xref: /minix3/lib/libc/net/nsdispatch.c (revision d19d7d58aa5cd1165eefe1a0d807c8afe282db62)
1 /*	$NetBSD: nsdispatch.c,v 1.34 2009/02/05 13:21:11 lukem Exp $	*/
2 
3 /*-
4  * Copyright (c) 1997, 1998, 1999, 2004 The NetBSD Foundation, Inc.
5  * All rights reserved.
6  *
7  * This code is derived from software contributed to The NetBSD Foundation
8  * by Luke Mewburn; and by Jason R. Thorpe.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29  * POSSIBILITY OF SUCH DAMAGE.
30  */
31 
32 /*-
33  * Copyright (c) 2003 Networks Associates Technology, Inc.
34  * All rights reserved.
35  *
36  * Portions of this software were developed for the FreeBSD Project by
37  * Jacques A. Vidrine, Safeport Network Services, and Network
38  * Associates Laboratories, the Security Research Division of Network
39  * Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035
40  * ("CBOSS"), as part of the DARPA CHATS research program.
41  *
42  * Redistribution and use in source and binary forms, with or without
43  * modification, are permitted provided that the following conditions
44  * are met:
45  * 1. Redistributions of source code must retain the above copyright
46  *    notice, this list of conditions and the following disclaimer.
47  * 2. Redistributions in binary form must reproduce the above copyright
48  *    notice, this list of conditions and the following disclaimer in the
49  *    documentation and/or other materials provided with the distribution.
50  *
51  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
52  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
53  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
54  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
55  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
56  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
57  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
58  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
59  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
60  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
61  * SUCH DAMAGE.
62  */
63 
64 #include <sys/cdefs.h>
65 #if defined(LIBC_SCCS) && !defined(lint)
66 __RCSID("$NetBSD: nsdispatch.c,v 1.34 2009/02/05 13:21:11 lukem Exp $");
67 #endif /* LIBC_SCCS and not lint */
68 
69 #include "namespace.h"
70 
71 #include <sys/types.h>
72 #include <sys/param.h>
73 #include <sys/stat.h>
74 #include <sys/queue.h>
75 
76 #include <assert.h>
77 #ifdef __ELF__
78 #include <dlfcn.h>
79 #endif /* __ELF__ */
80 #include <err.h>
81 #include <fcntl.h>
82 #define _NS_PRIVATE
83 #include <nsswitch.h>
84 #include <stdarg.h>
85 #include <stdio.h>
86 #include <stdlib.h>
87 #include <string.h>
88 #include <unistd.h>
89 
90 #include "reentrant.h"
91 
92 extern	FILE 	*_nsyyin;
93 extern	int	 _nsyyparse(void);
94 
95 
96 #ifdef __weak_alias
97 __weak_alias(nsdispatch,_nsdispatch)
98 #endif
99 
100 
101 /*
102  * default sourcelist: `files'
103  */
104 const ns_src __nsdefaultsrc[] = {
105 	{ NSSRC_FILES,	NS_SUCCESS },
106 	{ 0, 0 },
107 };
108 
109 const ns_src __nsdefaultcompat[] = {
110 	{ NSSRC_COMPAT,	NS_SUCCESS },
111 	{ 0, 0 }
112 };
113 
114 const ns_src __nsdefaultcompat_forceall[] = {
115 	{ NSSRC_COMPAT,	NS_SUCCESS | NS_FORCEALL },
116 	{ 0, 0 }
117 };
118 
119 const ns_src __nsdefaultfiles[] = {
120 	{ NSSRC_FILES,	NS_SUCCESS },
121 	{ 0, 0 },
122 };
123 
124 const ns_src __nsdefaultfiles_forceall[] = {
125 	{ NSSRC_FILES,	NS_SUCCESS | NS_FORCEALL },
126 	{ 0, 0 },
127 };
128 
129 const ns_src __nsdefaultnis[] = {
130 	{ NSSRC_NIS,	NS_SUCCESS },
131 	{ 0, 0 }
132 };
133 
134 const ns_src __nsdefaultnis_forceall[] = {
135 	{ NSSRC_NIS,	NS_SUCCESS | NS_FORCEALL },
136 	{ 0, 0 }
137 };
138 
139 
140 /* Database, source mappings. */
141 static	u_int			 _nsmapsize;
142 static	ns_dbt			*_nsmap;
143 
144 /* Nsswitch modules. */
145 static	u_int			 _nsmodsize;
146 static	ns_mod			*_nsmod;
147 
148 /* Placeholder for built-in modules' dlopen() handles. */
149 static	void			*_nsbuiltin = &_nsbuiltin;
150 
151 #ifdef _REENTRANT
152 /*
153  * Global nsswitch data structures are mostly read-only, but we update them
154  * when we read or re-read nsswitch.conf.
155  */
156 static 	rwlock_t		_nslock = RWLOCK_INITIALIZER;
157 
158 /*
159  * List of threads currently in nsdispatch().  We use this to detect
160  * recursive calls and avoid reloading configuration in such cases,
161  * which could cause deadlock.
162  */
163 struct _ns_drec {
164 	LIST_ENTRY(_ns_drec)	list;
165 	thr_t			thr;
166 };
167 static LIST_HEAD(, _ns_drec) _ns_drec = LIST_HEAD_INITIALIZER(&_ns_drec);
168 static mutex_t _ns_drec_lock = MUTEX_INITIALIZER;
169 #endif /* _REENTRANT */
170 
171 #ifndef __ELF__
172 #define	is_dynamic()		(0)	/* don't bother - switch to ELF! */
173 #elif __GNUC_PREREQ__(4,2)
174 static int rtld_DYNAMIC __attribute__((__weakref__, __alias__("_DYNAMIC")));
175 #define	is_dynamic()		(&rtld_DYNAMIC != NULL)
176 #else
177 extern int _DYNAMIC __weak_reference(_DYNAMIC);
178 #define	is_dynamic()		(&_DYNAMIC != NULL)
179 #endif
180 
181 /*
182  * size of dynamic array chunk for _nsmap and _nsmap[x].srclist (and other
183  * growing arrays).
184  */
185 #define NSELEMSPERCHUNK		8
186 
187 /*
188  * Dynamically growable arrays are used for lists of databases, sources,
189  * and modules.  The following "vector" API is used to isolate the
190  * common operations.
191  */
192 typedef void	(*_nsvect_free_elem)(void *);
193 
194 static void *
195 _nsvect_append(const void *elem, void *vec, u_int *count, size_t esize)
196 {
197 	void	*p;
198 
199 	if ((*count % NSELEMSPERCHUNK) == 0) {
200 		p = realloc(vec, (*count + NSELEMSPERCHUNK) * esize);
201 		if (p == NULL)
202 			return (NULL);
203 		vec = p;
204 	}
205 	memmove((void *)(((uintptr_t)vec) + (*count * esize)), elem, esize);
206 	(*count)++;
207 	return (vec);
208 }
209 
210 static void *
211 _nsvect_elem(u_int i, void *vec, u_int count, size_t esize)
212 {
213 
214 	if (i < count)
215 		return ((void *)((uintptr_t)vec + (i * esize)));
216 	else
217 		return (NULL);
218 }
219 
220 static void
221 _nsvect_free(void *vec, u_int *count, size_t esize, _nsvect_free_elem free_elem)
222 {
223 	void	*elem;
224 	u_int	 i;
225 
226 	for (i = 0; i < *count; i++) {
227 		elem = _nsvect_elem(i, vec, *count, esize);
228 		if (elem != NULL)
229 			(*free_elem)(elem);
230 	}
231 	if (vec != NULL)
232 		free(vec);
233 	*count = 0;
234 }
235 #define	_NSVECT_FREE(v, c, s, f)					\
236 do {									\
237 	_nsvect_free((v), (c), (s), (f));				\
238 	(v) = NULL;							\
239 } while (/*CONSTCOND*/0)
240 
241 static int
242 _nsdbtcmp(const void *a, const void *b)
243 {
244 
245 	return (strcasecmp(((const ns_dbt *)a)->name,
246 	    ((const ns_dbt *)b)->name));
247 }
248 
249 static int
250 _nsmodcmp(const void *a, const void *b)
251 {
252 
253 	return (strcasecmp(((const ns_mod *)a)->name,
254 	    ((const ns_mod *)b)->name));
255 }
256 
257 static int
258 _nsmtabcmp(const void *a, const void *b)
259 {
260 	int	cmp;
261 
262 	cmp = strcmp(((const ns_mtab *)a)->name,
263 	    ((const ns_mtab *)b)->name);
264 	if (cmp)
265 		return (cmp);
266 
267 	return (strcasecmp(((const ns_mtab *)a)->database,
268 	    ((const ns_mtab *)b)->database));
269 }
270 
271 static void
272 _nsmodfree(ns_mod *mod)
273 {
274 
275 	free(__UNCONST(mod->name));
276 	if (mod->handle == NULL)
277 		return;
278 	if (mod->unregister != NULL)
279 		(*mod->unregister)(mod->mtab, mod->mtabsize);
280 #ifdef __ELF__
281 	if (mod->handle != _nsbuiltin)
282 		(void) dlclose(mod->handle);
283 #endif /* __ELF__ */
284 }
285 
286 /*
287  * Load a built-in or dyanamically linked module.  If the `reg_fn'
288  * argument is non-NULL, assume a built-in module and use `reg_fn'
289  * to register it.  Otherwise, search for a dynamic nsswitch module.
290  */
291 static int
292 _nsloadmod(const char *source, nss_module_register_fn reg_fn)
293 {
294 #ifdef __ELF__
295 	char	buf[PATH_MAX];
296 #endif
297 	ns_mod	mod, *new;
298 
299 	memset(&mod, 0, sizeof(mod));
300 	mod.name = strdup(source);
301 	if (mod.name == NULL)
302 		return (-1);
303 
304 	if (reg_fn != NULL) {
305 		/*
306 		 * The placeholder is required, as a NULL handle
307 		 * represents an invalid module.
308 		 */
309 		mod.handle = _nsbuiltin;
310 	} else if (!is_dynamic()) {
311 		goto out;
312 	} else {
313 #ifdef __ELF__
314 		if (snprintf(buf, sizeof(buf), "nss_%s.so.%d", mod.name,
315 		    NSS_MODULE_INTERFACE_VERSION) >= (int)sizeof(buf))
316 			goto out;
317 		mod.handle = dlopen(buf, RTLD_LOCAL | RTLD_LAZY);
318 		if (mod.handle == NULL) {
319 #ifdef _NSS_DEBUG
320 			/*
321 			 * This gets pretty annoying, since the built-in
322 			 * sources are not yet modules.
323 			 */
324 			/* XXX log some error? */
325 #endif
326 			goto out;
327 		}
328 		reg_fn = (nss_module_register_fn) dlsym(mod.handle,
329 		    "nss_module_register");
330 		if (reg_fn == NULL) {
331 			(void) dlclose(mod.handle);
332 			mod.handle = NULL;
333 			/* XXX log some error? */
334 			goto out;
335 		}
336 #else /* ! __ELF__ */
337 		mod.handle = NULL;
338 #endif /* __ELF__ */
339 	}
340 	mod.mtab = (*reg_fn)(mod.name, &mod.mtabsize, &mod.unregister);
341 	if (mod.mtab == NULL || mod.mtabsize == 0) {
342 #ifdef __ELF__
343 		if (mod.handle != _nsbuiltin)
344 			(void) dlclose(mod.handle);
345 #endif /* __ELF__ */
346 		mod.handle = NULL;
347 		/* XXX log some error? */
348 		goto out;
349 	}
350 	if (mod.mtabsize > 1)
351 		qsort(mod.mtab, mod.mtabsize, sizeof(mod.mtab[0]),
352 		    _nsmtabcmp);
353  out:
354 	new = _nsvect_append(&mod, _nsmod, &_nsmodsize, sizeof(*_nsmod));
355 	if (new == NULL) {
356 		_nsmodfree(&mod);
357 		return (-1);
358 	}
359 	_nsmod = new;
360 	/* _nsmodsize already incremented */
361 
362 	qsort(_nsmod, _nsmodsize, sizeof(*_nsmod), _nsmodcmp);
363 	return (0);
364 }
365 
366 static void
367 _nsloadbuiltin(void)
368 {
369 
370 	/* Do nothing, for now. */
371 }
372 
373 int
374 _nsdbtaddsrc(ns_dbt *dbt, const ns_src *src)
375 {
376 	void		*new;
377 	const ns_mod	*mod;
378 	ns_mod		 modkey;
379 
380 	_DIAGASSERT(dbt != NULL);
381 	_DIAGASSERT(src != NULL);
382 
383 	new = _nsvect_append(src, dbt->srclist, &dbt->srclistsize,
384 	    sizeof(*src));
385 	if (new == NULL)
386 		return (-1);
387 	dbt->srclist = new;
388 	/* dbt->srclistsize already incremented */
389 
390 	modkey.name = src->name;
391 	mod = bsearch(&modkey, _nsmod, _nsmodsize, sizeof(*_nsmod),
392 	    _nsmodcmp);
393 	if (mod == NULL)
394 		return (_nsloadmod(src->name, NULL));
395 
396 	return (0);
397 }
398 
399 void
400 _nsdbtdump(const ns_dbt *dbt)
401 {
402 	unsigned int	i;
403 
404 	_DIAGASSERT(dbt != NULL);
405 
406 	printf("%s (%d source%s):", dbt->name, dbt->srclistsize,
407 	    dbt->srclistsize == 1 ? "" : "s");
408 	for (i = 0; i < dbt->srclistsize; i++) {
409 		printf(" %s", dbt->srclist[i].name);
410 		if (!(dbt->srclist[i].flags &
411 		    (NS_UNAVAIL|NS_NOTFOUND|NS_TRYAGAIN)) &&
412 		    (dbt->srclist[i].flags & NS_SUCCESS))
413 			continue;
414 		printf(" [");
415 		if (!(dbt->srclist[i].flags & NS_SUCCESS))
416 			printf(" SUCCESS=continue");
417 		if (dbt->srclist[i].flags & NS_UNAVAIL)
418 			printf(" UNAVAIL=return");
419 		if (dbt->srclist[i].flags & NS_NOTFOUND)
420 			printf(" NOTFOUND=return");
421 		if (dbt->srclist[i].flags & NS_TRYAGAIN)
422 			printf(" TRYAGAIN=return");
423 		printf(" ]");
424 	}
425 	printf("\n");
426 }
427 
428 static void
429 _nssrclist_free(ns_src **src, u_int srclistsize)
430 {
431 	u_int	i;
432 
433 	for (i = 0; i < srclistsize; i++) {
434 		if ((*src)[i].name != NULL)
435 			free(__UNCONST((*src)[i].name));
436 	}
437 	free(*src);
438 	*src = NULL;
439 }
440 
441 static void
442 _nsdbtfree(ns_dbt *dbt)
443 {
444 
445 	_nssrclist_free(&dbt->srclist, dbt->srclistsize);
446 	if (dbt->name != NULL)
447 		free(__UNCONST(dbt->name));
448 }
449 
450 int
451 _nsdbtput(const ns_dbt *dbt)
452 {
453 	ns_dbt	*p;
454 	void	*new;
455 	u_int	i;
456 
457 	_DIAGASSERT(dbt != NULL);
458 
459 	for (i = 0; i < _nsmapsize; i++) {
460 		p = _nsvect_elem(i, _nsmap, _nsmapsize, sizeof(*_nsmap));
461 		if (strcasecmp(dbt->name, p->name) == 0) {
462 					/* overwrite existing entry */
463 			if (p->srclist != NULL)
464 				_nssrclist_free(&p->srclist, p->srclistsize);
465 			memmove(p, dbt, sizeof(*dbt));
466 			return (0);
467 		}
468 	}
469 	new = _nsvect_append(dbt, _nsmap, &_nsmapsize, sizeof(*_nsmap));
470 	if (new == NULL)
471 		return (-1);
472 	_nsmap = new;
473 	/* _nsmapsize already incremented */
474 
475 	return (0);
476 }
477 
478 /*
479  * This function is called each time nsdispatch() is called.  If this
480  * is the first call, or if the configuration has changed, (re-)prepare
481  * the global data used by NSS.
482  */
483 static int
484 _nsconfigure(void)
485 {
486 #ifdef _REENTRANT
487 	static mutex_t	_nsconflock = MUTEX_INITIALIZER;
488 #endif
489 	static time_t	_nsconfmod;
490 	struct stat	statbuf;
491 
492 	mutex_lock(&_nsconflock);
493 
494 	if (stat(_PATH_NS_CONF, &statbuf) == -1) {
495 		/*
496 		 * No nsswitch.conf; just use whatever configuration we
497 		 * currently have, or fall back on the defaults specified
498 		 * by the caller.
499 		 */
500 		mutex_unlock(&_nsconflock);
501 		return (0);
502 	}
503 
504 	if (statbuf.st_mtime <= _nsconfmod) {
505 		/* Internal state is up-to-date with nsswitch.conf. */
506 		mutex_unlock(&_nsconflock);
507 		return (0);
508 	}
509 
510 	/*
511 	 * Ok, we've decided we need to update the nsswitch configuration
512 	 * structures.  Acquire a write-lock on _nslock while continuing
513 	 * to hold _nsconflock.  Acquiring a write-lock blocks while
514 	 * waiting for other threads already holding a read-lock to clear.
515 	 * We hold _nsconflock for the duration, and update the time stamp
516 	 * at the end of the update operation, at which time we release
517 	 * both locks.
518 	 */
519 	rwlock_wrlock(&_nslock);
520 
521 	_nsyyin = fopen(_PATH_NS_CONF, "r");
522 	if (_nsyyin == NULL) {
523 		/*
524 		 * Unable to open nsswitch.conf; behave as though the
525 		 * stat() above failed.  Even though we have already
526 		 * updated _nsconfmod, if the file reappears, the
527 		 * mtime will change.
528 		 */
529 		goto out;
530 	}
531 
532 	_NSVECT_FREE(_nsmap, &_nsmapsize, sizeof(*_nsmap),
533 	    (_nsvect_free_elem) _nsdbtfree);
534 	_NSVECT_FREE(_nsmod, &_nsmodsize, sizeof(*_nsmod),
535 	    (_nsvect_free_elem) _nsmodfree);
536 
537 	_nsloadbuiltin();
538 
539 	_nsyyparse();
540 	(void) fclose(_nsyyin);
541 	if (_nsmapsize != 0)
542 		qsort(_nsmap, _nsmapsize, sizeof(*_nsmap), _nsdbtcmp);
543 
544 	_nsconfmod = statbuf.st_mtime;
545 
546  out:
547 	rwlock_unlock(&_nslock);
548 	mutex_unlock(&_nsconflock);
549 	return (0);
550 }
551 
552 static nss_method
553 _nsmethod(const char *source, const char *database, const char *method,
554     const ns_dtab disp_tab[], void **cb_data)
555 {
556 	int	curdisp;
557 	ns_mod	*mod, modkey;
558 	ns_mtab	*mtab, mtabkey;
559 
560 	if (disp_tab != NULL) {
561 		for (curdisp = 0; disp_tab[curdisp].src != NULL; curdisp++) {
562 			if (strcasecmp(source, disp_tab[curdisp].src) == 0) {
563 				*cb_data = disp_tab[curdisp].cb_data;
564 				return (disp_tab[curdisp].callback);
565 			}
566 		}
567 	}
568 
569 	modkey.name = source;
570 	mod = bsearch(&modkey, _nsmod, _nsmodsize, sizeof(*_nsmod),
571 	    _nsmodcmp);
572 	if (mod != NULL && mod->handle != NULL) {
573 		mtabkey.database = database;
574 		mtabkey.name = method;
575 		mtab = bsearch(&mtabkey, mod->mtab, mod->mtabsize,
576 		    sizeof(mod->mtab[0]), _nsmtabcmp);
577 		if (mtab != NULL) {
578 			*cb_data = mtab->mdata;
579 			return (mtab->method);
580 		}
581 	}
582 
583 	*cb_data = NULL;
584 	return (NULL);
585 }
586 
587 int
588 /*ARGSUSED*/
589 nsdispatch(void *retval, const ns_dtab disp_tab[], const char *database,
590 	    const char *method, const ns_src defaults[], ...)
591 {
592 	static int	 _nsdispatching;
593 #ifdef _REENTRANT
594 	struct _ns_drec	 drec, *ldrec;
595 #endif
596 	va_list		 ap;
597 	int		 i, result;
598 	ns_dbt		 key;
599 	const ns_dbt	*dbt;
600 	const ns_src	*srclist;
601 	int		 srclistsize;
602 	nss_method	 cb;
603 	void		*cb_data;
604 
605 	/* retval may be NULL */
606 	/* disp_tab may be NULL */
607 	_DIAGASSERT(database != NULL);
608 	_DIAGASSERT(method != NULL);
609 	_DIAGASSERT(defaults != NULL);
610 	if (database == NULL || method == NULL || defaults == NULL)
611 		return (NS_UNAVAIL);
612 
613 	/*
614 	 * In both the threaded and non-threaded cases, avoid reloading
615 	 * the configuration if the current thread is already running
616 	 * nsdispatch() (i.e. recursive call).
617 	 *
618 	 * In the non-threaded case, this avoids changing the data structures
619 	 * while we're using them.
620 	 *
621 	 * In the threaded case, this avoids trying to take a write lock
622 	 * while the current thread holds a read lock (which would result
623 	 * in deadlock).
624 	 */
625 #ifdef _REENTRANT
626 	if (__isthreaded) {
627 		drec.thr = thr_self();
628 		mutex_lock(&_ns_drec_lock);
629 		LIST_FOREACH(ldrec, &_ns_drec, list) {
630 			if (ldrec->thr == drec.thr)
631 				break;
632 		}
633 		LIST_INSERT_HEAD(&_ns_drec, &drec, list);
634 		mutex_unlock(&_ns_drec_lock);
635 		if (ldrec == NULL && _nsconfigure()) {
636 			mutex_lock(&_ns_drec_lock);
637 			LIST_REMOVE(&drec, list);
638 			mutex_unlock(&_ns_drec_lock);
639 			return (NS_UNAVAIL);
640 		}
641 	} else
642 #endif /* _REENTRANT */
643 	if (_nsdispatching++ == 0 && _nsconfigure()) {
644 		_nsdispatching--;
645 		return (NS_UNAVAIL);
646 	}
647 
648 	rwlock_rdlock(&_nslock);
649 
650 	key.name = database;
651 	dbt = bsearch(&key, _nsmap, _nsmapsize, sizeof(*_nsmap), _nsdbtcmp);
652 	if (dbt != NULL) {
653 		srclist = dbt->srclist;
654 		srclistsize = dbt->srclistsize;
655 	} else {
656 		srclist = defaults;
657 		srclistsize = 0;
658 		while (srclist[srclistsize].name != NULL)
659 			srclistsize++;
660 	}
661 	result = 0;
662 
663 	for (i = 0; i < srclistsize; i++) {
664 		cb = _nsmethod(srclist[i].name, database, method,
665 		    disp_tab, &cb_data);
666 		result = 0;
667 		if (cb != NULL) {
668 			va_start(ap, defaults);
669 			result = (*cb)(retval, cb_data, ap);
670 			va_end(ap);
671 			if (defaults[0].flags & NS_FORCEALL)
672 				continue;
673 			if (result & srclist[i].flags)
674 				break;
675 		}
676 	}
677 	result &= NS_STATUSMASK;	/* clear private flags in result */
678 
679 	rwlock_unlock(&_nslock);
680 
681 #ifdef _REENTRANT
682 	if (__isthreaded) {
683 		mutex_lock(&_ns_drec_lock);
684 		LIST_REMOVE(&drec, list);
685 		mutex_unlock(&_ns_drec_lock);
686 	} else
687 #endif /* _REENTRANT */
688 		_nsdispatching--;
689 
690 	return (result ? result : NS_NOTFOUND);
691 }
692