简单linux字符设备驱动程序

本文代码参考《LINUX设备驱动程序》第三章 字符设备驱动程序

本文中的“字符设备”是一段大小为PAGE_SIZE的内存空间

功能：向字符设备写入字符串；从字符设备读出字符串

代码：

1. scull.c

 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/errno.h>
 #include <linux/types.h>
 #include <linux/cdev.h>
 #include <asm/uaccess.h>

 #include "scull.h"

 int scull_major = SCULL_MAJOR;
 int scull_minor = ;

 module_param(scull_major, int, S_IRUGO);
 module_param(scull_minor, int, S_IRUGO);

 struct scull_dev *scull_device;

 int scull_trim(struct scull_dev *dev)
 {
     if (dev)
     {
         if (dev->data)
         {
             kfree(dev->data);
         }
         dev->data = NULL;
         dev->size = ;
     }
     return ;
 }

 int scull_open(struct inode *inode, struct file *filp)
 {
     struct scull_dev *dev;

     dev = container_of(inode->i_cdev, struct scull_dev, cdev);
     filp->private_data = dev;

     if ((filp->f_flags & O_ACCMODE) == O_WRONLY)
     {
         if (down_interruptible(&dev->sem))
         {
             return -ERESTARTSYS;
         }
         scull_trim(dev);
         up(&dev->sem);
     }

     return ;
 }

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

 ssize_t scull_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
 {
     struct scull_dev *dev = filp->private_data;
     ssize_t retval = ;

     if (down_interruptible(&dev->sem))
     {
         return -ERESTARTSYS;
     }
     if (*f_pos >= dev->size)
     {
         goto out;
     }
     if (*f_pos + count > dev->size)
     {
         count = dev->size - *f_pos;
     }

     if (!dev->data)
     {
         goto out;
     }

     if (copy_to_user(buf, dev->data + *f_pos, count))
     {
         retval = -EFAULT;
         goto out;
     }

     *f_pos += count;
     retval = count;

     out:
         up(&dev->sem);
         return retval;
 }

 ssize_t scull_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos)
 {
     struct scull_dev *dev = filp->private_data;
     ssize_t retval = -ENOMEM;

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

     if (!dev->data)
     {
         dev->data = kmalloc(SCULL_BUFFER_SIZE, GFP_KERNEL);
         if (!dev->data)
         {
             goto out;
         }
         memset(dev->data, , SCULL_BUFFER_SIZE);
      }

     if (count > SCULL_BUFFER_SIZE - dev->size)
     {
         count = SCULL_BUFFER_SIZE - dev->size;
     }

     if (copy_from_user(dev->data + dev->size, buf, count))
     {
         retval = -EFAULT;
         goto out;
     }

     dev->size += count;
     retval = count;

     out:
         up(&dev->sem);
         return retval;
 }

 loff_t scull_llseek(struct file *filp, loff_t off, int whence)
 {
     struct scull_dev *dev = filp->private_data;
     loff_t newpos;

     switch(whence)
     {
         case :
             newpos = off;
             break;
         case :
             newpos = filp->f_pos + off;
             break;
         case :
             newpos = dev->size + off;
             break;
         default:
             return -EINVAL;
     }
     if (newpos < )
     {
         return -EINVAL;
     }
     filp->f_pos = newpos;
     return newpos;
 }

 struct file_operations scull_fops = {
     .owner = THIS_MODULE,
     .llseek = scull_llseek,
     .read = scull_read,
     .write = scull_write,
     .open = scull_open,
     .release = scull_release,
 };

 void  scull_cleanup_module(void)
 {
     dev_t devno = MKDEV(scull_major, scull_minor);

     if (scull_device)
     {
         scull_trim(scull_device);
         cdev_del(&scull_device->cdev);
         kfree(scull_device);
     }
     unregister_chrdev_region(devno, );
 }

 static void scull_setup_cdev(struct scull_dev *dev)
 {
     int err, devno = MKDEV(scull_major, scull_minor);

     cdev_init(&dev->cdev, &scull_fops);
     dev->cdev.owner = THIS_MODULE;
     dev->cdev.ops = &scull_fops;
     err = cdev_add(&dev->cdev, devno, );

     if (err)
     {
         printk(KERN_NOTICE "Error %d adding scull", err);
     }
 }

 static int __init scull_init_module(void)
 {
     int result;
     dev_t dev = ;

     if (scull_major)
     {
         dev = MKDEV(scull_major, scull_minor);
         result = register_chrdev_region(dev, , "scull");
     }
     else
     {
         result = alloc_chrdev_region(&dev, scull_minor, , "scull");
         scull_major = MAJOR(dev);
     }
     if (result < )
     {
         printk(KERN_WARNING "scull: can't get major %d\n", scull_major);
         return result;
     }

     scull_device = kmalloc(sizeof(struct scull_dev), GFP_KERNEL);
     if (!scull_device)
     {
         result = -ENOMEM;
         goto fail;
     }
     memset(scull_device, , sizeof(struct scull_dev));

     init_MUTEX(&scull_device->sem);

     scull_setup_cdev(scull_device);

     return ;

     fail:
         scull_cleanup_module();
         return result;
 }

 module_init(scull_init_module);
 module_exit(scull_cleanup_module);

 MODULE_LICENSE("GPL");

2. scull.h

 #ifndef _SCULL_H
 #define _SCULL_H

 #define SCULL_MAJOR 0
 #define SCULL_BUFFER_SIZE PAGE_SIZE

 struct scull_dev {
     char *data;
     unsigned long size;
     struct semaphore sem;
     struct cdev cdev;
 };

 #endif

3. Makefile

 obj-m += scull.o

 CURRENT_PATH:=$(shell pwd)
 LINUX_KERNEL:=$(shell uname -r)
 LINUX_KERNEL_PATH:=/usr/src/kernels/$(LINUX_KERNEL)

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

4. 验证效果

1) make

2) insmod scull.ko

3) cat /proc/devices | grep scull    //获取字符设备scull的主设备号,我的是248

4) cd /dev/

5) mknod scull c 248 0

6) echo hello, world > scull    //向字符设备写入“hello, world”

7) cat scull    //读出字符设备中的内容，这里应该显示“hello, world”