INFO "globalmem is set to zero\n");
break;
default:
return -EINVAL; /*其他不支持的命令*/
}
return 0;
}
/*文件操作结构体*/
static const struct file_operations globalmem_fops = {
.owner = THIS_MODULE,
.llseek = globalmem_llseek,
.read = globalmem_read,
.write = globalmem_write,
.ioctl = globalmem_ioctl,
.open = globalmem_open,
.release = globalmem_release,
};
/*初始化并添加 cdev 结构体*/
static void globalmem_setup_cdev (struct globalmem_dev *dev, int index)
{
int err;
int devno = MKDEV (globalmem_major, 0);
cdev_init (&dev->cdev, &globalmem_fops); /*初始化cdev结构体*/
dev->cdev.owner = THIS_MODULE;
dev->cdev.ops = &globalmem_fops;
err = cdev_add (&dev->cdev, devno, 1);
if (err) {
printk (KERN_NOTICE "Error %d adding globalmem", err);
}
}
/*globalmem 设备驱动模块加载函数*/
int globalmem_init (void)
{
int result;
dev_t devno = MKDEV (globalmem_major, 0);
/*申请字符设备驱动区域*/
if (globalmem_major) {
result = register_chrdev_region (devno, 1, "globalmem");
} else { /*预设设备号已被占用,动态申请一个*/
result = alloc_chrdev_region (&devno, 0, 1, "globalmem");
globalmem_major = MAJOR (devno); /*分离出主设备号*/
}
if (result < 0)
return result;
globalmem_devp = kmalloc (sizeof (struct globalmem_dev), GFP_KERNEL);
if (!globalmem_devp) { /*申请失败*/
result = -ENOMEM;
goto fail_malloc;
}
memset (globalmem_devp, 0, sizeof (struct globalmem_dev));
globalmem_setup_cdev (globalmem_devp, 0);
return 0;
fail_malloc:
unregister_chrdev_region (devno, 1);
return result;
}
/*globalmem 设备驱动模块卸载函数*/
void globalmem_exit (void)
{
cdev_del (&dev.cdev); /*删除 cdev 结构*/
kfree (globalmem_devp);
unregister_chrdev_region (MKDEV (globalmem_major, 0), 1); /*注销设备区域*/
}
MODULE_AUTHOR ("Song Baohua");
MODULE_LICENSE ("Dula BSD/GPL");
module_param (globalmem_major, int, S_IRUGO);
module_init (globalmem_init);
module_exit (globalmem_exit);
编译成功后，使用 insmod 命令把模块加载到内核中，通过 lsmod 命令可以看到模块已经被成功加载：beyes@linux-beyes:~/Drivers/my/globalmem> lsmod
Module Size Used by
globalmem 7308 0
... ...
再通过 cat 命令查看 /proc/devices 文件，发现多出了主设备号为 240 的字符设备：beyes@linux-beyes:~/Drivers/my/globalmem> cat /proc/devices
Character devices:
...
240 globalmem
...
现在通过 mknod 命令创建设备节点：beyes@linux-beyes:~/Drivers/my/globalmem> sudo mknod /dev/globalmem c 240 0
beyes@linux-beyes:~/Drivers/my/globalmem> ll /dev/globalmem
crw-r--r-- 1 root root 240, 0 09-01 12:37 /dev/globalmem
验证一下设备的工作，现在向设备写入一个 hello world :linux-beyes:/home/beyes/Drivers/my/globalmem # echo 'hello world' > /dev/globalmem
linux-beyes:/home/beyes/Drivers/my/globalmem # cat /dev/globalmem
hello world
cat: /dev/globalmem: 没有那个设备或地址 written 12 bytes(s) from 0
count is: 4096 and *ppos is: 0
right to copy_to_user()?
read 4096 bytes(s) from 0
count is: 4096 and *ppos is: 4096
p is 4096
第 1 行，向设备写 12 个字节，即 hello world 外加 1 个换行符；
第 2 行，从这 1 行输出可以看出，传到 globalmem_read() 函数的 size 就是 4096 个字节，也就是说，cat 一次用一个内存页来读取设备；
第 3 行，这一行测试可以忽略；
第 4 行，输出读取了多少字节；
第 5 行，注意，到了这里，实际上函数再一次被调用了，这是 cat 命令操作造成的结果。在这里，也可以看到，文件指针已经偏移到了 4096 这里；
第 6 行，由于指针已经越界，所以返回 ENXIO 错误号，这个错误号正是表示没有找到相关设备！这也就是 cat 在输出 hello world 后又输出无法找到设备的提示了。 |
|
窥视卡
雷达卡
发表于 2009-9-1 16:47:28
收藏
提升卡
置顶卡
沉默卡
喧嚣卡
变色卡
千斤顶
显身卡
楼主