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diff --git a/Documentation/userspace-api/netlink/c-code-gen.rst b/Documentation/userspace-api/netlink/c-code-gen.rst new file mode 100644 index 0000000000..89de42c133 --- /dev/null +++ b/Documentation/userspace-api/netlink/c-code-gen.rst @@ -0,0 +1,107 @@ +.. SPDX-License-Identifier: BSD-3-Clause + +============================== +Netlink spec C code generation +============================== + +This document describes how Netlink specifications are used to render +C code (uAPI, policies etc.). It also defines the additional properties +allowed in older families by the ``genetlink-c`` protocol level, +to control the naming. + +For brevity this document refers to ``name`` properties of various +objects by the object type. For example ``$attr`` is the value +of ``name`` in an attribute, and ``$family`` is the name of the +family (the global ``name`` property). + +The upper case is used to denote literal values, e.g. ``$family-CMD`` +means the concatenation of ``$family``, a dash character, and the literal +``CMD``. + +The names of ``#defines`` and enum values are always converted to upper case, +and with dashes (``-``) replaced by underscores (``_``). + +If the constructed name is a C keyword, an extra underscore is +appended (``do`` -> ``do_``). + +Globals +======= + +``c-family-name`` controls the name of the ``#define`` for the family +name, default is ``$family-FAMILY-NAME``. + +``c-version-name`` controls the name of the ``#define`` for the version +of the family, default is ``$family-FAMILY-VERSION``. + +``max-by-define`` selects if max values for enums are defined as a +``#define`` rather than inside the enum. + +Definitions +=========== + +Constants +--------- + +Every constant is rendered as a ``#define``. +The name of the constant is ``$family-$constant`` and the value +is rendered as a string or integer according to its type in the spec. + +Enums and flags +--------------- + +Enums are named ``$family-$enum``. The full name can be set directly +or suppressed by specifying the ``enum-name`` property. +Default entry name is ``$family-$enum-$entry``. +If ``name-prefix`` is specified it replaces the ``$family-$enum`` +portion of the entry name. + +Boolean ``render-max`` controls creation of the max values +(which are enabled by default for attribute enums). + +Attributes +========== + +Each attribute set (excluding fractional sets) is rendered as an enum. + +Attribute enums are traditionally unnamed in netlink headers. +If naming is desired ``enum-name`` can be used to specify the name. + +The default attribute name prefix is ``$family-A`` if the name of the set +is the same as the name of the family and ``$family-A-$set`` if the names +differ. The prefix can be overridden by the ``name-prefix`` property of a set. +The rest of the section will refer to the prefix as ``$pfx``. + +Attributes are named ``$pfx-$attribute``. + +Attribute enums end with two special values ``__$pfx-MAX`` and ``$pfx-MAX`` +which are used for sizing attribute tables. +These two names can be specified directly with the ``attr-cnt-name`` +and ``attr-max-name`` properties respectively. + +If ``max-by-define`` is set to ``true`` at the global level ``attr-max-name`` +will be specified as a ``#define`` rather than an enum value. + +Operations +========== + +Operations are named ``$family-CMD-$operation``. +If ``name-prefix`` is specified it replaces the ``$family-CMD`` +portion of the name. + +Similarly to attribute enums operation enums end with special count and max +attributes. For operations those attributes can be renamed with +``cmd-cnt-name`` and ``cmd-max-name``. Max will be a define if ``max-by-define`` +is ``true``. + +Multicast groups +================ + +Each multicast group gets a define rendered into the kernel uAPI header. +The name of the define is ``$family-MCGRP-$group``, and can be overwritten +with the ``c-define-name`` property. + +Code generation +=============== + +uAPI header is assumed to come from ``<linux/$family.h>`` in the default header +search path. It can be changed using the ``uapi-header`` global property. |