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

    >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
    >

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