设备驱动(四)

实现操作集合

实现open

统计计数，检查错误
申请资源

识别次设备号，如果必要更新f_op指针

实现realse

open逆操作

实现

实现read

          copy_to_user

返回值为未被读取的字节数

实现write

          copy_from_user

          返回值为未被读取的字节数

实现unlocked_ioctl

          capable(CAP_SYS_ADMIN)

          

copy_to_user,copy_from效率比较低，可以将驱动中的内存映射到用户空间提高访问效率，摄像头驱动使用该方式

命令字     

设备类型	序列号	方向	数据尺寸
8bit	8bit	2bit(无,读,写,读写)	8~14bit

创建命令字宏

__IO(type, num)

__IOR(type, num, count)

__IOW(type, num, count)

__IORW(type, num, count)

如果直接操作设备节点, 可以不执行open函数

          cat /dev/hello

          echo abc > /dev/hello

应用程序调用open,close流程

APP 

1. fd = open("/dev/hello", O_RDONLY);
2. close(fd);

VFS

1. 根据"/dev/hello"中包含的设备号，找cdev结构体
2. 根据cdev创建inode, file
3. 创建文件描述符fd
4. 调用驱动中的open函数，如果操作集合或者open函数没有实现，清空已申请的资源，返回负的错误码
5. 将fd与file关联
6. 返回fd
7. 释放申请的资源
8. 执行驱动中的release函数

1583 struct file_operations {

1584     struct module *owner;

1585     loff_t (*llseek) (struct file *, loff_t, int);

1586     ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);

1587     ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);

1588     ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);

1589     ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);

1590     int (*readdir) (struct file *, void *, filldir_t);

1591     unsigned int (*poll) (struct file *, struct poll_table_struct *);

1592     long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);

1593     long (*compat_ioctl) (struct file *, unsigned int, unsigned long);

1594     int (*mmap) (struct file *, struct vm_area_struct *);

1595     int (*open) (struct inode *, struct file *);

1596     int (*flush) (struct file *, fl_owner_t id);

1597     int (*release) (struct inode *, struct file *);

1598     int (*fsync) (struct file *, loff_t, loff_t, int datasync);

1599     int (*aio_fsync) (struct kiocb *, int datasync);

1600     int (*fasync) (int, struct file *, int);

1601     int (*lock) (struct file *, int, struct file_lock *);

1602     ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);

1603     unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);

1604     int (*check_flags)(int);

1605     int (*flock) (struct file *, int, struct file_lock *);

1606     ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);

1607     ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);

1608     int (*setlease)(struct file *, long, struct file_lock **);

1609     long (*fallocate)(struct file *file, int mode, loff_t offset,

1610               loff_t len);

1611 };