netdev - Re: [PATCH] ieee802154: add rx LQI from userspace

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Message-ID: <20180709211754.v2oqe3y77fvdd5qa@x220t>
Date:   Mon, 9 Jul 2018 17:17:54 -0400
From:   Alexander Aring <aring@...atatu.com>
To:     Stefan Schmidt <stefan@...enfreihafen.org>
Cc:     Clément Péron <peron.clem@...il.com>,
        Romuald Cari <romuald.cari@...ialet.com>,
        linux-wpan@...r.kernel.org, Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@....samsung.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Clément Peron <clement.peron@...ialet.com>
Subject: Re: [PATCH] ieee802154: add rx LQI from userspace

On Mon, Jul 09, 2018 at 10:49:08AM +0200, Stefan Schmidt wrote:
> Hello Clement.
> 
> Finally coming to review the patch. Sorry for the delay.
....
> >  
> > +	if (ro->want_lqi) {
> > +		err = put_cmsg(msg, SOL_IEEE802154, WPAN_WANTLQI,
> > +			       sizeof(uint8_t), &(mac_cb(skb)->lqi));
> > +		if (err)
> > +			goto done;
> > +	}
> > +
> 
> I am wondering a bit about the LQI you get back here. Maybe Alex can
> also shed some lights on it. The LQI value stored here is always from
> the last frame send (to any peer)? Or is it the last frame send to this
> specific peer?
>

LQI is available only for per received frame [0], it's important to store
it always when address information are available for the received frame.
The peer you get from the socket layer so far I understood.

Storing means: maybe with some intelligent logic behind to calculate the
average... one LQI value alone don't say anything. With this patch you
can do such logic in user space as a LQI to peer database[1].

Otherwise we already talked about a similar handling as wireless does
with "iw ... station dump" to have such handling in kernel - out of
scope of this discussion.

Side notes:

[0] Ack frames has no address information but it refers to a transmitted
    frame with address information... so not always true. But ack
    handling is offloaded anyhow in the most cases.

[1] Getting complicated how to map a short/pan _and_ extended to _ONE_
    peer entry. -> MLME assoc()/IPv6 ndisc information are needed here.

- Alex