代码：编写一个简单的字符设备驱动——创建多个同类型设备

编写同类型多个设备字符驱动应注意一下几个问题：

1、申请设备号alloc_chrdev_region时须指定次设备号范围；

2、动态分配设备空间时同时分配NUM个设备的空间；

3、根据次设备号和统一的主设备号生成针对单个设备的devno，然后完成cdev_add注册；

4、设备文件的device_create中可以指定第五个参数来区别不同设备的设备文件（节点）名称；

5、卸载函数中注意循环卸载设备文件以及注销设备；

6、注销设备号；

遗留问题：通过cdev_add中指定count参数应该可以完成多个设备的同时注册，但cdev_del中并没有devno做入参，

                  暂未确认一次调用是否可以完成对多个设备的注销，留待日后解决。

代码如下：

#include <linux/module.h>#include <linux/fs.h>#include <linux/init.h>#include <linux/cdev.h>#include <linux/slab.h>#include <linux/uaccess.h>#include <linux/device.h>#define MAX_SIZE          0x1000#define MEM_CLEAR         0x1#define MEM_PRINT         0x2#define DEVICE_NUM        4static struct class *class;static struct device *classdev;struct virtdev_dev{struct cdev cdev;unsigned char mem[MAX_SIZE];};struct virtdev_dev *devp;dev_t devno;int major;static int virtdev_open(struct inode *inode, struct file *filp){struct virtdev_dev *dev = container_of(inode->i_cdev, struct virtdev_dev, cdev);filp->private_data = dev;return 0;}static int virtdev_release(struct inode *inode, struct file *filp){return 0;}static long virtdev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg){struct virtdev_dev *dev = filp->private_data;switch (cmd){case MEM_CLEAR:memset(dev->mem, 0, MAX_SIZE);printk(KERN_INFO "virtdev is set to zero.\n");break;case MEM_PRINT:printk(KERN_INFO "copying string OK!\n");break;default:return -EINVAL;}return 0;}static ssize_t virtdev_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 virtdev_dev *dev = filp->private_data;if (p >= MAX_SIZE)return -EINVAL;if (count > MAX_SIZE - p)count = MAX_SIZE - p;if (copy_to_user(buf, dev->mem + p, count))ret = -EINVAL;else{*ppos += count;ret = count;printk(KERN_INFO "read %u byte(s) from %lu\n", count, p);}return ret;}static ssize_t virtdev_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 virtdev_dev *dev = filp->private_data;if (p >= MAX_SIZE)return -EINVAL;if (count > MAX_SIZE - p)count = MAX_SIZE - p;if (copy_from_user(dev->mem + p, buf, count))ret = -EINVAL;else{*ppos += count;ret = count;printk(KERN_INFO "write %u byte(s) from %lu\n", count, p);}return ret;}static loff_t virtdev_llseek(struct file *filp, loff_t offset, int orig){loff_t ret = 0;switch (orig){case 0:if (offset < 0){ret = -EINVAL;break;}if (offset > MAX_SIZE){ret = -EINVAL;break;}filp->f_pos = offset;ret = filp->f_pos;break;case 1:if ((filp->f_pos + offset) < 0 ){ret = -EINVAL;break;}if ((filp->f_pos + offset) > MAX_SIZE){ret = -EINVAL;break;}filp->f_pos += offset;ret = filp->f_pos;break;default:ret = -EINVAL;break;}return ret;}static const struct file_operations virtdev_fops ={.owner  =  THIS_MODULE,.llseek =  virtdev_llseek,.read   =  virtdev_read,.write  =  virtdev_write,.unlocked_ioctl = virtdev_ioctl,.open   =  virtdev_open,.release = virtdev_release,};static char *chardev_devnode(struct device *dev, umode_t *mode){    if (mode)        *mode = 0666;    return NULL;}static void virtdev_setup_cdev(struct virtdev_dev *dev, int index){int err;int ret;int devno = MKDEV(major, index);classdev = device_create(class, NULL, devno, NULL, "virtdev%d", index);if (IS_ERR(class)){ret = PTR_ERR(classdev);printk(KERN_ERR "device create error %d\n", ret);class_destroy(class);}cdev_init(&dev->cdev, &virtdev_fops);dev->cdev.owner = THIS_MODULE;err = cdev_add(&dev->cdev, devno, 1);if (err)printk(KERN_NOTICE "Error %d adding virtdev%d", err, index);}static int __init virtdev_init(void){int ret;int i;ret = alloc_chrdev_region(&devno, 0, DEVICE_NUM, "virtdev");if (ret < 0)return ret;major = MAJOR(devno);devp = kzalloc(sizeof(struct virtdev_dev) * DEVICE_NUM, GFP_KERNEL);if (!devp){ret = -ENOMEM;goto fail_malloc;}class = class_create(NULL, "virtdev");if (IS_ERR(class)){ret = PTR_ERR(class);printk(KERN_ERR "class create error %d\n", ret);goto fail_malloc;}class->devnode = chardev_devnode;for (i = 0; i < DEVICE_NUM; i++)virtdev_setup_cdev(devp + i, i);return 0;fail_malloc:unregister_chrdev_region(devno, 1);return ret;}static void __exit virtdev_exit(void){int i;int devno;for (i = 0; i < DEVICE_NUM; i++){devno = MKDEV(major, i);device_destroy(class, devno);cdev_del(&((devp+i)->cdev));}class_destroy(class);kfree(devp);unregister_chrdev_region(MKDEV(major, 0), DEVICE_NUM);}module_init(virtdev_init);module_exit(virtdev_exit);MODULE_AUTHOR("lql");MODULE_LICENSE("GPL");

运行结果显示：

加载模块是/proc/devices文件中有virtdev设备生成，/dev路径下有virtdev0、virtdev1、virtdev2、virtdev3设备文件生成；

加载模块是/proc/devices文件中删除virtdev设备，/dev路径下删除virtdev0、virtdev1、virtdev2、virtdev3设备文件；