linux-kernel - Re: [PATCH 0/6] Symbol namespaces

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Date:   Mon, 16 Jul 2018 17:33:56 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Martijn Coenen <maco@...roid.com>
Cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Oliver Neukum <oneukum@...e.com>,
        Arnd Bergmann <arnd@...db.de>, Jessica Yu <jeyu@...nel.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Sam Ravnborg <sam@...nborg.org>, linux-kbuild@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-usb@...r.kernel.org,
        usb-storage@...ts.one-eyed-alien.net, linux-scsi@...r.kernel.org,
        linux-arch@...r.kernel.org, maco@...gle.com, sspatil@...gle.com,
        malchev@...gle.com, joelaf@...gle.com
Subject: Re: [PATCH 0/6] Symbol namespaces

On Mon, Jul 16, 2018 at 02:21:19PM +0200, Martijn Coenen wrote:
> As of Linux 4.17, there are more than 30000 exported symbols
> in the kernel. There seems to be some consensus amongst
> kernel devs that the export surface is too large, and hard
> to reason about.
> 
> Generally, these symbols fall in one of these categories:
> 1) Symbols actually meant for drivers
> 2) Symbols that are only exported because functionality is
>    split over multiple modules, yet they really shouldn't
>    be used by modules outside of their own subsystem
> 3) Symbols really only meant for in-tree use
> 
> When module developers try to upstream their code, it
> regularly turns out that they are using exported symbols
> that they really shouldn't be using. This problem is even
> bigger for drivers that are currently out-of-tree, which
> may be using many symbols that they shouldn't be using,
> and that break when those symbols are removed or modified.
> 
> This patch allows subsystem maintainers to partition their
> exported symbols into separate namespaces, and module
> authors to import such namespaces only when needed.
> 
> This allows subsystem maintainers to more easily limit
> availability of these namespaced symbols to other parts of
> the kernel. It can also be used to partition the set of
> exported symbols for documentation purposes; for example,
> a set of symbols that is really only used for debugging
> could be in a "SUBSYSTEM_DEBUG" namespace.

To give people a bit more background here, this is something that both
Andi Kleen and I talked about over a decade ago.  Martijn based his work
on Andi's original patches and made them all work well, something that I
was unable to do :)

His addition of using the build system to automatically generate a patch
for a subsystem based on the symbol namespace changes is frickin
amazing.

Great work here, this is something that I have wanted for the kernel for
a long time.

greg k-h