epoll_event结构体一般用在epoll机制中，其定义如下：
struct epoll_event
{
uint32_t events; /* epoll events */
epoll_data_t data; /* user data variable */
} __attribute__ ((__packed__));
typedef union epoll_data
{
void *ptr;
int fd;
uint32_t u32;
uint64_t u64;
} epoll_data_t;