[dpdk-dev] [PATCH v2] doc: announce ABI change for rte_eth_dev structure

[Ananyev, Konstantin]

> 
> This is an ABI deprecation notice for DPDK 16.11 in librte_ether about
> changes in rte_eth_dev and rte_eth_desc_lim structures.
> 
> As discussed in that thread:
> 
> http://dpdk.org/ml/archives/dev/2015-September/023603.html
> 
> Different NIC models depending on HW offload requested might impose
> different requirements on packets to be TX-ed in terms of:
> 
>  - Max number of fragments per packet allowed
>  - Max number of fragments per TSO segments
>  - The way pseudo-header checksum should be pre-calculated
>  - L3/L4 header fields filling
>  - etc.
> 
> 
> MOTIVATION:
> -----------
> 
> 1) Some work cannot (and didn't should) be done in rte_eth_tx_burst.
>    However, this work is sometimes required, and now, it's an
>    application issue.
> 
> 2) Different hardware may have different requirements for TX offloads,
>    other subset can be supported and so on.
> 
> 3) Some parameters (eg. number of segments in ixgbe driver) may hung
>    device. These parameters may be vary for different devices.
> 
>    For example i40e HW allows 8 fragments per packet, but that is after
>    TSO segmentation. While ixgbe has a 38-fragment pre-TSO limit.
> 
> 4) Fields in packet may require different initialization (like eg. will
>    require pseudo-header checksum precalculation, sometimes in a
>    different way depending on packet type, and so on). Now application
>    needs to care about it.
> 
> 5) Using additional API (rte_eth_tx_prep) before rte_eth_tx_burst let to
>    prepare packet burst in acceptable form for specific device.
> 
> 6) Some additional checks may be done in debug mode keeping tx_burst
>    implementation clean.
> 
> 
> PROPOSAL:
> ---------
> 
> To help user to deal with all these varieties we propose to:
> 
> 1. Introduce rte_eth_tx_prep() function to do necessary preparations of
>    packet burst to be safely transmitted on device for desired HW
>    offloads (set/reset checksum field according to the hardware
>    requirements) and check HW constraints (number of segments per
>    packet, etc).
> 
>    While the limitations and requirements may differ for devices, it
>    requires to extend rte_eth_dev structure with new function pointer
>    "tx_pkt_prep" which can be implemented in the driver to prepare and
>    verify packets, in devices specific way, before burst, what should to
>    prevent application to send malformed packets.
> 
> 2. Also new fields will be introduced in rte_eth_desc_lim:
>    nb_seg_max and nb_mtu_seg_max, providing an information about max
>    segments in TSO and non-TSO packets acceptable by device.
> 
>    This information is useful for application to not create/limit
>    malicious packet.
> 
> 
> APPLICATION (CASE OF USE):
> --------------------------
> 
> 1) Application should to initialize burst of packets to send, set
>    required tx offload flags and required fields, like l2_len, l3_len,
>    l4_len, and tso_segsz
> 
> 2) Application passes burst to the rte_eth_tx_prep to check conditions
>    required to send packets through the NIC.
> 
> 3) The result of rte_eth_tx_prep can be used to send valid packets
>    and/or restore invalid if function fails.
> 
> eg.
> 
> 	for (i = 0; i < nb_pkts; i++) {
> 
> 		/* initialize or process packet */
> 
> 		bufs[i]->tso_segsz = 800;
> 		bufs[i]->ol_flags = PKT_TX_TCP_SEG | PKT_TX_IPV4
> 				| PKT_TX_IP_CKSUM;
> 		bufs[i]->l2_len = sizeof(struct ether_hdr);
> 		bufs[i]->l3_len = sizeof(struct ipv4_hdr);
> 		bufs[i]->l4_len = sizeof(struct tcp_hdr);
> 	}
> 
> 	/* Prepare burst of TX packets */
> 	nb_prep = rte_eth_tx_prep(port, 0, bufs, nb_pkts);
> 
> 	if (nb_prep < nb_pkts) {
> 		printf("tx_prep failed\n");
> 
> 		/* drop or restore invalid packets */
> 
> 	}
> 
> 	/* Send burst of TX packets */
> 	nb_tx = rte_eth_tx_burst(port, 0, bufs, nb_prep);
> 
> 	/* Free any unsent packets. */
> 
> 
> 
> Signed-off-by: Tomasz Kulasek <tomaszx.kulasek at intel.com>
> ---
>  doc/guides/rel_notes/deprecation.rst |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
> index f502f86..485aacb 100644
> --- a/doc/guides/rel_notes/deprecation.rst
> +++ b/doc/guides/rel_notes/deprecation.rst
> @@ -41,3 +41,10 @@ Deprecation Notices
>  * The mempool functions for single/multi producer/consumer are deprecated and
>    will be removed in 16.11.
>    It is replaced by rte_mempool_generic_get/put functions.
> +
> +* In 16.11 ABI changes are plained: the ``rte_eth_dev`` structure will be
> +  extended with new function pointer ``tx_pkt_prep`` allowing verification
> +  and processing of packet burst to meet HW specific requirements before
> +  transmit. Also new fields will be added to the ``rte_eth_desc_lim`` structure:
> +  ``nb_seg_max`` and ``nb_mtu_seg_max`` provideing information about number of
> +  segments limit to be transmitted by device for TSO/non-TSO packets.
> --

Acked-by: Konstantin Ananyev <konstantin.ananyev at intel.com>

> 1.7.9.5