netdev - Re: [klibc] [PATCH net-next] net: uapi: Provide an UAPI definition of 'struct sockaddr'

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Message-Id: <212d2e51-abc1-47bb-8666-755917cad889@app.fastmail.com>
Date: Tue, 20 Jan 2026 23:31:05 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "H. Peter Anvin" <hpa@...or.com>,
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 "Eric Dumazet" <edumazet@...gle.com>,
 "Kuniyuki Iwashima" <kuniyu@...gle.com>, "Paolo Abeni" <pabeni@...hat.com>,
 "Willem de Bruijn" <willemb@...gle.com>,
 "Xi Ruoyao" <libc-alpha@...rceware.org>,
 "Carlos O'Donell" <carlos@...hat.com>,
 "Adhemerval Zanella Netto" <adhemerval.zanella@...aro.org>,
 "Rich Felker" <dalias@...c.org>
Cc: Netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org,
 linux-api@...r.kernel.org, klibc@...or.com
Subject: Re: [klibc] [PATCH net-next] net: uapi: Provide an UAPI definition of 'struct
 sockaddr'

On Tue, Jan 20, 2026, at 19:50, H. Peter Anvin wrote:
> On 2026-01-05 05:50, Arnd Bergmann wrote:
>> 
>> This looks like the right approach to me. I have previously
>> tried to introduce a 'struct __kernel_sockaddr' structure and
>> use that in uapi headers in place of the libc sockaddr, but
>> that seemed worse in the end, and introduce the same problems
>> as using the existing __kernel_sockaddr_storage.
>> 
>
> You say "the same problems". It's not clear to me what that means.

I must have accidentally cut that from my reply, sorry.
Looking at it again now, I think I ran into problems with the
flexible array that was removed from the in-kernel sockaddr
structure in commit 2b5e9f9b7e41 ("net: Convert struct sockaddr
to fixed-size "sa_data[14]""), so there is a good chance it works
now with the (once more) fixed-size version.

The other problem is that the structures that embed 'sockaddr'
are used a lot inside of the kernel, in particular in 'ifreq',
so changing the uapi sockaddr to __kernel_sockaddr requires
additional changes wherever the struct members are passed
by reference.

> Based on my own libc experience, hacking both a minimal (klibc) and a
> maximal (glibc) libc, there are a *lot* of advantages to having
> __kernel_* definitions available, *regardless* of if they are exported
> into the libc namespace at all.

Absolutely, I am totally in agreement about this in general, which
is why I tried this approach first.

      Arnd