Adding attributes

Step 2: define a pair of operations

struct sysfs_ops {
        ssize_t (*show)(struct kobject *kobject, 
                        struct attribute *attr,
                        char *buffer);
        ssize_t (*store)(struct kobject *kobject,
                         struct attribute *attr,
                         const char *buffer,
                         size_t buflen);
};

The "show" function encodes the value
Return length of result

The "store" function sets a new value
Found in buffer
Return length of data consumed