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122 files changed, 1096 insertions, 563 deletions
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst index 9a60a5d60e38..7313d354f20e 100644 --- a/Documentation/bpf/btf.rst +++ b/Documentation/bpf/btf.rst @@ -148,16 +148,16 @@ The ``btf_type.size * 8`` must be equal to or greater than ``BTF_INT_BITS()`` for the type. The maximum value of ``BTF_INT_BITS()`` is 128. The ``BTF_INT_OFFSET()`` specifies the starting bit offset to calculate values -for this int. For example, a bitfield struct member has: * btf member bit -offset 100 from the start of the structure, * btf member pointing to an int -type, * the int type has ``BTF_INT_OFFSET() = 2`` and ``BTF_INT_BITS() = 4`` +for this int. For example, a bitfield struct member has: + * btf member bit offset 100 from the start of the structure, + * btf member pointing to an int type, + * the int type has ``BTF_INT_OFFSET() = 2`` and ``BTF_INT_BITS() = 4`` Then in the struct memory layout, this member will occupy ``4`` bits starting from bits ``100 + 2 = 102``. Alternatively, the bitfield struct member can be the following to access the same bits as the above: - * btf member bit offset 102, * btf member pointing to an int type, * the int type has ``BTF_INT_OFFSET() = 0`` and ``BTF_INT_BITS() = 4`` diff --git a/Documentation/networking/bpf_flow_dissector.rst b/Documentation/networking/bpf_flow_dissector.rst new file mode 100644 index 000000000000..b375ae2ec2c4 --- /dev/null +++ b/Documentation/networking/bpf_flow_dissector.rst @@ -0,0 +1,126 @@ +.. 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 prog |