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

From: Matthias Maennich
Date: Wed Aug 28 2019 - 06:56:36 EST

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

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:


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

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@xxxxxxxx>
Reviewed-by: Martijn Coenen <maco@xxxxxxxxxxx>
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
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(sym, sec) \
#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")