From: =?UTF-8?B?Iua9mOWNq+W5syhQZXRlciBQYW4pIg==?= Date: Mon, 10 May 2010 02:36:57 +0000 Subject: Re: [PATCH] ext2/ext3:useless code for return value Message-Id: <4BE77149.8050307@redflag-linux.com> List-Id: References: <4BE2C5D5.2050207@redflag-linux.com> <20100507162348.GD3265@atrey.karlin.mff.cuni.cz> In-Reply-To: <20100507162348.GD3265@atrey.karlin.mff.cuni.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Jan Kara Cc: tj@kernel.org, Christoph Lameter , hch@lst.de, akpm@linux-foundation.org, adilger@sun.com, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org On 05/08/2010 12:23 AM, Jan Kara wrote: >> 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) >> >> --- >> 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 You got the point! Many thanks. Regards -- Peter Pan Red Flag Software Co.,Ltd