epoll_event, epoll_data, epoll_data_t - epoll event

       The  epoll_event  structure  specifies data that the kernel should save and return when the corresponding
       file descriptor becomes ready.

       Standard C library (libc)

       epoll_event, epoll_data, epoll_data_t - epoll event

epoll_wait(2), epoll_ctl(2)

Linux man-pages 6.9.1                              2024-05-02                                 epoll_event(3type)

       Linux.

#include<sys/epoll.h>structepoll_event{uint32_tevents;  /* Epoll events */
           epoll_data_tdata;    /* User data variable */
       };unionepoll_data{void*ptr;intfd;uint32_tu32;uint64_tu64;};typedefunionepoll_dataepoll_data_t;

Clibrary/kerneldifferences
       The Linux kernel headers also provide this type, with a slightly different definition:

           #include <linux/eventpoll.h>

           struct epoll_event {
               __poll_t  events;
               __u64     data;
           };