Re: [dpdk-dev] [PATCH] ethdev: introduce generic copy rte flow action

[Jerin Jacob <jerinjacobk@gmail.com>]

On Fri, Jan 8, 2021 at 12:02 PM Alexander Kozyrev <akozyrev@nvidia.com> wrote:
>
> Implement a generic copy flow API to allow copying of an arbitrary
> header field (as well as mark, metadata or tag) to another item.
>
> This generic copy mechanism removes the necessity to implement a
> separate RTE Flow action every time we need to modify a new packet
> field in the future. A user-provided value can be used from a
> specified tag/metadata or directly copied from other packet field.
>
> The number of bits to copy as well as the offset to start from can
> be specified to allow a partial copy or copy into an arbitrary
> place in a packet for greater flexibility.
>
> RFC: http://patches.dpdk.org/patch/85384/
>
> Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com>
> ---

>
> +Action: ``COPY_ITEM``
> +^^^^^^^^^^^^^^^^^^^^^
> +
> +Copy ``width`` bits from ``src`` item to ``dst`` item.
> +
> +An arbitrary header field (as well as mark, metadata or tag values)
> +can be used as both source and destination items as set by ``item``.
> +
> +Inner packet header fields can be accessed using the ``index`` and
> +it is possible to start the copy from the ``offset`` bits in an item.
> +
> +.. _table_rte_flow_action_copy_item:
> +
> +.. table:: COPY_ITEM
> +
> +   +-----------------------------------------+
> +   | Field         | Value                   |
> +   +===============+=========================+
> +   | ``dst``       | destination item        |
> +   | ``src``       | source item             |
> +   | ``width``     | number of bits to copy  |



Overall it is a good improvement.

I think, if we add transform "op" here then it can be more generic. In
other words, A generic packet transform and copy operation is just one
of the operations.
ie.. making it as rte_flow_action_xform_item and introduce COPY, ADD,
SUB, etc transform along with existing rte_flow_action_copy_item
fields.

It may useful for expressing P4 packet transforms to rte_flow.

The current generation of Marvell HW does not have COPY transform so I
am leaving suggestions to vendors with this HW capablity.


> +   +---------------+-------------------------+




> +
> +.. _table_rte_flow_action_copy_data:
> +
> +.. table:: destination/source item definition
> +
> +   +----------------------------------------------------------+
> +   | Field         | Value                                    |
> +   +===============+==========================================+
> +   | ``item``      | ID of a packet field/mark/metadata/tag   |
> +   | ``index``     | index of outer/inner header or tag array |
> +   | ``offset``    | number of bits to skip during the copy   |
> +   +---------------+------------------------------------------+
> +