Added <ifaddrs.h> interface with functions getifaddrs', freeifaddrs'.

This implementation supports only IPv4.
	* inet/ifaddrs.h: New file.
	* sysdeps/generic/ifaddrs.c: New file.
	* sysdeps/gnu/ifaddrs.c: New file.
	* inet/test-ifaddrs.c: New file.
	* inet/Makefile (routines): Add ifaddrs.
	(headers): Add ifaddrs.h here.
	(tests): Add test-ifaddrs.
	* inet/Versions (GLIBC_2.3): New set, add getifaddrs and freeifaddrs.

	* resolv/res_hconf.c (_res_hconf_reorder_addrs): Use an explicit
	socket call to get an AF_INET socket, instead of using __opensock.
	The SIOCGIFNETMASK ioctl will work only with a PF_INET socket.

	* sysdeps/generic/ifreq.h (__ifreq): Take third argument SOCKFD,
	if not -1 use it instead of calling __opensock.
	* sysdeps/unix/sysv/linux/ifreq.h (__ifreq): Likewise.
	* sysdeps/mach/hurd/ifreq.h (__ifreq): Take new argument and ignore it.
	* resolv/res_hconf.c (_res_hconf_reorder_addrs): Pass new argument.

	* sysdeps/mach/hurd/ifreq.h: New file.
	* sysdeps/generic/ifreq.h (__if_freereq): Take second argument NUM_IFS.
	* sysdeps/unix/sysv/linux/ifreq.h (__if_freereq): Likewise.
	* resolv/res_hconf.c (_res_hconf_reorder_addrs): Update caller.

inet/test-ifaddrs.c

@@ -0,0 +1,82 @@
+/* Test listing of network interface addresses.
+   Copyright (C) 2002 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 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 <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ifaddrs.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+int
+main (void)
+{
+  int failures = 0;
+  struct ifaddrs *ifaces, *ifa;
+
+  if (getifaddrs (&ifaces) < 0)
+    {
+      if (errno != ENOSYS)
+	{
+	  printf ("Couldn't get any interfaces: %s.\n", strerror (errno));
+	  exit (1);
+	}
+      /* The function is simply not implemented.  */
+      exit (0);
+    }
+
+  puts ("\
+Name           Flags   Address         Netmask         Broadcast/Destination");
+
+  for (ifa = ifaces; ifa != NULL; ifa = ifa->ifa_next)
+    {
+      char abuf[64], mbuf[64], dbuf[64];
+      inline const char *addr_string (struct sockaddr *sa, char *buf)
+	{
+	  switch (sa->sa_family)
+	    {
+	    case AF_INET:
+	      return inet_ntop (AF_INET,
+				&((struct sockaddr_in *) sa)->sin_addr,
+				buf, sizeof abuf);
+	    case AF_INET6:
+	      return inet_ntop (AF_INET6,
+				&((struct sockaddr_in6 *) sa)->sin6_addr,
+				buf, sizeof abuf);
+	    case AF_UNSPEC:
+	      return "---";
+	    default:
+	      ++failures;
+	      printf ("sa_family=%d %08x\n", sa->sa_family,
+		      *(int*)&((struct sockaddr_in *) sa)->sin_addr.s_addr);
+	      return "<unexpected sockaddr family>";
+	    }
+	}
+      printf ("%-15s%#.4x  %-15s %-15s %-15s\n",
+	      ifa->ifa_name, ifa->ifa_flags,
+	      addr_string (ifa->ifa_addr, abuf),
+	      addr_string (ifa->ifa_netmask, mbuf),
+	      addr_string (ifa->ifa_broadaddr, dbuf));
+    }
+
+  freeifaddrs (ifaces);
+
+  return failures ? 1 : 0;
+}