cmsg_nxthdr.c

它通过提供glibc兼容使得应用程序移植到较小的c 库时相当得容易. 它能够应用到带虚拟存储的Linux和uClinux上.在大多数带MMU部件的平台上为使它更加紧凑,它也能够编译成共享库.uClib

/* Return point to next ancillary data entry in message header.
   Copyright (C) 1997, 1998 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#define __FORCE_GLIBC
#include <features.h>
#include <sys/socket.h>


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;
}