c - Linux : Can Recvmsg be used to receive the IP_TOS of every incoming packet

Question

可以使用 recvmsg() 获取每个传入数据包的 IP_TOS 字段，还是只显示为特定套接字设置的 IP_TOS 值。如果没有，是否有人知道获取每个传入数据包的 IP_TOS 值的解决方案。我正在使用 UDP 应用程序，因此无法像 TCP 那样在应用程序层查看 IP_TOS 字段。谢谢。

添加我目前编写的代码，以防有帮助:

struct msghdr msg; 
struct iovec iov[1];  
memset(&msg, '\0', sizeof(msg));
msg.msg_iov = iov;
msg.msg_iovlen = 1;
iov[0].iov_base = (char *) &pkt;
iov[0].iov_len = sizeof(pkt);

struct cmsghdr cmsgcmsg[1];  
msg.msg_control = cmsgcmsg;
msg.msg_controllen = sizeof(struct cmsghdr);


nRet = recvmsg(udpSocket, &msg, 0);

if (nRet > 0) {
    struct cmsghdr *cmsg;
    for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = CMSG_NXTHDR(&msg,cmsg)) {

    if ((cmsg->cmsg_level == IPPROTO_IP) && (cmsg->cmsg_type == IP_TOS) &&
    (cmsg->cmsg_len) ){
              int tos = *(uint8_t *)CMSG_DATA(cmsg);
              int isecn =  ((tos & INET_ECN_MASK) == INET_ECN_CE);
            printf("the tos = %i , is ecn = %d \n", tos, isecn); 

     }
    }

Answer 1

我终于设法解决了这个问题，并在此处添加代码以供其他人使用。我希望这对其他人有帮助。这是用于 IP_TTL 的:

设置 UDPSocket 接收 IP_TTL 值:

int ttl = 60;
if(setsockopt(udpSocket, IPPROTO_IP, IP_RECVTTL, &ttl,sizeof(ttl))<0) 
{
    printf("cannot set recvttl\n");
} 
else
{
    printf("socket set to recvttl\n");
}

并通过以下方式从每个数据包中检索 IP_TTL 值(以下程序可以通过 iov[0] 检索数据消息，下面给出代码片段):

struct msghdr msg; 
struct iovec iov[1];  
memset(&msg, '\0', sizeof(msg));
msg.msg_iov = iov;
msg.msg_iovlen = 1;
iov[0].iov_base = (char *) &pkt;
iov[0].iov_len = sizeof(pkt);

int *ttlptr=NULL;
int received_ttl = 0;

int cmsg_size = sizeof(struct cmsghdr)+sizeof(received_ttl); // NOTE: Size of header + size of data
char buf[CMSG_SPACE(sizeof(received_ttl))];
msg.msg_control = buf; // Assign buffer space for control header + header data/value
msg.msg_controllen = sizeof(buf); //just initializing it

nRet = recvmsg(udpSocket, &msg, 0);



if (nRet > 0) {
    struct cmsghdr *cmsg;
    for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = CMSG_NXTHDR(&msg,cmsg)) {

          if ((cmsg->cmsg_level == IPPROTO_IP) && (cmsg->cmsg_type == IP_TTL) &&
          (cmsg->cmsg_len) ){
                ttlptr = (int *) CMSG_DATA(cmsg);
                received_ttl = *ttlptr;
                printf("received_ttl = %i and %d \n", ttlptr, received_ttl); 
               break;
           }
    }
}

可以通过以下方式发送和获取数据消息:

发送方:

struct DATA_to_SEND pkt;
struct msghdr msg; 
struct iovec iov[1];  
memset(&msg, '\0', sizeof(msg));
msg.msg_iov = iov;
msg.msg_iovlen = 1;
iov[0].iov_base = (char *) &pkt;
iov[0].iov_len = sizeof(pkt);
nRet = sendmsg(udpSocket, &msg,0); 

接收方(假设 DATA_To_SEND 有一个名为“seq”的参数):

struct DATA_to_SEND pkt;
seqNum = ((struct DATA_to_SEND *) iov[0].iov_base)->seq;

---

以下是IP_TOS。设置套接字接收IP_TOS:

unsigned char set = 0x03;
if(setsockopt(udpSocket, IPPROTO_IP, IP_RECVTOS, &set,sizeof(set))<0) 
{
    printf("cannot set recvtos\n");
} 
else
{
        printf("socket set to recvtos\n");

并通过以下方式从每个数据包 header 中检索 IP_TOS 值:

 struct PC_Pkt pkt;
 int *ecnptr;
 unsigned char received_ecn;

 struct msghdr msg; 
 struct iovec iov[1];  
 memset(&msg, '\0', sizeof(msg));
 msg.msg_iov = iov; 
 msg.msg_iovlen = 1;
 iov[0].iov_base = (char *) &pkt;
 iov[0].iov_len = sizeof(pkt);

 int cmsg_size = sizeof(struct cmsghdr)+sizeof(received_ecn);
 char buf[CMSG_SPACE(sizeof(received_ecn))];
 msg.msg_control = buf;
 msg.msg_controllen = sizeof(buf); 

 nRet = recvmsg(udpSocket, &msg, 0);

 if (nRet > 0) {
struct cmsghdr *cmsg;
for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL;
cmsg = CMSG_NXTHDR(&msg,cmsg)) {
         if ((cmsg->cmsg_level == IPPROTO_IP) && 
         (cmsg->cmsg_type == IP_TOS) && (cmsg->cmsg_len) ){
                ecnptr = (int *) CMSG_DATA(cmsg);
        received_ecn = *ecnptr;
        int isecn =  ((received_ecn & INET_ECN_MASK) == INET_ECN_CE);

                printf("received_ecn = %i and %d, is ECN CE marked = %d \n", ecnptr, received_ecn, isecn); 

                 break;
    }
     }
}