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

[Shyam Shrivastav]

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 at 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!