linux-kernel - Re: [PATCH] ocfs2: update seq_file index in ocfs2_dlm_seq

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Message-ID: <590D31E0-4131-4E14-88B4-20660E830660@oracle.com>
Date: Sat, 15 Feb 2025 00:23:52 +0000
From: Wengang Wang <wen.gang.wang@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: Joseph Qi <joseph.qi@...ux.alibaba.com>,
        "ocfs2-devel@...ts.linux.dev"
	<ocfs2-devel@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ocfs2: update seq_file index in ocfs2_dlm_seq_next



> On Feb 14, 2025, at 3:55 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> On Mon, 11 Nov 2024 17:35:49 +0800 Joseph Qi <joseph.qi@...ux.alibaba.com> wrote:
> 
>> 
>> 
>> On 11/11/24 3:04 PM, Wengang Wang wrote:
>>> 
>>> 
>>>> On Nov 10, 2024, at 5:38 PM, Joseph Qi <joseph.qi@...ux.alibaba.com> wrote:
>>>> 
>>>> 
>>>> 
>>>> On 11/9/24 3:28 AM, Wengang Wang wrote:
>>>>> The following INFO level message was seen:
>>>>> 
>>>>> seq_file: buggy .next function ocfs2_dlm_seq_next [ocfs2] did not
>>>>> update position index
>>>>> 
>>>>> Fix:
>>>>> Updata m->index to make seq_read_iter happy though the index its self makes
>>>>> no sense to ocfs2_dlm_seq_next.
>>>>> 
>>>>> Signed-off-by: Wengang Wang <wen.gang.wang@...cle.com>
>>>>> ---
>>>>> fs/ocfs2/dlmglue.c | 1 +
>>>>> 1 file changed, 1 insertion(+)
>>>>> 
>>>>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>>>>> index 60df52e4c1f8..349d131369cf 100644
>>>>> --- a/fs/ocfs2/dlmglue.c
>>>>> +++ b/fs/ocfs2/dlmglue.c
>>>>> @@ -3120,6 +3120,7 @@ static void *ocfs2_dlm_seq_next(struct seq_file *m, void *v, loff_t *pos)
>>>>> }
>>>>> spin_unlock(&ocfs2_dlm_tracking_lock);
>>>>> 
>>>>> + m->index++;
>>>> 
>>>> We can directly use '(*pos)++' instead.
>>>> 
>>> 
>>> The input/output "pos” indicates more an offset into the file. Actually the output for an item is not really 1 byte in length, so incrementing the offset by 1 sounds a bit strange to me. Instead If we increment the “index”, It would be easier to understand it as  for next item. Though updating “index” or updating “*pos” instead makes no difference to binary running, the code understanding is different.  I know other seq_operations.next functions are directly incrementing the “*pos”, I think updating “index” is better. Well, if you persist (*pos)++, I will also let it go.
>>> 
>>> From seq_read_iter(), the input pos is equivalent to '&m->index'. So the
>> above two ways seems have no functional difference.
>> IMO, we'd better hide the m->index logic into seqfile and just use pos
>> instead like other .next implementations.
> 
> Did we ever fix this?

Yes, fix is already in upstream code.

Thanks,
Wengang