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Subject: Re: [PATCH] nl80211: allow more operations for mesh and ad-hoc
 interfaces
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     linux-wireless@vger.kernel.org
References: <20191029115602.78990-1-markus.theil@tu-ilmenau.de>
 <4b9c7b36f175667a76609c6560618bb48a321ed8.camel@sipsolutions.net>
 <f9828fb2-eda9-5e05-7683-0c180e994f43@tu-ilmenau.de>
 <48aa046256186ecc3aaffb9c6642ab44ae91bbd4.camel@sipsolutions.net>
From:   Markus Theil <markus.theil@tu-ilmenau.de>
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Organization: TU Ilmenau
Message-ID: <8adc192a-ceed-b943-318c-61ad06a04e2c@tu-ilmenau.de>
Date:   Wed, 30 Oct 2019 15:10:15 +0100
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In-Reply-To: <48aa046256186ecc3aaffb9c6642ab44ae91bbd4.camel@sipsolutions.net>
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On 30.10.19 15:04, Johannes Berg wrote:
> On Wed, 2019-10-30 at 14:40 +0100, Markus Theil wrote:
>> Mesh interfaces are allowed to perform EDCA according to the standard
>> 802.11-2016.
> Well, they *have to* in a sense :-)
>
> [...]
>> Changing beacons on the fly from user-space in these modes is only
>> useful, if vendor-specific elements are used, which can change over time.
>>
>> All in all I can nevertheless understand your point, that these changes
>> could be "wrong" from a pragmatic point of view.
> No no, that's not even it. The problem is that you're focusing too much
> on the standard without understanding how the stack works.
>
> Take the QoS parameters again for example. Setting them from userspace
> is wrong because that data will immediately be forgotten and killed
> again by the call to ieee80211_set_wmm_default() in that code.
>
> Or look at how the change_beacon call is handled - the data you set here
> will never even be used for IBSS or mesh because in mac80211
> ieee80211_change_beacon() will quite possibly even crash when you call
> it for a non-AP interface since it accesses sdata->u.ap.beacon without
> any other checks.
>
> So while the *idea* of being able to change beacons or WMM parameters
> *might* be correct, this kind of implementation is (fairly obviously)
> completely wrong.
>
> johannes
>
Ok, thank you for the clarification :)

Markus