linux-kernel - Re: [PATCH] kbuild: announce removal of SUBDIRS if used

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Date:   Fri, 23 Nov 2018 08:04:39 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kbuild@...r.kernel.org
Cc:     Sam Ravnborg <sam@...nborg.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-watchdog@...r.kernel.org,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-doc@...r.kernel.org, Jim Cromie <jim.cromie@...il.com>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        Brian Norris <computersforpeace@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org,
        Boris Brezillon <boris.brezillon@...tlin.com>
Subject: Re: [PATCH] kbuild: announce removal of SUBDIRS if used

On Wed, 2018-11-21 at 00:04 +0900, Masahiro Yamada wrote:
> SUBDIRS has been kept as a backward compatibility since
> commit ("[PATCH] kbuild: external module support") in 2002.
> 
> We do not need multiple ways to do the same thing, so I will remove
> SUBDIRS after the Linux 5.3 release. I cleaned up in-tree code, and
> updated the document so that nobody would try to use it.
> 
> Meanwhile, display the following warning if SUBDIRS is used.
> 
> Makefile:189: ================= WARNING ================
> Makefile:190: 'SUBDIRS' will be removed after Linux 5.3
> Makefile:191: Please use 'M=' or 'KBUILD_EXTMOD' instead
> Makefile:192: ==========================================
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

No, please don't do this. This is effectively a kernel←→user ABI.

The instructions for building a kernel module have been this, for
*ages*:

 echo 'obj-m := mymod.o' > Makefile
 make -C /lib/modules/`uname -r`/build SUBDIRS=`pwd`

People have muscle memory, they have it encoded into various of their
own makefiles and build scripts. Please don't make it stop working
unless there's actually a really good reason to do so.



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