C++ CMSG_ALIGN函數代碼示例

int ip_cmsg_send(struct net *net, struct msghdr *msg, struct ipcm_cookie *ipc)
{
	int err;
	struct cmsghdr *cmsg;

	for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg)) {
		if (!CMSG_OK(msg, cmsg))
			return -EINVAL;
		if (cmsg->cmsg_level != SOL_IP)
			continue;
		switch (cmsg->cmsg_type) {
		case IP_RETOPTS:
			err = cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr));
			err = ip_options_get(net, &ipc->opt, CMSG_DATA(cmsg),
					     err < 40 ? err : 40);
			if (err)
				return err;
			break;
		case IP_PKTINFO:
		{
			struct in_pktinfo *info;
			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct in_pktinfo)))
				return -EINVAL;
			info = (struct in_pktinfo *)CMSG_DATA(cmsg);
			ipc->oif = info->ipi_ifindex;
			ipc->addr = info->ipi_spec_dst.s_addr;
			break;
		}
		default:
			return -EINVAL;
		}
	}
	return 0;
}

struct cmsghdr *
__cmsg_nxthdr (struct msghdr *mhdr, struct cmsghdr *cmsg)
{
  if ((size_t) cmsg->cmsg_len < sizeof (struct cmsghdr))
    /* The kernel header does this so there may be a reason.  */
    return NULL;

  cmsg = (struct cmsghdr *) ((unsigned char *) cmsg
			     + CMSG_ALIGN (cmsg->cmsg_len));
  if ((unsigned char *) (cmsg + 1) > ((unsigned char *) mhdr->msg_control
				      + mhdr->msg_controllen)
      || ((unsigned char *) cmsg + CMSG_ALIGN (cmsg->cmsg_len)
	  > ((unsigned char *) mhdr->msg_control + mhdr->msg_controllen)))
    /* No more entries.  */
    return NULL;
  return cmsg;
}

cmsghdr* cmsg_nxthdr(msghdr* msg, cmsghdr* cmsg) {
  cmsghdr* ptr;
  ptr = reinterpret_cast<cmsghdr*>(reinterpret_cast<char*>(cmsg) + CMSG_ALIGN(cmsg->cmsg_len));
  size_t len = reinterpret_cast<char*>(ptr+1) - reinterpret_cast<char*>(msg->msg_control);
  if (len > msg->msg_controllen) {
    return NULL;
  }
  return ptr;
}

/*
 * The function __cmsg_nxthd() is missing in Android 4.4, but the Android NDK
 * header files in the version we are using are referencing it and we use it in
 * our code, this functions was added in version 5.0. To make IoTivity
 * dynamically loadable at load time on Android KitKat 4.4 add this functions
 * as a weak symbol, so it will be used if the c lib does not provide it, like
 * on Android < 5.0 This code was taken from these two resources:
 * https://raw.githubusercontent.com/android/platform_bionic/master/libc/bionic/__cmsg_nxthdr.cpp
 * https://github.com/android/platform_bionic/commit/ff64831b0965c16c95c9f81a148f30a6ef3a6c64
 */
struct cmsghdr* __attribute__((weak)) __cmsg_nxthdr(struct msghdr* msg, struct cmsghdr* cmsg)
{
    struct cmsghdr* ptr;
    ptr = (struct cmsghdr*)(((unsigned char*) cmsg) + CMSG_ALIGN(cmsg->cmsg_len));
    size_t len = (unsigned long)((char*)(ptr+1) - (char*) msg->msg_control);
    if (len > msg->msg_controllen) {
        return NULL;
    }
    return ptr;
}

inline struct cmsghdr * fixed_uclibc_cmsg_nxthdr(void *__ctl, __kernel_size_t __size,
					       struct cmsghdr *__cmsg)
{
	struct cmsghdr * __ptr;

	__ptr = (struct cmsghdr*)(((unsigned char *) __cmsg) +  CMSG_ALIGN(__cmsg->cmsg_len));
	if ((unsigned long)((char*)(__ptr+1) - (char *) __ctl) > __size)
		return (struct cmsghdr *)0;

	return __ptr;
}

int main(int argc, char *argv[])
{	
	fprintf(stdout, "CMSG_ALIGN:%ld\n", (long)CMSG_ALIGN(sizeof(int)));
	fprintf(stdout, "CMSG_SPACE:%ld\n", (long)CMSG_SPACE(sizeof(int)));	
	fprintf(stdout, "CMSG_LEN:%ld\n", (long)CMSG_LEN(sizeof(int)));
	fprintf(stdout, "sizeof cmsg :%ld\n", (long)sizeof(struct cmsghdr));
#if 0
#define CMSG_ALIGN(len) ( ((len)+sizeof(long)-1) & ~(sizeof(long)-1) )
#define CMSG_SPACE(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + CMSG_ALIGN(len))
#define CMSG_LEN(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + (len))
#endif
	return 0;
}

static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
{
	int *fdp = (int*)CMSG_DATA(cmsg);
	struct scm_fp_list *fpl = *fplp;
	struct file **fpp;
	int i, num;

	num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);

	if (num <= 0)
		return 0;

	if (num > SCM_MAX_FD)
		return -EINVAL;

	if (!fpl)
	{
		fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
		if (!fpl)
			return -ENOMEM;
		*fplp = fpl;
		fpl->count = 0;
		fpl->max = SCM_MAX_FD;
		fpl->user = NULL;
	}
	fpp = &fpl->fp[fpl->count];

	if (fpl->count + num > fpl->max)
		return -EINVAL;

	/*
	 *	Verify the descriptors and increment the usage count.
	 */

	for (i=0; i< num; i++)
	{
		int fd = fdp[i];
		struct file *file;

		if (fd < 0 || !(file = fget_raw(fd)))
			return -EBADF;
		*fpp++ = file;
		fpl->count++;
	}

	if (!fpl->user)
		fpl->user = get_uid(current_user());

	return num;
}

/**
 * Put a portion of ancillary data into msg ancillary data buffer.
 *
 * man cmsg says: Use CMSG_FIRSTHDR() on the msghdr to get the first
 * control message and CMSG_NEXTHDR() to get all subsequent ones.  In
 * each control message, initialize cmsg_len (with CMSG_LEN()), the
 * other cmsghdr header fields, and the data portion using
 * CMSG_DATA().  Finally, the msg_controllen field of the msghdr
 * should be set to the sum of the CMSG_SPACE() of the length of all
 * control messages in the buffer.
 */
void ci_put_cmsg(struct cmsg_state *cmsg_state,
                 int level, int type, socklen_t len, const void* data)
{

  int data_space, data_len = len;

  /* Calls to CMSG_FIRSTHDR and CMSG_NEXTHDR already check that there
   * is enough space for the cmsghdr itself, so just need to check
   * that it is != NULL here
   */
  if( cmsg_state->msg->msg_flags & MSG_CTRUNC )
    return;
  if( cmsg_state->cm == NULL ) {
    cmsg_state->msg->msg_flags |= MSG_CTRUNC;
    return;
  }

  data_space = ((unsigned char*)cmsg_state->msg->msg_control + 
                cmsg_state->msg->msg_controllen) - 
    (unsigned char*)CMSG_DATA(cmsg_state->cm);
  if( data_space < 0 ) {
    cmsg_state->msg->msg_flags |= MSG_CTRUNC;
    return;
  }

  if( data_len > data_space ) {
    cmsg_state->msg->msg_flags |= MSG_CTRUNC;
    data_len = data_space;
  }

  cmsg_state->cm->cmsg_len   = CMSG_LEN(data_len);
  cmsg_state->cm->cmsg_level = level;
  cmsg_state->cm->cmsg_type  = type;

  memcpy(CMSG_DATA(cmsg_state->cm), data, data_len);

  cmsg_state->cmsg_bytes_used += CMSG_SPACE(data_len);

  if( cmsg_state->msg->msg_flags & MSG_CTRUNC )
    return;

#if !defined(NEED_A_WORKAROUND_FOR_GLIBC_BUG_13500) || defined(__KERNEL__)
  cmsg_state->cm = CMSG_NXTHDR(cmsg_state->msg, cmsg_state->cm);
#else
  /* space has been already checked so just updating ptr */
  cmsg_state->cm = (struct cmsghdr*)(((char*)(cmsg_state->cm))
      + (CMSG_ALIGN(cmsg_state->cm->cmsg_len)));
#endif
}

static int
__msgwrite (int sock, void *data, size_t cnt)
{
#ifndef SCM_CREDENTIALS
  /* We cannot implement this reliably.  */
  __set_errno (ENOSYS);
  return -1;
#else
  struct iovec iov;
  struct msghdr msg;
  struct cmsghdr *cmsg = &cm.cmsg;
  struct ucred cred;
  int len;

  /* XXX I'm not sure, if gete?id() is always correct, or if we should use
     get?id(). But since keyserv needs geteuid(), we have no other chance.
     It would be much better, if the kernel could pass both to the server. */
  cred.pid = __getpid ();
  cred.uid = __geteuid ();
  cred.gid = __getegid ();

  memcpy (CMSG_DATA(cmsg), &cred, sizeof (struct ucred));
  cmsg->cmsg_level = SOL_SOCKET;
  cmsg->cmsg_type = SCM_CREDENTIALS;
  cmsg->cmsg_len = sizeof(*cmsg) + sizeof(struct ucred);

  iov.iov_base = data;
  iov.iov_len = cnt;

  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;
  msg.msg_name = NULL;
  msg.msg_namelen = 0;
  msg.msg_control = cmsg;
  msg.msg_controllen = CMSG_ALIGN(cmsg->cmsg_len);
  msg.msg_flags = 0;

 restart:
  len = sendmsg (sock, &msg, 0);
  if (len >= 0)
    return len;
  if (errno == EINTR)
    goto restart;
  return -1;

#endif
}

ssize_t
DaemonSocketPDU::Receive(int aFd)
{
  struct iovec iv;
  memset(&iv, 0, sizeof(iv));
  iv.iov_base = GetData(0);
  iv.iov_len = GetAvailableSpace();

  uint8_t cmsgbuf[CMSG_SPACE(sizeof(int)* MAX_NFDS)];

  struct msghdr msg;
  memset(&msg, 0, sizeof(msg));
  msg.msg_iov = &iv;
  msg.msg_iovlen = 1;
  msg.msg_control = cmsgbuf;
  msg.msg_controllen = sizeof(cmsgbuf);

  ssize_t res = TEMP_FAILURE_RETRY(recvmsg(aFd, &msg, MSG_NOSIGNAL));
  if (res < 0) {
    MOZ_ASSERT(errno != EBADF); /* internal error */
    OnError("recvmsg", errno);
    return -1;
  }
  if (msg.msg_flags & (MSG_CTRUNC | MSG_OOB | MSG_ERRQUEUE)) {
    return -1;
  }

  SetRange(0, res);

  struct cmsghdr* chdr = CMSG_FIRSTHDR(&msg);

  for (; chdr; chdr = CMSG_NXTHDR(&msg, chdr)) {
    if (NS_WARN_IF(!CMSGHDR_CONTAINS_FD(chdr))) {
      continue;
    }
    // Retrieve sent file descriptors.
    size_t fdCount = (chdr->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr))) / sizeof(int);
    for (size_t i = 0; i < fdCount; i++) {
      int* receivedFd = static_cast<int*>(CMSG_DATA(chdr)) + i;
      mReceivedFds.AppendElement(*receivedFd);
    }
  }

  return res;
}

static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
{
	int *fdp = (int*)CMSG_DATA(cmsg);
	struct scm_fp_list *fpl = *fplp;
	struct file **fpp;
	int i, num;

	num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);

	if (num <= 0)
		return 0;

	if (num > SCM_MAX_FD)
		return -EINVAL;

	if (!fpl)
	{
		fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
		if (!fpl)
			return -ENOMEM;
		*fplp = fpl;
		fpl->count = 0;
<<<<<<< HEAD

static int
udp_output(struct inpcb *inp, struct mbuf *m, struct sockaddr *addr,
    struct mbuf *control, struct thread *td)
{
	struct udpiphdr *ui;
	int len = m->m_pkthdr.len;
	struct in_addr faddr, laddr;
	struct cmsghdr *cm;
	struct inpcbinfo *pcbinfo;
	struct sockaddr_in *sin, src;
	int cscov_partial = 0;
	int error = 0;
	int ipflags;
	u_short fport, lport;
	int unlock_udbinfo;
	u_char tos;
	uint8_t pr;
	uint16_t cscov = 0;

	/*
	 * udp_output() may need to temporarily bind or connect the current
	 * inpcb.  As such, we don't know up front whether we will need the
	 * pcbinfo lock or not.  Do any work to decide what is needed up
	 * front before acquiring any locks.
	 */
	if (len + sizeof(struct udpiphdr) > IP_MAXPACKET) {
		if (control)
			m_freem(control);
		m_freem(m);
		return (EMSGSIZE);
	}

	src.sin_family = 0;
	INP_RLOCK(inp);
	tos = inp->inp_ip_tos;
	if (control != NULL) {
		/*
		 * XXX: Currently, we assume all the optional information is
		 * stored in a single mbuf.
		 */
		if (control->m_next) {
			INP_RUNLOCK(inp);
			m_freem(control);
			m_freem(m);
			return (EINVAL);
		}
		for (; control->m_len > 0;
		    control->m_data += CMSG_ALIGN(cm->cmsg_len),
		    control->m_len -= CMSG_ALIGN(cm->cmsg_len)) {
			cm = mtod(control, struct cmsghdr *);
			if (control->m_len < sizeof(*cm) || cm->cmsg_len == 0
			    || cm->cmsg_len > control->m_len) {
				error = EINVAL;
				break;
			}
			if (cm->cmsg_level != IPPROTO_IP)
				continue;

			switch (cm->cmsg_type) {
			case IP_SENDSRCADDR:
				if (cm->cmsg_len !=
				    CMSG_LEN(sizeof(struct in_addr))) {
					error = EINVAL;
					break;
				}
				bzero(&src, sizeof(src));
				src.sin_family = AF_INET;
				src.sin_len = sizeof(src);
				src.sin_port = inp->inp_lport;
				src.sin_addr =
				    *(struct in_addr *)CMSG_DATA(cm);
				break;

			case IP_TOS:
				if (cm->cmsg_len != CMSG_LEN(sizeof(u_char))) {
					error = EINVAL;
					break;
				}
				tos = *(u_char *)CMSG_DATA(cm);
				break;

			default:
				error = ENOPROTOOPT;
				break;
			}
			if (error)
				break;
		}
		m_freem(control);
	}
	if (error) {
		INP_RUNLOCK(inp);
		m_freem(m);
		return (error);
	}

	/*
	 * Depending on whether or not the application has bound or connected
	 * the socket, we may have to do varying levels of work.  The optimal
	 * case is for a connected UDP socket, as a global lock isn't
//.........這裏部分代碼省略.........

/* There is a lot of hair here because the alignment rules (and
 * thus placement) of cmsg headers and length are different for
 * 32-bit apps.  -DaveM
 */
int cmsghdr_from_user_compat_to_kern(struct msghdr *kmsg, struct sock *sk,
			       unsigned char *stackbuf, int stackbuf_size)
{
	struct compat_cmsghdr __user *ucmsg;
	struct cmsghdr *kcmsg, *kcmsg_base;
	compat_size_t ucmlen;
	__kernel_size_t kcmlen, tmp;
	int err = -EFAULT;

	kcmlen = 0;
	kcmsg_base = kcmsg = (struct cmsghdr *)stackbuf;
	ucmsg = CMSG_COMPAT_FIRSTHDR(kmsg);
	while (ucmsg != NULL) {
		if (get_user(ucmlen, &ucmsg->cmsg_len))
			return -EFAULT;

		/* Catch bogons. */
		if (!CMSG_COMPAT_OK(ucmlen, ucmsg, kmsg))
			return -EINVAL;

		tmp = ((ucmlen - CMSG_COMPAT_ALIGN(sizeof(*ucmsg))) +
		       CMSG_ALIGN(sizeof(struct cmsghdr)));
		tmp = CMSG_ALIGN(tmp);
		kcmlen += tmp;
		ucmsg = cmsg_compat_nxthdr(kmsg, ucmsg, ucmlen);
	}
	if (kcmlen == 0)
		return -EINVAL;

	/* The kcmlen holds the 64-bit version of the control length.
	 * It may not be modified as we do not stick it into the kmsg
	 * until we have successfully copied over all of the data
	 * from the user.
	 */
	if (kcmlen > stackbuf_size)
		kcmsg_base = kcmsg = sock_kmalloc(sk, kcmlen, GFP_KERNEL);
	if (kcmsg == NULL)
		return -ENOBUFS;

	/* Now copy them over neatly. */
	memset(kcmsg, 0, kcmlen);
	ucmsg = CMSG_COMPAT_FIRSTHDR(kmsg);
	while (ucmsg != NULL) {
		if (__get_user(ucmlen, &ucmsg->cmsg_len))
			goto Efault;
		if (!CMSG_COMPAT_OK(ucmlen, ucmsg, kmsg))
			goto Einval;
		tmp = ((ucmlen - CMSG_COMPAT_ALIGN(sizeof(*ucmsg))) +
		       CMSG_ALIGN(sizeof(struct cmsghdr)));
		if ((char *)kcmsg_base + kcmlen - (char *)kcmsg < CMSG_ALIGN(tmp))
			goto Einval;
		kcmsg->cmsg_len = tmp;
		tmp = CMSG_ALIGN(tmp);
		if (__get_user(kcmsg->cmsg_level, &ucmsg->cmsg_level) ||
		    __get_user(kcmsg->cmsg_type, &ucmsg->cmsg_type) ||
		    copy_from_user(CMSG_DATA(kcmsg),
				   CMSG_COMPAT_DATA(ucmsg),
				   (ucmlen - CMSG_COMPAT_ALIGN(sizeof(*ucmsg)))))
			goto Efault;

		/* Advance. */
		kcmsg = (struct cmsghdr *)((char *)kcmsg + tmp);
		ucmsg = cmsg_compat_nxthdr(kmsg, ucmsg, ucmlen);
	}

	/* Ok, looks like we made it.  Hook it up and return success. */
	kmsg->msg_control = kcmsg_base;
	kmsg->msg_controllen = kcmlen;
	return 0;

Einval:
	err = -EINVAL;
Efault:
	if (kcmsg_base != (struct cmsghdr *)stackbuf)
		sock_kfree_s(sk, kcmsg_base, kcmlen);
	return err;
}

static struct ip6_flowlabel *
fl_create(struct net *net, struct sock *sk, struct in6_flowlabel_req *freq,
	  char __user *optval, int optlen, int *err_p)
{
	struct ip6_flowlabel *fl = NULL;
	int olen;
	int addr_type;
	int err;

	olen = optlen - CMSG_ALIGN(sizeof(*freq));
	err = -EINVAL;
	if (olen > 64 * 1024)
		goto done;

	err = -ENOMEM;
	fl = kzalloc(sizeof(*fl), GFP_KERNEL);
	if (fl == NULL)
		goto done;

	if (olen > 0) {
		struct msghdr msg;
		struct flowi6 flowi6;
		int junk;

		err = -ENOMEM;
		fl->opt = kmalloc(sizeof(*fl->opt) + olen, GFP_KERNEL);
		if (fl->opt == NULL)
			goto done;

		memset(fl->opt, 0, sizeof(*fl->opt));
		fl->opt->tot_len = sizeof(*fl->opt) + olen;
		err = -EFAULT;
		if (copy_from_user(fl->opt+1, optval+CMSG_ALIGN(sizeof(*freq)), olen))
			goto done;

		msg.msg_controllen = olen;
		msg.msg_control = (void*)(fl->opt+1);
		memset(&flowi6, 0, sizeof(flowi6));

		err = datagram_send_ctl(net, sk, &msg, &flowi6, fl->opt, &junk,
					&junk, &junk);
		if (err)
			goto done;
		err = -EINVAL;
		if (fl->opt->opt_flen)
			goto done;
		if (fl->opt->opt_nflen == 0) {
			kfree(fl->opt);
			fl->opt = NULL;
		}
	}

	fl->fl_net = hold_net(net);
	fl->expires = jiffies;
	err = fl6_renew(fl, freq->flr_linger, freq->flr_expires);
	if (err)
		goto done;
	fl->share = freq->flr_share;
	addr_type = ipv6_addr_type(&freq->flr_dst);
	if ((addr_type & IPV6_ADDR_MAPPED) ||
	    addr_type == IPV6_ADDR_ANY) {
		err = -EINVAL;
		goto done;
	}
	fl->dst = freq->flr_dst;
	atomic_set(&fl->users, 1);
	switch (fl->share) {
	case IPV6_FL_S_EXCL:
	case IPV6_FL_S_ANY:
		break;
	case IPV6_FL_S_PROCESS:
		fl->owner = current->pid;
		break;
	case IPV6_FL_S_USER:
		fl->owner = current_euid();
		break;
	default:
		err = -EINVAL;
		goto done;
	}
	return fl;

done:
	fl_free(fl);
	*err_p = err;
	return NULL;
}

static bool_t
rendezvous_request (SVCXPRT *xprt, struct rpc_msg *errmsg)
{
  int sock;
  struct unix_rendezvous *r;
  struct sockaddr_un addr;
  struct sockaddr_in in_addr;
  socklen_t len;

  r = (struct unix_rendezvous *) xprt->xp_p1;
again:
  len = sizeof (struct sockaddr_un);
  if ((sock = accept (xprt->xp_sock, (struct sockaddr *) &addr, &len)) < 0)
    {
      if (errno == EINTR)
	goto again;
      if (errno == EMFILE)
        {
          struct timespec ts = { .tv_sec = 0, .tv_nsec = 50000000 };
          __nanosleep(&ts , NULL);
        }
      return FALSE;
    }
  /*
   * make a new transporter (re-uses xprt)
   */
  memset (&in_addr, '\0', sizeof (in_addr));
  in_addr.sin_family = AF_UNIX;
  xprt = makefd_xprt (sock, r->sendsize, r->recvsize);
  memcpy (&xprt->xp_raddr, &in_addr, sizeof (in_addr));
  xprt->xp_addrlen = len;
  return FALSE;		/* there is never an rpc msg to be processed */
}

static enum xprt_stat
rendezvous_stat (SVCXPRT *xprt)
{
  return XPRT_IDLE;
}

static void
svcunix_destroy (SVCXPRT *xprt)
{
  struct unix_conn *cd = (struct unix_conn *) xprt->xp_p1;

  xprt_unregister (xprt);
  __close (xprt->xp_sock);
  if (xprt->xp_port != 0)
    {
      /* a rendezvouser socket */
      xprt->xp_port = 0;
    }
  else
    {
      /* an actual connection socket */
      XDR_DESTROY (&(cd->xdrs));
    }
  mem_free ((caddr_t) cd, sizeof (struct unix_conn));
  mem_free ((caddr_t) xprt, sizeof (SVCXPRT));
}

#ifdef SCM_CREDENTIALS
struct cmessage {
  struct cmsghdr cmsg;
  struct ucred cmcred;
  /* hack to make sure we have enough memory */
  char dummy[(CMSG_ALIGN (sizeof (struct ucred)) - sizeof (struct ucred) + sizeof (long))];
};

/* XXX This is not thread safe, but since the main functions in svc.c
   and the rpcgen generated *_svc functions for the daemon are also not
   thread safe and uses static global variables, it doesn't matter. */
static struct cmessage cm;
#endif

static int
__msgread (int sock, void *data, size_t cnt)
{
  struct iovec iov;
  struct msghdr msg;
  int len;

  iov.iov_base = data;
  iov.iov_len = cnt;

  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;
  msg.msg_name = NULL;
  msg.msg_namelen = 0;
#ifdef SCM_CREDENTIALS
  msg.msg_control = (caddr_t) &cm;
  msg.msg_controllen = sizeof (struct cmessage);
#endif
  msg.msg_flags = 0;

#ifdef SO_PASSCRED
  {
    int on = 1;
    if (__setsockopt (sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof (on)))
      return -1;
//.........這裏部分代碼省略.........