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

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Message-ID: <7b4a204e-5cb5-411a-bcb6-99e281fdc470@linux.alibaba.com>
Date: Mon, 17 Mar 2025 14:43:48 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Chao Yu <chao@...nel.org>
Cc: 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 2025/3/17 14:42, Chao Yu wrote:
> 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;

Yeah, we'd better to move all checks into
z_erofs_load_lcluster_from_disk() later.

> 
>>
>> 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.

Yes.

Thanks,
Gao Xiang

> 
> Thanks,
> 
>>
>> Thanks,
>> Gao Xiang
>>