Re: [patch] uniform POLLRDHUP handling between epoll and poll/select ...

["Michael Kerrisk" <mtk-manpages@gmx.net>]

Davide,

> Like reported by Michael Kerrisk, POLLRDHUP handling was not consistent 
> between epoll and poll/select, since in epoll it was unmaskeable. This 
> patch brings uniformity in POLLRDHUP handling.
[...]
> diff -Nru linux-2.6.16/fs/eventpoll.c linux-2.6.16.mod/fs/eventpoll.c
> --- linux-2.6.16/fs/eventpoll.c	2006-04-03 20:08:23.000000000 -0700
> +++ linux-2.6.16.mod/fs/eventpoll.c	2006-04-03 20:09:51.000000000 -0700
> @@ -599,7 +599,7 @@
>   	switch (op) {
>   	case EPOLL_CTL_ADD:
>   		if (!epi) {
> -			epds.events |= POLLERR | POLLHUP | POLLRDHUP;
> +			epds.events |= POLLERR | POLLHUP;
> 
>   			error = ep_insert(ep, &epds, tfile, fd);
>   		} else
> @@ -613,7 +613,7 @@
>   		break;
>   	case EPOLL_CTL_MOD:
>   		if (epi) {
> -			epds.events |= POLLERR | POLLHUP | POLLRDHUP;
> +			epds.events |= POLLERR | POLLHUP;
>   			error = ep_modify(ep, epi, &epds);
>   		} else
>   			error = -ENOENT;

This makes things consistent -- but in the opposite way
from what I thought they might be.  (The alternative would of 
course have been to make POLLRDHUP un-maskable in both epoll 
and poll().)

So I'm curious: what is the rationale for making POLLRDHUP 
maskable when POLLHUP is not?   Is it an issue of ABI 
compatibility; or something else?

Cheers,

Michael

-- 
Michael Kerrisk
maintainer of Linux man pages Sections 2, 3, 4, 5, and 7 

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