linux-ext4 - Re: [PATCH] ext4: fix loop in do

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Date:	Sat, 29 Nov 2008 19:36:52 -0500
From:	Bill Davidsen <davidsen@....com>
To:	roel kluin <roel.kluin@...il.com>
CC:	tytso@....edu, adilger@....com, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: fix loop in do_split()

roel kluin wrote:
> unsigned i >= 0 is always true
> 
> Signed-off-by: Roel Kluin <roel.kluin@...il.com>
> ---
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 63adcb7..389cf60 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -1198,7 +1198,7 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
>  	/* Split the existing block in the middle, size-wise */
>  	size = 0;
>  	move = 0;
> -	for (i = count-1; i >= 0; i--) {
> +	for (i = count-1; i < count; i--) {
>  		/* is more than half of this entry in 2nd half of the block? */
>  		if (size + map[i].size/2 > blocksize/2)
>  			break;
> 
While this unsigned wrap method is technically valid, it certainly isn't 
obvious, and making code readable should be a goal as well as making it correct. 
  After all, code which is hard to read is hard to understand, making it hard to 
maintain. I therefore suggest the simpler form:
	for (i = count; i--; ) {
which gives the same i values inside the loop, but does assume that the reader 
remembers that i is unsigned, and intuitively understand wraparound while 
passing zero.

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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