From owner-freebsd-current  Thu May 10  8:39:47 2001
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Date: Thu, 10 May 2001 08:39:53 -0700
From: Terry Lambert <tlambert2@mindspring.com>
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To: Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp>
Cc: John Baldwin <jhb@FreeBSD.ORG>, current@FreeBSD.ORG
Subject: Re: select(2) converted to use a condition variable, and optimis
References: <200105091020.f49AK7P05497@rina.r.dl.itc.u-tokyo.ac.jp>
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Seigo Tanimura wrote:
> A quick and hopefully efficient solution to those problems is to
> fhold() struct file's first, then enter polling loop. That seems much
> cheaper than to work on free()ing a vnode or a socket with holding a
> process lock, provided that struct filedesc and file are protected
> properly (and we have to do it anyway).

Let me once again point out that fhold(), like crhold(),
should act as an l-valued function that takes an r-value
as an "argument", as in:

	a = crhold(b);
	q = fhold(r);
etc. (for all such functions).

The reason is that you can not replace it with an instrumented
function, otherwise, which would permit you to catch subtle
errors that:

	a = b;
	crhold(a);
	q = r;
	fhold(r);

etc. may cause (yes, I know I have held the r-calue in one
case and the l-value in the other in the above example; the
kernel itself does this all over the place, and I think it's
an error).

I also think that they should use common base macros: it is
exceedingly dangerous to have multiple hold semantics in the
kernel.

-- Terry

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