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struct resolv_context objects provide a temporary resolver context which does not change during a name lookup operation. Only when the outmost context is created, the stub resolver configuration is verified to be current (at present, only against previous res_init calls). Subsequent attempts to obtain the context will reuse the result of the initial verification operation. struct resolv_context can also be extended in the future to store data which needs to be deallocated during thread cancellation.
131 lines
5.0 KiB
C
131 lines
5.0 KiB
C
/* Definitions related to res_init linked into libc instead of libresolv.
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Copyright (C) 1995-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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/*
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* Copyright (c) 1995-1999 by Internet Software Consortium.
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
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* ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
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* CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
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* DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
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* PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
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* ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
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* SOFTWARE.
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*/
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#include <atomic.h>
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#include <limits.h>
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#include <sys/types.h>
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#include <netinet/in.h>
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#include <arpa/nameser.h>
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#include <resolv.h>
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#include <libc-lock.h>
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#include <resolv-internal.h>
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/* We have atomic increment operations on 64-bit platforms. */
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#if __WORDSIZE == 64
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# define atomicinclock(lock) (void) 0
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# define atomicincunlock(lock) (void) 0
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# define atomicinc(var) catomic_increment (&(var))
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#else
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__libc_lock_define_initialized (static, lock);
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# define atomicinclock(lock) __libc_lock_lock (lock)
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# define atomicincunlock(lock) __libc_lock_unlock (lock)
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# define atomicinc(var) ++var
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#endif
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int
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res_init (void)
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{
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/* These three fields used to be statically initialized. This made
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it hard to use this code in a shared library. It is necessary,
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now that we're doing dynamic initialization here, that we
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preserve the old semantics: if an application modifies one of
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these three fields of _res before res_init is called,
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res_init will not alter them. Of course, if an application is
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setting them to _zero_ before calling res_init, hoping to
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override what used to be the static default, we can't detect it
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and unexpected results will follow. Zero for any of these fields
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would make no sense, so one can safely assume that the
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applications were already getting unexpected results.
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_res.options is tricky since some apps were known to diddle the
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bits before res_init was first called. We can't replicate that
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semantic with dynamic initialization (they may have turned bits
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off that are set in RES_DEFAULT). Our solution is to declare
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such applications "broken". They could fool us by setting
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RES_INIT but none do (yet). */
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if (!_res.retrans)
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_res.retrans = RES_TIMEOUT;
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if (!_res.retry)
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_res.retry = RES_DFLRETRY;
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if (!(_res.options & RES_INIT))
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_res.options = RES_DEFAULT;
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else if (_res.nscount > 0)
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__res_iclose (&_res, true); /* Close any VC sockets. */
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/* This one used to initialize implicitly to zero, so unless the app
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has set it to something in particular, we can randomize it *
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now. */
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if (!_res.id)
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_res.id = res_randomid ();
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atomicinclock (lock);
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/* Request all threads to re-initialize their resolver states,
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resolv.conf might have changed. */
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atomicinc (__res_initstamp);
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atomicincunlock (lock);
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return __res_vinit (&_res, 1);
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}
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/* This needs to be after the use of _res in res_init, above. */
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#undef _res
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/* The resolver state for use by single-threaded programs.
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This differs from plain `struct __res_state _res;' in that it doesn't
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create a common definition, but a plain symbol that resides in .bss,
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which can have an alias. */
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struct __res_state _res __attribute__ ((nocommon));
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#undef __resp
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__thread struct __res_state *__resp = &_res;
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extern __thread struct __res_state *__libc_resp
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__attribute__ ((alias ("__resp"))) attribute_hidden;
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#include <shlib-compat.h>
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/* We declare this with compat_symbol so that it's not
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visible at link time. Programs must use the accessor functions. */
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#ifdef SHARED
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compat_symbol (libc, _res, _res, GLIBC_2_0);
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#endif
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#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_2)
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# undef res_init
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extern int __res_init_weak (void);
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weak_extern (__res_init_weak);
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strong_alias (__res_init, __res_init_weak);
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compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);
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#endif
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