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.. SPDX-License-Identifier: GPL-2.0-only
.. Copyright (C) 2022 Red Hat, Inc.
========
Redirect
========
XDP_REDIRECT
############
Supported maps
--------------
XDP_REDIRECT works with the following map types:
- ``BPF_MAP_TYPE_DEVMAP``
- ``BPF_MAP_TYPE_DEVMAP_HASH``
- ``BPF_MAP_TYPE_CPUMAP``
- ``BPF_MAP_TYPE_XSKMAP``
For more information on these maps, please see the specific map documentation.
Process
-------
.. kernel-doc:: net/core/filter.c
:doc: xdp redirect
.. note::
Not all drivers support transmitting frames after a redirect, and for
those that do, not all of them support non-linear frames. Non-linear xdp
bufs/frames are bufs/frames that contain more than one fragment.
Debugging packet drops
----------------------
Silent packet drops for XDP_REDIRECT can be debugged using:
- bpf_trace
- perf_record
bpf_trace
^^^^^^^^^
The following bpftrace command can be used to capture and count all XDP tracepoints:
.. code-block:: none
sudo bpftrace -e 'tracepoint:xdp:* { @cnt[probe] = count(); }'
Attaching 12 probes...
^C
@cnt[tracepoint:xdp:mem_connect]: 18
@cnt[tracepoint:xdp:mem_disconnect]: 18
@cnt[tracepoint:xdp:xdp_exception]: 19605
@cnt[tracepoint:xdp:xdp_devmap_xmit]: 1393604
@cnt[tracepoint:xdp:xdp_redirect]: 22292200
.. note::
The various xdp tracepoints can be found in ``source/include/trace/events/xdp.h``
The following bpftrace command can be used to extract the ``ERRNO`` being returned as
part of the err parameter:
.. code-block:: none
sudo bpftrace -e \
'tracepoint:xdp:xdp_redirect*_err {@redir_errno[-args->err] = count();}
tracepoint:xdp:xdp_devmap_xmit {@devmap_errno[-args->err] = count();}'
perf record
^^^^^^^^^^^
The perf tool also supports recording tracepoints:
.. code-block:: none
perf record -a -e xdp:xdp_redirect_err \
-e xdp:xdp_redirect_map_err \
-e xdp:xdp_exception \
-e xdp:xdp_devmap_xmit
References
===========
- https://github.com/xdp-project/xdp-tutorial/tree/master/tracing02-xdp-monitor
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