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:

quoted

On 21/08/2024 18:43, Eric Dumazet wrote:

quoted

On Wed, Aug 21, 2024 at 5:07 PM Alexander Lobakin
[off-list ref] wrote:  

quoted

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!