static struct file_operations i2c_ops = {  
    .owner = THIS_MODULE,  
    .open  = sfax8_i2c_debug_open,  
    .read  = sfax8_i2c_debug_read,  
    .write  = sfax8_i2c_debug_write,  
    .llseek  = default_llseek,  
    .release = single_release,  
};   //创建debug节点，并有debug的作用

static struct i2c_algorithm i2c_sf_algo = {  
    .master_xfer    = i2c_sf_xfer,    //进行数据传输  
    .functionality  = i2c_sf_func,  
};  

static const struct file_operations i2cdev_fops = {  
    .owner      = THIS_MODULE,  
    .llseek     = no_llseek,  
    .read       = i2cdev_read,  
    .write      = i2cdev_write,    
    .unlocked_ioctl = i2cdev_ioctl,  
    .open       = i2cdev_open,  
    .release    = i2cdev_release,  
};   //对i2c设备的数据传输过程

struct i2c_rdwr_ioctl_data {  
    struct i2c_msg __user \*msgs;    /\* pointers to   i2c_msgs \*/  
    __u32 nmsgs;            /\* number of i2c_msgs \*/  
};  
/* This is the structure as used in the I2C_RDWR ioctl call */ 
 
struct i2c_msg {  
    __u16 addr; /* slave address */  
    __u16 flags;  
    __u16 len;      /* msg length */  
    __u8 *buf;      /* pointer to msg data */  
};  
//an I2C transaction segment beginning with START  

struct i2c_adapter {                                                         
    struct module *owner;                                                    
    unsigned int class;       /* classes to allow probing for */             
    const struct i2c_algorithm *algo; /* the algorithm to access the bus */  
    void *algo_data;                                                                                                                                                       
    struct rt_mutex bus_lock;        /* data fields that are valid for all devices */                                                                                                               
    int timeout;            /* in jiffies */                               
    int retries;                                                           
    struct device dev;      /* the adapter device */                                                                                                                     
};                                                                         
/*                                                                         
 * i2c_adapter is the structure used to identify a physical i2c bus along  
 * with the access algorithms necessary to access it.                      
 */