linux-kernel - Re: [PATCH] ext2/ext3:useless code for return value

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Message-ID: <20100507162348.GD3265@atrey.karlin.mff.cuni.cz>
Date:	Fri, 7 May 2010 18:23:48 +0200
From:	Jan Kara <jack@...e.cz>
To:	"潘卫平(Peter Pan)" 
	<wppan@...flag-linux.com>
Cc:	tj@...nel.org, Christoph Lameter <cl@...ux-foundation.org>,
	hch@....de, akpm@...ux-foundation.org, adilger@....com,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] ext2/ext3:useless code for return value

> When rsv is the right hand side of goal, we should return NULL,
> because now rsv's prev is NULL, or we return rsv.
> 
> Signed-off-by: Peter Pan(潘卫平) <wppan@...flag-linux.com>
> 
> ---
>  fs/ext2/balloc.c |    6 +-----
>  fs/ext3/balloc.c |    6 +-----
>  2 files changed, 2 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
> index 3cf038c..023990f 100644
> --- a/fs/ext2/balloc.c
> +++ b/fs/ext2/balloc.c
> @@ -323,11 +323,7 @@ search_reserve_window(struct rb_root *root,
> ext2_fsblk_t goal)
>  	 * side of the interval containing the goal.  If it's the RHS,
>  	 * we need to back up one.
>  	 */
> -	if (rsv->rsv_start > goal) {
> -		n = rb_prev(&rsv->rsv_node);
> -		rsv = rb_entry(n, struct ext2_reserve_window_node, rsv_node);
> -	}
> -	return rsv;
> +    return (rsv->rsv_start < goal) ? rsv : NULL;
  Hmm, I'm not sure I understand your reasoning. Suppose we have an RB-tree
with two intervals 0-10, 20-30. Interval 0-10 is in the root. Now we search
for goal 15. In the root we go to right because 10<15, in the next node we go
to left because 15 < 20. Then the loop terminates. Now your code would return
NULL but previous code would return rb_prev of interval 20-30 which is 0-10.
And that is what we want as far as I understand what we expect from the
function...

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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