sysdeps/unix/sysv/linux/opensock.c

   1 /* Copyright (C) 1999, 2001, 2002, 2007 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 #ifdef NEED_AF_IUCV
  58       { AF_IUCV, "net/iucv" }
  59 #endif
  60     };
  61 #define nafs (sizeof (afs) / sizeof (afs[0]))
  62   char fname[sizeof "/proc/" + 14];
  63   int result;
  64   int has_proc;
  65   size_t cnt;
  66
  67   /* We already know which family to use from the last call.  Use it
  68      again.  */
  69   if (last_family != 0)
  70     {
  71       assert (last_type != 0);
  72
  73       result = __socket (last_family, last_type, 0);
  74       if (result != -1 || errno != EAFNOSUPPORT)
  75         /* Maybe the socket type isn't supported anymore (module is
  76            unloaded).  In this case again try to find the type.  */
  77         return result;
  78
  79       /* Reset the values.  They seem not valid anymore.  */
  80       last_family = 0;
  81       last_type = 0;
  82     }
  83
  84   /* Check whether the /proc filesystem is available.  */
  85   has_proc = __access ("/proc/net", R_OK) != -1;
  86   strcpy (fname, "/proc/");
  87
  88   /* Iterate over the interface families and find one which is
  89      available.  */
  90   for (cnt = 0; cnt < nafs; ++cnt)
  91     {
  92       int type = SOCK_DGRAM;
  93
  94       if (has_proc && afs[cnt].procname[0] != '\0')
  95         {
  96           strcpy (fname + 6, afs[cnt].procname);
  97           if (__access (fname, R_OK) == -1)
  98             /* The /proc entry is not available.  I.e., we cannot
  99                create a socket of this type (without loading the
 100                module).  Don't look for it since this might trigger
 101                loading the module.  */
 102             continue;
 103         }
 104
 105       if (afs[cnt].family == AF_NETROM || afs[cnt].family == AF_X25)
 106         type = SOCK_SEQPACKET;
 107
 108       result = __socket (afs[cnt].family, type, 0);
 109       if (result != -1)
 110         {
 111           /* Found an available family.  */
 112           last_type = type;
 113           last_family = afs[cnt].family;
 114           return result;
 115         }
 116     }
 117
 118   /* None of the protocol families is available.  It is unclear what kind
 119      of error is returned.  ENOENT seems like a reasonable choice.  */
 120   __set_errno (ENOENT);
 121   return -1;
 122 }