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

/jeff