dns_mt.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License, Version 1.0 only
* (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
* 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 (c) 1993, 1998-2001 by Sun Microsystems, Inc.
* All rights reserved.
*/
#pragma ident "%Z%%M% %I% %E% SMI"
/*
* 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 *);
#pragma weak res_gethostbyname
#define RES_SET_NO_HOSTS_FALLBACK "__res_set_no_hosts_fallback"
extern void __res_set_no_hosts_fallback(void);
#pragma weak __res_set_no_hosts_fallback
#define RES_UNSET_NO_HOSTS_FALLBACK "__res_unset_no_hosts_fallback"
extern void __res_unset_no_hosts_fallback(void);
#pragma weak __res_unset_no_hosts_fallback
#define RES_GET_RES "__res_get_res"
extern struct __res_state *__res_get_res(void);
#pragma weak __res_get_res
#define RES_ENABLE_MT "__res_enable_mt"
extern int __res_enable_mt(void);
#pragma weak __res_enable_mt
#define RES_DISABLE_MT "__res_disable_mt"
extern int __res_disable_mt(void);
#pragma weak __res_disable_mt
#define RES_GET_H_ERRNO "__res_get_h_errno"
extern int *__res_get_h_errno();
#pragma weak __res_get_h_errno
#define __H_ERRNO "__h_errno"
extern int *__h_errno(void);
#define RES_OVERRIDE_RETRY "__res_override_retry"
extern int __res_override_retry(int);
#pragma weak __res_override_retry
static void __fallback_set_no_hosts(void);
static int *__fallback_h_errno(void);
static int __fallback_override_retry(int);
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)() = 0;
int (*disable_mt)() = 0;
int *(*get_h_errno)(void) = 0;
int (*override_retry)(int) = 0;
/* Usually set from the Makefile */
#ifndef NSS_DNS_LIBRESOLV
#define NSS_DNS_LIBRESOLV "libresolv.so.2"
#endif
/* From libresolv */
extern int h_errno;
void
_nss_dns_init(void)
{
struct hostent *(*f_hostent_ptr)();
void *reslib, (*f_void_ptr)();
/* If no libresolv library, then load one */
if ((f_hostent_ptr = res_gethostbyname) == 0) {
if ((reslib =
RES_SET_NO_HOSTS_FALLBACK)) != 0) {
}
RES_SET_NO_HOSTS_FALLBACK)) != 0) {
}
/* Set number of resolver retries */
RES_OVERRIDE_RETRY)) == 0) {
}
/*
* Select h_errno retrieval function. A BIND 8.2.2
* libresolv.so.2 will have __h_errno, a BIND 8.1.2
* one will have __res_get_h_errno, and other
* versions may have nothing at all.
*
* functions which are also dependent on the version
* of the BIND libresolv.so.2 being used.
*/
__H_ERRNO)) != 0) {
/* BIND 8.2.2 libresolv.so.2 is MT safe. */
} else {
if ((get_h_errno =
RES_GET_H_ERRNO)) == 0) {
}
/*
* Pre-BIND 8.2.2 was not MT safe. Try to
*/
RES_ENABLE_MT)) != 0 &&
RES_DISABLE_MT)) == 0) {
enable_mt = 0;
}
}
}
} else {
/* Libresolv already loaded */
if ((f_void_ptr = __res_set_no_hosts_fallback) != 0) {
}
if ((f_void_ptr = __res_unset_no_hosts_fallback) != 0) {
}
if ((override_retry = __res_override_retry) == 0) {
}
if ((get_h_errno = __h_errno) == 0 &&
(get_h_errno = __res_get_h_errno) == 0) {
}
if (get_h_errno == __h_errno) {
} else {
if ((enable_mt = __res_enable_mt) != 0 &&
(disable_mt = __res_disable_mt) == 0) {
enable_mt = 0;
}
}
}
}
/*
*
* 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);
}
/*
* Return pointer to the global h_errno variable
*/
static int *
__fallback_h_errno(void) {
return (&h_errno);
}
/*
* This function is called when the resolver library doesn't provide its
* own function to establish an override retry. If we can get a pointer
* to the per-thread _res (i.e., set_res_retry != 0), we set the retries
* directly, and return the previous number of retries. Otherwise, there's
* nothing to do.
*/
static int
__fallback_override_retry(int retry) {
struct __res_state *res;
int old_retry = 0;
if (set_res_retry != 0) {
res = set_res_retry();
}
return (old_retry);
}
static void
__fallback_set_no_hosts(void) {
}
/*
* and to set the number of retries.
*/
void
/*
* Try to enable MT mode. If that isn't possible, mask signals,
* and mutex_lock.
*/
*mt_disabled = 1;
(void) sigfillset(&newmask);
}
/*
* libresolv knows about that file).
*/
(*set_no_hosts_fallback)();
/*
* The NS switch wants to handle retries on its own.
*/
}
void
if (mt_disabled) {
} else {
(void) (*disable_mt)();
}
(*unset_no_hosts_fallback)();
(void) (*override_retry)(old_retry);
}