《Linux设备驱动程序》读书笔记:字符设备驱动程序（一）

看不容易抽点空下来看书，现在留点痕迹吧！

一：创建设备类型

      四个全局持久的字符设备scull0-scull3

二：主次设备号

     主设备号：代表设备类型

     次设备号 : 一个编号

     MAJOR(dev_t dev)

     MINOR(dev_t dev)

     MKDEV(int major, int minor)

     注册释放

     register_chrdev_region

     alloc_chrdev_region

     unregister_chrdev_region

三： file_operations

     

struct file_operations {
	struct module *owner;
	loff_t (*llseek) (struct file *, loff_t, int);
	ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
	ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
	ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
	int (*readdir) (struct file *, void *, filldir_t);
	unsigned int (*poll) (struct file *, struct poll_table_struct *);
	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
	long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
	int (*mmap) (struct file *, struct vm_area_struct *);
	int (*open) (struct inode *, struct file *);
	int (*flush) (struct file *, fl_owner_t id);
	int (*release) (struct inode *, struct file *);
	int (*fsync) (struct file *, loff_t, loff_t, int datasync);
	int (*aio_fsync) (struct kiocb *, int datasync);
	int (*fasync) (int, struct file *, int);
	int (*lock) (struct file *, int, struct file_lock *);
	ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
	unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
	int (*check_flags)(int);
	int (*flock) (struct file *, int, struct file_lock *);
	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
	ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
	int (*setlease)(struct file *, long, struct file_lock **);
	long (*fallocate)(struct file *file, int mode, loff_t offset,
			  loff_t len);
};

实例化

struct file_operations scull_fops = {
	.owner =    THIS_MODULE,
	.llseek =   scull_llseek, //移位
	.read =     scull_read, //读
	.write =    scull_write, //写
	.ioctl =    scull_ioctl, //ioctrl
	.open =     scull_open, //打开
	.release =  scull_release, //释放
};

注意scull_open函数, 里面使用了一个C语言的技巧:

container_of

通过结构体成员的地位获取结构体实例的地址(原理在于通过地址0算出成员的偏移再相减，注意里面要将地址转成char*类型, 和UEFI里的宏CR一样)

#define container_of(ptr, type, member) ({			\
	const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
	(type *)( (char *)__mptr - offsetof(type,member) );})

int scull_open(struct inode *inode, struct file *filp)
{
	struct scull_dev *dev; /* device information */

	dev = container_of(inode->i_cdev, struct scull_dev, cdev);
	filp->private_data = dev; /* for other methods */ //注意:private_data在open时可以保存设备指针

	/* now trim to 0 the length of the device if open was write-only */
	if ( (filp->f_flags & O_ACCMODE) == O_WRONLY) {
		if (down_interruptible(&dev->sem))
			return -ERESTARTSYS;
		scull_trim(dev); /* ignore errors */
		up(&dev->sem);
	}
	return 0;          /* success */
}

四： 内核struct file

     注意:private_data在open时可以保存设备指针

五 : 内存组织

struct scull_dev {
	struct scull_qset *data;  /* Pointer to first quantum set */
	int quantum;              /* the current quantum size */
	int qset;                 /* the current array size */
	unsigned long size;       /* amount of data stored here */
	unsigned int access_key;  /* used by sculluid and scullpriv */
	struct semaphore sem;     /* mutual exclusion semaphore     */
	struct cdev cdev;	  /* Char device structure		*/
};

struct scull_qset {
	void **data;
	struct scull_qset *next;
};