sysdeps/unix/sysv/linux/opensock.c

   1 /* Copyright (C) 1999-2014 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 #include <kernel-features.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       { AF_UNIX, "net/unix" },
  40       { AF_INET, "" },
  41       { AF_INET6, "net/if_inet6" },
  42       { AF_AX25, "net/ax25" },
  43       { AF_NETROM, "net/nr" },
  44       { AF_ROSE, "net/rose" },
  45       { AF_IPX, "net/ipx" },
  46       { AF_APPLETALK, "net/appletalk" },
  47       { AF_ECONET, "sys/net/econet" },
  48       { AF_ASH, "sys/net/ash" },
  49       { AF_X25, "net/x25" },
  50 #ifdef NEED_AF_IUCV
  51       { AF_IUCV, "net/iucv" }
  52 #endif
  53     };
  54 #define nafs (sizeof (afs) / sizeof (afs[0]))
  55   char fname[sizeof "/proc/" + 14];
  56   int result;
  57   int has_proc;
  58   size_t cnt;
  59
  60   /* We already know which family to use from the last call.  Use it
  61      again.  */
  62   if (last_family != 0)
  63     {
  64       assert (last_type != 0);
  65
  66 #ifdef SOCK_CLOEXEC
  67 # ifndef __ASSUME_SOCK_CLOEXEC
  68       if (__have_sock_cloexec >= 0)
  69 # endif
  70         {
  71           result = __socket (last_family, last_type | SOCK_CLOEXEC, 0);
  72 # ifndef __ASSUME_SOCK_CLOEXEC
  73           if (__have_sock_cloexec == 0)
  74             __have_sock_cloexec = result != -1 || errno != EINVAL ? 1 : -1;
  75 # endif
  76         }
  77 #endif
  78 #ifndef __ASSUME_SOCK_CLOEXEC
  79 # ifdef SOCK_CLOEXEC
  80       if (__have_sock_cloexec < 0)
  81 # endif
  82         result = __socket (last_family, last_type, 0);
  83 #endif
  84       if (result != -1 || errno != EAFNOSUPPORT)
  85         /* Maybe the socket type isn't supported anymore (module is
  86            unloaded).  In this case again try to find the type.  */
  87         return result;
  88
  89       /* Reset the values.  They seem not valid anymore.  */
  90       last_family = 0;
  91       last_type = 0;
  92     }
  93
  94   /* Check whether the /proc filesystem is available.  */
  95   has_proc = __access ("/proc/net", R_OK) != -1;
  96   strcpy (fname, "/proc/");
  97
  98   /* Iterate over the interface families and find one which is
  99      available.  */
 100   for (cnt = 0; cnt < nafs; ++cnt)
 101     {
 102       int type = SOCK_DGRAM;
 103
 104       if (has_proc && afs[cnt].procname[0] != '\0')
 105         {
 106           strcpy (fname + 6, afs[cnt].procname);
 107           if (__access (fname, R_OK) == -1)
 108             /* The /proc entry is not available.  I.e., we cannot
 109                create a socket of this type (without loading the
 110                module).  Don't look for it since this might trigger
 111                loading the module.  */
 112             continue;
 113         }
 114
 115       if (afs[cnt].family == AF_NETROM || afs[cnt].family == AF_X25)
 116         type = SOCK_SEQPACKET;
 117
 118 #ifdef SOCK_CLOEXEC
 119 # ifndef __ASSUME_SOCK_CLOEXEC
 120       if (__have_sock_cloexec >= 0)
 121 # endif
 122         {
 123           result = __socket (afs[cnt].family, type | SOCK_CLOEXEC, 0);
 124 # ifndef __ASSUME_SOCK_CLOEXEC
 125           if (__have_sock_cloexec == 0)
 126             __have_sock_cloexec = result != -1 || errno != EINVAL ? 1 : -1;
 127 # endif
 128         }
 129 #endif
 130 #ifndef __ASSUME_SOCK_CLOEXEC
 131 # ifdef SOCK_CLOEXEC
 132       if (__have_sock_cloexec < 0)
 133 # endif
 134         result = __socket (afs[cnt].family, type, 0);
 135 #endif
 136       if (result != -1)
 137         {
 138           /* Found an available family.  */
 139           last_type = type;
 140           last_family = afs[cnt].family;
 141           return result;
 142         }
 143     }
 144
 145   /* None of the protocol families is available.  It is unclear what kind
 146      of error is returned.  ENOENT seems like a reasonable choice.  */
 147   __set_errno (ENOENT);
 148   return -1;
 149 }