How to strip CRC - FCS from message

[Yasin CANER]

Hello,

Enviroment information;

DPDK versiyon 17.05
Kernel version 4.4.0
OS - Ubuntu 16.05
INTEL NIC XL710
Last i40e driver and NVM is installed.

ethtool -k ens2f2 :
tx-checksumming: on
        tx-checksum-ipv4: on
        tx-checksum-ip-generic: off [fixed]
        tx-checksum-ipv6: on
        tx-checksum-fcoe-crc: off [fixed]
        tx-checksum-sctp: on
rx-fcs: off [fixed]
rx-all: off [fixed]

What is CRC or FCS :

https://www.firewall.cx/networking-topics/ethernet/ethernet-frame-formats/201-ethernet-ii.html

State:


  *   Even if strip_crc flag is up in port_config, NIC doesnt strip CRC.
  *   After stripping Ethernet Header from message-buf, CRC still there. So it breaks fragmentation when specific byte length income. For Example; Message with IP  header -> 1480, Ether Header 6+6+2 = 14 byte. Frame length looks 1498 byte.  Looks like 4 byte Crc, it has. After Ether header is stripped , 1488 byte left.
[code]
static struct rte_eth_conf port_conf = {
    .rxmode =
        {
            .header_split   = 0, /* Header Split disabled */
            .hw_ip_checksum = 0, /* IP checksum offload disabled */
            .hw_vlan_filter = 0, /* VLAN filtering disabled */
            .jumbo_frame    = 0, /* Jumbo Frame Support disabled */
            .hw_strip_crc   = 1, /* CRC stripped by hardware */
        },
    .txmode =
        {
            .mq_mode = ETH_MQ_TX_NONE,
        },
};
[/code]


Is there any function to strip CRC bytes or what is best way? Big thanks to help.

I have an idea that,

After stripping Ethernet Header ,

  *   If total length of message is bigger than IP header length , there is a CRC, it needs to strip somehow?
  *   If total length of message is equal to IP header length, no problem.
  *   If total length of message is less than IP header length, message is broken.

Best Regards.

___
Yasin CANER
Lider Mühendis
Ulak Haberleşme A.Ş. Ankara

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