[dpdk-dev] Where is the padding code in DPDK?

[Burakov, Anatoly]

On 13-Nov-18 7:16 AM, Sam wrote:
> Hi all,
> 
> As we know, ethernet frame must longer then 64B.
> 
> So if I create rte_mbuf and fill it with just 60B data, will
> rte_eth_tx_burst add padding data, let the frame longer then 64B
> 
> If it does, where is the code?
> 

Others can correct me if i'm wrong here, but specifically in case of 
64-byte packets, these are the shortest valid packets that you can send, 
and a 64-byte packet will actually carry only 60 bytes' worth of packet 
data, because there's a 4-byte CRC frame at the end (see Ethernet frame 
format). If you enabled CRC offload, then your NIC will append the 4 
bytes at transmit. If you haven't, then it's up to each individual 
driver/NIC to accept/reject such a packet because it can rightly be 
considered malformed.

In addition, your NIC may add e.g. VLAN tags or other stuff, again 
depending on hardware offloads that you have enabled in your TX 
configuration, which may push the packet size beyond 64 bytes while 
having only 60 bytes of actual packet data.

-- 
Thanks,
Anatoly