linux-kernel - Re: [f2fs-dev] [PATCH 1/1] f2fs: fix args passed to trace_f2fs_lookup

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Message-ID: <6ad8c3c7-a3e0-1a52-5a10-6b535b1ed7d3@gmail.com>
Date:   Mon, 29 May 2023 20:41:46 +0800
From:   Wu Bo <wubo.oduw@...il.com>
To:     Chao Yu <chao@...nel.org>, Wu Bo <bo.wu@...o.com>
Cc:     jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [f2fs-dev] [PATCH 1/1] f2fs: fix args passed to
 trace_f2fs_lookup_end


On 2023/5/29 18:18, Chao Yu wrote:
> On 2023/5/29 12:13, Wu Bo wrote:
>> On Sat, May 27, 2023 at 09:01:41AM +0800, Chao Yu wrote:
>>> On 2023/5/27 1:21, Jaegeuk Kim wrote:
>>>> On 05/24, Wu Bo wrote:
>>>>> The NULL return of 'd_splice_alias' dosen't mean error.
>>>>>
>>>>> Signed-off-by: Wu Bo <bo.wu@...o.com>
>>>>> ---
>>>>>    fs/f2fs/namei.c | 2 +-
>>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
>>>>> index 77a71276ecb1..e5a3e39ce90c 100644
>>>>> --- a/fs/f2fs/namei.c
>>>>> +++ b/fs/f2fs/namei.c
>>>>> @@ -577,7 +577,7 @@ static struct dentry *f2fs_lookup(struct inode 
>>>>> *dir, struct dentry *dentry,
>>>>>    #endif
>>>>>        new = c(inode, dentry);
>>>>>        err = PTR_ERR_OR_ZERO(new);
>>>>> -    trace_f2fs_lookup_end(dir, dentry, ino, !new ? -ENOENT : err);
>>>>> +    trace_f2fs_lookup_end(dir, new ? new : dentry, ino, err);
>>>>
>>>> Shouldn't give an error pointer to the dentry field.
>>>>
>>>> How about just giving the err?
>>>>
>>>> -       err = PTR_ERR_OR_ZERO(new);
>>>> -       trace_f2fs_lookup_end(dir, dentry, ino, !new ? -ENOENT : err);
>>>> +       trace_f2fs_lookup_end(dir, dentry, ino, PTR_ERR_OR_ZERO(new));
>>>
>>> static inline int __must_check PTR_ERR_OR_ZERO(__force const void *ptr)
>>> {
>>>     if (IS_ERR(ptr))
>>>         return PTR_ERR(ptr);
>>>     else
>>>         return 0;
>>> }
>>>
>>> For below two cases, PTR_ERR_OR_ZERO(new) will return zero:
>>> a) f2fs_lookup found existed dentry
>>> b) f2fs_lookup didn't find existed dentry (-ENOENT case)
>>>
>>> So in below commit, I passed -ENOENT to tracepoint for case b), so 
>>> we can
>>> distinguish result of f2fs_lookup in tracepoint, actually, -ENOENT 
>>> is expected
>>> value when we create a new file/directory.
>>>
>>> Commit 84597b1f9b05 ("f2fs: fix wrong value of tracepoint parameter")
>> I can see this commit is try to distinguish the dentry not existed case.
>> But a normal case which dentry is exactly found will also go through
>> 'd_splice_alias', and its return is also NULL. This makes the 
>> tracepoint always
>> print 'err:-2' like the following:
>>        ls-11676   [004] .... 329281.943118: f2fs_lookup_end: dev = 
>> (254,39), pino = 4451, name:Alarms, ino:7093, err:-2
>>        ls-11676   [004] .... 329281.943145: f2fs_lookup_end: dev = 
>> (254,39), pino = 4451, name:Notifications, ino:7094, err:-2
>>        ls-11676   [004] .... 329281.943172: f2fs_lookup_end: dev = 
>> (254,39), pino = 4451, name:Pictures, ino:7095, err:-2
>> Even these lookup are acctually successful, this is a bit strange.
>
> Ah, I misunderstand return value's meaning of .lookup.
>
> So, how about this? it only update err if d_splice_alias() returns a 
> negative
> value?
>
> if (IS_ERR(new))
>     err = PTR_ERR(new);
> trace_f2fs_lookup_end(dir, new ? new : dentry, ino, err);
>
> Thanks,
>
Yes, this will be better.

>>>
>>>>
>>>>
>>>>>        return new;
>>>>>    out_iput:
>>>>>        iput(inode);
>>>>> -- 
>>>>> 2.35.3
>>>
>>>
>>> _______________________________________________
>>> Linux-f2fs-devel mailing list
>>> Linux-f2fs-devel@...ts.sourceforge.net
>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel