write_fd.cpp

#include<sys/types.h>
#include<sys/stat.h>
#include<sys/socket.h>
#define NULL 0
ssize_t write_fd(int fd, void *ptr, size_t nbytes,int sendfd)
{
	struct msghdr msg;
	struct iovec iov[1];
	union{
		struct cmsghdr cm;
		char control[CMSG_SPACE(sizeof(int))];
	}control_un;
	struct cmsghdr *cmptr;
	msg.msg_control = control_un.control;
	msg.msg_controllen = sizeof(control_un.control);
	cmptr = CMSG_FIRSTHDR(&msg);
	cmptr->cmsg_len = CMSG_LEN(sizeof(int));
	cmptr->cmsg_level= SOL_SOCKET;
	cmptr->cmsg_type = SCM_RIGHTS;
	*((int*)CMSG_DATA(cmptr)) = sendfd;

	msg.msg_name = NULL;
	msg.msg_namelen = 0;

	iov[0].iov_base = ptr;
	iov[0].iov_len = nbytes;
	msg.msg_iov = iov;
	msg.msg_iovlen = 1;
	return (sendmsg(fd,&msg,0));
}