sysdeps/unix/sysv/linux/cmsg_nxthdr.c

   1 /* Return point to next ancillary data entry in message header.
   2    Copyright (C) 1997, 1998 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #include <sys/socket.h>
  21
  22
  23 struct cmsghdr *
  24 __cmsg_nxthdr (struct msghdr *mhdr, struct cmsghdr *cmsg)
  25 {
  26   if ((size_t) cmsg->cmsg_len < sizeof (struct cmsghdr))
  27     /* The kernel header does this so there may be a reason.  */
  28     return NULL;
  29
  30   cmsg = (struct cmsghdr *) ((unsigned char *) cmsg
  31                              + CMSG_ALIGN (cmsg->cmsg_len));
  32   if ((unsigned char *) (cmsg + 1) >= ((unsigned char *) mhdr->msg_control
  33                                        + mhdr->msg_controllen)
  34       || ((unsigned char *) cmsg + CMSG_ALIGN (cmsg->cmsg_len)
  35           >= ((unsigned char *) mhdr->msg_control + mhdr->msg_controllen)))
  36     /* No more entries.  */
  37     return NULL;
  38   return cmsg;
  39 }