linux-kernel - [PATCH v5 06/11] export: allow definition default namespaces in Makefiles or sources

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Message-Id: <20190906103235.197072-7-maennich@google.com>
Date:   Fri,  6 Sep 2019 11:32:30 +0100
From:   Matthias Maennich <maennich@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     kernel-team@...roid.com, maennich@...gle.com, arnd@...db.de,
        gregkh@...uxfoundation.org, jeyu@...nel.org,
        joel@...lfernandes.org, lucas.de.marchi@...il.com,
        maco@...roid.com, sspatil@...gle.com, will@...nel.org,
        yamada.masahiro@...ionext.com, linux-kbuild@...r.kernel.org,
        linux-modules@...r.kernel.org, linux-usb@...r.kernel.org,
        usb-storage@...ts.one-eyed-alien.net
Subject: [PATCH v5 06/11] export: allow definition default namespaces in
 Makefiles or sources

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>
Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 d59461e71478..2c5468d8ea9a 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")
-- 
2.23.0.187.g17f5b7556c-goog