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authorStanislav Fomichev <sdf@google.com>2019-04-18 16:47:52 -0700
committerAlexei Starovoitov <ast@kernel.org>2019-04-18 16:59:42 -0700
commit80695946737dff4cfc1ecdefd4ebf300f132d8ee (patch)
tree74d70ac1348ef9558386c089911a99f1fe28aa47 /Documentation/networking
parent849f257f61ff7dde49d59c62802e5913ff7a7cbb (diff)
bpf: move BPF_PROG_TYPE_FLOW_DISSECTOR documentation to a new common place
In commit da7031491786 ("bpf: Document BPF_PROG_TYPE_CGROUP_SYSCTL") Andrey proposes to put per-prog type docs under Documentation/bpf/ Let's move flow dissector documentation there as well. Signed-off-by: Stanislav Fomichev <sdf@google.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'Documentation/networking')
-rw-r--r--Documentation/networking/bpf_flow_dissector.rst126
-rw-r--r--Documentation/networking/index.rst1
2 files changed, 0 insertions, 127 deletions
diff --git a/Documentation/networking/bpf_flow_dissector.rst b/Documentation/networking/bpf_flow_dissector.rst
deleted file mode 100644
index b375ae2ec2c4..000000000000
--- a/Documentation/networking/bpf_flow_dissector.rst
+++ /dev/null
@@ -1,126 +0,0 @@
-.. SPDX-License-Identifier: GPL-2.0
-
-==================
-BPF Flow Dissector
-==================
-
-Overview
-========
-
-Flow dissector is a routine that parses metadata out of the packets. It's
-used in the various places in the networking subsystem (RFS, flow hash, etc).
-
-BPF flow dissector is an attempt to reimplement C-based flow dissector logic
-in BPF to gain all the benefits of BPF verifier (namely, limits on the
-number of instructions and tail calls).
-
-API
-===
-
-BPF flow dissector programs operate on an ``__sk_buff``. However, only the
-limited set of fields is allowed: ``data``, ``data_end`` and ``flow_keys``.
-``flow_keys`` is ``struct bpf_flow_keys`` and contains flow dissector input
-and output arguments.
-
-The inputs are:
- * ``nhoff`` - initial offset of the networking header
- * ``thoff`` - initial offset of the transport header, initialized to nhoff
- * ``n_proto`` - L3 protocol type, parsed out of L2 header
-
-Flow dissector BPF program should fill out the rest of the ``struct
-bpf_flow_keys`` fields. Input arguments ``nhoff/thoff/n_proto`` should be
-also adjusted accordingly.
-
-The return code of the BPF program is either BPF_OK to indicate successful
-dissection, or BPF_DROP to indicate parsing error.
-
-__sk_buff->data
-===============
-
-In the VLAN-less case, this is what the initial state of the BPF flow
-dissector looks like::
-
- +------+------+------------+-----------+
- | DMAC | SMAC | ETHER_TYPE | L3_HEADER |
- +------+------+------------+-----------+
- ^
- |
- +-- flow dissector starts here
-
-
-.. code:: c
-
- skb->data + flow_keys->nhoff point to the first byte of L3_HEADER
- flow_keys->thoff = nhoff
- flow_keys->n_proto = ETHER_TYPE
-
-In case of VLAN, flow dissector can be called with the two different states.
-
-Pre-VLAN parsing::
-
- +------+------+------+-----+-----------+-----------+
- | DMAC | SMAC | TPID | TCI |ETHER_TYPE | L3_HEADER |
- +------+------+------+-----+-----------+-----------+
- ^
- |
- +-- flow dissector starts here
-
-.. code:: c
-
- skb->data + flow_keys->nhoff point the to first byte of TCI
- flow_keys->thoff = nhoff
- flow_keys->n_proto = TPID
-
-Please note that TPID can be 802.1AD and, hence, BPF program would
-have to parse VLAN information twice for double tagged packets.
-
-
-Post-VLAN parsing::
-
- +------+------+------+-----+-----------+-----------+
- | DMAC | SMAC | TPID | TCI |ETHER_TYPE | L3_HEADER |
- +------+------+------+-----+-----------+-----------+
- ^
- |
- +-- flow dissector starts here
-
-.. code:: c
-
- skb->data + flow_keys->nhoff point the to first byte of L3_HEADER
- flow_keys->thoff = nhoff
- flow_keys->n_proto = ETHER_TYPE
-
-In this case VLAN information has been processed before the flow dissector
-and BPF flow dissector is not required to handle it.
-
-
-The takeaway here is as follows: BPF flow dissector program can be called with
-the optional VLAN header and should gracefully handle both cases: when single
-or double VLAN is present and when it is not present. The same program
-can be called for both cases and would have to be written carefully to
-handle both cases.
-
-
-Reference Implementation
-========================
-
-See ``tools/testing/selftests/bpf/progs/bpf_flow.c`` for the reference
-implementation and ``tools/testing/selftests/bpf/flow_dissector_load.[hc]``
-for the loader. bpftool can be used to load BPF flow dissector program as well.
-
-The reference implementation is organized as follows:
- * ``jmp_table`` map that contains sub-programs for each supported L3 protocol
- * ``_dissect`` routine - entry point; it does input ``n_proto`` parsing and
- does ``bpf_tail_call`` to the appropriate L3 handler
-
-Since BPF at this point doesn't support looping (or any jumping back),
-jmp_table is used instead to handle multiple levels of encapsulation (and
-IPv6 options).
-
-
-Current Limitations
-===================
-BPF flow dissector doesn't support exporting all the metadata that in-kernel
-C-based implementation can export. Notable example is single VLAN (802.1Q)
-and double VLAN (802.1AD) tags. Please refer to the ``struct bpf_flow_keys``
-for a set of information that's currently can be exported from the BPF context.
diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst
index 984e68f9e026..5449149be496 100644
--- a/Documentation/networking/index.rst
+++ b/Documentation/networking/index.rst
@@ -9,7 +9,6 @@ Contents:
netdev-FAQ
af_xdp
batman-adv
- bpf_flow_dissector
can
can_ucan_protocol
device_drivers/freescale/dpaa2/index