linux-kernel - Re: [PATCH net-next] Remove DECnet support from kernel

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Message-ID: <po9s7-9snp-9so3-n6r5-qs217ss1633o@vanv.qr>
Date:   Mon, 9 Jan 2023 09:14:34 +0100 (CET)
From:   Jan Engelhardt <jengelh@...i.de>
To:     Jiri Slaby <jirislaby@...nel.org>
cc:     Stephen Hemminger <stephen@...workplumber.org>,
        netdev@...r.kernel.org, David Ahern <dsahern@...nel.org>,
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Subject: Re: [PATCH net-next] Remove DECnet support from kernel


On Monday 2023-01-09 08:04, Jiri Slaby wrote:
> On 18. 08. 22, 2:43, Stephen Hemminger wrote:
>> DECnet is an obsolete network protocol
>
> this breaks userspace. Some projects include linux/dn.h:
>
>  https://codesearch.debian.net/search?q=include.*linux%2Fdn.h&literal=0
>
> I found Trinity fails to build:
> net/proto-decnet.c:5:10: fatal error: linux/dn.h: No such file or directory
>     5 | #include <linux/dn.h>
>
> Should we provide the above as empty files?

Not a good idea. There may be configure tests / code that merely checks for
dn.h existence without checking for specific contents/defines. If you provide
empty files, this would fail to build:

#include "config.h"
#ifdef HAVE_LINUX_DN_H
#	include <linux/dn.h>
#endif
int main() {
#ifdef HAVE_LINUX_DN_H
	socket(AF_DECNET, 0, DNPROTO_NSP); // or whatever
#else
	...
#endif
}

So, with my distro hat on, outright removing header files feels like the
slightly lesser of two evils. Given the task to port $arbitrary software
between operating systems, absent header files is something more or less
"regularly" encountered, so one could argue we are "trained" to deal with it.
But missing individual defines is a much deeper dive into the APIs and
software to patch it out.