text: #ifndef __sys
  #error "The __sys macro is required"
  #endif
  
  static void scm_fdset_init_chunk(struct scm_fdset *fdset, int nr_fds,
  		void *data, unsigned ch_size)
  {
  	struct cmsghdr *cmsg;
  	static char dummy;
  
  	fdset->hdr.msg_controllen = CMSG_LEN(sizeof(int) * nr_fds);
  
  	cmsg		= CMSG_FIRSTHDR(&fdset->hdr);
  	cmsg->cmsg_len	= fdset->hdr.msg_controllen;
  
  	if (data) {
  		fdset->iov.iov_base = data;
  		fdset->iov.iov_len = nr_fds * ch_size;
  	} else {
  		fdset->iov.iov_base = &dummy;
  		fdset->iov.iov_len = 1;
  	}
  }
  
  static int *scm_fdset_init(struct scm_fdset *fdset, struct sockaddr_un *saddr,
  		int saddr_len)
  {
  	struct cmsghdr *cmsg;
  
  	BUILD_BUG_ON(sizeof(fdset->msg_buf) < (CMSG_SPACE(sizeof(int) * CR_SCM_MAX_FD)));
  
  	fdset->iov.iov_base		= (void *)0xdeadbeef;
  
  	fdset->hdr.msg_iov		= &fdset->iov;
  	fdset->hdr.msg_iovlen		= 1;
  	fdset->hdr.msg_name		= (struct sockaddr *)saddr;
  	fdset->hdr.msg_namelen		= saddr_len;
  
  	fdset->hdr.msg_control		= &fdset->msg_buf;
  	fdset->hdr.msg_controllen	= CMSG_LEN(sizeof(int) * CR_SCM_MAX_FD);
  
  	cmsg				= CMSG_FIRSTHDR(&fdset->hdr);
  	cmsg->cmsg_len			= fdset->hdr.msg_controllen;
  	cmsg->cmsg_level		= SOL_SOCKET;
  	cmsg->cmsg_type			= SCM_RIGHTS;
  
  	return (int *)CMSG_DATA(cmsg);
  }
  
  int send_fds(int sock, struct sockaddr_un *saddr, int len,
  		int *fds, int nr_fds, void *data, unsigned ch_size)
  {
  	/* In musl_libc the msghdr structure has pads which has to be zeroed */
  	struct scm_fdset fdset = {};
  	int *cmsg_data;
  	int i, min_fd, ret;
  
  	cmsg_data = scm_fdset_init(&fdset, saddr, len);
  	for (i = 0; i < nr_fds; i += min_fd) {
  		min_fd = min(CR_SCM_MAX_FD, nr_fds - i);
  		scm_fdset_init_chunk(&fdset, min_fd, data, ch_size);
  		memcpy(cmsg_data, &fds[i], sizeof(int) * min_fd);
  
  		ret = __sys(sendmsg)(sock, &fdset.hdr, 0);
  		if (ret <= 0)
  			return ret ? : -1;
  
  		if (data)
  			data += min_fd * ch_size;
  	}
  
  	return 0;
  }
  
  int __recv_fds(int sock, int *fds, int nr_fds, void *data, unsigned ch_size, int flags)
  {
  	/* In musl_libc the msghdr structure has pads which has to be zeroed */
  	struct scm_fdset fdset = {};
  	struct cmsghdr *cmsg;
  	int *cmsg_data;
  	int ret;
  	int i, min_fd;
  
  	cmsg_data = scm_fdset_init(&fdset, NULL, 0);
  	for (i = 0; i < nr_fds; i += min_fd) {
  		min_fd = min(CR_SCM_MAX_FD, nr_fds - i);
  		scm_fdset_init_chunk(&fdset, min_fd, data, ch_size);
  
  		ret = __sys(recvmsg)(sock, &fdset.hdr, flags);
  		if (ret <= 0)
  			return ret ? __sys_err(ret) : -ENOMSG;
  
  		cmsg = CMSG_FIRSTHDR(&fdset.hdr);
  		if (!cmsg || cmsg->cmsg_type != SCM_RIGHTS)
  			return -EINVAL;
  		if (fdset.hdr.msg_flags & MSG_CTRUNC)
  			return -ENFILE;
  
  		min_fd = (cmsg->cmsg_len - sizeof(struct cmsghdr)) / sizeof(int);
  		/*
  		 * In case if kernel screwed the recipient, most probably
  		 * the caller stack frame will be overwriten, just scream
  		 * and exit.
  		 *
  		 * FIXME Need to sanitize util.h to be able to include it
  		 * into files which do not have glibc and a couple of
  		 * sys_write_ helpers. Meawhile opencoded BUG_ON here.
  		 */
  		BUG_ON(min_fd > CR_SCM_MAX_FD);
  
  		if (unlikely(min_fd <= 0))
  			return -EBADFD;
  
  		memcpy(&fds[i], cmsg_data, sizeof(int) * min_fd);
  		if (data)
  			data += ch_size * min_fd;
  	}
  
  	return 0;
  }
  
  