linux-ext4 - Re: [PATCH 2/5] ext2: code cleanup by calling ext2_group_last_block

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Date:   Thu, 7 Nov 2019 10:21:17 +0100
From:   Jan Kara <jack@...e.cz>
To:     Chengguang Xu <cgxu519@...ernel.net>
Cc:     Jan Kara <jack@...e.cz>, jack <jack@...e.com>,
        linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/5] ext2: code cleanup by calling
 ext2_group_last_block_no()

On Thu 07-11-19 10:54:43, Chengguang Xu wrote:
>  ---- 在 星期三, 2019-11-06 23:42:36 Jan Kara <jack@...e.cz> 撰写 ----
>  > On Mon 04-11-19 19:40:33, Chengguang Xu wrote:
>  > > Call common helper ext2_group_last_block_no() to
>  > > calculate group last block number.
>  > > 
>  > > Signed-off-by: Chengguang Xu <cgxu519@...ernel.net>
>  > 
>  > Thanks for the patch! I've applied it (as well as 1/5) and added attached
>  > simplification on top.
>  > 
> 
> In ext2_try_to_allocate()
> 
> +		if (my_rsv->_rsv_end < group_last_block)
> +			end = my_rsv->_rsv_end - group_first_block + 1;
> +		if (grp_goal < start || grp_goal > end)
> 
> Based on original code, shouldn't it be  if (grp_goal < start || grp_goal
> >=end) ?

Hum, that's a good point. The original code actually had an off-by-one bug
because 'end' is really the last block that can be used so grp_goal == end
still makes sense. And my cleanup fixed it. Now looking at the code in
ext2_try_to_allocate() we also have a similar bug in the loop allocating
blocks. There we can also go upto 'end' inclusive. Added a patch to fix
that. Thanks for pointing me to this!

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR