sysdeps/unix/sysv/linux/opensock.c

   1 /* Copyright (C) 1999, 2001, 2002, 2007, 2008 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       /* 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 #ifdef SOCK_CLOEXEC
  74 # ifndef __ASSUME_SOCK_CLOEXEC
  75       if (__have_sock_cloexec >= 0)
  76 # endif
  77         {
  78           result = __socket (last_family, last_type | SOCK_CLOEXEC, 0);
  79 # ifndef __ASSUME_SOCK_CLOEXEC
  80           if (__have_sock_cloexec == 0)
  81             __have_sock_cloexec = result != -1 || errno != EINVAL ? 1 : -1;
  82 # endif
  83         }
  84 #endif
  85 #ifndef __ASSUME_SOCK_CLOEXEC
  86 # ifdef SOCK_CLOEXEC
  87       if (__have_sock_cloexec < 0)
  88 # endif
  89         result = __socket (last_family, last_type, 0);
  90 #endif
  91       if (result != -1 || errno != EAFNOSUPPORT)
  92         /* Maybe the socket type isn't supported anymore (module is
  93            unloaded).  In this case again try to find the type.  */
  94         return result;
  95
  96       /* Reset the values.  They seem not valid anymore.  */
  97       last_family = 0;
  98       last_type = 0;
  99     }
 100
 101   /* Check whether the /proc filesystem is available.  */
 102   has_proc = __access ("/proc/net", R_OK) != -1;
 103   strcpy (fname, "/proc/");
 104
 105   /* Iterate over the interface families and find one which is
 106      available.  */
 107   for (cnt = 0; cnt < nafs; ++cnt)
 108     {
 109       int type = SOCK_DGRAM;
 110
 111       if (has_proc && afs[cnt].procname[0] != '\0')
 112         {
 113           strcpy (fname + 6, afs[cnt].procname);
 114           if (__access (fname, R_OK) == -1)
 115             /* The /proc entry is not available.  I.e., we cannot
 116                create a socket of this type (without loading the
 117                module).  Don't look for it since this might trigger
 118                loading the module.  */
 119             continue;
 120         }
 121
 122       if (afs[cnt].family == AF_NETROM || afs[cnt].family == AF_X25)
 123         type = SOCK_SEQPACKET;
 124
 125 #ifdef SOCK_CLOEXEC
 126 # ifndef __ASSUME_SOCK_CLOEXEC
 127       if (__have_sock_cloexec >= 0)
 128 # endif
 129         {
 130           result = __socket (afs[cnt].family, type | SOCK_CLOEXEC, 0);
 131 # ifndef __ASSUME_SOCK_CLOEXEC
 132           if (__have_sock_cloexec == 0)
 133             __have_sock_cloexec = result != -1 || errno != EINVAL ? 1 : -1;
 134 # endif
 135         }
 136 #endif
 137 #ifndef __ASSUME_SOCK_CLOEXEC
 138 # ifdef SOCK_CLOEXEC
 139       if (__have_sock_cloexec < 0)
 140 # endif
 141         result = __socket (afs[cnt].family, type, 0);
 142 #endif
 143       if (result != -1)
 144         {
 145           /* Found an available family.  */
 146           last_type = type;
 147           last_family = afs[cnt].family;
 148           return result;
 149         }
 150     }
 151
 152   /* None of the protocol families is available.  It is unclear what kind
 153      of error is returned.  ENOENT seems like a reasonable choice.  */
 154   __set_errno (ENOENT);
 155   return -1;
 156 }