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 <atomic.h>
  19 #include <limits.h>
  20 #include <sys/types.h>
  21 #include <netinet/in.h>
  22 #include <arpa/nameser.h>
  23 #include <resolv.h>
  24 #include <bits/libc-lock.h>
  25
  26
  27 /* The following bit is copied from res_data.c (where it is #ifdef'ed
  28    out) since res_init() should go into libc.so but the rest of that
  29    file should not.  */
  30
  31 extern unsigned long long int __res_initstamp attribute_hidden;
  32 /* We have atomic increment operations on 64-bit platforms.  */
  33 #if __WORDSIZE == 64
  34 # define atomicinclock(lock) (void) 0
  35 # define atomicincunlock(lock) (void) 0
  36 # define atomicinc(var) atomic_increment (&(var))
  37 #else
  38 __libc_lock_define_initialized (static, lock);
  39 # define atomicinclock(lock) __libc_lock_lock (lock)
  40 # define atomicincunlock(lock) __libc_lock_unlock (lock)
  41 # define atomicinc(var) ++var
  42 #endif
  43
  44 int
  45 res_init(void) {
  46         extern int __res_vinit(res_state, int);
  47
  48         /*
  49          * These three fields used to be statically initialized.  This made
  50          * it hard to use this code in a shared library.  It is necessary,
  51          * now that we're doing dynamic initialization here, that we preserve
  52          * the old semantics: if an application modifies one of these three
  53          * fields of _res before res_init() is called, res_init() will not
  54          * alter them.  Of course, if an application is setting them to
  55          * _zero_ before calling res_init(), hoping to override what used
  56          * to be the static default, we can't detect it and unexpected results
  57          * will follow.  Zero for any of these fields would make no sense,
  58          * so one can safely assume that the applications were already getting
  59          * unexpected results.
  60          *
  61          * _res.options is tricky since some apps were known to diddle the bits
  62          * before res_init() was first called. We can't replicate that semantic
  63          * with dynamic initialization (they may have turned bits off that are
  64          * set in RES_DEFAULT).  Our solution is to declare such applications
  65          * "broken".  They could fool us by setting RES_INIT but none do (yet).
  66          */
  67         if (!_res.retrans)
  68                 _res.retrans = RES_TIMEOUT;
  69         if (!_res.retry)
  70                 _res.retry = 4;
  71         if (!(_res.options & RES_INIT))
  72                 _res.options = RES_DEFAULT;
  73         else if (_res.nscount > 0) {
  74                 __res_nclose (&_res);   /* Close any VC sockets.  */
  75
  76                 for (int ns = 0; ns < MAXNS; ns++) {
  77                         free (_res._u._ext.nsaddrs[ns]);
  78                         _res._u._ext.nsaddrs[ns] = NULL;
  79                 }
  80         }
  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         atomicinclock (lock);
  90         /* Request all threads to re-initialize their resolver states,
  91            resolv.conf might have changed.  */
  92         atomicinc (__res_initstamp);
  93         atomicincunlock (lock);
  94
  95         return (__res_vinit(&_res, 1));
  96 }
  97
  98 /* Initialize resp if RES_INIT is not yet set or if res_init in some other
  99    thread requested re-initializing.  */
 100 int
 101 __res_maybe_init (res_state resp, int preinit)
 102 {
 103         if (resp->options & RES_INIT) {
 104                 if (__res_initstamp != resp->_u._ext.initstamp) {
 105                         if (resp->nscount > 0) {
 106                                 __res_nclose (resp);
 107                                 for (int ns = 0; ns < MAXNS; ns++) {
 108                                         free (resp->_u._ext.nsaddrs[ns]);
 109                                         resp->_u._ext.nsaddrs[ns] = NULL;
 110                                 }
 111                                 return __res_vinit (resp, 1);
 112                         }
 113                 }
 114                 return 0;
 115         } else if (preinit) {
 116                 if (!resp->retrans)
 117                         resp->retrans = RES_TIMEOUT;
 118                 if (!resp->retry)
 119                         resp->retry = 4;
 120                 resp->options = RES_DEFAULT;
 121                 if (!resp->id)
 122                         resp->id = res_randomid ();
 123                 return __res_vinit (resp, 1);
 124         } else
 125                 return __res_ninit (resp);
 126 }
 127 libc_hidden_def (__res_maybe_init)
 128 \f
 129 /* This needs to be after the use of _res in res_init, above.  */
 130 #undef _res
 131
 132 /* The resolver state for use by single-threaded programs.
 133    This differs from plain `struct __res_state _res;' in that it doesn't
 134    create a common definition, but a plain symbol that resides in .bss,
 135    which can have an alias.  */
 136 struct __res_state _res __attribute__((section (".bss")));
 137
 138 #include <tls.h>
 139
 140 #if USE___THREAD
 141 #undef __resp
 142 __thread struct __res_state *__resp = &_res;
 143 extern __thread struct __res_state *__libc_resp
 144   __attribute__ ((alias ("__resp"))) attribute_hidden;
 145 #endif
 146
 147 /* We declare this with compat_symbol so that it's not
 148    visible at link time.  Programs must use the accessor functions.  */
 149 #if defined HAVE_ELF && defined SHARED && defined DO_VERSIONING
 150 # include <shlib-compat.h>
 151 compat_symbol (libc, _res, _res, GLIBC_2_0);
 152 #endif
 153
 154 #include <shlib-compat.h>
 155
 156 #if SHLIB_COMPAT(libc, GLIBC_2_0, GLIBC_2_2)
 157 # undef res_init
 158 extern int __res_init_weak (void);
 159 weak_extern (__res_init_weak);
 160 strong_alias (__res_init, __res_init_weak);
 161 compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);
 162 #endif