linux-kernel - Re: [PATCH] erofs: fix compacted_{4b_initial, 2b} when compacted_4b

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Date:   Mon, 13 Sep 2021 16:48:45 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Yue Hu <zbestahu@...il.com>
Cc:     xiang@...nel.org, chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, huyue2@...ong.com,
        zhangwen@...ong.com, zbestahu@....com
Subject: Re: [PATCH] erofs: fix compacted_{4b_initial, 2b} when
 compacted_4b_initial > totalidx

Hi Yue,

On Mon, Sep 13, 2021 at 03:24:05PM +0800, Yue Hu wrote:
> From: Yue Hu <huyue2@...ong.com>
> 
> mkfs.erofs will treat compacted_4b_initial & compacted_2b as 0 if
> compacted_4b_initial > totalidx, kernel should be aligned with it
> accordingly.

There is no difference between compacted_4b_initial or compacted_4b_end
for compacted 4B. Since in this way totalidx for compact 2B won't larger
than 16 (number of lclusters in a compacted 2B pack.)

So it can be handled in either compacted_4b_initial or compacted_4b_end
cases, because there are all compacted 4B.

Thanks,
Gao Xiang

> 
> Signed-off-by: Yue Hu <huyue2@...ong.com>
> ---
>  fs/erofs/zmap.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
> index 9fb98d8..4f941b6 100644
> --- a/fs/erofs/zmap.c
> +++ b/fs/erofs/zmap.c
> @@ -369,7 +369,10 @@ static int compacted_load_cluster_from_disk(struct z_erofs_maprecorder *m,
>  	if (compacted_4b_initial == 32 / 4)
>  		compacted_4b_initial = 0;
>  
> -	if (vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B)
> +	if (compacted_4b_initial > totalidx) {
> +		compacted_4b_initial = 0;
> +		compacted_2b = 0;
> +	} else if (vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B)
>  		compacted_2b = rounddown(totalidx - compacted_4b_initial, 16);
>  	else
>  		compacted_2b = 0;
> -- 
> 1.9.1