Date: Fri, 30 May 2003 16:24:34 +0200
From: Andries Brouwer <aebr@win.tue.nl>
To: William Lee Irwin III <wli@holomorphy.com>,
       viro@parcelfarce.linux.theplanet.co.uk,
       Stewart Smith <stewartsmith@mac.com>, linux-kernel@vger.kernel.org,
       trivial@rustcorp.com.au
Subject: Re: buffer_head.b_bsize type
Message-ID: <20030530162434.A2700@pclin040.win.tue.nl>
References: <746529B0-91C0-11D7-9488-00039346F142@mac.com> <20030529103503.GZ8978@holomorphy.com> <20030529111517.GP14138@parcelfarce.linux.theplanet.co.uk> <20030529112841.GA8978@holomorphy.com>
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In-Reply-To: <20030529112841.GA8978@holomorphy.com>; from wli@holomorphy.com on Thu, May 29, 2003 at 04:28:41AM -0700
Sender: linux-kernel-owner@vger.kernel.org

On Thu, May 29, 2003 at 04:28:41AM -0700, William Lee Irwin III wrote:

> The thought behind my comment was that it didn't make sense to allow
> the representation to go negative. There of course shouldn't ever be
> any need to allow >= 2GB b_size to be representable.

Not about this particular case, but as a general remark:
Use of unsigned is dangerous - use of int is far preferable,
everywhere that is possible.

With ints the test a+b > c is equivalent to the test a > c-b.
Intuition works.

As soon as there is some unsigned in an expression comparisons
get counterintuitive because -1 is very large.
Thus, 1+sizeof(int) > 3 is true, but 1 > 3-sizeof(int) is false.

It has happened several times that kernel code was broken because
some variable (that always was nonnegative) was made unsigned.

Andries

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