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 /* This file contains the definitions related to res_init which are
  19    linked into libc instead of libresolv.  */
  20
  21 #include <atomic.h>
  22 #include <limits.h>
  23 #include <sys/types.h>
  24 #include <netinet/in.h>
  25 #include <arpa/nameser.h>
  26 #include <resolv.h>
  27 #include <libc-lock.h>
  28
  29 extern unsigned long long int __res_initstamp attribute_hidden;
  30 /* We have atomic increment operations on 64-bit platforms.  */
  31 #if __WORDSIZE == 64
  32 # define atomicinclock(lock) (void) 0
  33 # define atomicincunlock(lock) (void) 0
  34 # define atomicinc(var) catomic_increment (&(var))
  35 #else
  36 __libc_lock_define_initialized (static, lock);
  37 # define atomicinclock(lock) __libc_lock_lock (lock)
  38 # define atomicincunlock(lock) __libc_lock_unlock (lock)
  39 # define atomicinc(var) ++var
  40 #endif
  41
  42 int
  43 res_init(void) {
  44         /*
  45          * These three fields used to be statically initialized.  This made
  46          * it hard to use this code in a shared library.  It is necessary,
  47          * now that we're doing dynamic initialization here, that we preserve
  48          * the old semantics: if an application modifies one of these three
  49          * fields of _res before res_init() is called, res_init() will not
  50          * alter them.  Of course, if an application is setting them to
  51          * _zero_ before calling res_init(), hoping to override what used
  52          * to be the static default, we can't detect it and unexpected results
  53          * will follow.  Zero for any of these fields would make no sense,
  54          * so one can safely assume that the applications were already getting
  55          * unexpected results.
  56          *
  57          * _res.options is tricky since some apps were known to diddle the bits
  58          * before res_init() was first called. We can't replicate that semantic
  59          * with dynamic initialization (they may have turned bits off that are
  60          * set in RES_DEFAULT).  Our solution is to declare such applications
  61          * "broken".  They could fool us by setting RES_INIT but none do (yet).
  62          */
  63         if (!_res.retrans)
  64                 _res.retrans = RES_TIMEOUT;
  65         if (!_res.retry)
  66                 _res.retry = RES_DFLRETRY;
  67         if (!(_res.options & RES_INIT))
  68                 _res.options = RES_DEFAULT;
  69         else if (_res.nscount > 0)
  70                 __res_iclose (&_res, true);     /* Close any VC sockets.  */
  71
  72         /*
  73          * This one used to initialize implicitly to zero, so unless the app
  74          * has set it to something in particular, we can randomize it now.
  75          */
  76         if (!_res.id)
  77                 _res.id = res_randomid();
  78
  79         atomicinclock (lock);
  80         /* Request all threads to re-initialize their resolver states,
  81            resolv.conf might have changed.  */
  82         atomicinc (__res_initstamp);
  83         atomicincunlock (lock);
  84
  85         return (__res_vinit(&_res, 1));
  86 }
  87
  88 /* Initialize resp if RES_INIT is not yet set or if res_init in some other
  89    thread requested re-initializing.  */
  90 int
  91 __res_maybe_init (res_state resp, int preinit)
  92 {
  93         if (resp->options & RES_INIT) {
  94                 if (__res_initstamp != resp->_u._ext.initstamp) {
  95                         if (resp->nscount > 0)
  96                                 __res_iclose (resp, true);
  97                         return __res_vinit (resp, 1);
  98                 }
  99                 return 0;
 100         } else if (preinit) {
 101                 if (!resp->retrans)
 102                         resp->retrans = RES_TIMEOUT;
 103                 if (!resp->retry)
 104                         resp->retry = RES_DFLRETRY;
 105                 resp->options = RES_DEFAULT;
 106                 if (!resp->id)
 107                         resp->id = res_randomid ();
 108                 return __res_vinit (resp, 1);
 109         } else
 110                 return __res_ninit (resp);
 111 }
 112 libc_hidden_def (__res_maybe_init)
 113 \f
 114 /* This needs to be after the use of _res in res_init, above.  */
 115 #undef _res
 116
 117 /* The resolver state for use by single-threaded programs.
 118    This differs from plain `struct __res_state _res;' in that it doesn't
 119    create a common definition, but a plain symbol that resides in .bss,
 120    which can have an alias.  */
 121 struct __res_state _res __attribute__ ((nocommon));
 122
 123 #undef __resp
 124 __thread struct __res_state *__resp = &_res;
 125 extern __thread struct __res_state *__libc_resp
 126   __attribute__ ((alias ("__resp"))) attribute_hidden;
 127
 128 #include <shlib-compat.h>
 129
 130 /* We declare this with compat_symbol so that it's not
 131    visible at link time.  Programs must use the accessor functions.  */
 132 #ifdef SHARED
 133 compat_symbol (libc, _res, _res, GLIBC_2_0);
 134 #endif
 135
 136 #if SHLIB_COMPAT(libc, GLIBC_2_0, GLIBC_2_2)
 137 # undef res_init
 138 extern int __res_init_weak (void);
 139 weak_extern (__res_init_weak);
 140 strong_alias (__res_init, __res_init_weak);
 141 compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);
 142 #endif