Plan 9 from User Space's /usr/local/plan9/src/lib9/sendfd.c

#include <u.h>
#define NOPLAN9DEFINES
#include <libc.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <unistd.h>
#include <errno.h>

#ifndef CMSG_ALIGN
#	ifdef __sun__
#		define CMSG_ALIGN _CMSG_DATA_ALIGN
#	else
#		define CMSG_ALIGN(len) (((len)+sizeof(long)-1) & ~(sizeof(long)-1))
#	endif
#endif

#ifndef CMSG_SPACE
#	define CMSG_SPACE(len) (CMSG_ALIGN(sizeof(struct cmsghdr))+CMSG_ALIGN(len))
#endif

#ifndef CMSG_LEN
#	define CMSG_LEN(len) (CMSG_ALIGN(sizeof(struct cmsghdr))+(len))
#endif

int
sendfd(int s, int fd)
{
	char buf[1];
	struct iovec iov;
	struct msghdr msg;
	struct cmsghdr *cmsg;
	int n;
	char cms[CMSG_SPACE(sizeof(int))];
	
	buf[0] = 0;
	iov.iov_base = buf;
	iov.iov_len = 1;

	memset(&msg, 0, sizeof msg);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	msg.msg_control = (caddr_t)cms;
	msg.msg_controllen = CMSG_LEN(sizeof(int));

	cmsg = CMSG_FIRSTHDR(&msg);
	cmsg->cmsg_len = CMSG_LEN(sizeof(int));
	cmsg->cmsg_level = SOL_SOCKET;
	cmsg->cmsg_type = SCM_RIGHTS;
	memmove(CMSG_DATA(cmsg), &fd, sizeof(int));

	if((n=sendmsg(s, &msg, 0)) != iov.iov_len)
		return -1;
	return 0;
}

int
recvfd(int s)
{
	int n;
	int fd;
	char buf[1];
	struct iovec iov;
	struct msghdr msg;
	struct cmsghdr *cmsg;
	char cms[CMSG_SPACE(sizeof(int))];

	iov.iov_base = buf;
	iov.iov_len = 1;

	memset(&msg, 0, sizeof msg);
	msg.msg_name = 0;
	msg.msg_namelen = 0;
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;

	msg.msg_control = (caddr_t)cms;
	msg.msg_controllen = sizeof cms;

	if((n=recvmsg(s, &msg, 0)) < 0)
		return -1;
	if(n == 0){
		werrstr("unexpected EOF");
		return -1;
	}
	cmsg = CMSG_FIRSTHDR(&msg);
	memmove(&fd, CMSG_DATA(cmsg), sizeof(int));
	return fd;
}

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Copyright © 2005 Lucent Technologies, Russ Cox, MIT.
See license for details.