linux-kernel - Re: [PATCH v2 06/10] export: allow definition default namespaces in Makefiles or sources

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Date:   Tue, 13 Aug 2019 20:16:40 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Matthias Maennich <maennich@...gle.com>
Cc:     linux-kernel@...r.kernel.org, maco@...roid.com,
        kernel-team@...roid.com, arnd@...db.de, geert@...ux-m68k.org,
        hpa@...or.com, jeyu@...nel.org, joel@...lfernandes.org,
        kstewart@...uxfoundation.org, linux-arch@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-modules@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-usb@...r.kernel.org, lucas.de.marchi@...il.com,
        maco@...gle.com, michal.lkml@...kovi.net, mingo@...hat.com,
        oneukum@...e.com, pombredanne@...b.com, sam@...nborg.org,
        sboyd@...eaurora.org, sspatil@...gle.com,
        stern@...land.harvard.edu, tglx@...utronix.de,
        usb-storage@...ts.one-eyed-alien.net, x86@...nel.org,
        yamada.masahiro@...ionext.com,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v2 06/10] export: allow definition default namespaces in
 Makefiles or sources

On Tue, Aug 13, 2019 at 01:17:03PM +0100, Matthias Maennich wrote:
> To avoid excessive usage of EXPORT_SYMBOL_NS(sym, MY_NAMESPACE), where
> MY_NAMESPACE will always be the namespace we are exporting to, allow
> exporting all definitions of EXPORT_SYMBOL() and friends by defining
> DEFAULT_SYMBOL_NAMESPACE.
> 
> For example, to export all symbols defined in usb-common into the
> namespace USB_COMMON, add a line like this to drivers/usb/common/Makefile:
> 
>   ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=USB_COMMON
> 
> That is equivalent to changing all EXPORT_SYMBOL(sym) definitions to
> EXPORT_SYMBOL_NS(sym, USB_COMMON). Subsequently all symbol namespaces
> functionality will apply.
> 
> Another way of making use of this feature is to define the namespace
> within source or header files similar to how TRACE_SYSTEM defines are
> used:
>   #undef DEFAULT_SYMBOL_NAMESPACE
>   #define DEFAULT_SYMBOL_NAMESPACE USB_COMMON
> 
> Please note that, as opposed to TRACE_SYSTEM, DEFAULT_SYMBOL_NAMESPACE
> has to be defined before including include/linux/export.h.
> 
> If DEFAULT_SYMBOL_NAMESPACE is defined, a symbol can still be exported
> to another namespace by using EXPORT_SYMBOL_NS() and friends with
> explicitly specifying the namespace.
> 
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Reviewed-by: Martijn Coenen <maco@...roid.com>
> Signed-off-by: Matthias Maennich <maennich@...gle.com>
> ---
>  include/linux/export.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/export.h b/include/linux/export.h
> index 8e12e05444d1..1fb243abdbc4 100644
> --- a/include/linux/export.h
> +++ b/include/linux/export.h
> @@ -166,6 +166,12 @@ struct kernel_symbol {
>  #define __EXPORT_SYMBOL ___EXPORT_SYMBOL
>  #endif
>  
> +#ifdef DEFAULT_SYMBOL_NAMESPACE
> +#undef __EXPORT_SYMBOL
> +#define __EXPORT_SYMBOL(sym, sec)				\
> +	__EXPORT_SYMBOL_NS(sym, sec, DEFAULT_SYMBOL_NAMESPACE)
> +#endif
> +
>  #define EXPORT_SYMBOL(sym) __EXPORT_SYMBOL(sym, "")
>  #define EXPORT_SYMBOL_GPL(sym) __EXPORT_SYMBOL(sym, "_gpl")
>  #define EXPORT_SYMBOL_GPL_FUTURE(sym) __EXPORT_SYMBOL(sym, "_gpl_future")
> -- 
> 2.23.0.rc1.153.gdeed80330f-goog
> 

Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>