resolv/res_libc.c

   1 /*
   2  * Copyright (c) 1995-1999 by Internet Software Consortium.
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
   9  * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
  10  * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
  11  * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
  12  * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
  13  * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
  14  * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
  15  * SOFTWARE.
  16  */
  17
  18 #include <sys/types.h>
  19 #include <netinet/in.h>
  20 #include <arpa/nameser.h>
  21 #include <resolv.h>
  22
  23 #undef _res
  24
  25 #include <tls.h>
  26
  27 #if USE_TLS && HAVE___THREAD
  28 /* With __thread support, this per-thread variable is used in all cases.  */
  29 __thread struct __res_state _res;
  30 extern __thread struct __res_state __libc_res __attribute__ ((alias ("_res")))
  31   attribute_hidden;
  32 # define _res __libc_res
  33 #else
  34 /* The resolver state for use by single-threaded programs.  */
  35 struct __res_state _res;
  36 #endif
  37
  38 /* This function is used to access the resolver state in
  39    single-threaded programs.  */
  40 struct __res_state *
  41 weak_const_function
  42 __res_state (void)
  43 {
  44   return &_res;
  45 }
  46 \f
  47
  48 /* The following bit is copied from res_data.c (where it is #ifdef'ed
  49    out) since res_init() should go into libc.so but the rest of that
  50    file should not.  */
  51
  52 int
  53 res_init(void) {
  54         extern int __res_vinit(res_state, int);
  55
  56         /*
  57          * These three fields used to be statically initialized.  This made
  58          * it hard to use this code in a shared library.  It is necessary,
  59          * now that we're doing dynamic initialization here, that we preserve
  60          * the old semantics: if an application modifies one of these three
  61          * fields of _res before res_init() is called, res_init() will not
  62          * alter them.  Of course, if an application is setting them to
  63          * _zero_ before calling res_init(), hoping to override what used
  64          * to be the static default, we can't detect it and unexpected results
  65          * will follow.  Zero for any of these fields would make no sense,
  66          * so one can safely assume that the applications were already getting
  67          * unexpected results.
  68          *
  69          * _res.options is tricky since some apps were known to diddle the bits
  70          * before res_init() was first called. We can't replicate that semantic
  71          * with dynamic initialization (they may have turned bits off that are
  72          * set in RES_DEFAULT).  Our solution is to declare such applications
  73          * "broken".  They could fool us by setting RES_INIT but none do (yet).
  74          */
  75         if (!_res.retrans)
  76                 _res.retrans = RES_TIMEOUT;
  77         if (!_res.retry)
  78                 _res.retry = 4;
  79         if (!(_res.options & RES_INIT))
  80                 _res.options = RES_DEFAULT;
  81
  82         /*
  83          * This one used to initialize implicitly to zero, so unless the app
  84          * has set it to something in particular, we can randomize it now.
  85          */
  86         if (!_res.id)
  87                 _res.id = res_randomid();
  88
  89         return (__res_vinit(&_res, 1));
  90 }
  91 \f
  92
  93 #include <shlib-compat.h>
  94
  95 #if SHLIB_COMPAT(libc, GLIBC_2_0, GLIBC_2_2)
  96 # undef res_init
  97 strong_alias (__res_init, __res_init_weak);
  98 weak_extern (__res_init_weak);
  99 compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);
 100 #endif