[dpdk-users] Questions about locating the rte_mbuf payload

[Sungho Hong]

Hello I have sent the packet with the data "hellohellohello*"
in a message struct using DPDK

    struct message{
    data[PKT_SIZE]
    }

I am sending this data from a client to server, and the server receives
this data. the data received in the server can be viewed from the packet
dump provided by DPDK. You can see the data I am sending "hello"s right at
the bottom of the log

    00000000: A0 36 9F 83 AB BC 00 1B 21 A6 D4 D4 08 00 45 00 |
.6......!.....E.
    00000010: 01 49 7C 60 00 00 80 11 C9 37 0A DA 6E 59 0A DA |
.I|`.....7..nY..
    00000020: 6F FF 44 5C 44 5C 01 35 DF 27 7B 22 6E 61 6D 65 |
o.D\D\.5.'{"name
    00000030: 73 70 61 63 65 73 22 3A 20 5B 31 33 37 30 34 36 | spaces":
[137046
    00000040: 36 31 39 33 2C 20 32 39 33 31 32 37 36 38 39 36 | 6193,
2931276896
    00000050: 2C 20 31 33 32 34 30 31 33 30 39 31 2C 20 31 33 | ,
1324013091, 13
    00000060: 35 32 37 38 34 34 35 32 2C 20 31 34 33 33 32 37 | 52784452,
143327
    00000070: 32 31 36 36 2C 20 32 32 30 31 36 38 30 30 31 36 | 2166,
2201680016
    00000080: 2C 20 31 33 35 39 38 30 30 32 37 30 2C 20 31 34 | ,
1359800270, 14
    00000090: 37 31 30 37 33 36 34 39 2C 20 31 39 37 34 38 36 | 71073649,
197486
    000000A0: 31 33 39 32 2C 20 32 32 33 38 33 34 32 39 32 38 | 1392,
2238342928
    000000B0: 2C 20 31 33 37 32 38 31 35 32 32 31 2C 20 33 30 | ,
1372815221, 30
    000000C0: 37 33 32 34 31 37 36 30 2C 20 37 36 32 35 31 36 | 73241760,
762516
    000000D0: 39 35 35 2C 20 31 32 39 34 33 35 36 37 36 34 2C | 955,
1294356764,
    000000E0: 20 31 35 32 30 34 39 31 39 39 35 5D 2C 20 22 64 |
1520491995], "d
    000000F0: 69 73 70 6C 61 79 6E 61 6D 65 22 3A 20 22 22 2C |
isplayname": "",
    00000100: 20 22 76 65 72 73 69 6F 6E 22 3A 20 5B 32 2C 20 |  "version":
[2,
    00000110: 30 5D 2C 20 22 68 6F 73 74 5F 69 6E 74 22 3A 20 | 0],
"host_int":
    00000120: 32 30 39 37 36 33 35 34 38 32 33 39 38 34 38 32 |
2097635482398482
    00000130: 38 34 35 36 30 36 31 34 37 35 30 34 32 32 37 38 |
8456061475042278
    00000140: 33 35 34 37 35 37 32 2C 20 22 70 6F 72 74 22 3A | 3547572,
"port":
    00000150: 20 31 37 35 30 30 7D 68 65 6C 6C 6F 68 65 6C 6C |
17500}hellohell
    00000160: 6F 68 65 6C 6C 6F 68 65 6C 6C 6F 68 65 6C 6C 6F |
ohellohellohello
    00000170: 68 65 6C 6C 6F 68 65 6C 6C 6F 68 65 6C 6C 6F 00 |
hellohellohello.


The problem is I cannot locate the data offset by reading the rte_mbuf
provided by dpdk. I need to extract the "hello"s using the correct method
that is provided by DPDK, but I could not find a good way.

I have tried the size headers and the buf_address pointers to locate the
location of the struct message, but I have no idea how to pin point the
exact address of the data-offset using DPDK structures.


char *rtn = NULL;
rtn = rte_pktmbuf_mtod(m, char *); // points to the start of the data

struct ether_hdr *eth;
eth = rte_pktmbuf_mtod(m, struct ether_hdr *);
// rtn+=sizeof(eth);

rtn = m->buf_addr;


if(rtn!=NULL) {
printf("length hdr: %ld\n", sizeof(struct ether_hdr));
printf("length eth: %ld\n", sizeof(eth));
printf("length m->buf_add: %ld\n", sizeof(m->buf_addr));

printf("length message: %ld\n", sizeof(struct message));

// 336
printf("rte_pktmbuf_mtod: %s\n", rtn);  // lenght of the offset: 456
rte_pktmbuf_dump(stdout, m, 1024);
}


Would anyone familiar with DPDK, have a good answer for this?


Best