linux-kernel - Re: [PATCH 1/1] debugfs: use IS

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Message-ID: <c170c646-0db4-52ac-6008-4a9199609ee0@amd.com>
Date:   Fri, 3 Sep 2021 08:27:34 +0200
From:   Christian König <christian.koenig@....com>
To:     "Das, Nirmoy" <nirmoy.das@....com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org,
        Nirmoy Das <nirmoy.aiemd@...il.com>
Subject: Re: [PATCH 1/1] debugfs: use IS_ERR to check for error

Am 02.09.21 um 19:01 schrieb Das, Nirmoy:
>
> On 9/2/2021 6:34 PM, Greg KH wrote:
>> On Thu, Sep 02, 2021 at 05:10:24PM +0200, Christian König wrote:
>>> Am 02.09.21 um 14:20 schrieb Greg KH:
>>>> On Thu, Sep 02, 2021 at 02:03:12PM +0200, Christian König wrote:
>>>>> Am 02.09.21 um 12:38 schrieb Greg KH:
>>>>>> On Thu, Sep 02, 2021 at 12:29:17PM +0200, Nirmoy Das wrote:
>>>>>>> debugfs_create_file() returns encoded error so
>>>>>>> use IS_ERR for checking return value.
>>>>>>>
>>>>>>> References: 
>>>>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fdrm%2Famd%2F-%2Fissues%2F1686&amp;data=04%7C01%7Cnirmoy.das%40amd.com%7C7a1f1095c0d64416576c08d96e2f7b38%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637661973378236086%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=g9BQRJG8gvjGFq6oj5vk9PCemQ39U19CLmkMNHVUafg%3D&amp;reserved=0
>>>>>>> Signed-off-by: Nirmoy Das <nirmoy.das@....com>
>>>>>>> ---
>>>>>>>     fs/debugfs/inode.c | 2 +-
>>>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
>>>>>>> index 8129a430d789..2f117c57160d 100644
>>>>>>> --- a/fs/debugfs/inode.c
>>>>>>> +++ b/fs/debugfs/inode.c
>>>>>>> @@ -528,7 +528,7 @@ void debugfs_create_file_size(const char 
>>>>>>> *name, umode_t mode,
>>>>>>>     {
>>>>>>>         struct dentry *de = debugfs_create_file(name, mode, 
>>>>>>> parent, data, fops);
>>>>>>> -    if (de)
>>>>>>> +    if (!IS_ERR(de))
>>>>>>>             d_inode(de)->i_size = file_size;
>>>>>>>     }
>>>>>>>     EXPORT_SYMBOL_GPL(debugfs_create_file_size);
>>>>>>> -- 
>>>>>>> 2.32.0
>>>>>>>
>>>>>> Ah, good catch, I'll queue this up after 5.15-rc1 is out, thanks!
>>>>> Thinking more about this if I'm not completely mistaken
>>>>> debugfs_create_file() returns -ENODEV when debugfs is disabled and 
>>>>> NULL on
>>>>> any other error.
>>>> How can this function be called if debugfs is not enabled in the 
>>>> system
>>>> configuration?  This _is_ the debugfs core code.
>>> Well, that's what I meant. The original code is correct and Nirmoy's 
>>> patch
>>> here is breaking it.
>> Ah, yes, sorry, you are right.  This function can not return an error
>> value, if something went wrong, the result will always be NULL.
>
>
> I just realized that we don't return NULL on error anymore:
>
> commit ff9fb72bc07705c00795ca48631f7fffe24d2c6b
> Author: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Date:   Wed Jan 23 11:28:14 2019 +0100
>
>     debugfs: return error values, not NULL
>
>
> and the current doc also says "If an error occurs, ERR_PTR(-ERROR) 
> will be returned."
>
> If I am not missing anything, this patch should be fine.

Ah! Yes, now that makes sense.

Looks like that my memory and the documentation under 
https://www.kernel.org/doc/htmldocs/filesystems/API-debugfs-create-file.html 
is outdated.

I can update my memory, but I have no idea where this documentation 
comes from and how to fix it.

Regards,
Christian.

>
>
> Regards,
>
> Nirmoy
>
>>
>>> Nirmoys other patch is for a driver and there the function can 
>>> indeed return
>>> both error code and NULL.
>> You should never be checking this stuff in a caller anyway, so no, don't
>> do it there either.
>>
>> thanks,
>>
>> greg k-h