netdev - Re: [PATCH v3 2/3] net: add kcov handle to skb extensions

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Date:   Tue, 27 Oct 2020 09:13:29 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Aleksandr Nogikh <nogikh@...gle.com>
Cc:     Aleksandr Nogikh <aleksandrnogikh@...il.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Johannes Berg <johannes@...solutions.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Marco Elver <elver@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH v3 2/3] net: add kcov handle to skb extensions

On Tue, Oct 27, 2020 at 8:31 AM Aleksandr Nogikh <nogikh@...gle.com> wrote:
>
> On Mon, Oct 26, 2020 at 7:57 PM Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
> [...]
> > If the handle does not need to be set if zero, why then set it if the
> > skb has extensions?
>
> The point of that condition is to avoid unnecessary allocations of skb extension
> objects. At the same time, one would expect skb_get_kcov_handle to return the
> latest value that was set via skb_set_kcov_handle. So if a buffer already has a
> non-zero kcov_handle and skb_set_kcov_handle is called to set it to zero, it
> should be set to zero.

I see. I thought it was some best effort approach: if there happens to
be space, use it, but don't allocate. Which I did not understand.
Could you rephrase the comment to make more clear that this is about
clearing a possibly previously set value.


> > skb_ext_add and skb_ext_find are not defined unless CONFIG_SKB_EXTENSIONS.
> >
> > Perhaps CONFIG_KCOV should be made to select that?
>
> Yes, thank you for pointing it out. I’ll fix it in the next version.