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Add documentation for BPF_MAP_TYPE_DEVMAP and BPF_MAP_TYPE_DEVMAP_HASH including kernel version introduced, usage and examples. Add documentation that describes XDP_REDIRECT. Signed-off-by: Maryam Tahhan <mtahhan@redhat.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20221115144921.165483-1-mtahhan@redhat.com
81 lines
2 KiB
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81 lines
2 KiB
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.. SPDX-License-Identifier: GPL-2.0-only
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.. Copyright (C) 2022 Red Hat, Inc.
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========
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Redirect
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========
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XDP_REDIRECT
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############
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Supported maps
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--------------
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XDP_REDIRECT works with the following map types:
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- ``BPF_MAP_TYPE_DEVMAP``
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- ``BPF_MAP_TYPE_DEVMAP_HASH``
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- ``BPF_MAP_TYPE_CPUMAP``
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- ``BPF_MAP_TYPE_XSKMAP``
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For more information on these maps, please see the specific map documentation.
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Process
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-------
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.. kernel-doc:: net/core/filter.c
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:doc: xdp redirect
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.. note::
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Not all drivers support transmitting frames after a redirect, and for
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those that do, not all of them support non-linear frames. Non-linear xdp
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bufs/frames are bufs/frames that contain more than one fragment.
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Debugging packet drops
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----------------------
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Silent packet drops for XDP_REDIRECT can be debugged using:
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- bpf_trace
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- perf_record
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bpf_trace
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^^^^^^^^^
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The following bpftrace command can be used to capture and count all XDP tracepoints:
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.. code-block:: none
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sudo bpftrace -e 'tracepoint:xdp:* { @cnt[probe] = count(); }'
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Attaching 12 probes...
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^C
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@cnt[tracepoint:xdp:mem_connect]: 18
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@cnt[tracepoint:xdp:mem_disconnect]: 18
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@cnt[tracepoint:xdp:xdp_exception]: 19605
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@cnt[tracepoint:xdp:xdp_devmap_xmit]: 1393604
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@cnt[tracepoint:xdp:xdp_redirect]: 22292200
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.. note::
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The various xdp tracepoints can be found in ``source/include/trace/events/xdp.h``
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The following bpftrace command can be used to extract the ``ERRNO`` being returned as
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part of the err parameter:
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.. code-block:: none
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sudo bpftrace -e \
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'tracepoint:xdp:xdp_redirect*_err {@redir_errno[-args->err] = count();}
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tracepoint:xdp:xdp_devmap_xmit {@devmap_errno[-args->err] = count();}'
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perf record
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^^^^^^^^^^^
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The perf tool also supports recording tracepoints:
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.. code-block:: none
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perf record -a -e xdp:xdp_redirect_err \
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-e xdp:xdp_redirect_map_err \
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-e xdp:xdp_exception \
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-e xdp:xdp_devmap_xmit
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References
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===========
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- https://github.com/xdp-project/xdp-tutorial/tree/master/tracing02-xdp-monitor
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