linux-kernel - Re: [usb-storage] Re: [PATCH v4 12/12] RFC: watchdog: export core symbols in WATCHDOG

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Date:   Thu, 5 Sep 2019 13:16:17 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Matthew Dharm <mdharm-usb@...-eyed-alien.net>,
        Guenter Roeck <linux@...ck-us.net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Matthias Maennich <maennich@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Lucas De Marchi <lucas.de.marchi@...il.com>,
        Martijn Coenen <maco@...roid.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Will Deacon <will@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        linux-modules@...r.kernel.org,
        linux-usb <linux-usb@...r.kernel.org>,
        USB Mass Storage on Linux 
        <usb-storage@...ts.one-eyed-alien.net>,
        LINUXWATCHDOG <linux-watchdog@...r.kernel.org>
Subject: Re: [usb-storage] Re: [PATCH v4 12/12] RFC: watchdog: export core
 symbols in WATCHDOG_CORE namespace

+++ Arnd Bergmann [05/09/19 12:52 +0200]:
>On Thu, Sep 5, 2019 at 12:41 PM Jessica Yu <jeyu@...nel.org> wrote:
>> +++ Matthew Dharm [04/09/19 09:16 -0700]:
>> >On Wed, Sep 4, 2019 at 5:12 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
>> >HOWEVER, I have one question:  If these patches are included, and
>> >someone wants to introduce a bit of code which needs to use two
>> >symbols from different namespaces but with the same name, can that be
>> >done?  That is, if driver A has symbol 'foo' and driver B has symbol
>> >'foo' (both in their respective namespaces), and driver C wants to use
>> >A.foo and B.foo, can that be supported?
>>
>> As of now, we currently don't support this - modpost will warn if a
>> symbol is exported more than once (across modules + vmlinux), and the
>> module loader currently assumes exported symbol names are unique.  Do
>> you have a concrete use case? If there is a strong need for this, I
>> don't think it'd be too hard to implement.
>
>I think what would prevent this from working in general is that having
>two modules with the same exported symbol in different namespaces
>won't link if you try to build both modules into the kernel itself.
>
>      Arnd

Ah yeah, you are right. I only tried building an identically named
exported symbol in a module and in the kernel, and there I got away
with a modpost warning. But this breaks when building the module into
the kernel, so I guess this is out of the question.

Thanks,

Jessica