Re: [PATCH] cfg80211: introduce critical protocol indication from user-space

["Arend van Spriel" <arend@broadcom.com>]

On 04/09/2013 10:42 PM, Johannes Berg wrote:
> On Tue, 2013-04-09 at 21:54 +0200, Arend van Spriel wrote:
>
>> I should at least try :-) The given protocol can help the driver decide
>> what actions should be taken. As an example, for a streaming protocol
>> like Miracast [1] other wireless parameters/features may be changed as
>> for DHCP.
>
> Ok? I guess I don't really see what you'd do differently, but hey, what
> do I know :)

Understood. It was the input I received internally that they would, but 
I will discuss whether it makes sense to treat all in the same way.

>>>> + * @NL80211_CRIT_PROTO_UNSPEC: protocol unspecified.
>>>> + * @NL80211_CRIT_PROTO_BOOTP: BOOTP protocol.
>>>> + * @NL80211_CRIT_PROTO_EAPOL: EAPOL protocol.
>>>> + * @NL80211_CRIT_PROTO_ARP: ARP protocol for APIPA.
>>>
>>> Don't like IPv6? :-)
>>
>> I am a dark-ages guy :-p I think I will rename the BOOTP one and
>> indicate it should be used for BOOTP and DHCPv6.
>
> Might also be worth it to rename ARP to APIPA since ARP is ... well
> often done :-)

I chose ARP because APIPA is essentially not a protocol. As far as I 
understand it makes use of ARP to make sure the address in unique. I see 
your point and will change it. Then again it all may go away :-)

>>>> @@ -648,6 +648,9 @@ void cfg80211_mlme_unregister_socket(struct wireless_dev *wdev, u32 nlportid)
>>>>
>>>>    	spin_unlock_bh(&wdev->mgmt_registrations_lock);
>>>>
>>>> +	if (rdev->ops->crit_proto_stop)
>>>> +		rdev_crit_proto_stop(rdev, wdev);
>>>
>>> This is broken, you're not checking that it's the correct socket.
>>> Therefore, if you run, for example, "iw wlan0 link" while the critical
>>> operation is ongoing it will be aborted.
>>
>> I was wondering about that. Will change it checking nlportid, right?
>
> Well you have to store the nlportid (rather than crit_proto_started) and
> then check it.

Yeah, I surmised that already. If I would drop crit_proto_started and 
use the portid as a flag as well, I need an invalid portid. Is there a 
definition for that?

>>>> +	duration = min_t(u16, duration, NL80211_MAX_CRIT_PROT_DURATION);
>>>
>>> Why not reject it if too large (although then the max should be defined
>>> in the header file)? Is there a reason, like maybe wanting to be able to
>>> increase the kernel value later? If so, might want to have a comment?
>>
>> There were people in earlier discussions that considered a timeguard
>> appropriate, ie. not trusting user-space. I do not have a strong opinion
>> on this so....
>
> I'm not really arguing there shouldn't be any limit, but I guess I'm not
> sure why it should be limited rather than refusing anything above the
> limit? Maybe it'd be worthwhile to advertise the limit instead and then
> just take it?
>
> It really doesn't matter all that much though ... mostly I'm curious
> whether any design thought went into this :-)

I guess not :-( Thanks for clarifying you were talking about the 
limiting mechanism. I will modify that.

>>>> +	rdev_crit_proto_stop(rdev, wdev);
>>>
>>> What if it's not even started?
>>
>> That is handled in rdev_crit_proto_stop() itself.
>
> Oh, I see. In a way I guess that makes sense, but should this not return
> an error? Also, I'd like the rdev_* inlines to not actually have such
> logic, I tend to simply ignore them when reading ...

I was not aware of that coding principle although I could have seen a 
pattern looking at the other rdev_* inlines. I will take the logic out 
of it.

> Or maybe just give that another name / put it elsewhere? Maybe even give
> it a return value then to refuse stopping crit proto when it's not
> started?
>
>>> Do you expect drivers to call this function even when explicitly asked
>>> to stop? That should be documented then, I think.
>>
>> No, I don't and I will add that in documentation.
>
> I was going to say this is broken then ... but that's again only because
> the wrapper sets started=false. See what you did there? I totally
> ignored the rdev_*() wrapper code :)

Yeah, yeah. I got it the first time :-p

Regards,
Arend