Re: [dpdk-dev] [RFC 1/3] ethdev: extend flow metadata

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 6/4/19 12:32 AM, Yongseok Koh wrote:
> Currently, metadata can be set on egress path via mbuf tx_meatadata field
> with PKT_TX_METADATA flag and RTE_FLOW_ITEM_TYPE_RX_META matches metadata.
>
> This patch extends the usability.
>
> 1) RTE_FLOW_ACTION_TYPE_SET_META
>
> When supporting multiple tables, Tx metadata can also be set by a rule and
> matched by another rule. This new action allows metadata to be set as a
> result of flow match.
>
> 2) Metadata on ingress
>
> There's also need to support metadata on packet Rx. Metadata can be set by
> SET_META action and matched by META item like Tx. The final value set by
> the action will be delivered to application via mbuf metadata field with
> PKT_RX_METADATA ol_flag.
>
> For this purpose, mbuf->tx_metadata is moved as a separate new field and
> renamed to 'metadata' to support both Rx and Tx metadata.
>
> For loopback/hairpin packet, metadata set on Rx/Tx may or may not be
> propagated to the other path depending on HW capability.
>
> Signed-off-by: Yongseok Koh <yskoh@mellanox.com>

There is a mark on Rx which is delivered to application in hash.fdir.hi.
Why do we need one more 32-bit value set by NIC and delivered to 
application?
What is the difference between MARK and META on Rx?
When application should use MARK and when META?
Is there cases when both could be necessary?

Moreover, the third patch adds 32-bit tags which are not delivered to
application. May be META/MARK should be simply a kind of TAG (e.g. with
index 0 or marked using additional attribute) which is delivered to 
application?

(It is either API breakage (if tx_metadata is removed) or ABI breakage
if metadata and tx_metadata will share new location after shinfo).

Andrew.