tcp_send_splice : send data received on a pipe on standard input to a remote host
tcp_recv_splice : received data on a network socket, write to a pipe on stdout

I wrote this tiny utility, because I found that netcat and socat consume
way too much CPU for the little work they do. As I use them to send
harddisk-images/backups over the network I decided that I should try and
write something using the splice syscall which avoids copying data to/from
userspace from/to the kernel.

i.e. here, you can see socat copying the output of ntfsclone to a remote host:

  PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
 4606 chris      20   0  5664  1272  1036 R 84.9  0.1 14:21.88 socat -u STDIN TCP:192.168.2.123:1235
 4607 root       20   0 10400  5244  1956 R 46.2  0.5  7:56.81 ntfsclone -o - -s /dev/sda2
 3122 chris      20   0  8272  5732  2368 S  2.3  0.6  0:38.71 tmux

..and here's tcp_send_splice:

  PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
 5758 root       20   0 26036  3244  2004 D 35.3  0.3  0:20.67 ntfsclone -o - -s /dev/sda5
 5759 root       20   0  1888   336   296 S 24.2  0.0  0:13.78 tcp_send_splice 192.168.2.123 1234
 5587 chris      20   0  6668  3988  2348 S  1.4  0.4  0:01.90 tmux

Instead of consuming almost two times the CPU of ntfsclone, not it's only
consuming two thirds.

Usage:

	data_producer | tcp_send_splice another_host 1234
	tcp_recv_splice 1234 | data_consumer

You *HAVE* to have a pipe in there, otherwise it won't work.