linux设备驱动入门---globalmem字符设备驱动
/* globalmem字符设备驱动 * 作者：liwei.cai * 日期：2012-08-03 * globalmem.c */#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>#define GLOBALMEM_SIZE 0x1000 /* 全局内存大小：4KB */#define MEM_CLEAR 0x01 /* 清零全局内存 */#define GLOBALMEM_MAJOR 250 /* 预设的globalmem 的主设备号 */static int globalmem_major = GLOBALMEM_MAJOR;/* globalmem设备结构体 */struct globalmem_dev{struct cdev cdev; /* cdev结构体 */unsigned char mem[GLOBALMEM_SIZE]; /* 全局变量 */};//struct globalmem_dev dev; /* 设备结构体实例 */struct globalmem_dev *globalmem_devp; /* 设备结构体指针 *//* 文件打开函数 */int globalmem_open(struct inode *inode, struct file *filp){/* 将设备结构体指针赋值给文件私有数据指针 */filp->private_data = globalmem_devp;return 0;}/* 文件释放函数 */int globalmem_release(struct inode *inode, struct file *filp){return 0;}/* globalmem 设备驱动的读函数 */static ssize_t globalmem_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 globalmem_dev *dev = filp->private_data;//获得设备结构体指针/* 分析和获取有效的读长度 */if(p >= GLOBALMEM_SIZE) //要读的偏移位置越界{return count ? -ENXIO : 0;}if (count > GLOBALMEM_SIZE - p) //要读的字节太大{count = GLOBALMEM_SIZE - p;} /* 内核控件-->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 %ld \n", count, p);}return ret;}/* globalmem 设备驱动的写函数 */static ssize_t globalmem_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 globalmem_dev *dev = filp->private_data;//获取设备结构体指针/* 分析和获取有效的写长度 */if (p >= GLOBALMEM_SIZE) // 要写的偏移位置越界{return count ? -ENXIO : 0;}if (count > GLOBALMEM_SIZE - p) // 要写的字节数太多{count = GLOBALMEM_SIZE - p;}/* 用户空间 --> 内核空间 */if (copy_from_user(dev->mem + p, buf, count)){ret = -EFAULT;}else{*ppos += count;ret = count;printk(KERN_INFO "written %d bytes(s) from %ld \n", count, p);}return ret;}/* seek()函数对文件定位的起始位置可以是文件开头（SEEK_SET, 0）、 * 当前位置（SEEK_CUR，1）和文件尾（SEEK_END，2） */static loff_t globalmem_llseek(struct file *filp,loff_t offset, int orig){loff_t ret;switch(orig){case 0: //从文件开头开始偏移if (offset < 0){ret = -EINVAL;break;}if ((unsigned int)offset > GLOBALMEM_SIZE)// 偏移越界{ret = -EINVAL;break;}filp->f_pos = (unsigned int)offset;ret = filp->f_pos;break;case 1: //从当前位置开始偏移if((filp->f_pos + offset) > GLOBALMEM_SIZE) //偏移越界{ret = -EINVAL;break;}if ((filp->f_pos + offset) < 0){ret = -EINVAL;break;}filp->f_pos += offset;ret = filp->f_pos;break;default:ret = -EINVAL;}return ret;}/* ioctl(）函数接受MEM_CLEAR命令,这个命令会将全局内存的有效数据长度清零 * 对于设备不支持的命令，返回-EINCVAL */static int globalmem_ioctl(struct inode *inodep, struct file *filp, unsigned int cmd, unsigned long arg){struct globalmem_dev *dev = filp->private_data; /* 获得设备结构体指针 */switch(cmd){case MEM_CLEAR://清除全局内存memset(dev->mem, 0, GLOBALMEM_SIZE);printk(KERN_INFO "globalmem is set to zero\n");break;default:return -EINVAL;}return 0;}/* 与globalmem的cdev关联的file_operations结构体 */static const struct file_operations globalmem_fops ={.owner = THIS_MODULE,.llseek = globalmem_llseek,.read = globalmem_read,.write = globalmem_write,.ioctl = globalmem_ioctl,.open =globalmem_open,.release = globalmem_release,};/* 初始化并添加cdev结构体 */static void globalmem_setup_cdev(struct globalmem_dev *dev, int index){int err, devno = MKDEV(globalmem_major, index);cdev_init(&dev->cdev, &globalmem_fops);dev->cdev.owner = THIS_MODULE;dev->cdev.ops = &globalmem_fops;err = cdev_add(&dev->cdev, devno, 1);if(err){printk(KERN_NOTICE "ERROR %d adding LED%d", err, index);}}/* globalmem设备驱动模块加载函数 */int globalmem_init(void){int result;dev_t devno = MKDEV(globalmem_major, 0);/* 申请字符设备驱动区域 */if (globalmem_major){result = register_chrdev_region(devno, 1, "globalmem");}else{/* 动态加载主设备号 */result = alloc_chrdev_region(&devno, 0, 1, "globalmem");globalmem_major = MAJOR(devno);}if (result < 0){return result;}/* 动态申请设备结构体的内存 */globalmem_devp = kmalloc(sizeof(struct globalmem_dev), GFP_KERNEL);if (!globalmem_devp) //申请失败{result = -ENOMEM;goto fail_malloc;}memset(globalmem_devp, 0, sizeof(struct globalmem_dev));globalmem_setup_cdev(globalmem_devp, 0);return 0;fail_malloc:unregister_chrdev_region(devno, 1);return result;}/* globalmem设备驱动卸载函数 */void globalmem_exit(void){cdev_del(&globalmem_devp->cdev); //注销cdev//cdev_del(&dev.cdev); /* 删除cdev结构 */ kfree(globalmem_devp); //释放设备结构体内存unregister_chrdev_region(MKDEV(globalmem_major,0), 1); /*注销设备区域 */}MODULE_AUTHOR("Liwei.Cai");MODULE_LICENSE("Dual BSD/GPL");module_param(globalmem_major, int, S_IRUGO);module_init(globalmem_init);module_exit(globalmem_exit);