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Date: Wed, 9 Apr 1997 03:23:03 +1000
From: David Nugent <davidn@unique.usn.blaze.net.au>
To: Peter Wemm <peter@spinner.DIALix.COM>
Cc: freebsd-current@freebsd.org
Subject: Re: POLL & the Single FreeBSD'r
References: <199704030142.BAA04433@netfl15a.devetir.qld.gov.au> <860439710.357888@haywire.DIALix.COM>
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> I implemented an openbsd-style implementation of poll() some time ago
> but it was mixed up in the middle of the upages stuff so it lot left.
> Since then, NetBSD have done a much better implementation, I'm very tempted
> to back out what I've done and start from scratch while looking at the
> NetBSD method.  Basically, OpenBSD implemented poll() as an alternative
> interface to the select hooks in the kernel which means that poll() is
> limited to what select() can test for.  NetBSD did it a lot better, by
> replacing the select hooks by poll hooks, and updating both front-ends to
> use the new poll backend.  The main difference is that under NetBSD, you
> can poll for (say) ugent data on a socket as opposed to merely "readable".

Interesting. Does "urgent data" include, say, an {m,c,a}time
change on a file descriptor? If not, could it be implemented?

I'm guessting that "urgent data" in this context has the same
meaning with a socket with respect to tcp/ip transactions (ie.
OOB data), but the hook for poll() I'm suggesting would be
perfect for a process that sits and waits for updates or
accesses to a disk file. Processes that currently do that have
to either use alarm() or call select() with a timeout, and
both are fairly sloppy in terms of virtual memory usage.


Regards,

David Nugent - Unique Computing Pty Ltd - Melbourne, Australia
Voice +61-3-9791-9547  Data/BBS +61-3-9792-3507  3:632/348@fidonet
davidn@freebsd.org davidn@blaze.net.au http://www.blaze.net.au/~davidn/