C program zerocopy - c

Question

I want to send a zero copy in tcp. But　I do not know how to send the data in the sendfile.
Please tell me how the tcp zero copy of the socket communication.
#define BUFSIZE 10240
#define NUMBER 2
int main(void)
{
struct sockaddr_in server;
int s, n;
char buf[BUFSIZE];
char ada[BUFSIZE];
int optval = 1;
int i=0;
int j;
memset((void *) ada, (int)'a', sizeof(ada));
s = socket(AF_INET, SOCK_STREAM, 0);
setsockopt(s, SOL_TCP, TCP_CORK, &optval, sizeof(int));
memset((char *)&server, 0, sizeof(server));
server.sin_family = AF_INET;
server.sin_addr.s_addr = inet_addr("127.0.0.1");
server.sin_port = htons(5320);
connect(s, (struct sockaddr *)&server, sizeof(server));
for(j = 0; j <NUMBER ; j++){
memset((void *) ada,i+64, sizeof(ada));
sendto(s, ada, strlen(ada), 0, NULL, 0); // want to send zero-copy
i++;
sleep(1);
}
optval = 0;
setsockopt(s, SOL_TCP, TCP_CORK, &optval, sizeof(int));
close(s);
exit(0);
}
Also, is there a zero-copy send in other ways?

Answer 1

Zero-copy means no data copying between user space and kernel space. In this program, we are copying data from the user space buffer to kernel space to transmit that data using socket.
When we need to transfer data out from a file using a socket, we can use sendfile system call, passing it the socket and file descriptor.
Please refer to the link http://www.linuxjournal.com/article/6345?page=0,0 which gives useful information on zero copy.