- #ifndef _MEMDEV_H_
- #define _MEMDEV_H_
- #ifndef MEMDEV_MAJOR
- #define MEMDEV_MAJOR 0 /*预设的mem的主设备号*/
- #endif
- #ifndef MEMDEV_NR_DEVS
- #define MEMDEV_NR_DEVS 2 /*设备数*/
- #endif
- #ifndef MEMDEV_SIZE
- #define MEMDEV_SIZE 4096
- #endif
- /*mem设备描述结构体*/
- struct mem_dev
- {
- char *data;
- unsigned long size;
- struct semaphore sem; /* 定义信号量 */
- };
- #endif /* _MEMDEV_H_ */
- #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/init.h>
- #include <linux/cdev.h>
- #include <asm/io.h>
- #include <asm/system.h>
- #include <asm/uaccess.h>
- #include "memdev.h"
- static int mem_major = MEMDEV_MAJOR;
- module_param(mem_major, int, S_IRUGO);
- struct mem_dev *mem_devp; /*设备结构体指针*/
- struct cdev cdev;
- /*文件打开函数*/
- int mem_open(struct inode *inode, struct file *filp)
- {
- struct mem_dev *dev;
-
- /*获取次设备号*/
- int num = MINOR(inode->i_rdev);
- if (num >= MEMDEV_NR_DEVS)
- return -ENODEV;
- dev = &mem_devp[num];
-
- /*将设备描述结构指针赋值给文件私有数据指针*/
- filp->private_data = dev;
-
- return 0;
- }
- /*文件释放函数*/
- int mem_release(struct inode *inode, struct file *filp)
- {
- return 0;
- }
- /*读函数*/
- static ssize_t mem_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 mem_dev *dev = filp->private_data; /*获得设备结构体指针*/
- /* 获取信号量 */
- if (down_interruptible(&dev->sem))
- return -ERESTARTSYS;
-
- /*判断读位置是否有效*/
- if (p >= MEMDEV_SIZE)
- return 0;
- if (count > MEMDEV_SIZE - p)
- count = MEMDEV_SIZE - p;
- /*读数据到用户空间*/
- if (copy_to_user(buf, (void*)(dev->data + p), count))
- {
- ret = - EFAULT;
- goto out;
- }
- else
- {
- *ppos += count;
- ret = count;
-
- printk(KERN_INFO "read %d bytes(s) from %d\n", count, p);
- }
- out:
- /* 释放信号量 */
- up(&dev->sem);
- return ret;
- }
- /*写函数*/
- static ssize_t mem_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 mem_dev *dev = filp->private_data; /*获得设备结构体指针*/
- /* 获取信号量 */
- if (down_interruptible(&dev->sem))
- return -ERESTARTSYS;
- /*分析和获取有效的写长度*/
- if (p >= MEMDEV_SIZE)
- return 0;
- if (count > MEMDEV_SIZE - p)
- count = MEMDEV_SIZE - p;
-
- /*从用户空间写入数据*/
- if (copy_from_user(dev->data + p, buf, count)){
- ret = - EFAULT;
- goto out;
- }
- else
- {
- *ppos += count;
- ret = count;
-
- printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);
- }
- out:
- /* 释放信号量 */
- up(&dev->sem);
- return ret;
- }
- /* seek文件定位函数 */
- static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)
- {
- loff_t newpos;
- switch(whence) {
- case 0: /* SEEK_SET */
- newpos = offset;
- break;
- case 1: /* SEEK_CUR */
- newpos = filp->f_pos + offset;
- break;
- case 2: /* SEEK_END */
- newpos = MEMDEV_SIZE -1 + offset;
- break;
- default: /* can't happen */
- return -EINVAL;
- }
- if ((newpos<0) || (newpos>MEMDEV_SIZE))
- return -EINVAL;
-
- filp->f_pos = newpos;
- return newpos;
- }
- /*文件操作结构体*/
- static const struct file_operations mem_fops =
- {
- .owner = THIS_MODULE,
- .llseek = mem_llseek,
- .read = mem_read,
- .write = mem_write,
- .open = mem_open,
- .release = mem_release,
- };
- /*设备驱动模块加载函数*/
- static int memdev_init(void)
- {
- int result;
- int i;
- dev_t devno = MKDEV(mem_major, 0);
- /* 静态申请设备号*/
- if (mem_major)
- result = register_chrdev_region(devno, 2, "memdev");
- else /* 动态分配设备号 */
- {
- result = alloc_chrdev_region(&devno, 0, 2, "memdev");
- mem_major = MAJOR(devno);
- }
-
- if (result < 0)
- return result;
- /*初始化cdev结构*/
- cdev_init(&cdev, &mem_fops);
- cdev.owner = THIS_MODULE;
- cdev.ops = &mem_fops;
-
- /* 注册字符设备 */
- cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);
-
- /* 为设备描述结构分配内存*/
- mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
- if (!mem_devp) /*申请失败*/
- {
- result = - ENOMEM;
- goto fail_malloc;
- }
- memset(mem_devp, 0, sizeof(struct mem_dev));
-
- /*为设备分配内存*/
- for (i=0; i < MEMDEV_NR_DEVS; i++)
- {
- mem_devp[i].size = MEMDEV_SIZE;
- mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);
- memset(mem_devp[i].data, 0, MEMDEV_SIZE);
- /* 初始化信号量 */
- sema_init(&mem_devp[i].sem, 1);
- }
-
- return 0;
- fail_malloc:
- unregister_chrdev_region(devno, 1);
-
- return result;
- }
- /*模块卸载函数*/
- static void memdev_exit(void)
- {
- cdev_del(&cdev); /*注销设备*/
- kfree(mem_devp); /*释放设备结构体内存*/
- unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*释放设备号*/
- }
- MODULE_AUTHOR("David Xie");
- MODULE_LICENSE("GPL");
- module_init(memdev_init);
- module_exit(memdev_exit);
- #include <stdio.h>
- int main()
- {
- FILE *fp0 = NULL;
- char Buf[4096];
-
- /*初始化Buf*/
- strcpy(Buf,"Mem is char dev!");
- printf("BUF: %s\n",Buf);
-
- /*打开设备文件*/
- fp0 = fopen("/dev/memdev0","r+");
- if (fp0 == NULL)
- {
- printf("Open Memdev0 Error!\n");
- return -1;
- }
-
- /*写入设备*/
- fwrite(Buf, sizeof(Buf), 1, fp0);
-
- /*重新定位文件位置(思考没有该指令,会有何后果)*/
- fseek(fp0,0,SEEK_SET);
-
- /*清除Buf*/
- strcpy(Buf,"Buf is NULL!");
- printf("BUF: %s\n",Buf);
-
-
- /*读出设备*/
- fread(Buf, sizeof(Buf), 1, fp0);
-
- /*检测结果*/
- printf("BUF: %s\n",Buf);
-
- return 0;
- }
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