I have been trying to use sendfile system call for transferring data for a udp connection.

This option was available only for tcp initially but in the documentation of udp.c in the kernel it is given as a comment that "sendfile() on UDP works now."

My code snippet looks like this(at the server/transmitter):

/* open the file to be sent */

fd = open(bufin, O_RDONLY);
if (fd == -1) {
fprintf(stderr, "unable to open '%s': %s\n", bufin, strerror(errno));

fstat(fd, &stat_buf);
iov.iov_base = (caddr_t)fd;
iov.iov_len = stat_buf.st_size;

//remote is defined struct sockaddr_in remote; for remote/client address

apl_header.msg_name = (caddr_t) &remote;
apl_header.msg_namelen = sizeof(remote);
apl_header.msg_iov = &iov;
apl_header.msg_iovlen = 1;

printf("before sendfile\n");

if(setsockopt(sd,IPPROTO_UDP, UDP_CORK,&yes,sizeof(int)) == -1)
fprintf(stderr, "error from setsockopt: %s\n", strerror(errno));

if(sendmsg(sd, &apl_header, sizeof(apl_header)) == -1)
fprintf(stderr, "error from sendmsg: %s\n", strerror(errno));

offset = sendfile(sd,fd,&offset,stat_buf.st_size);

if (offset == -1)
fprintf(stderr, "error from sendfile: %s\n", strerror(errno));

setsockopt(sd,IPPROTO_UDP, UDP_CORK,&no,sizeof(int));

I get the error that "error from sendfile: Destination address required"

If someone has worked on a similar issue before then it would be great help if any tips or hints are provided.

Also is there a way i can debug the system call itself. Pointers to this will be of help