Documentation/networking/xsk-tx-metadata.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 AF_XDP TX Metadata
8 via :doc:`af_xdp`. Refer to :doc:`xdp-rx-metadata` on how to access similar
9 metadata on the receive side.
14 The headroom for the metadata is reserved via ``tx_metadata_len`` in
15 ``struct xdp_umem_reg``. The metadata length is therefore the same for
16 every socket that shares the same umem. The metadata layout is a fixed UAPI,
21 The headroom and the metadata itself should be located right before
22 ``xdp_desc->addr`` in the umem frame. Within a frame, the metadata
27     +-----------------+---------+----------------------------+
29     +-----------------+---------+----------------------------+
32                           xdp_desc->addr
36 use ``xdp_desc->addr - tx_metadata_len`` to locate
38 any metadata (i.e., the ones that don't have ``XDP_TX_METADATA`` option),
39 the metadata area is ignored by the kernel as well.
43 - ``XDP_TXMD_FLAGS_TIMESTAMP``: requests the device to put transmission
45 - ``XDP_TXMD_FLAGS_CHECKSUM``: requests the device to calculate L4
52 bit in the ``options`` field. Also note that in a multi-buffer packet
53 only the first chunk should carry the metadata.
68 Refer to ``xsk-flags`` features bitmask in
71 - ``tx-timestamp``: device supports ``XDP_TXMD_FLAGS_TIMESTAMP``
72 - ``tx-checksum``: device supports ``XDP_TXMD_FLAGS_CHECKSUM``
80 program that handles TX metadata. Also see https://github.com/fomichev/xskgen
81 for a more bare-bones example.