《linux设备驱动开发详解》学习之globalmem

来源：互联网发布：淘宝客服发展前景编辑：程序博客网时间：2024/05/19 05:01

1.代码：

#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
//#include <linux/slob_def.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>

#define GLOBALMEM_SIZE 0x1000 /*4KB*/
#define MEM_CLEAR 0x1 /*clear globale memory*/
#define GLOBALMEM_MAJOR 199 /**/

static globalmem_major = GLOBALMEM_MAJOR;

struct globalmem_dev
{
   struct cdev cdev;
   unsigned char mem[GLOBALMEM_SIZE];
   struct semaphore sem;
};
struct globalmem_dev *globalmem_devp;

int globalmem_open(struct inode* inode, struct file * filp)
{
   filp->private_data = globalmem_devp;
   return 0;
}

int globalmem_release(struct inode * inode, struct file * filp)
{
   return 0;
}

//static int globalmem_ioctl(struct inode * inodep, struct file * filp, unsigned int cmd, unsigned long arg)
static int globalmem_ioctl(struct file * filp, unsigned int cmd, unsigned long arg)
{
   struct globalmem_dev * dev = filp->private_data;

   switch(cmd)
   {
       case MEM_CLEAR:
           if(down_interruptible(&dev->sem))
           {
               return -ERESTARTSYS;
           }
           memset(dev->mem, 0, GLOBALMEM_SIZE);
           up(&dev->sem);
           printk(KERN_INFO "globalmem is set to 0\n");
           break;
       default:
           return -EINVAL;
   }

   return 0;
}

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;
   int ret = 0;
   struct globalmem_dev *dev = filp->private_data;

   if(p >= GLOBALMEM_SIZE)
   {
       return count ? -ENXIO:0;
   }

   if(count > GLOBALMEM_SIZE - p)
   {
       count = GLOBALMEM_SIZE - p;
   }

   if(down_interruptible(&dev->sem))
   {
       return -ERESTARTSYS;
   }

   if(copy_to_user(buf, (void*)(dev->mem + p), count))
   {
       ret = -EFAULT;
   }
   else
   {
       *ppos += count;
       ret = count;
       printk(KERN_EMERG "read %d byte(s) from %d\n", count, p);
   }

   up(&dev->sem);

   return ret;
}

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;

   if(p >= GLOBALMEM_SIZE)
   {
       return (count ? -ENXIO : 0);
   }
   if(count > GLOBALMEM_SIZE - p)
   {
       count = GLOBALMEM_SIZE - p;
   }

   if(down_interruptible(&dev->sem))
   {
       return -ERESTARTSYS;
   }

   if(copy_from_user(dev->mem + p, buf, count))
   {
       ret = -EFAULT;
   }
   else
   {
       *ppos += count;
       ret = count;

       printk(KERN_EMERG "written %d byte(s) from %d\n", count, p);
   }

   up(&dev->sem);

   return ret;
}

static loff_t globalmem_llseek(struct file * filp, loff_t offset, int orig)
{
   loff_t ret = 0;

   switch(orig)
   {
       case 0:
           if(offset < 0)
           {
               ret = -EINVAL;
               break;
           }
           if((unsigned int)offset > GLOBALMEM_SIZE)
           {
               ret = -EINVAL;
               break;
           }
           filp->f_pos = (unsigned int)offset;
           ret = filp->f_pos;
           break;
       case 1:
           if((filp->f_pos + offset) > GLOBALMEM_SIZE)
           {
               ret = -EINVAL;
               break;
           }
           if((filp->f_pos + offset) < 0)
           {
               ret = -EINVAL;
               break;
           }
           filp->f_pos += offset;
           ret = filp->f_pos;
           break;
   }

   return ret;
}

static const struct file_operations globalmem_fops =
{
   .owner = THIS_MODULE,
   .llseek = globalmem_llseek,
   .read = globalmem_read,
   .write = globalmem_write,
   .compat_ioctl = globalmem_ioctl,
   .open = globalmem_open,
   .write = globalmem_write,
};
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);
   dev->cdev.owner = THIS_MODULE;
   dev->cdev.ops = &globalmem_fops;
   err = cdev_add(&dev->cdev, devno, 1);

   if(err)
   {
       printk(KERN_EMERG "Error %d adding globalmem %d\n", err, index);
   }
}

int globalmem_init(void)
{
   int result;
   dev_t devno = MKDEV(globalmem_major, 0);

   if(globalmem_major)
   {
       result = register_chrdev_region(devno, 1, "globalmem");
   }
   else
   {
       result = alloc_chrdev_region(&devno, 0, 1, "globalmem");
       globalmem_major = MAJOR(devno);
   }

   if(result < 0)
   {
       return result;
   }

   globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);
   if(!globalmem_devp)
   {
       result = -ENOMEM;
       goto fail_malloc;
   }
   memset(globalmem_devp, 0, sizeof(struct globalmem_dev));

   globalmem_setup_cdev(globalmem_devp, 0);
   //init_MUTEX(&globalmem_devp->sem);
   mutex_init(&globalmem_devp->sem);
   return 0;

fail_malloc:
   unregister_chrdev_region(devno, 1);
   return result;
}

void globalmem_exit(void)
{
   cdev_del(&globalmem_devp->cdev);
   kfree(globalmem_devp);
   unregister_chrdev_region(MKDEV(globalmem_major, 0), 1);
}

MODULE_AUTHOR("hmy");
MODULE_LICENSE("Dual BSD/GPL");

module_param(globalmem_major, int, S_IRUGO);

module_init(globalmem_init);
module_exit(globalmem_exit);

2.编译

我的虚拟机kernel版本是：linux-headers-2.6.38-15-generic

在/usr/src/linux-headers-2.6.38-15-generic/drivers/下建立路径globalmem

<后来有试了一下，把源文件和makefile放到自己用户的路径下也是可以编译的>

把globalmem.c放在此目录下，编写Makefile，内容如下：

obj-m :=globalmem.o
KDIR :=/usr/src/linux-headers-2.6.38-15-generic
all :
make -C $(KDIR) M=$(shell pwd) modules
clean:
make -C $(KDIR) M=$(shell pwd) clean

在shell中make，globalmem.ko就能编译出来，中间可能会用到root权限。

注：编译的时候会有一些小问题，主要原因是我用的内核版本可能和例子用的不一样，导致编译不过

文件包含问题导致一些函数的声明找不到，如kfree,kmalloc, mutex_init等，这些细节需要自己好好找下了，不是太大的问题。

3.安装：

使用insmod globalmem.ko 命令安装这个驱动，但是最初安装是提示“insmod: error inserting 'globalmem.ko': -1 Device or resource busy”，

原因是设备号原来用的是254， cat /proc/devices 发现已经有设备使用254了，设备号重复，改成199就好了~

使用lsmod可以查看已安装的模块；

使用rmmod可以删除已安装的模块。