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From: Kalle Valo <kvalo@kernel.org>
To: Jeff Johnson <quic_jjohnson@quicinc.com>
Cc: Kang Yang <quic_kangyang@quicinc.com>,  <ath12k@lists.infradead.org>,
  <linux-wireless@vger.kernel.org>
Subject: Re: [PATCH v6 04/11] wifi: ath12k: add P2P IE in beacon template
References: <20240130040303.370590-1-quic_kangyang@quicinc.com>
	<20240130040303.370590-5-quic_kangyang@quicinc.com>
	<87bk8usx6d.fsf@kernel.org>
	<efda8b8e-0257-4779-b0c9-0903164b58c1@quicinc.com>
Date: Tue, 06 Feb 2024 11:52:35 +0200
In-Reply-To: <efda8b8e-0257-4779-b0c9-0903164b58c1@quicinc.com> (Jeff
	Johnson's message of "Mon, 5 Feb 2024 08:35:07 -0800")
Message-ID: <8734u5syvw.fsf@kernel.org>
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Jeff Johnson <quic_jjohnson@quicinc.com> writes:

> On 2/5/2024 8:17 AM, Kalle Valo wrote:
>> Kang Yang <quic_kangyang@quicinc.com> writes:
>>> +	if (WARN_ON(skb->len < ie_offset))
>>> +		return -EINVAL;
>>> +
>>> +	ie = (u8 *)cfg80211_find_vendor_ie(oui, oui_type,
>>> +					   skb->data + ie_offset,
>>> +					   skb->len - ie_offset);
>> 
>> So cfg80211_find_vendor_ie() returns:
>> 
>> static inline const u8 *
>> cfg80211_find_vendor_ie(unsigned int oui, int oui_type,
>> 			const u8 *ies, unsigned int len)
>> 
>> You are casting away the const here. I see that other drivers do the
>> same as the assumption is that the pointer points to the same buffer,
>> but I still don't really like casting away const. Thoughts?
>
> I'm not a fan of typecasting either.
>
> However, the problem here is that from the perspective of
> cfg80211_find_vendor_ie() the buffer is const (not modified in any way
> by the function), but from the perspective of every caller the buffer is
> part of a message that is in RAM.
>
> So you have to decide if you want to change the prototype to remove the
> const from cfg80211_find_vendor_ie() or if you want to keep the current
> semantic to cast away the const.
>
> This is one of the rare cases where I think the typecast is ok.

Makes sense, thanks for the comment.

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