Linux TCP 套接字时间戳选项

Question

引用此online kernel doc

• SO_TIMESTAMPING 在接收、传输或两者上生成时间戳。支持 多个时间戳来源，包括硬件。支持生成 流 套接字的时间戳。

Linux 支持 TCP 时间戳，我尝试编写一些演示代码来获取 TCP 数据包的任何时间戳。

服务器代码如下：

//Bind
if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
{
    perror("bind failed. Error");
    return 1;
}
puts("bind done");

//Listen
listen(socket_desc , 3);

//Accept and incoming connection
puts("Waiting for incoming connections...");
int c = sizeof(struct sockaddr_in);

client_sock = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c);
if (client_sock < 0)
{
    perror("accept failed");
    return 1;
}

// Note: I am trying to get software timestamp only here..
int oval = SOF_TIMESTAMPING_RX_SOFTWARE | SOF_TIMESTAMPING_SOFTWARE;
int olen = sizeof( oval );
if ( setsockopt( client_sock, SOL_SOCKET, SO_TIMESTAMPING, &oval, olen ) < 0 )
    { perror( "setsockopt TIMESTAMP"); exit(1); }

puts("Connection accepted");

char    buf[] = "----------------------------------------";
int len = strlen( buf );

struct iovec    myiov[1] = { {buf, len } };

unsigned char   cbuf[ 40 ] = { 0 };
int     clen = sizeof( cbuf ); 

struct msghdr   mymsghdr = { 0 };
mymsghdr.msg_name   = NULL;
mymsghdr.msg_namelen    = 0;
mymsghdr.msg_iov    = myiov;
mymsghdr.msg_iovlen = 1;
mymsghdr.msg_control    = cbuf;
mymsghdr.msg_controllen = clen;
mymsghdr.msg_flags  = 0;

int read_size = recvmsg( client_sock, &mymsghdr, 0);

if(read_size == 0)
{
  puts("Client disconnected");
  fflush(stdout);
}
else if(read_size == -1)
{
  perror("recv failed");
}
else
{
  struct msghdr *msgp = &mymsghdr;
  printf("msg received: %s \n",(char*)msgp->msg_iov[0].iov_base);// This line is successfully hit.
  // Additional info: print msgp->msg_controllen inside gdb is 0.
  struct cmsghdr    *cmsg;
  for ( cmsg = CMSG_FIRSTHDR( msgp );
      cmsg != NULL;
      cmsg = CMSG_NXTHDR( msgp, cmsg ) )
  {
    printf("Time GOT!\n"); // <-- This line is not hit.
    if (( cmsg->cmsg_level == SOL_SOCKET )
        &&( cmsg->cmsg_type == SO_TIMESTAMPING ))
      printf("TIME GOT2\n");// <-- of course , this line is not hit
  } 

}

任何想法为什么这里没有可用的时间戳？谢谢

解决方案 我可以使用带有 solarflare NIC 的 onload 来获取软件时间戳和硬件时间戳。 仍然不知道如何单独获取软件时间戳。

Answer 1

你在最后的 cmets 中给出的链接说：

I've discovered why it doesn't work. SIOCGSTAMP only works for UDP
packets or RAW sockets, but does not work for TCP. – Gio Mar 17 '16 at 9:331    

it doesn't make sense to ask for timestamps for TCP, because there's
no direct correlation between arriving packets and data becoming 
available. If you really want timestamps for TCP you'll have to use 
RAW sockets and implement your own TCP stack (or use a userspace TCP
library). – ecatmur Jul 4 '16 at 10:39