[dpdk-dev] [RFC] Generic flow director/filtering/classification API

[Liang, Cunming]

Hi Adrien,

On 7/6/2016 2:16 AM, Adrien Mazarguil wrote:
> Hi All,
>
> First, forgive me for this large message, I know our mailboxes already
> suffer quite a bit from the amount of traffic on this ML.
>
> This is not exactly yet another thread about how flow director should be
> extended, rather about a brand new API to handle filtering and
> classification for incoming packets in the most PMD-generic and
> application-friendly fashion we can come up with. Reasons described below.
>
> I think this topic is important enough to include both the users of this API
> as well as PMD maintainers. So far I have CC'ed librte_ether (especially
> rte_eth_ctrl.h contributors), testpmd and PMD maintainers (with and without
> a .filter_ctrl implementation), but if you know application maintainers
> other than testpmd who use FDIR or might be interested in this discussion,
> feel free to add them.
>
> The issues we found with the current approach are already summarized in the
> following document, but here is a quick summary for TL;DR folks:
>
> - PMDs do not expose a common set of filter types and even when they do,
>    their behavior more or less differs.
>
> - Applications need to determine and adapt to device-specific limitations
>    and quirks on their own, without help from PMDs.
>
> - Writing an application that creates flow rules targeting all devices
>    supported by DPDK is thus difficult, if not impossible.
>
> - The current API has too many unspecified areas (particularly regarding
>    side effects of flow rules) that make PMD implementation tricky.
>
> This RFC API handles everything currently supported by .filter_ctrl, the
> idea being to reimplement all of these to make them fully usable by
> applications in a more generic and well defined fashion. It has a very small
> set of mandatory features and an easy method to let applications probe for
> supported capabilities.
>
> The only downside is more work for the software control side of PMDs because
> they have to adapt to the API instead of the reverse. I think helpers can be
> added to EAL to assist with this.
>
> HTML version:
>
>   https://rawgit.com/6WIND/rte_flow/master/rte_flow.html
>
> PDF version:
>
>   https://rawgit.com/6WIND/rte_flow/master/rte_flow.pdf
>
> Related draft header file (for reference while reading the specification):
>
>   https://raw.githubusercontent.com/6WIND/rte_flow/master/rte_flow.h
>
> Git tree for completeness (latest .rst version can be retrieved from here):
>
>   https://github.com/6WIND/rte_flow
>
> What follows is the ReST source of the above, for inline comments and
> discussion. I intend to update that specification accordingly.
>
> ========================
> Generic filter interface
> ========================
>
> .. footer::
>
>     v0.6
>
> .. contents::
> .. sectnum::
> .. raw:: pdf
>
>     PageBreak
>
> Overview
> ========
>
> DPDK provides several competing interfaces added over time to perform packet
> matching and related actions such as filtering and classification.
>
> They must be extended to implement the features supported by newer devices
> in order to expose them to applications, however the current design has
> several drawbacks:
>
> - Complicated filter combinations which have not been hard-coded cannot be
>    expressed.
> - Prone to API/ABI breakage when new features must be added to an existing
>    filter type, which frequently happens.
>
>  From an application point of view:
>
> - Having disparate interfaces, all optional and lacking in features does not
>    make this API easy to use.
> - Seemingly arbitrary built-in limitations of filter types based on the
>    device they were initially designed for.
> - Undefined relationship between different filter types.
> - High complexity, considerable undocumented and/or undefined behavior.
>
> Considering the growing number of devices supported by DPDK, adding a new
> filter type each time a new feature must be implemented is not sustainable
> in the long term. Applications not written to target a specific device
> cannot really benefit from such an API.
>
> For these reasons, this document defines an extensible unified API that
> encompasses and supersedes these legacy filter types.
>
> .. raw:: pdf
>
>     PageBreak
>
> Current API
> ===========
>
> Rationale
> ---------
>
> The reason several competing (and mostly overlapping) filtering APIs are
> present in DPDK is due to its nature as a thin layer between hardware and
> software.
>
> Each subsequent interface has been added to better match the capabilities
> and limitations of the latest supported device, which usually happened to
> need an incompatible configuration approach. Because of this, many ended up
> device-centric and not usable by applications that were not written for that
> particular device.
>
> This document is not the first attempt to address this proliferation issue,
> in fact a lot of work has already been done both to create a more generic
> interface while somewhat keeping compatibility with legacy ones through a
> common call interface (``rte_eth_dev_filter_ctrl()`` with the
> ``.filter_ctrl`` PMD callback in ``rte_ethdev.h``).
>
> Today, these previously incompatible interfaces are known as filter types
> (``RTE_ETH_FILTER_*`` from ``enum rte_filter_type`` in ``rte_eth_ctrl.h``).
>
> However while trivial to extend with new types, it only shifted the
> underlying problem as applications still need to be written for one kind of
> filter type, which, as described in the following sections, is not
> necessarily implemented by all PMDs that support filtering.
>
> .. raw:: pdf
>
>     PageBreak
>
> Filter types
> ------------
>
> This section summarizes the capabilities of each filter type.
>
> Although the following list is exhaustive, the description of individual
> types may contain inaccuracies due to the lack of documentation or usage
> examples.
>
> Note: names are prefixed with ``RTE_ETH_FILTER_``.
>
> ``MACVLAN``
> ~~~~~~~~~~~
>
> Matching:
>
> - L2 source/destination addresses.
> - Optional 802.1Q VLAN ID.
> - Masking individual fields on a rule basis is not supported.
>
> Action:
>
> - Packets are redirected either to a given VF device using its ID or to the
>    PF.
>
> ``ETHERTYPE``
> ~~~~~~~~~~~~~
>
> Matching:
>
> - L2 source/destination addresses (optional).
> - Ethertype (no VLAN ID?).
> - Masking individual fields on a rule basis is not supported.
>
> Action:
>
> - Receive packets on a given queue.
> - Drop packets.
>
> ``FLEXIBLE``
> ~~~~~~~~~~~~
>
> Matching:
>
> - At most 128 consecutive bytes anywhere in packets.
> - Masking is supported with byte granularity.
> - Priorities are supported (relative to this filter type, undefined
>    otherwise).
>
> Action:
>
> - Receive packets on a given queue.
>
> ``SYN``
> ~~~~~~~
>
> Matching:
>
> - TCP SYN packets only.
> - One high priority bit can be set to give the highest possible priority to
>    this type when other filters with different types are configured.
>
> Action:
>
> - Receive packets on a given queue.
>
> ``NTUPLE``
> ~~~~~~~~~~
>
> Matching:
>
> - Source/destination IPv4 addresses (optional in 2-tuple mode).
> - Source/destination TCP/UDP port (mandatory in 2 and 5-tuple modes).
> - L4 protocol (2 and 5-tuple modes).
> - Masking individual fields is supported.
> - TCP flags.
> - Up to 7 levels of priority relative to this filter type, undefined
>    otherwise.
> - No IPv6.
>
> Action:
>
> - Receive packets on a given queue.
>
> ``TUNNEL``
> ~~~~~~~~~~
>
> Matching:
>
> - Outer L2 source/destination addresses.
> - Inner L2 source/destination addresses.
> - Inner VLAN ID.
> - IPv4/IPv6 source (destination?) address.
> - Tunnel type to match (VXLAN, GENEVE, TEREDO, NVGRE, IP over GRE, 802.1BR
>    E-Tag).
> - Tenant ID for tunneling protocols that have one.
> - Any combination of the above can be specified.
> - Masking individual fields on a rule basis is not supported.
>
> Action:
>
> - Receive packets on a given queue.
>
> .. raw:: pdf
>
>     PageBreak
>
> ``FDIR``
> ~~~~~~~~
>
> Queries:
>
> - Device capabilities and limitations.
> - Device statistics about configured filters (resource usage, collisions).
> - Device configuration (matching input set and masks)
>
> Matching:
>
> - Device mode of operation: none (to disable filtering), signature
>    (hash-based dispatching from masked fields) or perfect (either MAC VLAN or
>    tunnel).
> - L2 Ethertype.
> - Outer L2 destination address (MAC VLAN mode).
> - Inner L2 destination address, tunnel type (NVGRE, VXLAN) and tunnel ID
>    (tunnel mode).
> - IPv4 source/destination addresses, ToS, TTL and protocol fields.
> - IPv6 source/destination addresses, TC, protocol and hop limits fields.
> - UDP source/destination IPv4/IPv6 and ports.
> - TCP source/destination IPv4/IPv6 and ports.
> - SCTP source/destination IPv4/IPv6, ports and verification tag field.
> - Note, only one protocol type at once (either only L2 Ethertype, basic
>    IPv6, IPv4+UDP, IPv4+TCP and so on).
> - VLAN TCI (extended API).
> - At most 16 bytes to match in payload (extended API). A global device
>    look-up table specifies for each possible protocol layer (unknown, raw,
>    L2, L3, L4) the offset to use for each byte (they do not need to be
>    contiguous) and the related bitmask.
> - Whether packet is addressed to PF or VF, in that case its ID can be
>    matched as well (extended API).
> - Masking most of the above fields is supported, but simultaneously affects
>    all filters configured on a device.
> - Input set can be modified in a similar fashion for a given device to
>    ignore individual fields of filters (i.e. do not match the destination
>    address in a IPv4 filter, refer to **RTE_ETH_INPUT_SET_**
>    macros). Configuring this also affects RSS processing on **i40e**.
> - Filters can also provide 32 bits of arbitrary data to return as part of
>    matched packets.
>
> Action:
>
> - **RTE_ETH_FDIR_ACCEPT**: receive (accept) packet on a given queue.
> - **RTE_ETH_FDIR_REJECT**: drop packet immediately.
> - **RTE_ETH_FDIR_PASSTHRU**: similar to accept for the last filter in list,
>    otherwise process it with subsequent filters.
> - For accepted packets and if requested by filter, either 32 bits of
>    arbitrary data and four bytes of matched payload (only in case of flex
>    bytes matching), or eight bytes of matched payload (flex also) are added
>    to meta data.
>
> .. raw:: pdf
>
>     PageBreak
>
> ``HASH``
> ~~~~~~~~
>
> Not an actual filter type. Provides and retrieves the global device
> configuration (per port or entire NIC) for hash functions and their
> properties.
>
> Hash function selection: "default" (keep current), XOR or Toeplitz.
>
> This function can be configured per flow type (**RTE_ETH_FLOW_**
> definitions), supported types are:
>
> - Unknown.
> - Raw.
> - Fragmented or non-fragmented IPv4.
> - Non-fragmented IPv4 with L4 (TCP, UDP, SCTP or other).
> - Fragmented or non-fragmented IPv6.
> - Non-fragmented IPv6 with L4 (TCP, UDP, SCTP or other).
> - L2 payload.
> - IPv6 with extensions.
> - IPv6 with L4 (TCP, UDP) and extensions.
>
> ``L2_TUNNEL``
> ~~~~~~~~~~~~~
>
> Matching:
>
> - All packets received on a given port.
>
> Action:
>
> - Add tunnel encapsulation (VXLAN, GENEVE, TEREDO, NVGRE, IP over GRE,
>    802.1BR E-Tag) using the provided Ethertype and tunnel ID (only E-Tag
>    is implemented at the moment).
> - VF ID to use for tag insertion (currently unused).
> - Destination pool for tag based forwarding (pools are IDs that can be
>    affected to ports, duplication occurs if the same ID is shared by several
>    ports of the same NIC).
>
> .. raw:: pdf
>
>     PageBreak
>
> Driver support
> --------------
>
> ======== ======= ========= ======== === ====== ====== ==== ==== =========
> Driver   MACVLAN ETHERTYPE FLEXIBLE SYN NTUPLE TUNNEL FDIR HASH L2_TUNNEL
> ======== ======= ========= ======== === ====== ====== ==== ==== =========
> bnx2x
> cxgbe
> e1000            yes       yes      yes yes
> ena
> enic                                                  yes
> fm10k
> i40e     yes     yes                           yes    yes  yes
> ixgbe            yes                yes yes           yes       yes
> mlx4
> mlx5                                                  yes
> szedata2
> ======== ======= ========= ======== === ====== ====== ==== ==== =========
>
> Flow director
> -------------
>
> Flow director (FDIR) is the name of the most capable filter type, which
> covers most features offered by others. As such, it is the most widespread
> in PMDs that support filtering (i.e. all of them besides **e1000**).
>
> It is also the only type that allows an arbitrary 32 bits value provided by
> applications to be attached to a filter and returned with matching packets
> instead of relying on the destination queue to recognize flows.
>
> Unfortunately, even FDIR requires applications to be aware of low-level
> capabilities and limitations (most of which come directly from **ixgbe** and
> **i40e**):
>
> - Bitmasks are set globally per device (port?), not per filter.
> - Configuration state is not expected to be saved by the driver, and
>    stopping/restarting a port requires the application to perform it again
>    (API documentation is also unclear about this).
> - Monolithic approach with ABI issues as soon as a new kind of flow or
>    combination needs to be supported.
> - Cryptic global statistics/counters.
> - Unclear about how priorities are managed; filters seem to be arranged as a
>    linked list in hardware (possibly related to configuration order).
>
> Packet alteration
> -----------------
>
> One interesting feature is that the L2 tunnel filter type implements the
> ability to alter incoming packets through a filter (in this case to
> encapsulate them), thus the **mlx5** flow encap/decap features are not a
> foreign concept.
>
> .. raw:: pdf
>
>     PageBreak
>
> Proposed API
> ============
>
> Terminology
> -----------
>
> - **Filtering API**: overall framework affecting the fate of selected
>    packets, covers everything described in this document.
> - **Matching pattern**: properties to look for in received packets, a
>    combination of any number of items.
> - **Pattern item**: part of a pattern that either matches packet data
>    (protocol header, payload or derived information), or specifies properties
>    of the pattern itself.
> - **Actions**: what needs to be done when a packet matches a pattern.
> - **Flow rule**: this is the result of combining a *matching pattern* with
>    *actions*.
> - **Filter rule**: a less generic term than *flow rule*, can otherwise be
>    used interchangeably.
> - **Hit**: a flow rule is said to be *hit* when processing a matching
>    packet.
>
> Requirements
> ------------
>
> As described in the previous section, there is a growing need for a common
> method to configure filtering and related actions in a hardware independent
> fashion.
>
> The filtering API should not disallow any filter combination by design and
> must remain as simple as possible to use. It can simply be defined as a
> method to perform one or several actions on selected packets.
>
> PMDs are aware of the capabilities of the device they manage and should be
> responsible for preventing unsupported or conflicting combinations.
>
> This approach is fundamentally different as it places most of the burden on
> the software side of the PMD instead of having device capabilities directly
> mapped to API functions, then expecting applications to work around ensuing
> compatibility issues.
>
> Requirements for a new API:
>
> - Flexible and extensible without causing API/ABI problems for existing
>    applications.
> - Should be unambiguous and easy to use.
> - Support existing filtering features and actions listed in `Filter types`_.
> - Support packet alteration.
> - In case of overlapping filters, their priority should be well documented.
> - Support filter queries (for example to retrieve counters).
>
> .. raw:: pdf
>
>     PageBreak
>
> High level design
> -----------------
>
> The chosen approach to make filtering as generic as possible is by
> expressing matching patterns through lists of items instead of the flat
> structures used in DPDK today, enabling combinations that are not predefined
> and thus being more versatile.
>
> Flow rules can have several distinct actions (such as counting,
> encapsulating, decapsulating before redirecting packets to a particular
> queue, etc.), instead of relying on several rules to achieve this and having
> applications deal with hardware implementation details regarding their
> order.
>
> Support for different priority levels on a rule basis is provided, for
> example in order to force a more specific rule come before a more generic
> one for packets matched by both, however hardware support for more than a
> single priority level cannot be guaranteed. When supported, the number of
> available priority levels is usually low, which is why they can also be
> implemented in software by PMDs (e.g. to simulate missing priority levels by
> reordering rules).
>
> In order to remain as hardware agnostic as possible, by default all rules
> are considered to have the same priority, which means that the order between
> overlapping rules (when a packet is matched by several filters) is
> undefined, packet duplication may even occur as a result.
>
> PMDs may refuse to create overlapping rules at a given priority level when
> they can be detected (e.g. if a pattern matches an existing filter).
>
> Thus predictable results for a given priority level can only be achieved
> with non-overlapping rules, using perfect matching on all protocol layers.
>
> Support for multiple actions per rule may be implemented internally on top
> of non-default hardware priorities, as a result both features may not be
> simultaneously available to applications.
>
> Considering that allowed pattern/actions combinations cannot be known in
> advance and would result in an unpractically large number of capabilities to
> expose, a method is provided to validate a given rule from the current
> device configuration state without actually adding it (akin to a "dry run"
> mode).
>
> This enables applications to check if the rule types they need is supported
> at initialization time, before starting their data path. This method can be
> used anytime, its only requirement being that the resources needed by a rule
> must exist (e.g. a target RX queue must be configured first).
>
> Each defined rule is associated with an opaque handle managed by the PMD,
> applications are responsible for keeping it. These can be used for queries
> and rules management, such as retrieving counters or other data and
> destroying them.
>
> Handles must be destroyed before releasing associated resources such as
> queues.
>
> Integration
> -----------
>
> To avoid ABI breakage, this new interface will be implemented through the
> existing filtering control framework (``rte_eth_dev_filter_ctrl()``) using
> **RTE_ETH_FILTER_GENERIC** as a new filter type.
>
> However a public front-end API described in `Rules management`_ will
> be added as the preferred method to use it.
>
> Once discussions with the community have converged to a definite API, legacy
> filter types should be deprecated and a deadline defined to remove their
> support entirely.
>
> PMDs will have to be gradually converted to **RTE_ETH_FILTER_GENERIC** or
> drop filtering support entirely. Less maintained PMDs for older hardware may
> lose support at this point.
>
> The notion of filter type will then be deprecated and subsequently dropped
> to avoid confusion between both frameworks.
>
> Implementation details
> ======================
>
> Flow rule
> ---------
>
> A flow rule is the combination of a matching pattern with a list of actions,
> and is the basis of this API.
>
> Priorities
> ~~~~~~~~~~
>
> A priority can be assigned to a matching pattern.
>
> The default priority level is 0 and is also the highest. Support for more
> than a single priority level in hardware is not guaranteed.
>
> If a packet is matched by several filters at a given priority level, the
> outcome is undefined. It can take any path and can even be duplicated.
>
> Matching pattern
> ~~~~~~~~~~~~~~~~
>
> A matching pattern comprises any number of items of various types.
>
> Items are arranged in a list to form a matching pattern for packets. They
> fall in two categories:
>
> - Protocol matching (ANY, RAW, ETH, IPV4, IPV6, ICMP, UDP, TCP, VXLAN and so
>    on), usually associated with a specification structure. These must be
>    stacked in the same order as the protocol layers to match, starting from
>    L2.
>
> - Affecting how the pattern is processed (END, VOID, INVERT, PF, VF,
>    SIGNATURE and so on), often without a specification structure. Since they
>    are meta data that does not match packet contents, these can be specified
>    anywhere within item lists without affecting the protocol matching items.
>
> Most item specifications can be optionally paired with a mask to narrow the
> specific fields or bits to be matched.
>
> - Items are defined with ``struct rte_flow_item``.
> - Patterns are defined with ``struct rte_flow_pattern``.
>
> Example of an item specification matching an Ethernet header:
>
> +-----------------------------------------+
> | Ethernet                                |
> +==========+=========+====================+
> | ``spec`` | ``src`` | ``00:01:02:03:04`` |
> |          +---------+--------------------+
> |          | ``dst`` | ``00:2a:66:00:01`` |
> +----------+---------+--------------------+
> | ``mask`` | ``src`` | ``00:ff:ff:ff:00`` |
> |          +---------+--------------------+
> |          | ``dst`` | ``00:00:00:00:ff`` |
> +----------+---------+--------------------+
>
> Non-masked bits stand for any value, Ethernet headers with the following
> properties are thus matched:
>
> - ``src``: ``??:01:02:03:??``
> - ``dst``: ``??:??:??:??:01``
>
> Except for meta types that do not need one, ``spec`` must be a valid pointer
> to a structure of the related item type. A ``mask`` of the same type can be
> provided to tell which bits in ``spec`` are to be matched.
>
> A mask is normally only needed for ``spec`` fields matching packet data,
> ignored otherwise. See individual item types for more information.
>
> A ``NULL`` mask pointer is allowed and is similar to matching with a full
> mask (all ones) ``spec`` fields supported by hardware, the remaining fields
> are ignored (all zeroes), there is thus no error checking for unsupported
> fields.
>
> Matching pattern items for packet data must be naturally stacked (ordered
> from lowest to highest protocol layer), as in the following examples:
>
> +--------------+
> | TCPv4 as L4  |
> +===+==========+
> | 0 | Ethernet |
> +---+----------+
> | 1 | IPv4     |
> +---+----------+
> | 2 | TCP      |
> +---+----------+
>
> +----------------+
> | TCPv6 in VXLAN |
> +===+============+
> | 0 | Ethernet   |
> +---+------------+
> | 1 | IPv4       |
> +---+------------+
> | 2 | UDP        |
> +---+------------+
> | 3 | VXLAN      |
> +---+------------+
> | 4 | Ethernet   |
> +---+------------+
> | 5 | IPv6       |
> +---+------------+
> | 6 | TCP        |
> +---+------------+
>
> +-----------------------------+
> | TCPv4 as L4 with meta items |
> +===+=========================+
> | 0 | VOID                    |
> +---+-------------------------+
> | 1 | Ethernet                |
> +---+-------------------------+
> | 2 | VOID                    |
> +---+-------------------------+
> | 3 | IPv4                    |
> +---+-------------------------+
> | 4 | TCP                     |
> +---+-------------------------+
> | 5 | VOID                    |
> +---+-------------------------+
> | 6 | VOID                    |
> +---+-------------------------+
>
> The above example shows how meta items do not affect packet data matching
> items, as long as those remain stacked properly. The resulting matching
> pattern is identical to "TCPv4 as L4".
>
> +----------------+
> | UDPv6 anywhere |
> +===+============+
> | 0 | IPv6       |
> +---+------------+
> | 1 | UDP        |
> +---+------------+
>
> If supported by the PMD, omitting one or several protocol layers at the
> bottom of the stack as in the above example (missing an Ethernet
> specification) enables hardware to look anywhere in packets.
>
> It is unspecified whether the payload of supported encapsulations
> (e.g. VXLAN inner packet) is matched by such a pattern, which may apply to
> inner, outer or both packets.
>
> +---------------------+
> | Invalid, missing L3 |
> +===+=================+
> | 0 | Ethernet        |
> +---+-----------------+
> | 1 | UDP             |
> +---+-----------------+
>
> The above pattern is invalid due to a missing L3 specification between L2
> and L4. It is only allowed at the bottom and at the top of the stack.
>
> Meta item types
> ~~~~~~~~~~~~~~~
>
> These do not match packet data but affect how the pattern is processed, most
> of them do not need a specification structure. This particularity allows
> them to be specified anywhere without affecting other item types.
[LC] For the meta item(END, VOID, INVERT) and some data matching type 
like ANY and RAW,
it's all PMD responsible to understand the key character and to parse 
the header graph?
>
> ``END``
> ^^^^^^^
>
> End marker for item lists. Prevents further processing of items, thereby
> ending the pattern.
>
> - Its numeric value is **0** for convenience.
> - PMD support is mandatory.
> - Both ``spec`` and ``mask`` are ignored.
>
> +--------------------+
> | END                |
> +==========+=========+
> | ``spec`` | ignored |
> +----------+---------+
> | ``mask`` | ignored |
> +----------+---------+
>
> ``VOID``
> ^^^^^^^^
>
> Used as a placeholder for convenience. It is ignored and simply discarded by
> PMDs.
>
> - PMD support is mandatory.
> - Both ``spec`` and ``mask`` are ignored.
>
> +--------------------+
> | VOID               |
> +==========+=========+
> | ``spec`` | ignored |
> +----------+---------+
> | ``mask`` | ignored |
> +----------+---------+
>
> One usage example for this type is generating rules that share a common
> prefix quickly without reallocating memory, only by updating item types:
>
> +------------------------+
> | TCP, UDP or ICMP as L4 |
> +===+====================+
> | 0 | Ethernet           |
> +---+--------------------+
> | 1 | IPv4               |
> +---+------+------+------+
> | 2 | UDP  | VOID | VOID |
> +---+------+------+------+
> | 3 | VOID | TCP  | VOID |
> +---+------+------+------+
> | 4 | VOID | VOID | ICMP |
> +---+------+------+------+
>
> .. raw:: pdf
>
>     PageBreak
>
> ``INVERT``
> ^^^^^^^^^^
>
> Inverted matching, i.e. process packets that do not match the pattern.
>
> - Both ``spec`` and ``mask`` are ignored.
>
> +--------------------+
> | INVERT             |
> +==========+=========+
> | ``spec`` | ignored |
> +----------+---------+
> | ``mask`` | ignored |
> +----------+---------+
>
> Usage example in order to match non-TCPv4 packets only:
>
> +--------------------+
> | Anything but TCPv4 |
> +===+================+
> | 0 | INVERT         |
> +---+----------------+
> | 1 | Ethernet       |
> +---+----------------+
> | 2 | IPv4           |
> +---+----------------+
> | 3 | TCP            |
> +---+----------------+
>
> ``PF``
> ^^^^^^
>
> Matches packets addressed to the physical function of the device.
>
> - Both ``spec`` and ``mask`` are ignored.
>
> +--------------------+
> | PF                 |
> +==========+=========+
> | ``spec`` | ignored |
> +----------+---------+
> | ``mask`` | ignored |
> +----------+---------+
>
> ``VF``
> ^^^^^^
>
> Matches packets addressed to the given virtual function ID of the device.
>
> - Only ``spec`` needs to be defined, ``mask`` is ignored.
>
> +----------------------------------------+
> | VF                                     |
> +==========+=========+===================+
> | ``spec`` | ``vf``  | destination VF ID |
> +----------+---------+-------------------+
> | ``mask`` | ignored                     |
> +----------+-----------------------------+
>
> ``SIGNATURE``
> ^^^^^^^^^^^^^
>
> Requests hash-based signature dispatching for this rule.
>
> Considering this is a global setting on devices that support it, all
> subsequent filter rules may have to be created with it as well.
>
> - Only ``spec`` needs to be defined, ``mask`` is ignored.
>
> +--------------------+
> | SIGNATURE          |
> +==========+=========+
> | ``spec`` | TBD     |
> +----------+---------+
> | ``mask`` | ignored |
> +----------+---------+
>
> .. raw:: pdf
>
>     PageBreak
>
> Data matching item types
> ~~~~~~~~~~~~~~~~~~~~~~~~
>
> Most of these are basically protocol header definitions with associated
> bitmasks. They must be specified (stacked) from lowest to highest protocol
> layer.
>
> The following list is not exhaustive as new protocols will be added in the
> future.
>
> ``ANY``
> ^^^^^^^
>
> Matches any protocol in place of the current layer, a single ANY may also
> stand for several protocol layers.
>
> This is usually specified as the first pattern item when looking for a
> protocol anywhere in a packet.
>
> - A maximum value of **0** requests matching any number of protocol layers
>    above or equal to the minimum value, a maximum value lower than the
>    minimum one is otherwise invalid.
> - Only ``spec`` needs to be defined, ``mask`` is ignored.
>
> +-----------------------------------------------------------------------+
> | ANY                                                                   |
> +==========+=========+==================================================+
> | ``spec`` | ``min`` | minimum number of layers covered                 |
> |          +---------+--------------------------------------------------+
> |          | ``max`` | maximum number of layers covered, 0 for infinity |
> +----------+---------+--------------------------------------------------+
> | ``mask`` | ignored                                                    |
> +----------+------------------------------------------------------------+
>
> Example for VXLAN TCP payload matching regardless of outer L3 (IPv4 or IPv6)
> and L4 (UDP) both matched by the first ANY specification, and inner L3 (IPv4
> or IPv6) matched by the second ANY specification:
>
> +----------------------------------+
> | TCP in VXLAN with wildcards      |
> +===+==============================+
> | 0 | Ethernet                     |
> +---+-----+----------+---------+---+
> | 1 | ANY | ``spec`` | ``min`` | 2 |
> |   |     |          +---------+---+
> |   |     |          | ``max`` | 2 |
> +---+-----+----------+---------+---+
> | 2 | VXLAN                        |
> +---+------------------------------+
> | 3 | Ethernet                     |
> +---+-----+----------+---------+---+
> | 4 | ANY | ``spec`` | ``min`` | 1 |
> |   |     |          +---------+---+
> |   |     |          | ``max`` | 1 |
> +---+-----+----------+---------+---+
> | 5 | TCP                          |
> +---+------------------------------+
>
> .. raw:: pdf
>
>     PageBreak
>
> ``RAW``
> ^^^^^^^
>
> Matches a string of a given length at a given offset (in bytes), or anywhere
> in the payload of the current protocol layer (including L2 header if used as
> the first item in the stack).
>
> This does not increment the protocol layer count as it is not a protocol
> definition. Subsequent RAW items modulate the first absolute one with
> relative offsets.
>
> - Using **-1** as the ``offset`` of the first RAW item makes its absolute
>    offset not fixed, i.e. the pattern is searched everywhere.
> - ``mask`` only affects the pattern.
The RAW matching type allow offset & length which support anchor setting 
setting and string match.
It's not defined for a user defined packet layout. Sometimes, comparing 
payload raw data after a header require
{offset, length}. One typical case is 5-tuples matching. The 'PORT' of 
transport layer is an offset to the IP header.
It can't address by IP/ANY, as it requires to extract key from the field 
in ANY.

>
> +--------------------------------------------------------------+
> | RAW                                                          |
> +==========+=============+=====================================+
> | ``spec`` | ``offset``  | absolute or relative pattern offset |
> |          +-------------+-------------------------------------+
> |          | ``length``  | pattern length                      |
> |          +-------------+-------------------------------------+
> |          | ``pattern`` | byte string of the above length     |
> +----------+-------------+-------------------------------------+
> | ``mask`` | ``offset``  | ignored                             |
> |          +-------------+-------------------------------------+
> |          | ``length``  | ignored                             |
> |          +-------------+-------------------------------------+
> |          | ``pattern`` | bitmask with the same byte length   |
> +----------+-------------+-------------------------------------+
>
> Example pattern looking for several strings at various offsets of a UDP
> payload, using combined RAW items:
>
> +------------------------------------------+
> | UDP payload matching                     |
> +===+======================================+
> | 0 | Ethernet                             |
> +---+--------------------------------------+
> | 1 | IPv4                                 |
> +---+--------------------------------------+
> | 2 | UDP                                  |
> +---+-----+----------+-------------+-------+
> | 3 | RAW | ``spec`` | ``offset``  | -1    |
> |   |     |          +-------------+-------+
> |   |     |          | ``length``  | 3     |
> |   |     |          +-------------+-------+
> |   |     |          | ``pattern`` | "foo" |
> +---+-----+----------+-------------+-------+
> | 4 | RAW | ``spec`` | ``offset``  | 20    |
> |   |     |          +-------------+-------+
> |   |     |          | ``length``  | 3     |
> |   |     |          +-------------+-------+
> |   |     |          | ``pattern`` | "bar" |
> +---+-----+----------+-------------+-------+
> | 5 | RAW | ``spec`` | ``offset``  | -30   |
> |   |     |          +-------------+-------+
> |   |     |          | ``length``  | 3     |
> |   |     |          +-------------+-------+
> |   |     |          | ``pattern`` | "baz" |
> +---+-----+----------+-------------+-------+
>
> This translates to:
>
> - Locate "foo" in UDP payload, remember its offset.
> - Check "bar" at "foo"'s offset plus 20 bytes.
> - Check "baz" at "foo"'s offset minus 30 bytes.
>
> .. raw:: pdf
>
>     PageBreak
>
> ``ETH``
> ^^^^^^^
>
> Matches an Ethernet header.
>
> - ``dst``: destination MAC.
> - ``src``: source MAC.
> - ``type``: EtherType.
> - ``tags``: number of 802.1Q/ad tags defined.
> - ``tag[]``: 802.1Q/ad tag definitions, innermost first. For each one:
>
>   - ``tpid``: Tag protocol identifier.
>   - ``tci``: Tag control information.
>
> ``IPV4``
> ^^^^^^^^
>
> Matches an IPv4 header.
>
> - ``src``: source IP address.
> - ``dst``: destination IP address.
> - ``tos``: ToS/DSCP field.
> - ``ttl``: TTL field.
> - ``proto``: protocol number for the next layer.
>
> ``IPV6``
> ^^^^^^^^
>
> Matches an IPv6 header.
>
> - ``src``: source IP address.
> - ``dst``: destination IP address.
> - ``tc``: traffic class field.
> - ``nh``: Next header field (protocol).
> - ``hop_limit``: hop limit field (TTL).
>
> ``ICMP``
> ^^^^^^^^
>
> Matches an ICMP header.
>
> - TBD.
>
> ``UDP``
> ^^^^^^^
>
> Matches a UDP header.
>
> - ``sport``: source port.
> - ``dport``: destination port.
> - ``length``: UDP length.
> - ``checksum``: UDP checksum.
>
> .. raw:: pdf
>
>     PageBreak
>
> ``TCP``
> ^^^^^^^
>
> Matches a TCP header.
>
> - ``sport``: source port.
> - ``dport``: destination port.
> - All other TCP fields and bits.
>
> ``VXLAN``
> ^^^^^^^^^
>
> Matches a VXLAN header.
>
> - TBD.
>
> .. raw:: pdf
>
>     PageBreak
>
> Actions
> ~~~~~~~
>
> Each possible action is represented by a type. Some have associated
> configuration structures. Several actions combined in a list can be affected
> to a flow rule. That list is not ordered.
>
> At least one action must be defined in a filter rule in order to do
> something with matched packets.
>
> - Actions are defined with ``struct rte_flow_action``.
> - A list of actions is defined with ``struct rte_flow_actions``.
>
> They fall in three categories:
>
> - Terminating actions (such as QUEUE, DROP, RSS, PF, VF) that prevent
>    processing matched packets by subsequent flow rules, unless overridden
>    with PASSTHRU.
>
> - Non terminating actions (PASSTHRU, DUP) that leave matched packets up for
>    additional processing by subsequent flow rules.
>
> - Other non terminating meta actions that do not affect the fate of packets
>    (END, VOID, ID, COUNT).
>
> When several actions are combined in a flow rule, they should all have
> different types (e.g. dropping a packet twice is not possible). However
> considering the VOID type is an exception to this rule, the defined behavior
> is for PMDs to only take into account the last action of a given type found
> in the list. PMDs still perform error checking on the entire list.
>
> *Note that PASSTHRU is the only action able to override a terminating rule.*
[LC] I'm wondering how to address the meta data carried by mbuf, there's 
no mentioned here.
For packets hit one specific flow, usually there's something for CPU to 
identify the flow.
FDIR and RSS as an example, has id or key in mbuf. In addition, some 
meta may pointed by userdata in mbuf.
Any view on it ?

>
> .. raw:: pdf
>
>     PageBreak
>
> Example of an action that redirects packets to queue index 10:
>
> +----------------+
> | QUEUE          |
> +===========+====+
> | ``queue`` | 10 |
> +-----------+----+
>
> Action lists examples, their order is not significant, applications must
> consider all actions to be performed simultaneously:
>
> +----------------+
> | Count and drop |
> +=======+========+
> | COUNT |        |
> +-------+--------+
> | DROP  |        |
> +-------+--------+
>
> +--------------------------+
> | Tag, count and redirect  |
> +=======+===========+======+
> | ID    | ``id``    | 0x2a |
> +-------+-----------+------+
> | COUNT |                  |
> +-------+-----------+------+
> | QUEUE | ``queue`` | 10   |
> +-------+-----------+------+
>
> +-----------------------+
> | Redirect to queue 5   |
> +=======+===============+
> | DROP  |               |
> +-------+-----------+---+
> | QUEUE | ``queue`` | 5 |
> +-------+-----------+---+
>
> In the above example, considering both actions are performed simultaneously,
> its end result is that only QUEUE has any effect.
>
> +-----------------------+
> | Redirect to queue 3   |
> +=======+===========+===+
> | QUEUE | ``queue`` | 5 |
> +-------+-----------+---+
> | VOID  |               |
> +-------+-----------+---+
> | QUEUE | ``queue`` | 3 |
> +-------+-----------+---+
>
> As previously described, only the last action of a given type found in the
> list is taken into account. The above example also shows that VOID is
> ignored.
>
> .. raw:: pdf
>
>     PageBreak
>
> Action types
> ~~~~~~~~~~~~
>
> Common action types are described in this section. Like pattern item types,
> this list is not exhaustive as new actions will be added in the future.
>
> ``END`` (action)
> ^^^^^^^^^^^^^^^^
>
> End marker for action lists. Prevents further processing of actions, thereby
> ending the list.
>
> - Its numeric value is **0** for convenience.
> - PMD support is mandatory.
> - No configurable property.
>
> +---------------+
> | END           |
> +===============+
> | no properties |
> +---------------+
>
> ``VOID`` (action)
> ^^^^^^^^^^^^^^^^^
>
> Used as a placeholder for convenience. It is ignored and simply discarded by
> PMDs.
>
> - PMD support is mandatory.
> - No configurable property.
>
> +---------------+
> | VOID          |
> +===============+
> | no properties |
> +---------------+
>
> ``PASSTHRU``
> ^^^^^^^^^^^^
>
> Leaves packets up for additional processing by subsequent flow rules. This
> is the default when a rule does not contain a terminating action, but can be
> specified to force a rule to become non-terminating.
>
> - No configurable property.
>
> +---------------+
> | PASSTHRU      |
> +===============+
> | no properties |
> +---------------+
>
> Example to copy a packet to a queue and continue processing by subsequent
> flow rules:
>
> +--------------------------+
> | Copy to queue 8          |
> +==========+===============+
> | PASSTHRU |               |
> +----------+-----------+---+
> | QUEUE    | ``queue`` | 8 |
> +----------+-----------+---+
>
> ``ID``
> ^^^^^^
>
> Attaches a 32 bit value to packets.
>
> +----------------------------------------------+
> | ID                                           |
> +========+=====================================+
> | ``id`` | 32 bit value to return with packets |
> +--------+-------------------------------------+
>
> .. raw:: pdf
>
>     PageBreak
>
> ``QUEUE``
> ^^^^^^^^^
>
> Assigns packets to a given queue index.
>
> - Terminating by default.
>
> +--------------------------------+
> | QUEUE                          |
> +===========+====================+
> | ``queue`` | queue index to use |
> +-----------+--------------------+
>
> ``DROP``
> ^^^^^^^^
>
> Drop packets.
>
> - No configurable property.
> - Terminating by default.
> - PASSTHRU overrides this action if both are specified.
>
> +---------------+
> | DROP          |
> +===============+
> | no properties |
> +---------------+
>
> ``COUNT``
> ^^^^^^^^^
>
> Enables hits counter for this rule.
>
> This counter can be retrieved and reset through ``rte_flow_query()``, see
> ``struct rte_flow_query_count``.
>
> - Counters can be retrieved with ``rte_flow_query()``.
> - No configurable property.
>
> +---------------+
> | COUNT         |
> +===============+
> | no properties |
> +---------------+
>
> Query structure to retrieve and reset the flow rule hits counter:
>
> +------------------------------------------------+
> | COUNT query                                    |
> +===========+=====+==============================+
> | ``reset`` | in  | reset counter after query    |
> +-----------+-----+------------------------------+
> | ``hits``  | out | number of hits for this flow |
> +-----------+-----+------------------------------+
>
> ``DUP``
> ^^^^^^^
>
> Duplicates packets to a given queue index.
>
> This is normally combined with QUEUE, however when used alone, it is
> actually similar to QUEUE + PASSTHRU.
>
> - Non-terminating by default.
>
> +------------------------------------------------+
> | DUP                                            |
> +===========+====================================+
> | ``queue`` | queue index to duplicate packet to |
> +-----------+------------------------------------+
>
> .. raw:: pdf
>
>     PageBreak
>
> ``RSS``
> ^^^^^^^
>
> Similar to QUEUE, except RSS is additionally performed on packets to spread
> them among several queues according to the provided parameters.
>
> - Terminating by default.
>
> +---------------------------------------------+
> | RSS                                         |
> +==============+==============================+
> | ``rss_conf`` | RSS parameters               |
> +--------------+------------------------------+
> | ``queues``   | number of entries in queue[] |
> +--------------+------------------------------+
> | ``queue[]``  | queue indices to use         |
> +--------------+------------------------------+
>
> ``PF`` (action)
> ^^^^^^^^^^^^^^^
>
> Redirects packets to the physical function (PF) of the current device.
>
> - No configurable property.
> - Terminating by default.
>
> +---------------+
> | PF            |
> +===============+
> | no properties |
> +---------------+
>
> ``VF`` (action)
> ^^^^^^^^^^^^^^^
>
> Redirects packets to the virtual function (VF) of the current device with
> the specified ID.
>
> - Terminating by default.
>
> +---------------------------------------+
> | VF                                    |
> +========+==============================+
> | ``id`` | VF ID to redirect packets to |
> +--------+------------------------------+
>
> Planned types
> ~~~~~~~~~~~~~
>
> Other action types are planned but not defined yet. These actions will add
> the ability to alter matching packets in several ways, such as performing
> encapsulation/decapsulation of tunnel headers on specific flows.
>
> .. raw:: pdf
>
>     PageBreak
>
> Rules management
> ----------------
>
> A simple API with only four functions is provided to fully manage flows.
>
> Each created flow rule is associated with an opaque, PMD-specific handle
> pointer. The application is responsible for keeping it until the rule is
> destroyed.
>
> Flows rules are defined with ``struct rte_flow``.
>
> Validation
> ~~~~~~~~~~
>
> Given that expressing a definite set of device capabilities with this API is
> not practical, a dedicated function is provided to check if a flow rule is
> supported and can be created.
>
> ::
>
>   int
>   rte_flow_validate(uint8_t port_id,
>                     const struct rte_flow_pattern *pattern,
>                     const struct rte_flow_actions *actions);
>
> While this function has no effect on the target device, the flow rule is
> validated against its current configuration state and the returned value
> should be considered valid by the caller for that state only.
>
> The returned value is guaranteed to remain valid only as long as no
> successful calls to rte_flow_create() or rte_flow_destroy() are made in the
> meantime and no device parameter affecting flow rules in any way are
> modified, due to possible collisions or resource limitations (although in
> such cases ``EINVAL`` should not be returned).
>
> Arguments:
>
> - ``port_id``: port identifier of Ethernet device.
> - ``pattern``: pattern specification to check.
> - ``actions``: actions associated with the flow definition.
>
> Return value:
>
> - **0** if flow rule is valid and can be created. A negative errno value
>    otherwise (``rte_errno`` is also set), the following errors are defined.
> - ``-EINVAL``: unknown or invalid rule specification.
> - ``-ENOTSUP``: valid but unsupported rule specification (e.g. partial masks
>    are unsupported).
> - ``-EEXIST``: collision with an existing rule.
> - ``-ENOMEM``: not enough resources.
>
> .. raw:: pdf
>
>     PageBreak
>
> Creation
> ~~~~~~~~
>
> Creating a flow rule is similar to validating one, except the rule is
> actually created.
>
> ::
>
>   struct rte_flow *
>   rte_flow_create(uint8_t port_id,
>                   const struct rte_flow_pattern *pattern,
>                   const struct rte_flow_actions *actions);
>
> Arguments:
>
> - ``port_id``: port identifier of Ethernet device.
> - ``pattern``: pattern specification to add.
> - ``actions``: actions associated with the flow definition.
>
> Return value:
>
> A valid flow pointer in case of success, NULL otherwise and ``rte_errno`` is
> set to the positive version of one of the error codes defined for
> ``rte_flow_validate()``.
>
> Destruction
> ~~~~~~~~~~~
>
> Flow rules destruction is not automatic, and a queue should not be released
> if any are still attached to it. Applications must take care of performing
> this step before releasing resources.
>
> ::
>
>   int
>   rte_flow_destroy(uint8_t port_id,
>                    struct rte_flow *flow);
>
>
> Failure to destroy a flow rule may occur when other flow rules depend on it,
> and destroying it would result in an inconsistent state.
>
> This function is only guaranteed to succeed if flow rules are destroyed in
> reverse order of their creation.
>
> Arguments:
>
> - ``port_id``: port identifier of Ethernet device.
> - ``flow``: flow rule to destroy.
>
> Return value:
>
> - **0** on success, a negative errno value otherwise and ``rte_errno`` is
>    set.
>
> .. raw:: pdf
>
>     PageBreak
>
> Query
> ~~~~~
>
> Query an existing flow rule.
>
> This function allows retrieving flow-specific data such as counters. Data
> is gathered by special actions which must be present in the flow rule
> definition.
>
> ::
>
>   int
>   rte_flow_query(uint8_t port_id,
>                  struct rte_flow *flow,
>                  enum rte_flow_action_type action,
>                  void *data);
>
> Arguments:
>
> - ``port_id``: port identifier of Ethernet device.
> - ``flow``: flow rule to query.
> - ``action``: action type to query.
> - ``data``: pointer to storage for the associated query data type.
>
> Return value:
>
> - **0** on success, a negative errno value otherwise and ``rte_errno`` is
>    set.
>
> .. raw:: pdf
>
>     PageBreak
>
> Behavior
> --------
>
> - API operations are synchronous and blocking (``EAGAIN`` cannot be
>    returned).
>
> - There is no provision for reentrancy/multi-thread safety, although nothing
>    should prevent different devices from being configured at the same
>    time. PMDs may protect their control path functions accordingly.
>
> - Stopping the data path (TX/RX) should not be necessary when managing flow
>    rules. If this cannot be achieved naturally or with workarounds (such as
>    temporarily replacing the burst function pointers), an appropriate error
>    code must be returned (``EBUSY``).
>
> - PMDs, not applications, are responsible for maintaining flow rules
>    configuration when stopping and restarting a port or performing other
>    actions which may affect them. They can only be destroyed explicitly.
>
> .. raw:: pdf
>
>     PageBreak
>
> Compatibility
> -------------
>
> No known hardware implementation supports all the features described in this
> document.
>
> Unsupported features or combinations are not expected to be fully emulated
> in software by PMDs for performance reasons. Partially supported features
> may be completed in software as long as hardware performs most of the work
> (such as queue redirection and packet recognition).
>
> However PMDs are expected to do their best to satisfy application requests
> by working around hardware limitations as long as doing so does not affect
> the behavior of existing flow rules.
>
> The following sections provide a few examples of such cases, they are based
> on limitations built into the previous APIs.
>
> Global bitmasks
> ~~~~~~~~~~~~~~~
>
> Each flow rule comes with its own, per-layer bitmasks, while hardware may
> support only a single, device-wide bitmask for a given layer type, so that
> two IPv4 rules cannot use different bitmasks.
>
> The expected behavior in this case is that PMDs automatically configure
> global bitmasks according to the needs of the first created flow rule.
>
> Subsequent rules are allowed only if their bitmasks match those, the
> ``EEXIST`` error code should be returned otherwise.
>
> Unsupported layer types
> ~~~~~~~~~~~~~~~~~~~~~~~
>
> Many protocols can be simulated by crafting patterns with the `RAW`_ type.
>
> PMDs can rely on this capability to simulate support for protocols with
> fixed headers not directly recognized by hardware.
>
> ``ANY`` pattern item
> ~~~~~~~~~~~~~~~~~~~~
>
> This pattern item stands for anything, which can be difficult to translate
> to something hardware would understand, particularly if followed by more
> specific types.
>
> Consider the following pattern:
>
> +---+--------------------------------+
> | 0 | ETHER                          |
> +---+--------------------------------+
> | 1 | ANY (``min`` = 1, ``max`` = 1) |
> +---+--------------------------------+
> | 2 | TCP                            |
> +---+--------------------------------+
>
> Knowing that TCP does not make sense with something other than IPv4 and IPv6
> as L3, such a pattern may be translated to two flow rules instead:
>
> +---+--------------------+
> | 0 | ETHER              |
> +---+--------------------+
> | 1 | IPV4 (zeroed mask) |
> +---+--------------------+
> | 2 | TCP                |
> +---+--------------------+
>
> +---+--------------------+
> | 0 | ETHER              |
> +---+--------------------+
> | 1 | IPV6 (zeroed mask) |
> +---+--------------------+
> | 2 | TCP                |
> +---+--------------------+
>
> Note that as soon as a ANY rule covers several layers, this approach may
> yield a large number of hidden flow rules. It is thus suggested to only
> support the most common scenarios (anything as L2 and/or L3).
>
> .. raw:: pdf
>
>     PageBreak
>
> Unsupported actions
> ~~~~~~~~~~~~~~~~~~~
>
> - When combined with a `QUEUE`_ action, packet counting (`COUNT`_) and
>    tagging (`ID`_) may be implemented in software as long as the target queue
>    is used by a single rule.
>
> - A rule specifying both `DUP`_ + `QUEUE`_ may be translated to two hidden
>    rules combining `QUEUE`_ and `PASSTHRU`_.
>
> - When a single target queue is provided, `RSS`_ can also be implemented
>    through `QUEUE`_.
>
> Flow rules priority
> ~~~~~~~~~~~~~~~~~~~
>
> While it would naturally make sense, flow rules cannot be assumed to be
> processed by hardware in the same order as their creation for several
> reasons:
>
> - They may be managed internally as a tree or a hash table instead of a
>    list.
> - Removing a flow rule before adding another one can either put the new rule
>    at the end of the list or reuse a freed entry.
> - Duplication may occur when packets are matched by several rules.
>
> For overlapping rules (particularly in order to use the `PASSTHRU`_ action)
> predictable behavior is only guaranteed by using different priority levels.
>
> Priority levels are not necessarily implemented in hardware, or may be
> severely limited (e.g. a single priority bit).
>
> For these reasons, priority levels may be implemented purely in software by
> PMDs.
>
> - For devices expecting flow rules to be added in the correct order, PMDs
>    may destroy and re-create existing rules after adding a new one with
>    a higher priority.
>
> - A configurable number of dummy or empty rules can be created at
>    initialization time to save high priority slots for later.
>
> - In order to save priority levels, PMDs may evaluate whether rules are
>    likely to collide and adjust their priority accordingly.
>
> .. raw:: pdf
>
>     PageBreak
>
> API migration
> =============
>
> Exhaustive list of deprecated filter types and how to convert them to
> generic flow rules.
>
> ``MACVLAN`` to ``ETH`` → ``VF``, ``PF``
> ---------------------------------------
>
> `MACVLAN`_ can be translated to a basic `ETH`_ flow rule with a `VF
> (action)`_ or `PF (action)`_ terminating action.
>
> +------------------------------------+
> | MACVLAN                            |
> +--------------------------+---------+
> | Pattern                  | Actions |
> +===+=====+==========+=====+=========+
> | 0 | ETH | ``spec`` | any | VF,     |
> |   |     +----------+-----+ PF      |
> |   |     | ``mask`` | any |         |
> +---+-----+----------+-----+---------+
>
> ``ETHERTYPE`` to ``ETH`` → ``QUEUE``, ``DROP``
> ----------------------------------------------
>
> `ETHERTYPE`_ is basically an `ETH`_ flow rule with `QUEUE`_ or `DROP`_ as
> a terminating action.
>
> +------------------------------------+
> | ETHERTYPE                          |
> +--------------------------+---------+
> | Pattern                  | Actions |
> +===+=====+==========+=====+=========+
> | 0 | ETH | ``spec`` | any | QUEUE,  |
> |   |     +----------+-----+ DROP    |
> |   |     | ``mask`` | any |         |
> +---+-----+----------+-----+---------+
>
> ``FLEXIBLE`` to ``RAW`` → ``QUEUE``
> -----------------------------------
>
> `FLEXIBLE`_ can be translated to one `RAW`_ pattern with `QUEUE`_ as the
> terminating action and a defined priority level.
>
> +------------------------------------+
> | FLEXIBLE                           |
> +--------------------------+---------+
> | Pattern                  | Actions |
> +===+=====+==========+=====+=========+
> | 0 | RAW | ``spec`` | any | QUEUE   |
> |   |     +----------+-----+         |
> |   |     | ``mask`` | any |         |
> +---+-----+----------+-----+---------+
>
> ``SYN`` to ``TCP`` → ``QUEUE``
> ------------------------------
>
> `SYN`_ is a `TCP`_ rule with only the ``syn`` bit enabled and masked, and
> `QUEUE`_ as the terminating action.
>
> Priority level can be set to simulate the high priority bit.
>
> +---------------------------------------------+
> | SYN                                         |
> +-----------------------------------+---------+
> | Pattern                           | Actions |
> +===+======+==========+=============+=========+
> | 0 | ETH  | ``spec`` | N/A         | QUEUE   |
> |   |      +----------+-------------+         |
> |   |      | ``mask`` | empty       |         |
> +---+------+----------+-------------+         |
> | 1 | IPV4 | ``spec`` | N/A         |         |
> |   |      +----------+-------------+         |
> |   |      | ``mask`` | empty       |         |
> +---+------+----------+-------------+         |
> | 2 | TCP  | ``spec`` | ``syn`` = 1 |         |
> |   |      +----------+-------------+         |
> |   |      | ``mask`` | ``syn`` = 1 |         |
> +---+------+----------+-------------+---------+
>
> ``NTUPLE`` to ``IPV4``, ``TCP``, ``UDP`` → ``QUEUE``
> ----------------------------------------------------
>
> `NTUPLE`_ is similar to specifying an empty L2, `IPV4`_ as L3 with `TCP`_ or
> `UDP`_ as L4 and `QUEUE`_ as the terminating action.
>
> A priority level can be specified as well.
>
> +---------------------------------------+
> | NTUPLE                                |
> +-----------------------------+---------+
> | Pattern                     | Actions |
> +===+======+==========+=======+=========+
> | 0 | ETH  | ``spec`` | N/A   | QUEUE   |
> |   |      +----------+-------+         |
> |   |      | ``mask`` | empty |         |
> +---+------+----------+-------+         |
> | 1 | IPV4 | ``spec`` | any   |         |
> |   |      +----------+-------+         |
> |   |      | ``mask`` | any   |         |
> +---+------+----------+-------+         |
> | 2 | TCP, | ``spec`` | any   |         |
> |   | UDP  +----------+-------+         |
> |   |      | ``mask`` | any   |         |
> +---+------+----------+-------+---------+
>
> ``TUNNEL`` to ``ETH``, ``IPV4``, ``IPV6``, ``VXLAN`` (or other) → ``QUEUE``
> ---------------------------------------------------------------------------
>
> `TUNNEL`_ matches common IPv4 and IPv6 L3/L4-based tunnel types.
>
> In the following table, `ANY`_ is used to cover the optional L4.
>
> +------------------------------------------------+
> | TUNNEL                                         |
> +--------------------------------------+---------+
> | Pattern                              | Actions |
> +===+=========+==========+=============+=========+
> | 0 | ETH     | ``spec`` | any         | QUEUE   |
> |   |         +----------+-------------+         |
> |   |         | ``mask`` | any         |         |
> +---+---------+----------+-------------+         |
> | 1 | IPV4,   | ``spec`` | any         |         |
> |   | IPV6    +----------+-------------+         |
> |   |         | ``mask`` | any         |         |
> +---+---------+----------+-------------+         |
> | 2 | ANY     | ``spec`` | ``min`` = 0 |         |
> |   |         |          +-------------+         |
> |   |         |          | ``max`` = 0 |         |
> |   |         +----------+-------------+         |
> |   |         | ``mask`` | N/A         |         |
> +---+---------+----------+-------------+         |
> | 3 | VXLAN,  | ``spec`` | any         |         |
> |   | GENEVE, +----------+-------------+         |
> |   | TEREDO, | ``mask`` | any         |         |
> |   | NVGRE,  |          |             |         |
> |   | GRE,    |          |             |         |
> |   | ...     |          |             |         |
> +---+---------+----------+-------------+---------+
>
> .. raw:: pdf
>
>     PageBreak
>
> ``FDIR`` to most item types → ``QUEUE``, ``DROP``, ``PASSTHRU``
> ---------------------------------------------------------------
>
> `FDIR`_ is more complex than any other type, there are several methods to
> emulate its functionality. It is summarized for the most part in the table
> below.
>
> A few features are intentionally not supported:
>
> - The ability to configure the matching input set and masks for the entire
>    device, PMDs should take care of it automatically according to flow rules.
>
> - Returning four or eight bytes of matched data when using flex bytes
>    filtering. Although a specific action could implement it, it conflicts
>    with the much more useful 32 bits tagging on devices that support it.
>
> - Side effects on RSS processing of the entire device. Flow rules that
>    conflict with the current device configuration should not be
>    allowed. Similarly, device configuration should not be allowed when it
>    affects existing flow rules.
>
> - Device modes of operation. "none" is unsupported since filtering cannot be
>    disabled as long as a flow rule is present.
>
> - "MAC VLAN" or "tunnel" perfect matching modes should be automatically set
>    according to the created flow rules.
>
> +----------------------------------------------+
> | FDIR                                         |
> +---------------------------------+------------+
> | Pattern                         | Actions    |
> +===+============+==========+=====+============+
> | 0 | ETH,       | ``spec`` | any | QUEUE,     |
> |   | RAW        +----------+-----+ DROP,      |
> |   |            | ``mask`` | any | PASSTHRU   |
> +---+------------+----------+-----+------------+
> | 1 | IPV4,      | ``spec`` | any | ID         |
> |   | IPV6       +----------+-----+ (optional) |
> |   |            | ``mask`` | any |            |
> +---+------------+----------+-----+            |
> | 2 | TCP,       | ``spec`` | any |            |
> |   | UDP,       +----------+-----+            |
> |   | SCTP       | ``mask`` | any |            |
> +---+------------+----------+-----+            |
> | 3 | VF,        | ``spec`` | any |            |
> |   | PF,        +----------+-----+            |
> |   | SIGNATURE  | ``mask`` | any |            |
> |   | (optional) |          |     |            |
> +---+------------+----------+-----+------------+
>
> ``HASH``
> ~~~~~~~~
>
> Hashing configuration is set per rule through the `SIGNATURE`_ item.
>
> Since it is usually a global device setting, all flow rules created with
> this item may have to share the same specification.
>
> ``L2_TUNNEL`` to ``VOID`` → ``VXLAN`` (or others)
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> All packets are matched. This type alters incoming packets to encapsulate
> them in a chosen tunnel type, optionally redirect them to a VF as well.
>
> The destination pool for tag based forwarding can be emulated with other
> flow rules using `DUP`_ as the action.
>
> +----------------------------------------+
> | L2_TUNNEL                              |
> +---------------------------+------------+
> | Pattern                   | Actions    |
> +===+======+==========+=====+============+
> | 0 | VOID | ``spec`` | N/A | VXLAN,     |
> |   |      |          |     | GENEVE,    |
> |   |      |          |     | ...        |
> |   |      +----------+-----+------------+
> |   |      | ``mask`` | N/A | VF         |
> |   |      |          |     | (optional) |
> +---+------+----------+-----+------------+
>