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bpf/flow_dissector: document flags 

Describe what each input flag does and who uses it.

Acked-by: Petar Penkov <ppenkov@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Petar Penkov <ppenkov@google.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Stanislav Fomichev 2019-07-25 15:52:26 -07:00 committed by Alexei Starovoitov
parent 086f956821
commit 1ac6b126db
1 changed files with 18 additions and 0 deletions
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18
Documentation/bpf/prog_flow_dissector.rst
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@ -26,6 +26,7 @@ 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
* ``flags`` - optional flags
Flow dissector BPF program should fill out the rest of the ``struct
bpf_flow_keys`` fields. Input arguments ``nhoff/thoff/n_proto`` should be
@ -101,6 +102,23 @@ can be called for both cases and would have to be written carefully to
handle both cases.
Flags
=====
``flow_keys->flags`` might contain optional input flags that work as follows:
* ``BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG`` - tells BPF flow dissector to
continue parsing first fragment; the default expected behavior is that
flow dissector returns as soon as it finds out that the packet is fragmented;
used by ``eth_get_headlen`` to estimate length of all headers for GRO.
* ``BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL`` - tells BPF flow dissector to
stop parsing as soon as it reaches IPv6 flow label; used by
``___skb_get_hash`` and ``__skb_get_hash_symmetric`` to get flow hash.
* ``BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP`` - tells BPF flow dissector to stop
parsing as soon as it reaches encapsulated headers; used by routing
infrastructure.
Reference Implementation
========================