HAL

功能：

　　生成lights.xxx.so文件

　　构造所有硬件支持的light设备(主要在于set_light不同)供上层调用

源码分析：

LIGHTS_HARDWARE_MODULE_ID是light HAL的唯一标示，JNI通过该ID load对应的so文件。

主要关注lights_module_methods

struct hw_module_t HAL_MODULE_INFO_SYM = {
    .id = LIGHTS_HARDWARE_MODULE_ID,    // 唯一标示
    .methods = &lights_module_methods,
};

static struct hw_module_methods_t lights_module_methods = {
    .open =  open_lights,
};

open_lights:

　　构造硬件支持light设备给予上层使用，不同device设置不同的set_light回调函数

static int open_lights(const struct hw_module_t* module, char const* name, struct hw_device_t** device)
    // 不同类型的light设置对应的set_light
    if (0 == strcmp(LIGHT_ID_BACKLIGHT, name))
        set_light = set_light_backlight;
    else if (0 == strcmp(LIGHT_ID_NOTIFICATIONS, name))
        set_light = set_light_notifications;
    else if (0 == strcmp(LIGHT_ID_ATTENTION, name))
        set_light = set_light_attention;
    dev->set_light = set_light; // 设置set_light
    
    *device = (struct hw_device_t*)dev; // 输出型参数

set_light：

　　以背光为例，Framework传递下来的参数经转化后写入“/sys/class/leds/lcd-backlight/brightness”这个节点(该节点由kernel创建)，从而达到改变背光的目的。

static int
set_light_backlight(struct light_device_t* dev,
        struct light_state_t const* state)
{
    // 计算brightness，上层是0-255，底层为0-1023
    int brightness = rgb_to_brightness(state);    // state->color中有brightness值
    
    // 将brightness写入到brightness节点
    pthread_mutex_lock(&g_lock);
    err = write_int(LCD_FILE, brightness);    // "/sys/class/leds/lcd-backlight/brightness"
        fd = open(path, O_RDWR);
        int bytes = sprintf(buffer, "%d\n", value);    // int -> char
        int amt = write(fd, buffer, bytes);
        close(fd);
    pthread_mutex_unlock(&g_lock);
    return err;
}