recovery中event 事件实现

ref :  /bootable/recovery/events.c
         /bootable/recovery/ui.cpp
         /bootable/recovery/recovery.cpp
          /bootable/recovery/roots.cpp

与UI相关的地方，一般都会要与event （key ,touch）的发生关系

UI初始化：

void RecoveryUI::Init() {
    ev_init(input_callback, NULL);
    pthread_create(&input_t, NULL, input_thread, NULL);
}

#define MAX_DEVICES 16
//  获得/dev/input目录下所有文件的描述符，但是最多不能超过16个

//   这个与factory mode 中的miniui很类似

int ev_init(ev_callback input_cb, void *data)
{
    DIR *dir;
    struct dirent *de;
    int fd;

    dir = opendir("/dev/input");
    if(dir != 0) {
        while((de = readdir(dir))) {
            unsigned long ev_bits[BITS_TO_LONGS(EV_MAX)];

            if(strncmp(de->d_name,"event",5)) continue;
            fd = openat(dirfd(dir), de->d_name, O_RDONLY);
            if(fd < 0) continue;

            /* read the evbits of the input device */
            if (ioctl(fd, EVIOCGBIT(0, sizeof(ev_bits)), ev_bits) < 0) {
                close(fd);
                continue;
            }

            /* TODO: add ability to specify event masks. For now, just assume
             * that only EV_KEY and EV_REL event types are ever needed. */
            if (!test_bit(EV_KEY, ev_bits) && !test_bit(EV_REL, ev_bits)) {
                close(fd);
                continue;
            }

            ev_fds[ev_count].fd = fd;
            ev_fds[ev_count].events = POLLIN;
            ev_fdinfo[ev_count].cb = input_cb;
            ev_fdinfo[ev_count].data = data;
            ev_count++;
            ev_dev_count++;
            if(ev_dev_count == MAX_DEVICES) break;
        }
    }

    return 0;
}

// UI初始化的时候，会启动一个新的线程，来轮询event

pthread_create(&input_t, NULL, input_thread, NULL);

// Reads input events, handles special hot keys, and adds to the key queue.
void* RecoveryUI::input_thread(void *cookie)
{
    for (;;) {
        if (!ev_wait(-1))
            ev_dispatch();
    }
    return NULL;
}

//分发时间，cb是回调函数，ev_init的时候作为参数传入的

//  此时不代表，所有FD描述符都有事件发生，只能有至少有个一个有时间产生

void ev_dispatch(void)
{
    unsigned n;
    int ret;

    for (n = 0; n < ev_count; n++) {
        ev_callback cb = ev_fdinfo[n].cb;
        if (cb && (ev_fds[n].revents & ev_fds[n].events))
            cb(ev_fds[n].fd, ev_fds[n].revents, ev_fdinfo[n].data);
    }
}

//  读取文件描述符，读取时间内容发送给UI主线程

//   没有事件的话，就直接返回

int RecoveryUI::input_callback(int fd, short revents, void* data)
{
    struct input_event ev;
    int ret;

    ret = ev_get_input(fd, revents, &ev);
    if (ret)
        return -1;
    .......
    if (ev.type == EV_KEY && ev.code <= KEY_MAX)
        self->process_key(ev.code, ev.value);

    return 0;
}