Re: [dpdk-dev] About the data payload of rte_mbuf?

[Shyam Shrivastav <shrivastav.shyam@gmail.com>]

And if just payload length is required one can get by subtracting
(ip-hdr-len + tcp-offset) from total length in ip header ...

On Thu, Dec 6, 2018 at 11:18 AM Shyam Shrivastav <shrivastav.shyam@gmail.com>
wrote:

>
> As per my understanding
>
> payload = (uint8_t *)tcp_hdr + (tcp_hdr->data_off << 2);
>
> should be
>
> payload = (uint8_t *)tcp_hdr + (tcp_hdr->data_off >> 4) << 2);
>
> Note that data offset is 4 most significant bits of the byte, refer tcp
> header
>
>
>
> On Thu, Dec 6, 2018 at 9:15 AM bai bakari <912873551@qq.com> wrote:
>
>> Hi,
>>
>>
>> Now, I want to get the data payload of rte_mbuf, and i wrote the
>> following code:
>>
>>
>> struct ipv4_hdr *ipv4_hdr;
>> struct tcp_hdr *tcp_hdr;
>> uint32_t payload_len, ip_len;
>> uint8_t *payload = NULL;
>>
>>
>>
>> ipv4_hdr = rte_pktmbuf_mtod_offset(m, struct ipv4_hdr *, sizeof(struct
>> ether_hdr));
>> ip_len = ntohs(ipv4_hdr->total_length);
>>
>>
>>
>> if (ipv4_hdr->next_proto_id == IPPROTO_TCP) {
>>     tcp_hdr = (struct tcp_hdr *)((uint8_t *)ipv4_hdr +
>> ((ipv4_hdr->version_ihl & 0xf) << 2));
>>     payload = (uint8_t *)tcp_hdr + (tcp_hdr->data_off << 2);
>>     payload_len = ip_len - (payload - (uint8_t *)ipv4_hdr);
>>
>> }
>>
>>
>> when i send packets using dpdk-pktgen, i found:
>> ip_len = 46
>> ip_header_len = 20
>> but the tcp_header_len=(tcp_hdr->data_off << 2)=0,
>> and (payload - (uint8_t *)ipv4_hdr) = 340 > ip_len.
>>
>>
>> I'm confused, is there any errors about the code to compute the
>> payload_len of rte_mbuf?
>> I think maybe the dpdk-pktgen cannot send the packets with payload?
>>
>>
>> I'm a beginner, anyone can help me how to compute the payload_len of
>> rte_mbuf and test it?
>>
>>
>> Thank you in advance!
>
>