Re: [dpdk-dev] Questions about reading/writing/modifying packet header.

[Andriy Berestovskyy <aber@semihalf.com>]

Hi Ick-Sung,
Please see inline.

On Mon, Apr 18, 2016 at 2:14 PM, 최익성 <pnk003@naver.com> wrote:
> If I take an example, the worker assignment method using &amp; (not %) in load balancing was not fixed yet.

If the code works, there is nothing to fix, right? ;)


> Question #1) I would like to know how can I read/write/modify TCP/UDP/ICMP/IGMP/...  headers from packet in rte_mbuf.
>   I will really appreciate if I can be given an example code. I guess it would be somewhat complex.

For an example please have a look at parse_ethernet() in test-pmd:
http://dpdk.org/browse/dpdk/tree/app/test-pmd/csumonly.c#n171

The example usage is in the same file:

eth_hdr = rte_pktmbuf_mtod(m, struct ether_hdr *);
parse_ethernet(eth_hdr, &info);
l3_hdr = (char *)eth_hdr + info.l2_len;

if (info.l4_proto == IPPROTO_UDP) {
    udp_hdr = (struct udp_hdr *)((char *)l3_hdr + info.l3_len);
    udp_hdr->dst_port = ...
}

Then you might need to recalculate the L4 checksum, so have a look at
rte_ipv4_udptcp_cksum().


> Question #2) The IP checksum does not include 6 the ptr. 6 th ptr (ptr16[5]) is missing in the example code. Is it right?
>   ( ip_cksum += ptr16[5]; in the following code.)

The code seems fine, ptr16[5] is the checksum itself. It should be
zero, so we can skip it.


There is a users@dpdk.org mailing list now, so please use it for your
further questions. Here is the link for your convenience:
http://dpdk.org/ml

Regards,
Andriy