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

[Greg KH]

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@xxxxxxxx>
> Reviewed-by: Martijn Coenen <maco@xxxxxxxxxxx>
> Signed-off-by: Matthias Maennich <maennich@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxxxxxxxxxxx>