From owner-freebsd-net  Fri Dec 21  6:27:43 2001
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Date: Sat, 22 Dec 2001 01:27:32 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Alfred Perlstein <alfred@FreeBSD.org>
Cc: <wollman@FreeBSD.org>, <net@FreeBSD.org>,
	<cvs-committers@FreeBSD.org>, <cvs-all@FreeBSD.org>
Subject: Re: fifo fix (Re: cvs commit: src/sys/fs/fifofs fifo_vnops.c)
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On Tue, 18 Dec 2001, Alfred Perlstein wrote:

> > * Bruce Evans <bde@zeta.org.au> [011217 07:10] wrote:
> > > I'm not happy with frobbing the socket state.  I suggest frobbing the
> > > events mask instead.  Either use a flag to tell sopoll() to ignore
> > > SS_CANTRCVMORE, or use new events POLLIN_IGNORE_EOF and
> > > POLLRDNORM_IGNORE_EOF (convert the userland POLLIN/POLLRDNORM to these
> > > and change sopoll() to support them).
>
> Wait, please clarify, are you suggesting that POLLIN_IGNORE_EOF
> and POLLRDNORM_IGNORE_EOF must be used by userland applications?
> Or would it be an internal flag for the kernel so that here you'd
> see something like:
>
> filetmp.f_data = (caddr_t)ap->a_vp->v_fifoinfo->fi_readsock;
> if (filetmp.f_data) {
> 	if (ap->a_events & ~POLLIN)
> 		ap->a_events |= POLLIN_IGNORE_EOF;

I think it should be more like:

	if (ap->a_events & POLLIN)
		ap->a_events = (ap->a_events & ~POLLIN) | POLLIN_IGNORE_EOF;

We can't pass in flags that we don't really care about (POLLIN in
this case) since they will cause side effects (selrecord()...).

I might actually use a new variable instead of changing `ap'.

> 	/* same for POLLRDNORM */
> 	revents |= soo_poll(&filetmp, ap->a_events, ap->a_cred,
> 			ap->a_td);

Add something like:

	if (revents & POLLIN_IGNORE_EOF)
		revents = (revents & ~POLLIN_IGNORE_EOF) | POLLIN;

> }
>
> Or that the userland will just OR in POLLIN_IGNORE_EOF before calling
> poll(2).
>
> I'm not sure if I like the latter way of fixing things.

Userland might want to do this someday.  I would just make it easy for it
to do so.

Bruce


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