linux-kernel - Re: [RFC net-next 1/1] idpf: Don't hard code napi

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Message-ID: <20241002101727.349fc146@kernel.org>
Date: Wed, 2 Oct 2024 10:17:27 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Alexander Lobakin <aleksander.lobakin@...el.com>, Przemek Kitszel
 <przemyslaw.kitszel@...el.com>
Cc: Joe Damato <jdamato@...tly.com>, netdev@...r.kernel.org, Tony Nguyen
 <anthony.l.nguyen@...el.com>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, "moderated
 list:INTEL ETHERNET DRIVERS" <intel-wired-lan@...ts.osuosl.org>, open list
 <linux-kernel@...r.kernel.org>, Simon Horman <horms@...nel.org>
Subject: Re: [RFC net-next 1/1] idpf: Don't hard code napi_struct size

On Tue, 1 Oct 2024 07:44:36 -0700 Joe Damato wrote:
> > But if you change any core API, let's say rename a field used in several
> > drivers, you anyway need to adjust the affected drivers.  
> 
> Sorry, but that's a totally different argument.
> 
> There are obvious cases where touching certain parts of core would
> require changes to drivers, yes. I agree on that if I change an API
> or a struct field name, or remove an enum, then this affects drivers
> which must be updated.

+1

I fully agree with Joe. Drivers asserting the size of core structures
is both undue burden on core changes and pointless.
The former is subjective, as for the latter: most core structures 
will contain cold / slow path data, usually at the end. If you care
about performance of anything that follows a core struct you need
to align the next field yourself.

IDK how you want to fit this into your magic macros but complex
nested types should be neither ro, rw nor cold. They are separate.