2022-04-01 13:36:57 +08:00
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# 8.6 字符设备驱动
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2022-04-05 17:40:55 +08:00
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Linux 系统中,字符设备、块设备、网络设备是从使用角度来划分的。
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字符设备:是指只能一个字节一个字节读写的设备,不能随机读取设备内存中的某一数据,读取数据需要按照先后数据。字符设备是面向流的设备,常见的字符设备有鼠标、键盘、串口、控制台和 LED 设备等。
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块设备:是指可以从设备的任意位置读取一定长度数据的设备。块设备包括硬盘、磁盘、U 盘和 SD 卡等。
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## 字符设备驱动示例
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```cpp
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/**
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* @file demo_char.c
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* @author Rick Chan (cy187lion@sina.com)
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* @brief Linux char driver demo.
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* @version 0.1.0
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* @date 2020-04-27
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2022-04-16 13:41:10 +08:00
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*
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2022-04-05 17:40:55 +08:00
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* @copyright Copyright (c) 2020
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2022-04-16 13:41:10 +08:00
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*
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2022-04-05 17:40:55 +08:00
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/cdev.h>
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#include <linux/uaccess.h>
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#include <linux/fs.h>
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#include <linux/slab.h>
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#include <linux/device.h>
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MODULE_AUTHOR("Rick Chan");
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MODULE_LICENSE("GPL");
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#define DEMO_MAGIC 'R'
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#define DEMO_IOC_SIZE 8
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#define DEMO_CTL_IOC _IOC(_IOC_READ|_IOC_WRITE, DEMO_MAGIC, 0, DEMO_IOC_SIZE)
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#define DEMO_CTL_IO _IO(DEMO_MAGIC, 1)
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#define DEMO_CTL_IOR _IOR(DEMO_MAGIC, 2, uint16_t)
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#define DEMO_CTL_IOW _IOW(DEMO_MAGIC, 3, int32_t)
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#define DEMO_CTL_IOWR _IOWR(DEMO_MAGIC, 4, uint32_t)
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#define DEMO_CTL_MAX 5
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#define DEMO_MODULE_NAME "demo_char"
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#define DEMO_DEV_CNT 2
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// This is a test.
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#define DEMO_DATA_SIZE 5
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static int demo_major = 0;
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struct demo_dev
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{
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struct cdev cdev;
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struct device *dev;
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// This is a test.
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char demo_text[DEMO_DATA_SIZE];
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};
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struct class *class;
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struct demo_dev* demo_devp;
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static int demo_open(struct inode *inode, struct file *filp)
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{
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struct demo_dev *demo;
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demo = container_of(inode->i_cdev, struct demo_dev, cdev);
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filp->private_data = demo;
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return 0;
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}
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static int demo_release(struct inode *inode, struct file *filp)
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{
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return 0;
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}
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static loff_t demo_llseek(struct file *filp, loff_t offset, int origin)
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{
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struct demo_dev *devp = filp->private_data;
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loff_t ret;
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(void)devp;
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// This is a test.
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switch(origin)
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{
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case 0: // 从文件开头开始偏移
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if(offset<0)
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{
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ret = -EINVAL;
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break;
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}
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if((unsigned int)offset>DEMO_DATA_SIZE)
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{
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ret = -EINVAL;
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break;
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}
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filp->f_pos = (unsigned int)offset;
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ret = filp->f_pos;
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break;
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case 1: // 从当前位置开始偏移
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if((filp->f_pos+offset)>DEMO_DATA_SIZE)
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{
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ret = -EINVAL;
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break;
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}
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if((filp->f_pos+offset)<0)
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{
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ret = -EINVAL;
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break;
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}
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filp->f_pos += offset;
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ret = filp->f_pos;
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break;
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default:
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ret = -EINVAL;
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}
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return ret;
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return filp->f_pos;
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}
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static ssize_t demo_read(struct file *filp, char __user *buffer, size_t count, loff_t *position)
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{
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struct demo_dev *devp = filp->private_data;
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loff_t p = *position;
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ssize_t ret = 0;
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// This is a test.
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// 分析和获取有效的读长度
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if(DEMO_DATA_SIZE<=p) // 要读的偏移位置越界
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return 0; // End of a file
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if(DEMO_DATA_SIZE<(count+p)) // 要读的字节数太大
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count = DEMO_DATA_SIZE-p;
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if(copy_to_user((void*)buffer, &devp->demo_text[p], count))
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ret = -EFAULT;
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else
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{
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*position += count;
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ret = count;
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}
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return ret;
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}
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static ssize_t demo_write(struct file *filp, const char __user *buffer, size_t count, loff_t *position)
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{
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struct demo_dev *devp = filp->private_data;
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const char __user *p = buffer;
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(void)devp;
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return p-buffer;
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}
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static long demo_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
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{
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struct demo_dev *devp = filp->private_data;
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(void)devp;
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// 检测 cmd 合法性
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2022-04-16 13:41:10 +08:00
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if (DEMO_MAGIC!=_IOC_TYPE(cmd))
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2022-04-05 17:40:55 +08:00
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return -EINVAL;
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2022-04-16 13:41:10 +08:00
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if (DEMO_CTL_MAX<_IOC_NR(cmd))
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2022-04-05 17:40:55 +08:00
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return -EINVAL;
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switch(cmd)
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{
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case DEMO_CTL_IOC:
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{
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uint8_t tmp[DEMO_IOC_SIZE];
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copy_from_user(&tmp, (void*)arg, _IOC_SIZE(cmd));
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copy_to_user((void*)arg, &tmp, _IOC_SIZE(cmd));
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}
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break;
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case DEMO_CTL_IO:
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break;
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case DEMO_CTL_IOR:
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{
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uint16_t tmp = 0x55AA;
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copy_to_user((void*)arg, &tmp, _IOC_SIZE(cmd));
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}
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break;
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case DEMO_CTL_IOW:
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{
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int32_t tmp = 0;
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copy_from_user(&tmp, (void*)arg, _IOC_SIZE(cmd));
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}
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break;
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case DEMO_CTL_IOWR:
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{
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uint32_t tmp = 0;
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copy_from_user(&tmp, (void*)arg, _IOC_SIZE(cmd));
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copy_to_user((void*)arg, &tmp, _IOC_SIZE(cmd));
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}
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break;
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default:
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return -ENOIOCTLCMD;
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}
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return 0;
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}
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static int demo_mmap(struct file *filp, struct vm_area_struct *vma)
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{
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struct demo_dev *devp = filp->private_data;
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(void)devp;
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return 0;
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}
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static struct file_operations demo_fops = {
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.owner = THIS_MODULE,
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.open = demo_open,
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.release = demo_release,
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.llseek = demo_llseek,
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.read = demo_read,
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.write = demo_write,
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.unlocked_ioctl = demo_ioctl,
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.mmap = demo_mmap
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};
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static int demo_setup_cdev(struct demo_dev *devp, int index)
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{
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char name[16];
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int err, devno = MKDEV(demo_major, index);
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cdev_init(&devp->cdev, &demo_fops);
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devp->cdev.owner = THIS_MODULE;
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err = cdev_add(&devp->cdev, devno, 1);
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if(err)
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{
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printk(KERN_ERR "demo add cdev:%d error:%d.\r\n", index, err);
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goto out_cdev;
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}
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// 创建设备节点
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memset(name, 0, 16);
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sprintf(name, DEMO_MODULE_NAME"%d", index);
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printk(KERN_INFO "demo new dev name:%s", name);
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devp->dev = device_create(class, NULL, devp->cdev.dev, NULL, name);
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// This is a test.
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devp->demo_text[DEMO_DATA_SIZE-2] = '\n';
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devp->demo_text[DEMO_DATA_SIZE-1] = 0;
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sprintf(devp->demo_text, "%d", index);
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return 0;
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out_cdev:
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cdev_del(&devp->cdev);
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kfree(devp);
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return err;
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}
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static int __init demo_init(void)
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{
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int err, i;
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dev_t devno = MKDEV(demo_major, 0);
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printk(KERN_ALERT "demo_init.demo_major: %d\n", demo_major);
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if(demo_major) // 使用固定主设备号
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err = register_chrdev_region(devno, DEMO_DEV_CNT, DEMO_MODULE_NAME);
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else // 动态分配主设备号
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{
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err = alloc_chrdev_region(&devno, 0, DEMO_DEV_CNT, DEMO_MODULE_NAME);
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demo_major = MAJOR(devno);
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}
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if(err<0)
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return err;
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demo_devp = kzalloc(DEMO_DEV_CNT*sizeof(struct demo_dev), GFP_KERNEL);
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if(!demo_devp)
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{
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err = -ENOMEM;
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goto out;
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}
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// 创建设备类, 子设备属于同一个设备类
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class = class_create(THIS_MODULE, DEMO_MODULE_NAME);
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for(i=0; i<DEMO_DEV_CNT; i++)
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{
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err = demo_setup_cdev(&demo_devp[i], i);
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if(err)
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goto out_class;
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}
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return 0;
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out_class:
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class_destroy(class);
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out:
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unregister_chrdev_region(devno, DEMO_DEV_CNT);
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return err;
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}
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static void demo_clean_cdev(struct demo_dev *devp)
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{
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device_destroy(class, devp->cdev.dev);
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cdev_del(&devp->cdev);
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}
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static void __exit demo_exit(void)
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{
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int i;
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for(i=0; i<DEMO_DEV_CNT; i++)
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demo_clean_cdev(&demo_devp[i]);
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class_destroy(class);
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kfree(demo_devp);
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unregister_chrdev_region(MKDEV(demo_major, 0), DEMO_DEV_CNT);
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}
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// insmod 时可传入参数
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module_param(demo_major, int, S_IRUGO);
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module_init(demo_init);
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module_exit(demo_exit);
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MODULE_AUTHOR("Rick Chan <cy187lion@sina.com>");
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MODULE_DESCRIPTION("Char driver demo");
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MODULE_LICENSE("GPL");
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MODULE_VERSION("1.0.0");
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```
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Makefile 文件如下:
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```Makefile
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obj-m:= \
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|
|
demochar.o
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|
demochar-objs:= \
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|
demo_char.o
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|
|
EXTRA_CFLAGS += \
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|
|
-I$(PWD)
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|
|
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|
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|
|
all:
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|
|
$(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
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|
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|
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|
|
|
|
clean:
|
|
|
|
|
$(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
|
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|
|
|
```
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|
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|
|
编译和验证方法:
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|
|
|
|
|
|
|
```bash
|
|
|
|
|
make
|
|
|
|
|
sudo insmod demochar.ko demo_major=200
|
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|
|
|
ls /dev/demo*
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|
|
|
ll /sys/class/demo_char/
|
|
|
|
|
sudo rmmod demochar
|
|
|
|
|
```
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|
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|
|
|
|
|
## 字符设备驱动示例说明
|
|
|
|
|
|
|
|
|
|
### 设备分配设备号
|
|
|
|
|
|
|
|
|
|
MKDEV 是将主设备号和次设备号转换成 dev_t 类型的一个内核函数。dev_t 定义了设备号,为 32 位,其中高 12 位为主设备号,低 20 位为次设备号。使用下列宏可以从 dev_t 获得主设备号和次设备号。
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
MAJOR(dev_t dev)
|
|
|
|
|
MINOR(dev_t dev)
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
以下两段代码:
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
err = register_chrdev_region(devno, DEMO_DEV_CNT, DEMO_MODULE_NAME);
|
|
|
|
|
err = alloc_chrdev_region(&devno, 0, DEMO_DEV_CNT, DEMO_MODULE_NAME);
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
用于向系统静态/动态申请设备号。其原型如下:
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
int register_chrdev_region(dev_t from, unsigned count, const char *name);
|
|
|
|
|
int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, const char *name);
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
是否为动态注册是在驱动加载时决定的,module_param 用于指定该模块参数:
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
module_param(demo_major, int, S_IRUGO);
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
如果在加载驱动时没有指定设备号,则使用动态分配,否则使用静态分配。
|
|
|
|
|
|
|
|
|
|
### 分配内存资源
|
|
|
|
|
|
|
|
|
|
kzalloc 可实现内核内存空间的分配:
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
demo_devp = kzalloc(DEMO_DEV_CNT*sizeof(struct demo_dev), GFP_KERNEL);
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
用于分配 demo_dev 对象空间。
|
|
|
|
|
|
|
|
|
|
### 注册字符设备
|
|
|
|
|
|
|
|
|
|
cdev_add() 函数和 cdev_del() 函数分别向系统添加和删除一个 cdev 对象,完成字符设备的注册和注销。对应代码如下:
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
err = cdev_add(&devp->cdev, devno, 1);
|
|
|
|
|
cdev_del(&devp->cdev);
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
### udev 文件系统
|
|
|
|
|
|
|
|
|
|
示例代码通过:
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
class = class_create(THIS_MODULE, DEMO_MODULE_NAME);
|
|
|
|
|
devp->dev = device_create(class, NULL, devp->cdev.dev, NULL, name);
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
两个接口来与 udev 文件系统交互,产生用户态设备加载消息,生成设备节点。
|
|
|
|
|
|
|
|
|
|
### file_operations
|
|
|
|
|
|
|
|
|
|
示例通过以下代码注册了字符设备的操作接口函数:
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
static struct file_operations demo_fops = {
|
|
|
|
|
.owner = THIS_MODULE,
|
|
|
|
|
.open = demo_open,
|
|
|
|
|
.release = demo_release,
|
|
|
|
|
.llseek = demo_llseek,
|
|
|
|
|
.read = demo_read,
|
|
|
|
|
.write = demo_write,
|
|
|
|
|
.unlocked_ioctl = demo_ioctl,
|
|
|
|
|
.mmap = demo_mmap
|
|
|
|
|
};
|
|
|
|
|
|
|
|
|
|
cdev_init(&devp->cdev, &demo_fops);
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
### 访问用户态数据
|
|
|
|
|
|
|
|
|
|
内核中不能直接使用用户态数据,需要通过 copy_from_user() 和 copy_to_user() 将数据拷贝到内核,或将新数据拷贝回用户态。如 demo_read() 中的处理:
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
static ssize_t demo_read(struct file *filp, char __user *buffer, size_t count, loff_t *position)
|
|
|
|
|
{
|
|
|
|
|
struct demo_dev *devp = filp->private_data;
|
|
|
|
|
loff_t p = *position;
|
|
|
|
|
ssize_t ret = 0;
|
|
|
|
|
|
|
|
|
|
// This is a test.
|
|
|
|
|
// 分析和获取有效的读长度
|
|
|
|
|
if(DEMO_DATA_SIZE<=p) // 要读的偏移位置越界
|
|
|
|
|
return 0; // End of a file
|
|
|
|
|
if(DEMO_DATA_SIZE<(count+p)) // 要读的字节数太大
|
|
|
|
|
count = DEMO_DATA_SIZE-p;
|
|
|
|
|
|
|
|
|
|
if(copy_to_user((void*)buffer, &devp->demo_text[p], count))
|
|
|
|
|
ret = -EFAULT;
|
|
|
|
|
else
|
|
|
|
|
{
|
|
|
|
|
*position += count;
|
|
|
|
|
ret = count;
|
|
|
|
|
}
|
|
|
|
|
return ret;
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
### IOCTL 操作
|
|
|
|
|
|
|
|
|
|
示例定义了以下 IOCTL 类型:
|
|
|
|
|
|
|
|
|
|
```cpp
|
|
|
|
|
#define DEMO_MAGIC 'R'
|
|
|
|
|
#define DEMO_IOC_SIZE 8
|
|
|
|
|
#define DEMO_CTL_IOC _IOC(_IOC_READ|_IOC_WRITE, DEMO_MAGIC, 0, DEMO_IOC_SIZE)
|
|
|
|
|
#define DEMO_CTL_IO _IO(DEMO_MAGIC, 1)
|
|
|
|
|
#define DEMO_CTL_IOR _IOR(DEMO_MAGIC, 2, uint16_t)
|
|
|
|
|
#define DEMO_CTL_IOW _IOW(DEMO_MAGIC, 3, int32_t)
|
|
|
|
|
#define DEMO_CTL_IOWR _IOWR(DEMO_MAGIC, 4, uint32_t)
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
用户态调用 ioctl 接口时,必须使用相同的宏,最后才会在 demo_ioctl() 中进行对应的分派处理。
|
|
|
|
|
|
|
|
|
|
* _IOC:用于定义 IOCTL 命令。
|
|
|
|
|
* _IOR:用于创建只读命令。
|
|
|
|
|
* _IOW:用于创建只写命令。
|
|
|
|
|
* _IOWR:用于创建读写命令。
|
|
|
|
|
|
|
|
|
|
## 练习
|
|
|
|
|
|
|
|
|
|
1. 为字符设备驱动编写应用程序,用于验证各个接口。
|
|
|
|
|
2. 在字符设备驱动的 open、read、write、llseek、unlocked_ioctl 和 release 接口中增加 printk 函数,用于验证来自于用户态的操作。
|
|
|
|
|
3. 完善 demo_write() 函数,实现将用户数据写入内核空间,并最后可再通过 demo_read() 读出。
|