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

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Message-ID: <6545868d-464e-4b87-b0cf-28f34d77b694@nvidia.com>
Date: Mon, 26 Aug 2024 18:38:50 +0300
From: Gal Pressman <gal@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Eric Dumazet <edumazet@...gle.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 "David S. Miller" <davem@...emloft.net>, 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 26/08/2024 18:09, Jakub Kicinski wrote:
> On Sun, 25 Aug 2024 11:19:49 +0300 Gal Pressman wrote:
>> 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?
> 
> Keep in mind that include/uapi was introduced around v3.7, before 
> that IIUC everything under include/linux that wasn't protected by
> ifdef __KERNEL__ was uAPI. So all of include/linux/netdev_features.h

TIL, thanks!