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Date: Mon, 10 Nov 2003 12:41:09 -0500
From: marius aamodt eriksen <marius@monkey.org>
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cc: Niels Provos <provos@monkey.org>
Subject: kqueue, NOTE_EOF
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X-List-Received-Date: Mon, 10 Nov 2003 17:41:13 -0000

hi - 

in order to be able to preserve consistent semantics across poll,
select, and kqueue (EVFILT_READ), i propose the following change: on
EVFILT_READ, add an fflag NOTE_EOF which will return when the file
pointer *is* at the end of the file (effectively always returning on
EVFILT_READ, but setting the NOTE_EOF flag when it is at the end).

specifically, this allows libevent[1] to behave consistently across
underlying polling infrastructures (this has become a practical
issue).

in openbsd, this was a trivial change in filt_ufsread():

 kn->kn_data = ip->i_ffs_size - kn->kn_fp->f_offset;
+if (kn->kn_data == 0 && kn->kn_sfflags & NOTE_EOF) {
+	kn->kn_fflags |= NOTE_EOF;
+	return (1);
+}
+
 return (kn->kn_data != 0);

(and adding NOTE_EOF to event.h, of course)

what do you think about this?  can it be integrated into netbsd and
freebsd as well?  i have discussed this with provos@, and we seem to
agree this is a viable solution.

thanks,

marius.

[1] http://monkey.org/~provos/libevent

-- 
> marius@monkey.org > http://monkey.org/~marius