linux-kernel - Re: [PATCH v2] ext3, ext4: do_split() fix loop, with obvious unsigned wrap

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Message-ID: <20081202215758.GE20858@mit.edu>
Date:	Tue, 2 Dec 2008 16:57:58 -0500
From:	Theodore Tso <tytso@....edu>
To:	Bill Davidsen <davidsen@....com>
Cc:	roel kluin <roel.kluin@...il.com>, adilger@....com,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ext3, ext4: do_split() fix loop, with obvious
	unsigned wrap

On Tue, Dec 02, 2008 at 12:08:38PM -0500, Bill Davidsen wrote:
> Sorry, you are reading it wrong, the i values inside the loop are  
> identical to those in the original. The value of i starts at count, and  
> the test comes *before* the value is used inside the loop. The values of  
> i inside the loop start at count-1 and go to zero, just as it did in the  
> original. That's why the "i--" is there, the test is on the  
> unincremented value range count to one, but the value inside the loop is  
> correct (or at least is the same as the original patch).

You're right; my bad.  But with something like this:

>>> +	for (i = count; i--; ) {

...where there is no third part of the for loop, and a decrement in
the second part of the loop, just for clarity's sake, it's much better
to write it as a while loop.

						- Ted
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