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| author | Maryam Tahhan <mtahhan@redhat.com> | 2022-11-15 17:49:21 +0300 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2022-11-19 01:16:31 +0300 |
| commit | d1e91173cd29ba13c5953d1820a7543140feec93 (patch) | |
| tree | cc7551892865dd8ee07e5fac04710e6cc2c2da90 /Documentation/bpf/redirect.rst | |
| parent | f80e16b614f303b520465b7c704ff89fab800f2f (diff) | |
| download | linux-d1e91173cd29ba13c5953d1820a7543140feec93.tar.xz | |
bpf, docs: DEVMAPs and XDP_REDIRECT
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
Diffstat (limited to 'Documentation/bpf/redirect.rst')
| -rw-r--r-- | Documentation/bpf/redirect.rst | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/Documentation/bpf/redirect.rst b/Documentation/bpf/redirect.rst new file mode 100644 index 000000000000..2fa2b0b05004 --- /dev/null +++ b/Documentation/bpf/redirect.rst @@ -0,0 +1,81 @@ +.. 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 |