[dpdk-users] Why is udp packet, sent by dpdk, received with zero'd payload?

[Cliff Burdick]

If you look at the code for  rte_pktmbuf_prepend  it appears to be just
incrementing data_len and pkt_len by the same amount. My guess is that
those fields were not set to the correct values before you called
rte_pktmbuf_prepend().

On Wed, Jul 1, 2020 at 6:41 AM David Aldrich <david.aldrich.ntml at gmail.com>
wrote:

> I think this is where my lack of understanding is my problem.  Looking at
> the mbuf dump:
>
> dump mbuf at 0x53e4e92c0, iova=73e4e9340, buf_len=2176
>   pkt_len=57, ol_flags=c0000000000000, nb_segs=2, in_port=65535
>   segment at 0x53e4e92c0, data=0x53e4e9396, data_len=42
>   Dump data at [0x53e4e9396], len=42
> 00000000: 94 40 C9 1F C4 DB 94 40 C9 1E 13 7D 08 00 45 B8 | . at .....@...}..E.
> 00000010: 00 2B 00 00 00 00 40 11 F5 E8 C0 A8 01 69 C0 A8 | .+.... at ......i..
> 00000020: 01 68 0B B9 0B B8 00 17 64 2D |  |  |  |  |  |  | .h......d-
>   segment at 0x53e146e40, data=0x53e4fbbc0, data_len=15
>   Dump data at [0x53e4fbbc0], len=15
> 00000000: 48 65 6C 6C 6F 20 66 72 6F 6D 20 64 70 64 6B |  | Hello from dpdk
>
> It consists of two parts (segments?), of lengths 42 and 15. This makes sense to me as I first
> put the payload in the mbuf (15 bytes) and then added the Ethernet and L3 headers (42 bytes) by calling rte_pktmbuf_prepend().
>
> I guess only the first segment is getting transmitted?
>
>
> On Wed, Jul 1, 2020 at 1:57 PM Cliff Burdick <shaklee3 at gmail.com> wrote:
>
>> Are you setting data_len and packet_len in the mbuf before sending?
>>
>>
>> On Wed, Jul 1, 2020, 03:23 David Aldrich <david.aldrich.ntml at gmail.com>
>> wrote:
>>
>>>  Hi,
>>>
>>> I have a problem transmitting udp packets with dpdk-stable-18.11.8. I
>>> have
>>> posted a question about it on stackoverflow:
>>>
>>>
>>> https://stackoverflow.com/questions/62674596/why-is-udp-packet-sent-by-dpdk-received-with-zerod-payload
>>>
>>> I would be grateful for any comments either there or in this group
>>> please.
>>>
>>> Best regards
>>>
>>> David
>>>
>>