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

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Message-ID: <20210913170016.00007580.zbestahu@gmail.com>
Date:   Mon, 13 Sep 2021 17:00:16 +0800
From:   Yue Hu <zbestahu@...il.com>
To:     Gao Xiang <hsiangkao@...ux.alibaba.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

On Mon, 13 Sep 2021 16:48:45 +0800
Gao Xiang <hsiangkao@...ux.alibaba.com> wrote:

> 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.)

However, we can see compacted_2b is a big number for this case. It should
be pointless.

Thanks.

> 
> 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