setipv4sourcefilter.c

glibc 库, 不仅可以学习使用库函数,还可以学习函数的具体实现,是提高功力的好资料

/* Set IPv4 source filter.  Linux version.
   Copyright (C) 2004 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <[e-mail]>, 2004.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

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

#include <alloca.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/socket.h>


int
setipv4sourcefilter (int s, struct in_addr interface, struct in_addr group,
		     uint32_t fmode, uint32_t numsrc,
		     const struct in_addr *slist)
{
  /* We have to create an struct ip_msfilter object which we can pass
     to the kernel.  */
  size_t needed = IP_MSFILTER_SIZE (numsrc);
  int use_alloca = __libc_use_alloca (needed);

  struct ip_msfilter *imsf;
  if (use_alloca)
    imsf = (struct ip_msfilter *) alloca (needed);
  else
    {
      imsf = (struct ip_msfilter *) malloc (needed);
      if (imsf == NULL)
	return -1;
    }

  imsf->imsf_multiaddr = group;
  imsf->imsf_interface = interface;
  imsf->imsf_fmode = fmode;
  imsf->imsf_numsrc = numsrc;
  memcpy (imsf->imsf_slist, slist, numsrc * sizeof (struct in_addr));

  int result = __setsockopt (s, SOL_IP, IP_MSFILTER, imsf, needed);

  if (! use_alloca)
    {
      int save_errno = errno;
      free (imsf);
      __set_errno (save_errno);
    }

  return result;
}