netdev - Re: [PATCH net-next v2 1/4] selftests: net: Move some UAPI header inclusions after libc ones

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Message-ID: <20260130111949-4b4eb870-6df7-4026-a48c-730fa8660ad6@linutronix.de>
Date: Fri, 30 Jan 2026 11:22:18 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Matthieu Baerts <matttbe@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-api@...r.kernel.org, Arnd Bergmann <arnd@...db.de>, linux-kselftest@...r.kernel.org, 
	mptcp@...ts.linux.dev, linux-security-module@...r.kernel.org, bpf@...r.kernel.org, 
	libc-alpha@...rceware.org
Subject: Re: [PATCH net-next v2 1/4] selftests: net: Move some UAPI header
 inclusions after libc ones

(trimmed the recipient list)

Hi Matt,

On Mon, Jan 26, 2026 at 07:13:50PM +0100, Matthieu Baerts wrote:
> On 20/01/2026 15:10, Thomas Weißschuh wrote:
> > Interleaving inclusions of UAPI headers and libc headers is problematic.
> > Both sets of headers define conflicting symbols. To enable their
> > coexistence a compatibility-mechanism is in place.
> > 
> > An upcoming change will define 'struct sockaddr' from linux/socket.h.
> > However sys/socket.h from libc does not yet handle this case and a
> > symbol conflict will arise.
> > 
> > Furthermore libc-compat.h evaluates the state of the libc
> > inclusions only once, at the point it is included first. If another
> > problematic header from libc is included later, symbol conflicts arise.
> > This will trigger other duplicate definitions when linux/libc-compat.h
> > is added to linux/socket.h
> > 
> > Move the inclusion of UAPI headers after the inclusion of the glibc
> > ones, so the libc-compat.h continues to work correctly.
> 
> Thank you for looking at this!
> 
> Here is my (late, sorry) review for the modifications related to MPTCP:
> > diff --git a/tools/testing/selftests/net/mptcp/mptcp_diag.c b/tools/testing/selftests/net/mptcp/mptcp_diag.c
> > index 8e0b1b8d84b6..af25ebfd2915 100644
> > --- a/tools/testing/selftests/net/mptcp/mptcp_diag.c
> > +++ b/tools/testing/selftests/net/mptcp/mptcp_diag.c
> > @@ -1,11 +1,6 @@
> >  // SPDX-License-Identifier: GPL-2.0
> >  /* Copyright (c) 2025, Kylin Software */
> >  
> > -#include <linux/sock_diag.h>
> > -#include <linux/rtnetlink.h>
> > -#include <linux/inet_diag.h>
> > -#include <linux/netlink.h>
> > -#include <linux/compiler.h>
> >  #include <sys/socket.h>
> >  #include <netinet/in.h>
> >  #include <linux/tcp.h>
> 
> There is a remaining one (linux/tcp.h) here that you might want to move
> below too.

Good point.

> > @@ -17,6 +12,12 @@
> >  #include <errno.h>
> >  #include <stdio.h>
> >  
> > +#include <linux/sock_diag.h>
> > +#include <linux/rtnetlink.h>
> > +#include <linux/inet_diag.h>
> > +#include <linux/netlink.h>
> > +#include <linux/compiler.h>
> 
> Note that I just noticed this is the only file from this directory where
> the "includes" are not sorted by type and alphabetical order, see
> pm_nl_ctl.c as an example. A bit of a detail, but if you plan to send a
> v2, do you mind doing that too here while at it, please?

I'll send a v3 during the next cycle.

> If not, I can look at that later, but better to avoid doing that in
> parallel.

If you want to fix this up already during this cycle,
that would also be most welcome.


Thomas