Linux TCP socket timestamping option - sockets

Question

Quoting form this online kernel doc
SO_TIMESTAMPING
Generates timestamps on reception, transmission or both. Supports
multiple timestamp sources, including hardware. Supports generating
timestamps for stream sockets.
Linux supports TCP timestamping, and I tried to write some demo code to get any timestamp for TCP packet.
The server code as below:
//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
}
}
Any ideas why no timestamping is available here ? Thanks
Solution
I am able to get the software timestamp along with hardware timestamp using onload with solarflare NIC.
Still no idea how to get software timestamp alone.

Answer 1

The link you gave, in the comments at the end, says:
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