How do I use tcp_diag with C++?

Question

I've googled this all over the place, and I'm still at a loss. tcp_diag is supposed to replace /proc/net/tcp, but I can't find a shred of documentation on how to use it. Please tell me how to #include it, and what methods, classes and functions it has. Thanks!

Answer 1

You create a DGRAM socket with domain AF_NETLINK and protocol NETLINK_INET_DIAG. Then you use the netlink protocol to communicate with the kernel and get the information you need.

Further reading:

• http://kristrev.github.io/2013/07/26/passive-monitoring-of-sockets-on-linux
• http://www.linuxjournal.com/article/7356
• https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/tree/misc/ss.c

Answer 2

The tcp_diag kernel module does not supply C or C++ functions to call. It provides its interface by causing certain special "files" like /proc/net/tcp to exist. You can get that information directly by reading that file as an ordinary file, or with an executable tool such as ss or the older netstat.