linux-kernel - Re: [PATCH net-next v4 2/6] netdev_features: remove unused __UNUSED_NETIF_F

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Message-ID: <a1b025a9-4fa0-42d8-9ad7-5a3888574b3f@nvidia.com>
Date: Sun, 25 Aug 2024 11:19:49 +0300
From: Gal Pressman <gal@...dia.com>
To: Eric Dumazet <edumazet@...gle.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 David Ahern <dsahern@...nel.org>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Andrew Lunn <andrew@...n.ch>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 nex.sw.ncis.osdt.itp.upstreaming@...el.com, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v4 2/6] netdev_features: remove unused
 __UNUSED_NETIF_F_1

On 21/08/2024 18:43, Eric Dumazet wrote:
> On Wed, Aug 21, 2024 at 5:07 PM Alexander Lobakin
> <aleksander.lobakin@...el.com> wrote:
>>
>> NETIF_F_NO_CSUM was removed in 3.2-rc2 by commit 34324dc2bf27
>> ("net: remove NETIF_F_NO_CSUM feature bit") and became
>> __UNUSED_NETIF_F_1. It's not used anywhere in the code.
>> Remove this bit waste.
>>
>> It wasn't needed to rename the flag instead of removing it as
>> netdev features are not uAPI/ABI. Ethtool passes their names
>> and values separately with no fixed positions and the userspace
>> Ethtool code doesn't have any hardcoded feature names/bits, so
>> that new Ethtool will work on older kernels and vice versa.
> 
> This is only true for recent enough ethtool (>= 3.4)
> 
> You might refine the changelog to not claim this "was not needed".
> 
> Back in 2011 (and linux-2.6.39) , this was needed for sure.
> 
> I am not sure we have a documented requirement about ethtool versions.
> 

This is a nice history lesson, so before the features infrastructure the
feature bits were considered as "ABI"?

I couldn't find a point in time where they were actually defined in the
uapi files?