tty events in epoll queue after closing fd 0 - epoll

Question

consider the following case:
an EPOLLIN event is registered for fd 0 (stdin)
an EPOLLIN event is generated for fd 0 and implicitly queued for read within epoll
fd 0 is closed (and EPOLL_CTL_DELeted) before calling epoll_wait()
epoll_wait() is called to read the queued events
Now:
if stdin is a terminal, when epoll_wait() is called, the EPOLLIN event from step 2 will be reported
if stdin is not a terminal but a pipe, the EPOLLIN event from step 2 will not be reported
Why is the tty case different?
The test program:
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/epoll.h>
struct epoll_event event1 = {
.events = EPOLLIN,
.data = { .fd = 0}
};
int main(int argc, char **argv)
{
int epfd = epoll_create(1);
int rc;
epoll_ctl(epfd, EPOLL_CTL_ADD, 0, &event1);
sleep(2); //allow meself time to type false\n
printf("closing stdin ...\n");
close(0);
//even if i remove it explicitly the event will be found in the que after
epoll_ctl(epfd, EPOLL_CTL_DEL, 0, &event1);
printf("gathering events ...\n");
event1.events = 0;
event1.data.fd = -1;
rc = epoll_wait(epfd, &event1, 1, 0);
switch(rc) {
case 1:
printf("event received: event=%d on fd %d\n", event1.events, event1.data.fd);
break;
case 0:
printf("no events received");
break;
case -1:
printf("epoll_wait error\n");
break;
default:
printf("weird event count %d\n", rc);
}
return 0;
}
running the program with stdin from tty:
[root#tinkerbell src]# ./epolltest
false
closing stdin ...
gathering events ...
event received: event=1 on fd 0
[root#tinkerbell src]# false
[root#tinkerbell src]#
running the program with stdin from a pipe:
[root#tinkerbell src]# cat t.sh
#!/bin/bash
echo "bah";
sleep 10;
[root#tinkerbell src]# ./t.sh | ./epolltest
closing stdin ...
gathering events ...
no events received[root#tinkerbell src]#

Answer 1

different question but the answer can be applied here as well
Events caught by epoll comes from a file* since that is the
abstraction the kernel handles. Events really happen on the file* and
there's no way if you dup()ing 1000 times a single fd, to say that
events are for fd = 122.