doc: move namespaces.rst from kbuild/ to core-api/

We discussed a better location for this file, and agreed that
core-api/ is a good fit. Rename it to symbol-namespaces.rst
for disambiguation, and also add it to index.rst and MAINTAINERS.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>

1 files changed, 0 insertions, 154 deletions

diff --git a/Documentation/kbuild/namespaces.rst b/Documentation/kbuild/namespaces.rst
deleted file mode 100644
index 982ed7b568ac..000000000000
--- a/Documentation/kbuild/namespaces.rst
+++ /dev/null
@@ -1,154 +0,0 @@
-=================
-Symbol Namespaces
-=================
-
-The following document describes how to use Symbol Namespaces to structure the
-export surface of in-kernel symbols exported through the family of
-EXPORT_SYMBOL() macros.
-
-.. Table of Contents
-
-	=== 1 Introduction
-	=== 2 How to define Symbol Namespaces
-	   --- 2.1 Using the EXPORT_SYMBOL macros
-	   --- 2.2 Using the DEFAULT_SYMBOL_NAMESPACE define
-	=== 3 How to use Symbols exported in Namespaces
-	=== 4 Loading Modules that use namespaced Symbols
-	=== 5 Automatically creating MODULE_IMPORT_NS statements
-
-1. Introduction
-===============
-
-Symbol Namespaces have been introduced as a means to structure the export
-surface of the in-kernel API. It allows subsystem maintainers to partition
-their exported symbols into separate namespaces. That is useful for
-documentation purposes (think of the SUBSYSTEM_DEBUG namespace) as well as for
-limiting the availability of a set of symbols for use in other parts of the
-kernel. As of today, modules that make use of symbols exported into namespaces,
-are required to import the namespace. Otherwise the kernel will, depending on
-its configuration, reject loading the module or warn about a missing import.
-
-2. How to define Symbol Namespaces
-==================================
-
-Symbols can be exported into namespace using different methods. All of them are
-changing the way EXPORT_SYMBOL and friends are instrumented to create ksymtab
-entries.
-
-2.1 Using the EXPORT_SYMBOL macros
-==================================
-
-In addition to the macros EXPORT_SYMBOL() and EXPORT_SYMBOL_GPL(), that allow
-exporting of kernel symbols to the kernel symbol table, variants of these are
-available to export symbols into a certain namespace: EXPORT_SYMBOL_NS() and
-EXPORT_SYMBOL_NS_GPL(). They take one additional argument: the namespace.
-Please note that due to macro expansion that argument needs to be a
-preprocessor symbol. E.g. to export the symbol `usb_stor_suspend` into the
-namespace `USB_STORAGE`, use::
-
-	EXPORT_SYMBOL_NS(usb_stor_suspend, USB_STORAGE);
-
-The corresponding ksymtab entry struct `kernel_symbol` will have the member
-`namespace` set accordingly. A symbol that is exported without a namespace will
-refer to `NULL`. There is no default namespace if none is defined. `modpost`
-and kernel/module.c make use the namespace at build time or module load time,
-respectively.
-
-2.2 Using the DEFAULT_SYMBOL_NAMESPACE define
-=============================================
-
-Defining namespaces for all symbols of a subsystem can be very verbose and may
-become hard to maintain. Therefore a default define (DEFAULT_SYMBOL_NAMESPACE)
-is been provided, that, if set, will become the default for all EXPORT_SYMBOL()
-and EXPORT_SYMBOL_GPL() macro expansions that do not specify a namespace.
-
-There are multiple ways of specifying this define and it depends on the
-subsystem and the maintainer's preference, which one to use. The first option
-is to define the default namespace in the `Makefile` of the subsystem. E.g. 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 will affect all EXPORT_SYMBOL() and EXPORT_SYMBOL_GPL() statements. A
-symbol exported with EXPORT_SYMBOL_NS() while this definition is present, will
-still be exported into the namespace that is passed as the namespace argument
-as this argument has preference over a default symbol namespace.
-
-A second option to define the default namespace is directly in the compilation
-unit as preprocessor statement. The above example would then read::
-
-	#undef  DEFAULT_SYMBOL_NAMESPACE
-	#define DEFAULT_SYMBOL_NAMESPACE USB_COMMON
-
-within the corresponding compilation unit before any EXPORT_SYMBOL macro is
-used.
-
-3. How to use Symbols exported in Namespaces
-============================================
-
-In order to use symbols that are exported into namespaces, kernel modules need
-to explicitly import these namespaces. Otherwise the kernel might reject to
-load the module. The module code is required to use the macro MODULE_IMPORT_NS
-for the namespaces it uses symbols from. E.g. a module using the
-usb_stor_suspend symbol from above, needs to import the namespace USB_STORAGE
-using a statement like::
-
-	MODULE_IMPORT_NS(USB_STORAGE);
-
-This will create a `modinfo` tag in the module for each imported namespace.
-This has the side effect, that the imported namespaces of a module can be
-inspected with modinfo::
-
-	$ modinfo drivers/usb/storage/ums-karma.ko
-	[...]
-	import_ns:      USB_STORAGE
-	[...]
-
-
-It is advisable to add the MODULE_IMPORT_NS() statement close to other module
-metadata definitions like MODULE_AUTHOR() or MODULE_LICENSE(). Refer to section
-5. for a way to create missing import statements automatically.
-
-4. Loading Modules that use namespaced Symbols
-==============================================
-
-At module loading time (e.g. `insmod`), the kernel will check each symbol
-referenced from the module for its availability and whether the namespace it
-might be exported to has been imported by the module. The default behaviour of
-the kernel is to reject loading modules that don't specify sufficient imports.
-An error will be logged and loading will be failed with EINVAL. In order to
-allow loading of modules that don't satisfy this precondition, a configuration
-option is available: Setting MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS=y will
-enable loading regardless, but will emit a warning.
-
-5. Automatically creating MODULE_IMPORT_NS statements
-=====================================================
-
-Missing namespaces imports can easily be detected at build time. In fact,
-modpost will emit a warning if a module uses a symbol from a namespace
-without importing it.
-MODULE_IMPORT_NS() statements will usually be added at a definite location
-(along with other module meta data). To make the life of module authors (and
-subsystem maintainers) easier, a script and make target is available to fixup
-missing imports. Fixing missing imports can be done with::
-
-	$ make nsdeps
-
-A typical scenario for module authors would be::
-
-	- write code that depends on a symbol from a not imported namespace
-	- `make`
-	- notice the warning of modpost telling about a missing import
-	- run `make nsdeps` to add the import to the correct code location
-
-For subsystem maintainers introducing a namespace, the steps are very similar.
-Again, `make nsdeps` will eventually add the missing namespace imports for
-in-tree modules::
-
-	- move or add symbols to a namespace (e.g. with EXPORT_SYMBOL_NS())
-	- `make` (preferably with an allmodconfig to cover all in-kernel
-	  modules)
-	- notice the warning of modpost telling about a missing import
-	- run `make nsdeps` to add the import to the correct code location
-