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

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Date:   Thu, 2 Sep 2021 18:44:39 +0200
From:   "Das, Nirmoy" <nirmoy.das@....com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Christian König <christian.koenig@....com>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] debugfs: use IS_ERR to check for error


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.


The issue occurs when CONFIG_DEBUG_FS=y and CONFIG_DEBUG_FS_ALLOW_NONE=y 
config options are set, so a call to

debugfs_create_file() will return ERR_PTR(-EPERM) instead of NULL.


>
>> 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