sysdeps/unix/sysv/linux/opensock.c

   1 /* Copyright (C) 1999-2017 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, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <assert.h>
  19 #include <errno.h>
  20 #include <stdio.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <sys/socket.h>
  24
  25 /* Return a socket of any type.  The socket can be used in subsequent
  26    ioctl calls to talk to the kernel.  */
  27 int internal_function
  28 __opensock (void)
  29 {
  30   static int last_family;       /* Available socket family we will use.  */
  31   static int last_type;
  32   static const struct
  33   {
  34     int family;
  35     const char procname[15];
  36   } afs[] =
  37     {
  38       { AF_UNIX, "net/unix" },
  39       { AF_INET, "" },
  40       { AF_INET6, "net/if_inet6" },
  41       { AF_AX25, "net/ax25" },
  42       { AF_NETROM, "net/nr" },
  43       { AF_ROSE, "net/rose" },
  44       { AF_IPX, "net/ipx" },
  45       { AF_APPLETALK, "net/appletalk" },
  46       { AF_ECONET, "sys/net/econet" },
  47       { AF_ASH, "sys/net/ash" },
  48       { AF_X25, "net/x25" },
  49 #ifdef NEED_AF_IUCV
  50       { AF_IUCV, "net/iucv" }
  51 #endif
  52     };
  53 #define nafs (sizeof (afs) / sizeof (afs[0]))
  54   char fname[sizeof "/proc/" + 14];
  55   int result;
  56   int has_proc;
  57   size_t cnt;
  58
  59   /* We already know which family to use from the last call.  Use it
  60      again.  */
  61   if (last_family != 0)
  62     {
  63       assert (last_type != 0);
  64
  65       result = __socket (last_family, last_type | SOCK_CLOEXEC, 0);
  66       if (result != -1 || errno != EAFNOSUPPORT)
  67         /* Maybe the socket type isn't supported anymore (module is
  68            unloaded).  In this case again try to find the type.  */
  69         return result;
  70
  71       /* Reset the values.  They seem not valid anymore.  */
  72       last_family = 0;
  73       last_type = 0;
  74     }
  75
  76   /* Check whether the /proc filesystem is available.  */
  77   has_proc = __access ("/proc/net", R_OK) != -1;
  78   strcpy (fname, "/proc/");
  79
  80   /* Iterate over the interface families and find one which is
  81      available.  */
  82   for (cnt = 0; cnt < nafs; ++cnt)
  83     {
  84       int type = SOCK_DGRAM;
  85
  86       if (has_proc && afs[cnt].procname[0] != '\0')
  87         {
  88           strcpy (fname + 6, afs[cnt].procname);
  89           if (__access (fname, R_OK) == -1)
  90             /* The /proc entry is not available.  I.e., we cannot
  91                create a socket of this type (without loading the
  92                module).  Don't look for it since this might trigger
  93                loading the module.  */
  94             continue;
  95         }
  96
  97       if (afs[cnt].family == AF_NETROM || afs[cnt].family == AF_X25)
  98         type = SOCK_SEQPACKET;
  99
 100       result = __socket (afs[cnt].family, type | SOCK_CLOEXEC, 0);
 101       if (result != -1)
 102         {
 103           /* Found an available family.  */
 104           last_type = type;
 105           last_family = afs[cnt].family;
 106           return result;
 107         }
 108     }
 109
 110   /* None of the protocol families is available.  It is unclear what kind
 111      of error is returned.  ENOENT seems like a reasonable choice.  */
 112   __set_errno (ENOENT);
 113   return -1;
 114 }