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

[David Aldrich]

>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.

I'm sorry, but I don't understand. My calls to rte_pktmbuf_prepend are:


p_udp_hdr = (struct udp_hdr*)rte_pktmbuf_prepend(ptMbuf,
(uint16_t)sizeof(struct udp_hdr));
p_ip_hdr  = (struct ipv4_hdr*)rte_pktmbuf_prepend(ptMbuf,
(uint16_t)sizeof(struct ipv4_hdr));

are you saying that those calls are wrong?  When you say 'if you look
at the code' are you referring to this code?

(I thought it best that I should ask for clarification rather than guess).

Thanks


On Wed, Jul 1, 2020 at 3:59 PM Cliff Burdick <shaklee3 at gmail.com> wrote:

> 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
>>>>
>>>