驱动：
#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 <linux/slab.h> #include <linux/device.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 #define DEVICE_NAME "memdev" /*udev自动添加设备节点*/ struct class *mem_class; static int mem_major = MEMDEV_MAJOR; module_param(mem_major, int, S_IRUGO); struct mem_dev { struct cdev cdev; /*cdev结构体*/ unsigned char mem[MEMDEV_SIZE]; /*全局内存*/ }; struct mem_dev *mem_devp; /*设备结构体指针*/ /*文件打开函数*/ int mem_open(struct inode *inode, struct file *filp) { struct mem_dev *dev; dev=container_of(inode->i_cdev,struct mem_dev,cdev);//通过结构体成员的指针找到对应结构体的指针 /*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*/ /*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->mem+ p), count)) { ret = - EFAULT; } else { *ppos += count; ret = count; printk(KERN_INFO "read %d bytes(s) from postion %d\n", count, p); } 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*/ /*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->mem + p, buf, count)) ret = - EFAULT; else { *ppos += count; ret = count; printk(KERN_INFO "written %d bytes(s) to postion %d\n", count, p); } 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, }; /*初始化并注册cdev*/ static void mem_setup_cdev(struct mem_dev *dev, int index) { int err, devno = MKDEV(mem_major, index); cdev_init(&dev->cdev, &mem_fops); dev->cdev.owner = THIS_MODULE; dev->cdev.ops = &mem_fops; err = cdev_add(&dev->cdev, devno, 1); if (err) printk(KERN_NOTICE "Error %d adding LED%d", err, index); } /*设备驱动模块加载函数*/ static int memdev_init(void) { int result; dev_t devno = MKDEV(mem_major, 0); /* 静态申请设备号*/ if (mem_major) result = register_chrdev_region(devno, MEMDEV_NR_DEVS, DEVICE_NAME); else /* 动态分配设备号 */ { result = alloc_chrdev_region(&devno, 0, MEMDEV_NR_DEVS, DEVICE_NAME); mem_major = MAJOR(devno); } if (result < 0) return result; /* 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, 2*sizeof(struct mem_dev)); /*为设备分配内存*/ mem_setup_cdev(&mem_devp[0], 0); mem_setup_cdev(&mem_devp[1], 1); /*udev机制可以自动添加设备节点，只需要添加xxx_class这个类，以及device_create()*/ mem_class = class_create(THIS_MODULE, "mem_class");/*在sys目录下创建xx_class这个类,/sys/class/~*/ device_create(mem_class, NULL, mem_devp[0].cdev.dev, NULL, "memdev0");/*自动创建设备/dev/$DEVICE_NAME*/ device_create(mem_class, NULL, mem_devp[1].cdev.dev, NULL, "memdev1");/*自动创建设备/dev/$DEVICE_NAME*/ printk("memdev driver installed, with major %d\n", mem_major); printk("the device name is %s\n",DEVICE_NAME); return 0; fail_malloc: unregister_chrdev_region(devno, 1); return result; } /*模块卸载函数*/ static void memdev_exit(void) { device_destroy(mem_class, mem_devp[0].cdev.dev); device_destroy(mem_class, mem_devp[1].cdev.dev); class_destroy(mem_class); cdev_del(&(mem_devp[0].cdev)); /*注销设备*/ cdev_del(&(mem_devp[1].cdev)); 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*/ printk("memdev driver uninstalled\n"); } MODULE_AUTHOR("mhb@SEU"); MODULE_LICENSE("GPL"); module_init(memdev_init); module_exit(memdev_exit);
测试代码：
#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> #include <string.h> int main() { FILE *fp0 = NULL; char Buf[4096]; int result; /*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) { perror("Open Memdev0 Error!\n"); return -1; } /*写入设备*/ result = fwrite(Buf, sizeof(Buf), 1, fp0); if (result == -1) { perror("fwrite Error!\n"); return -1; } /*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); sleep(1); /*读出设备*/ result = fread(Buf, sizeof(Buf), 1, fp0); if (result == -1) { perror("fread Error!\n"); return -1; } /*检测结果*/ printf("BUF: %s\n",Buf); return 0; }