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Date:   Sat, 27 May 2023 09:01:41 +0800
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Subject: Re: [PATCH 1/1] f2fs: fix args passed to trace_f2fs_lookup_end
Content-Language: en-US
To:     Jaegeuk Kim <jaegeuk@kernel.org>, Wu Bo <bo.wu@vivo.com>
Cc:     linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, wubo.oduw@gmail.com
References: <20230524100812.80741-1-bo.wu@vivo.com>
 <ZHDqhy4E9iSnneLa@google.com>
From:   Chao Yu <chao@kernel.org>
In-Reply-To: <ZHDqhy4E9iSnneLa@google.com>
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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@vivo.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")

> 
> 
>>   	return new;
>>   out_iput:
>>   	iput(inode);
>> -- 
>> 2.35.3