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authorGreg Kroah-Hartman <gregkh@linuxfoundation.org>2025-08-20 20:42:41 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2025-08-20 20:42:41 +0300
commit5c40cd7db64a2949f268d7467b9be551a565d14b (patch)
treefb8a67f6edcb0c9922c256a598d675c1c04051d6 /Documentation/core-api/symbol-namespaces.rst
parent8bde384a2090759efc9b92f34300887d418a2a3a (diff)
parent25bf10be219d37d2fb221c93816a913f5f735530 (diff)
downloadlinux-rolling-stable.tar.xz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/core-api/symbol-namespaces.rst')
-rw-r--r--Documentation/core-api/symbol-namespaces.rst47
1 files changed, 18 insertions, 29 deletions
diff --git a/Documentation/core-api/symbol-namespaces.rst b/Documentation/core-api/symbol-namespaces.rst
index c6f59c5e2564..32fc73dc5529 100644
--- a/Documentation/core-api/symbol-namespaces.rst
+++ b/Documentation/core-api/symbol-namespaces.rst
@@ -6,18 +6,8 @@ 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
-===============
+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
@@ -31,15 +21,15 @@ its configuration, reject loading the module or warn about a missing import.
Additionally, it is possible to put symbols into a module namespace, strictly
limiting which modules are allowed to use these symbols.
-2. How to define Symbol Namespaces
-==================================
+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
-==================================
+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
@@ -57,8 +47,8 @@ refer to ``NULL``. There is no default namespace if none is defined. ``modpost``
and kernel/module/main.c make use the namespace at build time or module load
time, respectively.
-2.2 Using the DEFAULT_SYMBOL_NAMESPACE define
-=============================================
+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)
@@ -86,8 +76,8 @@ unit as preprocessor statement. The above example would then read::
within the corresponding compilation unit before the #include for
<linux/export.h>. Typically it's placed before the first #include statement.
-2.3 Using the EXPORT_SYMBOL_GPL_FOR_MODULES() macro
-===================================================
+Using the EXPORT_SYMBOL_GPL_FOR_MODULES() macro
+-----------------------------------------------
Symbols exported using this macro are put into a module namespace. This
namespace cannot be imported.
@@ -95,15 +85,15 @@ namespace cannot be imported.
The macro takes a comma separated list of module names, allowing only those
modules to access this symbol. Simple tail-globs are supported.
-For example:
+For example::
EXPORT_SYMBOL_GPL_FOR_MODULES(preempt_notifier_inc, "kvm,kvm-*")
will limit usage of this symbol to modules whoes name matches the given
patterns.
-3. How to use Symbols exported in Namespaces
-============================================
+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
@@ -125,11 +115,10 @@ inspected with modinfo::
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.
+metadata definitions like MODULE_AUTHOR() or MODULE_LICENSE().
-4. Loading Modules that use namespaced Symbols
-==============================================
+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
@@ -140,8 +129,8 @@ 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
-=====================================================
+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