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Diffstat (limited to 'Documentation/userspace-api/netlink/genetlink-legacy.rst')
-rw-r--r-- | Documentation/userspace-api/netlink/genetlink-legacy.rst | 88 |
1 files changed, 85 insertions, 3 deletions
diff --git a/Documentation/userspace-api/netlink/genetlink-legacy.rst b/Documentation/userspace-api/netlink/genetlink-legacy.rst index 3bf0bcdf21d8..802875a37a27 100644 --- a/Documentation/userspace-api/netlink/genetlink-legacy.rst +++ b/Documentation/userspace-api/netlink/genetlink-legacy.rst @@ -162,9 +162,91 @@ Other quirks (todo) Structures ---------- -Legacy families can define C structures both to be used as the contents -of an attribute and as a fixed message header. The plan is to define -the structs in ``definitions`` and link the appropriate attrs. +Legacy families can define C structures both to be used as the contents of +an attribute and as a fixed message header. Structures are defined in +``definitions`` and referenced in operations or attributes. Note that +structures defined in YAML are implicitly packed according to C +conventions. For example, the following struct is 4 bytes, not 6 bytes: + +.. code-block:: c + + struct { + u8 a; + u16 b; + u8 c; + } + +Any padding must be explicitly added and C-like languages should infer the +need for explicit padding from whether the members are naturally aligned. + +Here is the struct definition from above, declared in YAML: + +.. code-block:: yaml + + definitions: + - + name: message-header + type: struct + members: + - + name: a + type: u8 + - + name: b + type: u16 + - + name: c + type: u8 + +Fixed Headers +~~~~~~~~~~~~~ + +Fixed message headers can be added to operations using ``fixed-header``. +The default ``fixed-header`` can be set in ``operations`` and it can be set +or overridden for each operation. + +.. code-block:: yaml + + operations: + fixed-header: message-header + list: + - + name: get + fixed-header: custom-header + attribute-set: message-attrs + +Attributes +~~~~~~~~~~ + +A ``binary`` attribute can be interpreted as a C structure using a +``struct`` property with the name of the structure definition. The +``struct`` property implies ``sub-type: struct`` so it is not necessary to +specify a sub-type. + +.. code-block:: yaml + + attribute-sets: + - + name: stats-attrs + attributes: + - + name: stats + type: binary + struct: vport-stats + +C Arrays +-------- + +Legacy families also use ``binary`` attributes to encapsulate C arrays. The +``sub-type`` is used to identify the type of scalar to extract. + +.. code-block:: yaml + + attributes: + - + name: ports + type: binary + sub-type: u32 Multi-message DO ---------------- |