Documentation/networking/xdp-rx-metadata.rst

1 .. SPDX-License-Identifier: GPL-2.0
22 .. kernel-doc:: net/core/xdp.c
25 .. kernel-doc:: net/core/xdp.c
28 .. kernel-doc:: net/core/xdp.c
35 metadata available in which case the driver returns ``-ENODATA``.
38 implemented, the default ones that return ``-EOPNOTSUPP`` will be used
42 Within an XDP frame, the metadata layout (accessed via ``xdp_buff``) is
45   +----------+-----------------+------+
47   +----------+-----------------+------+
50    xdp_buff->data_meta   xdp_buff->data
60 :doc:`af_xdp` use-case implies that there is a contract between the BPF
62 the final consumer. Thus the BPF program manually allocates a fixed number of
65 ``xsk_umem__get_data() - METADATA_SIZE`` to locate that metadata.
67 ``METADATA_SIZE`` is an application-specific constant (``AF_XDP`` receive
70 Here is the ``AF_XDP`` consumer layout (note missing ``data_meta`` pointer)::
72   +----------+-----------------+------+
74   +----------+-----------------+------+
77                         rx_desc->address
85 the descriptors and populate ``skb`` metadata when doing this ``xdp_buff->skb``
87 ``skbs``. However, TC-BPF programs can access the XDP metadata area using
120 netlink. See ``xdp-rx-metadata-features`` attribute set in