linux-kernel - Re: [PATCH net-next v3] wifi: ath9k: Remove error checking for debugfs_create

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Message-ID: <87zg2ja4kb.fsf@toke.dk>
Date:   Tue, 22 Aug 2023 10:01:40 +0200
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     Kalle Valo <kvalo@...nel.org>
Cc:     Wang Ming <machel@...o.com>, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org, opensource.kernel@...o.com
Subject: Re: [PATCH net-next v3] wifi: ath9k: Remove error checking for
 debugfs_create_dir()

Kalle Valo <kvalo@...nel.org> writes:

> Toke Høiland-Jørgensen <toke@...e.dk> writes:
>
>> Kalle Valo <kvalo@...nel.org> writes:
>>
>>> Toke Høiland-Jørgensen <toke@...e.dk> writes:
>>>
>>>> Wang Ming <machel@...o.com> writes:
>>>>
>>>>> It is expected that most callers should _ignore_ the errors
>>>>> return by debugfs_create_dir() in ath9k_htc_init_debug().
>>>>>
>>>>> Signed-off-by: Wang Ming <machel@...o.com>
>>>>> ---
>>>>>  drivers/net/wireless/ath/ath9k/htc_drv_debug.c | 2 --
>>>>>  1 file changed, 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/net/wireless/ath/ath9k/htc_drv_debug.c b/drivers/net/wireless/ath/ath9k/htc_drv_debug.c
>>>>> index b3ed65e5c4da..85ad45771b44 100644
>>>>> --- a/drivers/net/wireless/ath/ath9k/htc_drv_debug.c
>>>>> +++ b/drivers/net/wireless/ath/ath9k/htc_drv_debug.c
>>>>> @@ -491,8 +491,6 @@ int ath9k_htc_init_debug(struct ath_hw *ah)
>>>>>  
>>>>>  	priv->debug.debugfs_phy = debugfs_create_dir(KBUILD_MODNAME,
>>>>>  					     priv->hw->wiphy->debugfsdir);
>>>>> -	if (!priv->debug.debugfs_phy)
>>>>> -		return -ENOMEM;
>>>>
>>>> Hmm, so it's true that all the debugfs_create* functions deal correctly
>>>> with the dir pointer being an error pointer, which means that it's
>>>> possible to just ignore the return value of debugfs_create_dir() without
>>>> anything breaking.
>>>
>>> The comment in debugfs_create_dir() states:
>>>
>>>  * NOTE: it's expected that most callers should _ignore_ the errors returned
>>>  * by this function. Other debugfs functions handle the fact that the "dentry"
>>>  * passed to them could be an error and they don't crash in that case.
>>>  * Drivers should generally work fine even if debugfs fails to init anyway.
>>>
>>>> However, it also seems kinda pointless to have all those calls if we
>>>> know they're going to fail, so I prefer v1 of this patch that just
>>>> fixed the IS_ERR check. No need to resend, we can just apply v1
>>>> instead...
>>>
>>> Because of the comment I'm leaning towards v3.
>>
>> Well, the comment says "most callers" :)
>>
>> I think having an early return like this is perfectly valid
>> optimisation, even if it doesn't really make any performance difference.
>> I don't feel incredibly strongly about it (given that the current check
>> is broken I guess the early return has never actually worked), so if you
>> feel like overriding your submaintainer on this, feel free ;)
>
> No no, I don't want to override anything :) Just making sure you were
> aware of the comment. v1 is in my pending branch right now.

Alright, cool :)

-Toke