netdev - Re: [PATCH net-next v4] net: linux/skbuff.h: combine SKB

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Date:   Mon, 16 Nov 2020 14:54:17 +0100
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org
Cc:     kernel test robot <lkp@...el.com>,
        Aleksandr Nogikh <nogikh@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, linux-next@...r.kernel.org,
        netdev@...r.kernel.org, Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net-next v4] net: linux/skbuff.h: combine SKB_EXTENSIONS +
 KCOV handling

Hi Randy,

On 16/11/2020 04:17, Randy Dunlap wrote:
> The previous Kconfig patch led to some other build errors as
> reported by the 0day bot and my own overnight build testing.
> 
> These are all in <linux/skbuff.h> when KCOV is enabled but
> SKB_EXTENSIONS is not enabled, so fix those by combining those conditions
> in the header file.
> 
> Also, add stubs for skb_ext_add() and skb_ext_find() to reduce the
> amount of ifdef-ery. (Jakub)

It makes sense, good idea!

Thank you for the new version!

> --- linux-next-20201113.orig/include/linux/skbuff.h
> +++ linux-next-20201113/include/linux/skbuff.h
> @@ -4137,7 +4137,6 @@ static inline void skb_set_nfct(struct s
>   #endif
>   }
>   
> -#ifdef CONFIG_SKB_EXTENSIONS
>   enum skb_ext_id {
>   #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
>   	SKB_EXT_BRIDGE_NF,
> @@ -4151,12 +4150,11 @@ enum skb_ext_id {
>   #if IS_ENABLED(CONFIG_MPTCP)
>   	SKB_EXT_MPTCP,
>   #endif
> -#if IS_ENABLED(CONFIG_KCOV)
>   	SKB_EXT_KCOV_HANDLE,
> -#endif

I don't think we should remove this #ifdef: the number of extensions are 
currently limited to 8, we might not want to always have KCOV there even 
if we don't want it. I think adding items in this enum only when needed 
was the intension of Florian (+cc) when creating these SKB extensions.
Also, this will increase a tiny bit some structures, see "struct skb_ext()".

But apart from that, I think we are fine, even if we add new extensions 
in the future after this kcov one.

So if we think it is better to remove these #ifdef here, we should be 
OK. But if we prefer not to do that, we should then not add stubs for 
skb_ext_{add,find}() and keep the ones for skb_[gs]et_kcov_handle().

Cheers,
Matt
-- 
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