linux-kernel - Re: [PATCH RFC net-next 7/7] netdev_features: convert NETIF_F_FCOE_MTU to IFF_FCOE

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Date: Thu, 11 Apr 2024 07:47:09 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, David Ahern
 <dsahern@...nel.org>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Andrew Lunn
 <andrew@...n.ch>, <nex.sw.ncis.osdt.itp.upstreaming@...el.com>,
 <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next 7/7] netdev_features: convert
 NETIF_F_FCOE_MTU to IFF_FCOE_MTU

On Thu, 11 Apr 2024 12:28:08 +0200 Alexander Lobakin wrote:
> > Any reason not to make it a bitfield? I haven't looked at the longer
> > patches but this one seems to be used like a basic bool.  
> 
> This whole enum could be made as bitfields, should we convert it? Would
> be a big patch tho ._.

As always, I haven't investigated closely :) But my thinking was -
we are at 34 bits in priv. We just need to convert 2 of them to
a bitfield, pick two with fewest uses. Then we can downgrade 
the field to u32 from ulonglong, and we can carry on adding bitfields?

> > But this definitely _is_ a uAPI change, right?  
> 
> Why?

It will be user visible, ethtool -k is losing a field.
Whether that's actually going to break anything depends on how silly
user space is.

As Andrew pointed out, definitely something that should be called out
in the commit message.