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, 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 #include <kernel-features.h>
  26
  27 /* Return a socket of any type.  The socket can be used in subsequent
  28    ioctl calls to talk to the kernel.  */
  29 int internal_function
  30 __opensock (void)
  31 {
  32   static int last_family;       /* Available socket family we will use.  */
  33   static int last_type;
  34   static const struct
  35   {
  36     int family;
  37     const char procname[15];
  38   } afs[] =
  39     {
  40       /* The 2.2 kernels cannot handle ioctl(SIOCGIFCONF) on AF_UNIX sockets.
  41          Give the kernel a chance to user inet sockets on old kernels.  */
  42 #if __LINUX_KERNEL_VERSION < 132096
  43       { AF_INET, "" },
  44       { AF_UNIX, "net/unix" },
  45 #else
  46       { AF_UNIX, "net/unix" },
  47       { AF_INET, "" },
  48 #endif
  49       { AF_INET6, "net/if_inet6" },
  50       { AF_AX25, "net/ax25" },
  51       { AF_NETROM, "net/nr" },
  52       { AF_ROSE, "net/rose" },
  53       { AF_IPX, "net/ipx" },
  54       { AF_APPLETALK, "net/appletalk" },
  55       { AF_ECONET, "sys/net/econet" },
  56       { AF_ASH, "sys/net/ash" },
  57       { AF_X25, "net/x25" },
  58 #ifdef NEED_AF_IUCV
  59       { AF_IUCV, "net/iucv" }
  60 #endif
  61     };
  62 #define nafs (sizeof (afs) / sizeof (afs[0]))
  63   char fname[sizeof "/proc/" + 14];
  64   int result;
  65   int has_proc;
  66   size_t cnt;
  67
  68   /* We already know which family to use from the last call.  Use it
  69      again.  */
  70   if (last_family != 0)
  71     {
  72       assert (last_type != 0);
  73
  74 #ifdef SOCK_CLOEXEC
  75 # ifndef __ASSUME_SOCK_CLOEXEC
  76       if (__have_sock_cloexec >= 0)
  77 # endif
  78         {
  79           result = __socket (last_family, last_type | SOCK_CLOEXEC, 0);
  80 # ifndef __ASSUME_SOCK_CLOEXEC
  81           if (__have_sock_cloexec == 0)
  82             __have_sock_cloexec = result != -1 || errno != EINVAL ? 1 : -1;
  83 # endif
  84         }
  85 #endif
  86 #ifndef __ASSUME_SOCK_CLOEXEC
  87 # ifdef SOCK_CLOEXEC
  88       if (__have_sock_cloexec < 0)
  89 # endif
  90         result = __socket (last_family, last_type, 0);
  91 #endif
  92       if (result != -1 || errno != EAFNOSUPPORT)
  93         /* Maybe the socket type isn't supported anymore (module is
  94            unloaded).  In this case again try to find the type.  */
  95         return result;
  96
  97       /* Reset the values.  They seem not valid anymore.  */
  98       last_family = 0;
  99       last_type = 0;
 100     }
 101
 102   /* Check whether the /proc filesystem is available.  */
 103   has_proc = __access ("/proc/net", R_OK) != -1;
 104   strcpy (fname, "/proc/");
 105
 106   /* Iterate over the interface families and find one which is
 107      available.  */
 108   for (cnt = 0; cnt < nafs; ++cnt)
 109     {
 110       int type = SOCK_DGRAM;
 111
 112       if (has_proc && afs[cnt].procname[0] != '\0')
 113         {
 114           strcpy (fname + 6, afs[cnt].procname);
 115           if (__access (fname, R_OK) == -1)
 116             /* The /proc entry is not available.  I.e., we cannot
 117                create a socket of this type (without loading the
 118                module).  Don't look for it since this might trigger
 119                loading the module.  */
 120             continue;
 121         }
 122
 123       if (afs[cnt].family == AF_NETROM || afs[cnt].family == AF_X25)
 124         type = SOCK_SEQPACKET;
 125
 126 #ifdef SOCK_CLOEXEC
 127 # ifndef __ASSUME_SOCK_CLOEXEC
 128       if (__have_sock_cloexec >= 0)
 129 # endif
 130         {
 131           result = __socket (afs[cnt].family, type | SOCK_CLOEXEC, 0);
 132 # ifndef __ASSUME_SOCK_CLOEXEC
 133           if (__have_sock_cloexec == 0)
 134             __have_sock_cloexec = result != -1 || errno != EINVAL ? 1 : -1;
 135 # endif
 136         }
 137 #endif
 138 #ifndef __ASSUME_SOCK_CLOEXEC
 139 # ifdef SOCK_CLOEXEC
 140       if (__have_sock_cloexec < 0)
 141 # endif
 142         result = __socket (afs[cnt].family, type, 0);
 143 #endif
 144       if (result != -1)
 145         {
 146           /* Found an available family.  */
 147           last_type = type;
 148           last_family = afs[cnt].family;
 149           return result;
 150         }
 151     }
 152
 153   /* None of the protocol families is available.  It is unclear what kind
 154      of error is returned.  ENOENT seems like a reasonable choice.  */
 155   __set_errno (ENOENT);
 156   return -1;
 157 }