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

[Davide Libenzi]

On Tue, 4 Apr 2006, Michael Kerrisk wrote:

> 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?

Yes, ABI compatibility.



- Davide


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