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

[Vlad Zolotarov]

On 07/22/2016 01:48 AM, Ananyev, Konstantin wrote:
>
>> 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>

Acked-by: Vlad Zolotarov <vladz at scylladb.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