简单字符设备驱动程序

理论知识参考Linux Device Driver, 3rd Edition。实验中使用主动分配主设备号，按照LDD3中说的最好是自动分配设备号，这里只是为了理解。实验步骤如下：（1）使用cat/proc/device查看字符设备主设备号，这里假设50主设备号没有使用而在本设备中使用。创建字符设备文件节点：mknod/dev/mycdev c 50 0修改设备文件权限：chmod 777/dev/mycdev其中的mycdev为步骤（2）中要安装的模块名。（2）编写驱动程序：注意代码中 #define MYCDEV_MAJOR （50）/* =====================================================================* Filename: mycdev.c** Description:** Version: 1.0 （02/26/2013）* Created: xhzuoxin（xiahouzuoxin@163.com）* Compiler: gcc*======================================================================*/#include<linux/init.h>#include<linux/module.h>#include<linux/types.h>#include<linux/fs.h>#include<linux/mm.h>#include<linux/sched.h>#include<linux/cdev.h>#include<asm/system.h>#include<asm/io.h>#include<asm/uaccess.h>#include<linux/kernel.h>#include<linux/errno.h>#include<linux/slab.h> MODULE_LICENSE（"GPL"）; #defineMYCDEV_MAJOR （50）#defineMYCDEV_SIZE 0x1000 staticdev_t mycdev_major = MYCDEV_MAJOR; structmycdev {struct cdev cdev;unsigned charmem[255];};//struct mycdev dev;structmycdev *devp; static int mycdev_open（structinode *inode,struct file *fp）{fp->private_data= devp; return 0;} static int mycdev_release（structinode *inode,struct file *fp）{return 0;} staticssize_t mycdev_read（struct file *fp,char __user *buf, size_t size, loff_t *pos）{unsigned long p =*pos;unsigned int count =size;struct mycdev *tmp_dev = fp->private_data; if （p >= MYCDEV_SIZE） {return -1;}if （count > MYCDEV_SIZE - p） {count =MYCDEV_SIZE - p;}if （copy_to_user（buf, （void*）（tmp_dev->mem + p）, count）！= 0） {printk（"read error！ "）;return -1;} else {*pos +=count;printk（KERN_INFO"read %d bytes from %ld ", count, p）;} return count;} staticssize_t mycdev_write（struct file *fp,const char __user*buf, size_t size, loff_t *pos）{unsigned long p =*pos;unsigned int count =size;struct mycdev *tmp_dev = fp->private_data; if （p > MYCDEV_SIZE） {return -1;}if （p > MYCDEV_SIZE - count） {count =MYCDEV_SIZE - p;}if （copy_from_user（（void*）（tmp_dev->mem + p）, buf, count）！= 0） {return -1;} else {*pos +=count;printk（KERN_INFO"write %d bytes from %ld ", count, p）;} return count;} staticloff_t mycdev_llseek（struct file *fp, loff_toff,int whence）{// structmycdev *dev = fp->private_data;loff_tnew_pos = 0; switch（whence） {case SEEK_SET:new_pos= off;break;case SEEK_CUR:new_pos= fp->f_pos + off;break;case SEEK_END:new_pos= MYCDEV_SIZE + off;} if （new_pos < 0） {return -EINVAL;} else {fp->f_pos= new_pos;return new_pos;}} /* paddingg struct file operation */static const structfile_operations mycdev_fops = {.owner =THIS_MODULE,.read =mycdev_read,.write =mycdev_write,.open =mycdev_open,.release =mycdev_release,.llseek =mycdev_llseek,}; static void setup_mycdev（structmycdev *dev,int index）{int ret;int devno = MKDEV（mycdev_major, index）; cdev_init（&dev->cdev,&mycdev_fops）;dev->cdev.owner= THIS_MODULE;dev->cdev.ops= &mycdev_fops;ret =cdev_add（&dev->cdev, devno, 1）; if （ret） {printk（"adding mycdev error！ "）;}} static int __init mycdev_init（void）{int ret;dev_tdevno = 0; if （mycdev_major） { /* 静态分配*/devno =MKDEV（mycdev_major, 0）;ret =register_chrdev_region（devno, 1, "mycdev"）;} else { /* 动态分配 */ret =alloc_chrdev_region（&devno, 0, 1, "mycdev"）;mycdev_major= MAJOR（devno）;}devp =kmalloc（sizeof（structmycdev）, GFP_KERNEL）;if （！devp） {ret =-ENOMEM;unregister_chrdev_region（devno,1）;return ret;}memset（devp,0, sizeof（structmycdev））; setup_mycdev（devp,0）; return 0;} static void __exit mycdev_exit（void）{printk（"mycdev module is leaving... "）;cdev_del（&devp->cdev）;kfree（devp）;unregister_chrdev_region（MKDEV（mycdev_major,0）, 1）;} module_init（mycdev_init）;module_exit（mycdev_exit）;