Linux驱动中继承与多态思想_C

一、函数实现多态

1. 定义全局模板函数集

//thermal_of.c
static struct thermal_zone_device_ops of_thermal_ops = {
    .get_trip_type = of_thermal_get_trip_type,
    .get_trip_temp = of_thermal_get_trip_temp,
    .set_trip_temp = of_thermal_set_trip_temp,
    .get_trip_hyst = of_thermal_get_trip_hyst,
    .set_trip_hyst = of_thermal_set_trip_hyst,
    .get_crit_temp = of_thermal_get_crit_temp,

    .bind = of_thermal_bind,
    .unbind = of_thermal_unbind,
};

2. 使用时继承全局模板函数集

//thermal_of.c
int __init of_parse_thermal_zones(void)
{
    ...
    struct thermal_zone_device_ops *ops = kmemdup(&of_thermal_ops, sizeof(*ops), GFP_KERNEL);
    ...
}

kmemdup 就是先分配一块内存，然后直接拷贝过去一份，拷贝的都是指针，这样既可以复用原来的，也可以修改为自己的，实现多态。

 

二、结构体多态

1. 参考binder.c

//参考内核中binder.c的 struct binder_object 的实现

struct object_header {
    int    type;
};

struct student_object {
    struct object_header hdr;
    int grade;
    int score;
}

struct teacher_object {
    struct object_header hdr;
    int rank;
    int suject;
}

struct worker_object {
    struct object_header hdr;
    int salary;
    int hour;
}

//实现结构体多态
struct people_object {
    union {
        struct object_header hdr; //复用这个hdr，可以省去一个int型空间
        struct student_object so;
        struct teacher_object to;
        struct worker_object wo;
    };
};

//处理多态
void dump_mesage(struct people_object *obj) {
    switch (obj->hdr.type) {
    case 1:
        printf("student: grade=%d, score=%d\n", obj->so.grade, obj->so.score);
    case 1:
        printf("teacher: rank=%d, suject=%d\n", obj->to.rank, obj->to.suject);
    case 1:
        printf("worker: salary=%d, hour=%d\n", obj->wo.salary, obj->wo.hour);
    default:
        break;
    }
    
}

有了执行hdr的指针后，可以统一使用 container_of() 来得到各个类型指针。