Re: [PATCH v3 06/11] export: allow definition default namespaces in Makefiles or sources

[Matthias Maennich <maennich@google.com>]

On Wed, Aug 28, 2019 at 12:49:51PM +0200, Jessica Yu wrote:
>+++ Matthias Maennich [21/08/19 12:49 +0100]:
>>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.
>
>This changelog provides a good summary of how to use
>DEFAULT_SYMBOL_NAMESPACE, I wonder if we should explicitly document
>its proper usage somewhere? (along with EXPORT_SYMBOL_NS*)
>The EXPORT_SYMBOL API is briefly documented in
>Documentation/kernel-hacking/hacking.rst - it might be slightly dated,
>but perhaps it'd fit there best?

I will add documentation along with the commits. Not only for the
macros, but in general to describe the feature.

>>Suggested-by: Arnd Bergmann <arnd@arndb.de>
>>Reviewed-by: Martijn Coenen <maco@android.com>
>>Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>Signed-off-by: Matthias Maennich <maennich@google.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
>>