summaryrefslogtreecommitdiff
path: root/Documentation/bpf/redirect.rst
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/bpf/redirect.rst')
-rw-r--r--Documentation/bpf/redirect.rst81
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