[dpdk-dev] Questions about reading/writing/modifying packet header.
최익성
pnk003 at naver.com
Mon Apr 18 14:14:12 CEST 2016
Dear DPDK exports.
I am Ick-Sung Choi living in South Korea.
Thank you very much for your contributions.
I studied a lot from your source codes.
However, actually I have a lot of codes/algorithms that I can't understand.
The codes seems to be incomplete, but it works in my test case.
If I take an example, the worker assignment method using & (not %) in load balancing was not fixed yet.
There are a lot of similar codes such as in rte_distributor_process() in distributor.
I have a few questions about reading/writing/modifying packet header. I know it is complex.
I will really appreciate if I can be given answer and some example codes.
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.
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 following code reads headers and write modified headers (used in DPDK source codes).
void swap_header_in_a_packet ( struct rte_mbuf *buf )
{
struct ether_hdr *eth_hdr;
struct ether_addr eth_src_addr, eth_dest_addr ;
struct ipv4_hdr *ip_hdr;
uint32_t ip_src_addr, ip_dest_addr ;
// Read Eternet header.
eth_hdr = rte_pktmbuf_mtod( buf, struct ether_hdr *);
// Extract MAC addresses.
ether_addr_copy(ð_hdr->s_addr, ð_src_addr );
ether_addr_copy(ð_hdr->d_addr, ð_dest_addr );
// Swap MAC addresses.
ether_addr_copy(ð_src_addr, ð_hdr->d_addr);
ether_addr_copy(ð_dest_addr, ð_hdr->s_addr);
// Swap IP addresses.
ip_hdr = (struct ipv4_hdr *)(rte_pktmbuf_mtod( buf, unsigned char *) + sizeof(struct ether_hdr));
ip_src_addr = (uint32_t) ip_hdr->src_addr; // source IP address.
ip_dest_addr = (uint32_t) ip_hdr->dst_addr; // destination IP address.
ip_hdr->src_addr = (uint32_t) ip_dest_addr ;
ip_hdr->dst_addr = (uint32_t) ip_src_addr ;
setup_simple_example_pkt_ip_headers( (char *) ip_hdr );
copy_buf_to_pkt(ð_hdr, sizeof(eth_hdr), buf, 0);
copy_buf_to_pkt(&ip_hdr, sizeof(ip_hdr), buf, sizeof(struct ether_hdr));
}
static void setup_simple_example_pkt_ip_headers( char *ip_hdr )
{
uint16_t *ptr16; uint32_t ip_cksum; // uint16_t pkt_len;
struct ipv4_hdr *ip_hdr1 = (struct ipv4_hdr *) ip_hdr ;
// Initialize UDP header.
/*
pkt_len = (uint16_t) (pkt_data_len + sizeof(struct udp_hdr));
udp_hdr->src_port = rte_cpu_to_be_16(UDP_SRC_PORT);
udp_hdr->dst_port = rte_cpu_to_be_16(UDP_DST_PORT);
udp_hdr->dgram_len = RTE_CPU_TO_BE_16(pkt_len);
udp_hdr->dgram_cksum = 0; // No UDP checksum.
*/
// Compute IP header checksum.
ptr16 = (uint16_t*) ip_hdr1;
ip_cksum = 0;
ip_cksum += ptr16[0]; ip_cksum += ptr16[1]; ip_cksum += ptr16[2]; ip_cksum += ptr16[3]; ip_cksum += ptr16[4];
ip_cksum += ptr16[5]; ? // 6 th ptr (ptr16[5]) is missing in the example code. Is it right?
ip_cksum += ptr16[6]; ip_cksum += ptr16[7];
ip_cksum += ptr16[8]; ip_cksum += ptr16[9];
// Reduce 32 bit checksum to 16 bits and complement it.
ip_cksum = ((ip_cksum & 0xFFFF0000) >> 16) + (ip_cksum & 0x0000FFFF);
if (ip_cksum > 65535) ip_cksum -= 65535;
ip_cksum = (~ip_cksum) & 0x0000FFFF;
if (ip_cksum == 0) ip_cksum = 0xFFFF;
ip_hdr1->hdr_checksum = (uint16_t) ip_cksum;
}
Is the Ben really coding machine? (as in the presentation.) ^^
Thank you very much.
Sincerely Yours,
Ick-Sung Choi.
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