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/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2008 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/*
* Copyright (c) 2013, Joyent, Inc. All rights reserved.
*/
/*
* dns_mt.c
*
* This file contains all the MT related routines for the DNS backend.
*/
#include "dns_common.h"
#include <dlfcn.h>
/*
* If the DNS name service switch routines are used in a binary that depends
* on an older libresolv (libresolv.so.1, say), then having nss_dns.so.1 or
* libnss_dns.a depend on a newer libresolv (libresolv.so.2) will cause
* relocation problems. In particular, copy relocation of the _res structure
* (which changes in size from libresolv.so.1 to libresolv.so.2) could
* cause corruption, and result in a number of strange problems, including
* core dumps. Hence, we check if a libresolv is already loaded.
*/
#pragma init(_nss_dns_init)
static void _nss_dns_init(void);
extern struct hostent *res_gethostbyname(const char *);
#define RES_SET_NO_HOSTS_FALLBACK "__joy_res_set_no_hosts_fallback"
extern void __joy_res_set_no_hosts_fallback(void);
#define RES_UNSET_NO_HOSTS_FALLBACK "__joy_res_unset_no_hosts_fallback"
extern void __joy_res_unset_no_hosts_fallback(void);
#define RES_GET_RES "__res_get_res"
extern struct __res_state *__res_get_res(void);
#define RES_ENABLE_MT "__res_enable_mt"
extern int __res_enable_mt(void);
#define RES_DISABLE_MT "__res_disable_mt"
extern int __res_disable_mt(void);
#define RES_GET_H_ERRNO "__res_get_h_errno"
extern int *__res_get_h_errno();
#define __H_ERRNO "__joy_h_errno"
extern int *__joy_h_errno(void);
#define RES_OVERRIDE_RETRY "__joy_res_override_retry"
extern int __joy_res_override_retry(int);
static void __fallback_set_no_hosts(void);
static int __is_mt_safe(void);
void (*set_no_hosts_fallback)(void) = __fallback_set_no_hosts;
void (*unset_no_hosts_fallback)(void) = __fallback_set_no_hosts;
struct __res_state *(*set_res_retry)() = 0;
int (*enable_mt)() = __is_mt_safe;
int (*disable_mt)() = __is_mt_safe;
int *(*get_h_errno)(void) = __joy_h_errno;
int (*override_retry)(int) = __joy_res_override_retry;
/* Usually set from the Makefile */
#ifndef NSS_DNS_LIBRESOLV
#define NSS_DNS_LIBRESOLV "libresolv.so.2"
#endif
/* From libresolv */
extern int h_errno;
mutex_t one_lane = DEFAULTMUTEX;
/* Because we link against libresolv_joy.so.2, this is relatively easy. */
void
_nss_dns_init(void)
{
enable_mt = __is_mt_safe;
disable_mt = __is_mt_safe;
}
/*
*
* Integration of BIND 8.1.2 introduced two new Sun private functions,
* __res_enable_mt() and __res_disable_mt(), that enabled and disabled
* MT mode per-thread. These functions are in the private libresolv.so.2
* interface, and intended for use by nss_dns.so.1.
*
* BIND 8.2.2 removed the need for those two functions. As similar
* functionality was provided in BIND further up the stack. However the
* functions remain to satisfy any application that directly called upon
* them. Only, __res_enable_mt() was modified to return failure.
* Indicated by a non-zero return value. So that those unconventional
* applications would not then presume that res_send() and friends are
* MT-safe, when in fact they are not.
*
* To prevent nss_dns from locking inappropriately __is_mt_safe() is
* called in place of __res_enable_mt() and __res_disable_mt() if BIND
* 8.2.2 libresolv.so.2 being used. __is_mt_safe() returns success
* indicated by a return code of zero. Signifying that no locking is
* necessary.
*
* MT applications making calls to gethostby*_r() or getipnodeby*()
* linked to libresolv.so.1 or linked statically with pre-BIND 8.2.2
* libresolv.a, doubtful as we don't ship a static version, would require
* locking within the nsswitch back-end. Hence the mechanism can not
* simply be removed.
*
*/
static int
__is_mt_safe(void) {
return (0);
}
static void
__fallback_set_no_hosts(void) {
}
/*
* Common code to enable/disable MT mode, set/unset no-/etc/hosts fallback,
* and to set the number of retries.
*/
void
switch_resolver_setup(int *mt_disabled, sigset_t *oldmask, int *old_retry) {
/*
* Try to enable MT mode. If that isn't possible, mask signals,
* and mutex_lock.
*/
*mt_disabled = 1;
if (enable_mt == 0 || (*mt_disabled = (*enable_mt)()) != 0) {
sigset_t newmask;
(void) sigfillset(&newmask);
(void) thr_sigsetmask(SIG_SETMASK, &newmask, oldmask);
(void) mutex_lock(&one_lane);
}
/*
* Disable any fallback to /etc/hosts (or /etc/inet/ipnodes, when
* libresolv knows about that file).
*/
(*set_no_hosts_fallback)();
/*
* The NS switch wants to handle retries on its own.
*/
*old_retry = (*override_retry)(1);
}
void
switch_resolver_reset(int mt_disabled, sigset_t oldmask, int old_retry) {
if (mt_disabled) {
(void) mutex_unlock(&one_lane);
(void) thr_sigsetmask(SIG_SETMASK, &oldmask, NULL);
} else {
(void) (*disable_mt)();
}
(*unset_no_hosts_fallback)();
(void) (*override_retry)(old_retry);
}
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