netdev - Re: [PATCH v5 2/3] net: add kcov handle to skb extensions

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Date:   Sat, 21 Nov 2020 21:58:37 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Florian Westphal <fw@...len.de>, Ido Schimmel <idosch@...sch.org>,
        Aleksandr Nogikh <aleksandrnogikh@...il.com>,
        davem@...emloft.net, edumazet@...gle.com, andreyknvl@...gle.com,
        dvyukov@...gle.com, elver@...gle.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        willemdebruijn.kernel@...il.com,
        Aleksandr Nogikh <nogikh@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH v5 2/3] net: add kcov handle to skb extensions

On Sat, 2020-11-21 at 12:55 -0800, Jakub Kicinski wrote:
> [snip]
> Ack, you have to figure out all the places anyway, the question is
> whether you put probes there or calls in the source code.
> 
> Shifting the maintenance burden but also BPF is flexibility.

Yeah, true. Though I'd argue also visibility - this stuff is pretty
simple now, if it gets into lots of lines of BPF code to track it that
is maintained "elsewhere", we won't see the bugs in it :-)

And it's kinda a thing that we as kernel developers _should_ be the ones
looking at since it's testing our code.

> Yup, the point is you can feed a raw skb pointer (and all other
> possible context you may want) to a BPF prog in kcov_remote_start() 
> and let BPF/BTF give you the handle it recorded in its maps.

Yeah, it's possible. Personally, I don't think it's worth the
complexity.

> It is more complicated. We can go back to an skb field if this work is
> expected to yield results for mac80211. Would you mind sending a patch?

I can do that, but I'm not going to be able to do it now/tonight (GMT+1
here), so probably only Monday/Tuesday or so, sorry.

johannes