linux-kernel - Re: [PATCH v5] erofs: use Z_EROFS_LCLUSTER_TYPE

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Message-ID: <1dd3b2a6-5431-4a2a-bccb-2a3672f5d1bd@kernel.org>
Date: Mon, 17 Mar 2025 14:42:19 +0800
From: Chao Yu <chao@...nel.org>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc: chao@...nel.org, linux-kernel@...r.kernel.org,
 Hongzhen Luo <hongzhen@...ux.alibaba.com>,
 linux-erofs mailing list <linux-erofs@...ts.ozlabs.org>
Subject: Re: [PATCH v5] erofs: use Z_EROFS_LCLUSTER_TYPE_MAX to simplify
 switches

On 3/17/25 14:15, Gao Xiang wrote:
> Hi Chao,
> 
> On 2025/3/17 14:03, Chao Yu wrote:
>> On 3/17/25 01:17, Gao Xiang wrote:
>>> Hi Chao,
>>>
> 
> ...
> 
>>>
>>> Previously, it was useful before Z_EROFS_LCLUSTER_TYPE_HEAD2 was
>>> introduced, but the `default:` case is already deadcode now.
>>
>> Xiang, thanks for the explanation.
>>
>> So seems it can happen when mounting last image w/ old kernel which can not
>> support newly introduced Z_EROFS_LCLUSTER_TYPE_* type, then it makes sense to
>> return EOPNOTSUPP.
> 
> Yeah.
> 
>>
>>>
>>>>
>>>> Btw, we'd better to do sanity check for m->type in z_erofs_load_full_lcluster(),
>>>> then we can treat m->type as reliable variable later.
>>>>
>>>>       advise = le16_to_cpu(di->di_advise);
>>>>       m->type = advise & Z_EROFS_LI_LCLUSTER_TYPE_MASK;
>>>>       if (m->type >= Z_EROFS_LCLUSTER_TYPE_MAX) {
>>>
>>> It's always false here.
>>
>> So, what do you think of this?
>>
>>  From af584b2eacd468f145e9ee31ccdeedb7355d5afd Mon Sep 17 00:00:00 2001
>> From: Chao Yu <chao@...nel.org>
>> Date: Mon, 17 Mar 2025 13:57:55 +0800
>> Subject: [PATCH] erofs: remove dead codes for cleanup
>>
>> z_erofs_extent_lookback() and z_erofs_get_extent_decompressedlen() tries
>> to do sanity check on m->type, however their caller z_erofs_map_blocks_fo()
>> has already checked that, so let's remove those dead codes.
> 
> z_erofs_extent_lookback() will (lookback) read new lcn in
> z_erofs_load_lcluster_from_disk() so it won't be covered by
> the original z_erofs_map_blocks_fo().

Xiang,

Oh, I see, changed here:

- z_erofs_extent_lookback
 - z_erofs_load_lcluster_from_disk
  - z_erofs_load_full_lcluster
  : m->type = advise & Z_EROFS_LI_LCLUSTER_TYPE_MASK;
 - z_erofs_load_compact_lcluster
 : m->type = type;

> 
> I think this check can be resolved in
> z_erofs_load_lcluster_from_disk() instead but maybe address
> for the next cycle? since there are already enough features
> for this cycle and I have to make sure no major issues....

Yeah, it's fine to check the cleanup later, let's keep focusing
on improving patches in dev now.

Thanks,

> 
> Thanks,
> Gao Xiang
>