sysdeps/unix/sysv/linux/opensock.c

   1 /* Copyright (C) 1999, 2001, 2002 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <stdio.h>
  22 #include <string.h>
  23 #include <unistd.h>
  24 #include <sys/socket.h>
  25
  26 /* Return a socket of any type.  The socket can be used in subsequent
  27    ioctl calls to talk to the kernel.  */
  28 int internal_function
  29 __opensock (void)
  30 {
  31   static int last_family;       /* Available socket family we will use.  */
  32   static int last_type;
  33   static const struct
  34   {
  35     int family;
  36     const char procname[15];
  37   } afs[] =
  38     {
  39       /* The 2.2 kernels cannot handle ioctl(SIOCGIFCONF) on AF_UNIX sockets.
  40          Give the kernel a chance to user inet sockets on old kernels.  */
  41 #if __LINUX_KERNEL_VERSION < 132096
  42       { AF_INET, "" },
  43       { AF_UNIX, "net/unix" },
  44 #else
  45       { AF_UNIX, "net/unix" },
  46       { AF_INET, "" },
  47 #endif
  48       { AF_INET6, "net/if_inet6" },
  49       { AF_AX25, "net/ax25" },
  50       { AF_NETROM, "net/nr" },
  51       { AF_ROSE, "net/rose" },
  52       { AF_IPX, "net/ipx" },
  53       { AF_APPLETALK, "net/appletalk" },
  54       { AF_ECONET, "sys/net/econet" },
  55       { AF_ASH, "sys/net/ash" },
  56       { AF_X25, "net/x25" }
  57     };
  58 #define nafs (sizeof (afs) / sizeof (afs[0]))
  59   char fname[sizeof "/proc/" + 14];
  60   int result;
  61   int has_proc;
  62   size_t cnt;
  63
  64   /* We already know which family to use from the last call.  Use it
  65      again.  */
  66   if (last_family != 0)
  67     {
  68       assert (last_type != 0);
  69
  70       result = __socket (last_family, last_type, 0);
  71       if (result != -1 || errno != EAFNOSUPPORT)
  72         /* Maybe the socket type isn't supported anymore (module is
  73            unloaded).  In this case again try to find the type.  */
  74         return result;
  75
  76       /* Reset the values.  They seem not valid anymore.  */
  77       last_family = 0;
  78       last_type = 0;
  79     }
  80
  81   /* Check whether the /proc filesystem is available.  */
  82   has_proc = __access ("/proc/net", R_OK) != -1;
  83   strcpy (fname, "/proc/");
  84
  85   /* Iterate over the interface families and find one which is
  86      available.  */
  87   for (cnt = 0; cnt < nafs; ++cnt)
  88     {
  89       int type = SOCK_DGRAM;
  90
  91       if (has_proc && afs[cnt].procname[0] != '\0')
  92         {
  93           strcpy (fname + 6, afs[cnt].procname);
  94           if (__access (fname, R_OK) == -1)
  95             /* The /proc entry is not available.  I.e., we cannot
  96                create a socket of this type (without loading the
  97                module).  Don't look for it since this might trigger
  98                loading the module.  */
  99             continue;
 100         }
 101
 102       if (afs[cnt].family == AF_NETROM || afs[cnt].family == AF_X25)
 103         type = SOCK_SEQPACKET;
 104
 105       result = __socket (afs[cnt].family, type, 0);
 106       if (result != -1)
 107         {
 108           /* Found an available family.  */
 109           last_type = type;
 110           last_family = afs[cnt].family;
 111           return result;
 112         }
 113     }
 114
 115   /* None of the protocol families is available.  It is unclear what kind
 116      of error is returned.  ENOENT seems like a reasonable choice.  */
 117   __set_errno (ENOENT);
 118   return -1;
 119 }