xref: /illumos-gate/usr/src/lib/libc/port/gen/getenv.c (revision 59f081ed)
17c478bd9Sstevel@tonic-gate /*
27c478bd9Sstevel@tonic-gate  * CDDL HEADER START
37c478bd9Sstevel@tonic-gate  *
47c478bd9Sstevel@tonic-gate  * The contents of this file are subject to the terms of the
5cb620785Sraf  * Common Development and Distribution License (the "License").
6cb620785Sraf  * You may not use this file except in compliance with the License.
77c478bd9Sstevel@tonic-gate  *
87c478bd9Sstevel@tonic-gate  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
97c478bd9Sstevel@tonic-gate  * or http://www.opensolaris.org/os/licensing.
107c478bd9Sstevel@tonic-gate  * See the License for the specific language governing permissions
117c478bd9Sstevel@tonic-gate  * and limitations under the License.
127c478bd9Sstevel@tonic-gate  *
137c478bd9Sstevel@tonic-gate  * When distributing Covered Code, include this CDDL HEADER in each
147c478bd9Sstevel@tonic-gate  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
157c478bd9Sstevel@tonic-gate  * If applicable, add the following below this CDDL HEADER, with the
167c478bd9Sstevel@tonic-gate  * fields enclosed by brackets "[]" replaced with your own identifying
177c478bd9Sstevel@tonic-gate  * information: Portions Copyright [yyyy] [name of copyright owner]
187c478bd9Sstevel@tonic-gate  *
197c478bd9Sstevel@tonic-gate  * CDDL HEADER END
207c478bd9Sstevel@tonic-gate  */
21cb620785Sraf 
227c478bd9Sstevel@tonic-gate /*
237257d1b4Sraf  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
247c478bd9Sstevel@tonic-gate  * Use is subject to license terms.
257c478bd9Sstevel@tonic-gate  */
267c478bd9Sstevel@tonic-gate 
277c478bd9Sstevel@tonic-gate /*	Copyright (c) 1988 AT&T	*/
287c478bd9Sstevel@tonic-gate /*	  All Rights Reserved  	*/
297c478bd9Sstevel@tonic-gate 
307257d1b4Sraf #pragma ident	"%Z%%M%	%I%	%E% SMI"
317c478bd9Sstevel@tonic-gate 
327257d1b4Sraf #pragma	weak _putenv = putenv
337c478bd9Sstevel@tonic-gate 
347257d1b4Sraf #include "lint.h"
357c478bd9Sstevel@tonic-gate #include <mtlib.h>
367c478bd9Sstevel@tonic-gate #include <sys/types.h>
377c478bd9Sstevel@tonic-gate #include <thread.h>
387c478bd9Sstevel@tonic-gate #include <synch.h>
397c478bd9Sstevel@tonic-gate #include <stdlib.h>
407c478bd9Sstevel@tonic-gate #include <errno.h>
417c478bd9Sstevel@tonic-gate #include <string.h>
427c478bd9Sstevel@tonic-gate #include <atomic.h>
437c478bd9Sstevel@tonic-gate 
447c478bd9Sstevel@tonic-gate #define	MIN_ENV_SIZE		128
457c478bd9Sstevel@tonic-gate 
46*59f081edSraf extern const char		**_environ;
477c478bd9Sstevel@tonic-gate extern void			clean_env();
487c478bd9Sstevel@tonic-gate 
497c478bd9Sstevel@tonic-gate /*
50*59f081edSraf  * For performance and consistency reasons we expand the _environ list using
517c478bd9Sstevel@tonic-gate  * the trusted "power of two, drop it on the floor" method. This allows for
527c478bd9Sstevel@tonic-gate  * a lockless, single pass implementation of getenv(), yet the memory leak
537c478bd9Sstevel@tonic-gate  * is bounded - in normal circumstances total wastage is never greater than
54*59f081edSraf  * 3x the space needed to hold any _environ list.
557c478bd9Sstevel@tonic-gate  *
56*59f081edSraf  * The only abnormal circumstance is if an application modifies the _environ
577c478bd9Sstevel@tonic-gate  * list pointer directly. Such an application does not conform to POSIX.1
587c478bd9Sstevel@tonic-gate  * 2001. However, we also care about standards which did not foresee this
59*59f081edSraf  * issue. For this reason we keep a working copy of our notion of _environ in
60*59f081edSraf  * my_environ. If, when we are called upon to modify _environ, we ever detect
61*59f081edSraf  * a mismatch between _environ and my_environ we discard all our assumptions
62*59f081edSraf  * concerning the location and size of the _environ list. As an additional
63*59f081edSraf  * precaution we only ever update _environ once we have finished manipulating
647c478bd9Sstevel@tonic-gate  * our working copy.
657c478bd9Sstevel@tonic-gate  *
667c478bd9Sstevel@tonic-gate  * The setenv() API is inherently leaky but we are completely at the mercy
677c478bd9Sstevel@tonic-gate  * of the application.
687c478bd9Sstevel@tonic-gate  *
697c478bd9Sstevel@tonic-gate  * To pacify leak detectors we chain all allocations which are at risk of
707c478bd9Sstevel@tonic-gate  * being leaked in either of the above two scenarios. chunk_list must only
717c478bd9Sstevel@tonic-gate  * be updated under the protection of update_lock.
727c478bd9Sstevel@tonic-gate  *
73*59f081edSraf  * Although we don't allocate the original _environ list it is likely that
747c478bd9Sstevel@tonic-gate  * we will leak this too. Accordingly, we create a reference in initenv().
757c478bd9Sstevel@tonic-gate  * However, we can't be held responsible for such leaks in abnormal (see
767c478bd9Sstevel@tonic-gate  * above) circumstances.
777c478bd9Sstevel@tonic-gate  */
787c478bd9Sstevel@tonic-gate 
797c478bd9Sstevel@tonic-gate typedef struct chunk {
807c478bd9Sstevel@tonic-gate 	struct chunk		*next;
817c478bd9Sstevel@tonic-gate } chunk_t;
827c478bd9Sstevel@tonic-gate 
837c478bd9Sstevel@tonic-gate static mutex_t			update_lock = DEFAULTMUTEX;
847c478bd9Sstevel@tonic-gate static const char		**orig_environ = NULL;
857c478bd9Sstevel@tonic-gate static const char		**my_environ = NULL;
867c478bd9Sstevel@tonic-gate static const char		**environ_base = NULL;
877c478bd9Sstevel@tonic-gate static int			environ_size = 0;
887c478bd9Sstevel@tonic-gate static int			environ_gen = 0;
897c478bd9Sstevel@tonic-gate static int			initenv_done = 0;
907c478bd9Sstevel@tonic-gate static chunk_t			*chunk_list = NULL;
917c478bd9Sstevel@tonic-gate 
927c478bd9Sstevel@tonic-gate /*
93*59f081edSraf  * Compute the size an _environ list including the terminating NULL entry.
94*59f081edSraf  * This is the only way we have to determine the size of an _environ list
957c478bd9Sstevel@tonic-gate  * we didn't allocate.
967c478bd9Sstevel@tonic-gate  */
977c478bd9Sstevel@tonic-gate static int
987c478bd9Sstevel@tonic-gate envsize(const char **e)
997c478bd9Sstevel@tonic-gate {
1007c478bd9Sstevel@tonic-gate 	int			size;
1017c478bd9Sstevel@tonic-gate 
1027c478bd9Sstevel@tonic-gate 	if (e == NULL)
1037c478bd9Sstevel@tonic-gate 		return (0);
1047c478bd9Sstevel@tonic-gate 
1057c478bd9Sstevel@tonic-gate 	for (size = 1; *e != NULL; e++)
1067c478bd9Sstevel@tonic-gate 		size++;
1077c478bd9Sstevel@tonic-gate 
1087c478bd9Sstevel@tonic-gate 	return (size);
1097c478bd9Sstevel@tonic-gate }
1107c478bd9Sstevel@tonic-gate 
1117c478bd9Sstevel@tonic-gate /*
1127c478bd9Sstevel@tonic-gate  * Initialization for the following scenarios:
113*59f081edSraf  * 1. The very first time we reference the _environ list we must call in the
114*59f081edSraf  *    NLSPATH janitor, make a reference to the original _environ list to keep
1157c478bd9Sstevel@tonic-gate  *    leak detectors happy, initialize my_environ and environ_base, and then
1167c478bd9Sstevel@tonic-gate  *    compute environ_size.
117*59f081edSraf  * 2. Whenever we detect that someone else has hijacked _environ (something
1187c478bd9Sstevel@tonic-gate  *    very abnormal) we need to reinitialize my_environ and environ_base,
1197c478bd9Sstevel@tonic-gate  *    and then recompute environ_size.
1207c478bd9Sstevel@tonic-gate  *
1217c478bd9Sstevel@tonic-gate  * The local globals my_environ, environ_base and environ_size may be used
1227c478bd9Sstevel@tonic-gate  * by others only if initenv_done is true and only under the protection of
1237c478bd9Sstevel@tonic-gate  * update_lock. However, our callers, who must NOT be holding update_lock,
124*59f081edSraf  * may safely test initenv_done or my_environ against _environ just prior to
1257c478bd9Sstevel@tonic-gate  * calling us because we test these again whilst holding update_lock.
1267c478bd9Sstevel@tonic-gate  */
1277c478bd9Sstevel@tonic-gate static void
1287c478bd9Sstevel@tonic-gate initenv()
1297c478bd9Sstevel@tonic-gate {
130*59f081edSraf 	if ((my_environ != _environ) || !initenv_done) {
131cb620785Sraf 		lmutex_lock(&update_lock);
132*59f081edSraf 		if ((my_environ != _environ) || !initenv_done) {
133cb620785Sraf 			if (!initenv_done) {
134cb620785Sraf 				/* Call the NLSPATH janitor in. */
135cb620785Sraf 				clean_env();
1367c478bd9Sstevel@tonic-gate 
137cb620785Sraf 				/* Pacify leak detectors in normal operation. */
138*59f081edSraf 				orig_environ = _environ;
1397c478bd9Sstevel@tonic-gate #ifdef __lint
140cb620785Sraf 				my_environ = orig_environ;
1417c478bd9Sstevel@tonic-gate #endif
142cb620785Sraf 			}
1437c478bd9Sstevel@tonic-gate 
144*59f081edSraf 			my_environ = _environ;
145cb620785Sraf 			environ_base = my_environ;
146cb620785Sraf 			environ_size = envsize(environ_base);
147cb620785Sraf 			membar_producer();
1487c478bd9Sstevel@tonic-gate 			initenv_done = 1;
1497c478bd9Sstevel@tonic-gate 		}
150cb620785Sraf 		lmutex_unlock(&update_lock);
1517c478bd9Sstevel@tonic-gate 	}
152cb620785Sraf 	membar_consumer();
1537c478bd9Sstevel@tonic-gate }
1547c478bd9Sstevel@tonic-gate 
1557c478bd9Sstevel@tonic-gate /*
156*59f081edSraf  * Search an _environ list for a particular entry. If name_only is set, then
1577c478bd9Sstevel@tonic-gate  * string must be the entry name only, and we return the value of the first
1587c478bd9Sstevel@tonic-gate  * match. Otherwise, string must be of the form "name=value", and we return
1597c478bd9Sstevel@tonic-gate  * the address of the first matching entry.
1607c478bd9Sstevel@tonic-gate  */
1617c478bd9Sstevel@tonic-gate static const char **
1627c478bd9Sstevel@tonic-gate findenv(const char **e, const char *string, int name_only, char **value)
1637c478bd9Sstevel@tonic-gate {
1647c478bd9Sstevel@tonic-gate 	char			target;
1657c478bd9Sstevel@tonic-gate 	const char		*s1;
1667c478bd9Sstevel@tonic-gate 	const char		*s2;
1677c478bd9Sstevel@tonic-gate 
1687c478bd9Sstevel@tonic-gate 	*value = NULL;
1697c478bd9Sstevel@tonic-gate 
1707c478bd9Sstevel@tonic-gate 	if (e == NULL)
1717c478bd9Sstevel@tonic-gate 		return (NULL);
1727c478bd9Sstevel@tonic-gate 
1737c478bd9Sstevel@tonic-gate 	target = name_only ? '\0' : '=';
1747c478bd9Sstevel@tonic-gate 
1757c478bd9Sstevel@tonic-gate 	for (; (s2 = *e) != NULL; e++) {
1767c478bd9Sstevel@tonic-gate 		s1 =  string;
1777c478bd9Sstevel@tonic-gate 
1787c478bd9Sstevel@tonic-gate 		/* Fast comparison for first char. */
1797c478bd9Sstevel@tonic-gate 		if (*s1 != *s2)
1807c478bd9Sstevel@tonic-gate 			continue;
1817c478bd9Sstevel@tonic-gate 
1827c478bd9Sstevel@tonic-gate 		/* Slow comparison for rest of string. */
1837c478bd9Sstevel@tonic-gate 		while (*s1 == *s2 && *s2 != '=') {
1847c478bd9Sstevel@tonic-gate 			s1++;
1857c478bd9Sstevel@tonic-gate 			s2++;
1867c478bd9Sstevel@tonic-gate 		}
1877c478bd9Sstevel@tonic-gate 
1887c478bd9Sstevel@tonic-gate 		if (*s1 == target && *s2 == '=') {
1897c478bd9Sstevel@tonic-gate 			*value = (char *)s2 + 1;
1907c478bd9Sstevel@tonic-gate 			return (e);
1917c478bd9Sstevel@tonic-gate 		}
1927c478bd9Sstevel@tonic-gate 	}
1937c478bd9Sstevel@tonic-gate 	return (NULL);
1947c478bd9Sstevel@tonic-gate }
1957c478bd9Sstevel@tonic-gate 
1967c478bd9Sstevel@tonic-gate /*
1977c478bd9Sstevel@tonic-gate  * Common code for putenv() and setenv(). We support the lockless getenv()
1987c478bd9Sstevel@tonic-gate  * by inserting new entries at the bottom of the list, and by growing the
1997c478bd9Sstevel@tonic-gate  * list using the trusted "power of two, drop it on the floor" method. We
200*59f081edSraf  * use a lock (update_lock) to protect all updates to the _environ list, but
2017c478bd9Sstevel@tonic-gate  * we are obliged to release this lock whenever we call malloc() or free().
2027c478bd9Sstevel@tonic-gate  * A generation number (environ_gen) is bumped whenever names are added to,
203*59f081edSraf  * or removed from, the _environ list so that we can detect collisions with
2047c478bd9Sstevel@tonic-gate  * other updaters.
2057c478bd9Sstevel@tonic-gate  *
2067c478bd9Sstevel@tonic-gate  * Return values
2077c478bd9Sstevel@tonic-gate  *   0 : success
2087c478bd9Sstevel@tonic-gate  *  -1 : with errno set
2097c478bd9Sstevel@tonic-gate  *  -2 : an entry already existed and overwrite was zero
2107c478bd9Sstevel@tonic-gate  */
2117c478bd9Sstevel@tonic-gate static int
2127c478bd9Sstevel@tonic-gate addtoenv(char *string, int overwrite)
2137c478bd9Sstevel@tonic-gate {
2147c478bd9Sstevel@tonic-gate 	char			*value;
2157c478bd9Sstevel@tonic-gate 	const char		**p;
2167c478bd9Sstevel@tonic-gate 	chunk_t			*new_chunk;
2177c478bd9Sstevel@tonic-gate 	const char		**new_environ;
2187c478bd9Sstevel@tonic-gate 	const char		**new_base;
2197c478bd9Sstevel@tonic-gate 	int			new_size;
2207c478bd9Sstevel@tonic-gate 	int			old_gen;
2217c478bd9Sstevel@tonic-gate 
222cb620785Sraf 	initenv();
2237c478bd9Sstevel@tonic-gate 
2247c478bd9Sstevel@tonic-gate 	lmutex_lock(&update_lock);
2257c478bd9Sstevel@tonic-gate 
2267c478bd9Sstevel@tonic-gate 	for (;;) {
2277c478bd9Sstevel@tonic-gate 		/*
2287c478bd9Sstevel@tonic-gate 		 * If the name already exists just overwrite the existing
2297c478bd9Sstevel@tonic-gate 		 * entry -- except when we were called by setenv() without
2307c478bd9Sstevel@tonic-gate 		 * the overwrite flag.
2317c478bd9Sstevel@tonic-gate 		 */
2327c478bd9Sstevel@tonic-gate 		if ((p = findenv(my_environ, string, 0, &value)) != NULL) {
2337c478bd9Sstevel@tonic-gate 			if (overwrite) {
2347c478bd9Sstevel@tonic-gate 				/*
2357c478bd9Sstevel@tonic-gate 				 * Replace the value in situ. No name was
2367c478bd9Sstevel@tonic-gate 				 * added, so there is no need to bump the
2377c478bd9Sstevel@tonic-gate 				 * generation number.
2387c478bd9Sstevel@tonic-gate 				 */
2397c478bd9Sstevel@tonic-gate 				*p = string;
2407c478bd9Sstevel@tonic-gate 				lmutex_unlock(&update_lock);
2417c478bd9Sstevel@tonic-gate 				return (0);
2427c478bd9Sstevel@tonic-gate 			} else {
2437c478bd9Sstevel@tonic-gate 				/* No change. */
2447c478bd9Sstevel@tonic-gate 				lmutex_unlock(&update_lock);
2457c478bd9Sstevel@tonic-gate 				return (-2);
2467c478bd9Sstevel@tonic-gate 			}
2477c478bd9Sstevel@tonic-gate 		}
2487c478bd9Sstevel@tonic-gate 
2497c478bd9Sstevel@tonic-gate 		/* Try to insert the new entry at the bottom of the list. */
2507c478bd9Sstevel@tonic-gate 		if (environ_base < my_environ) {
2517c478bd9Sstevel@tonic-gate 			/*
2527c478bd9Sstevel@tonic-gate 			 * The new value must be visible before we decrement
253*59f081edSraf 			 * the _environ list pointer.
2547c478bd9Sstevel@tonic-gate 			 */
2557c478bd9Sstevel@tonic-gate 			my_environ[-1] = string;
2567c478bd9Sstevel@tonic-gate 			membar_producer();
2577c478bd9Sstevel@tonic-gate 			my_environ--;
258*59f081edSraf 			_environ = my_environ;
2597c478bd9Sstevel@tonic-gate 
2607c478bd9Sstevel@tonic-gate 			/*
2617c478bd9Sstevel@tonic-gate 			 * We've added a name, so bump the generation number.
2627c478bd9Sstevel@tonic-gate 			 */
2637c478bd9Sstevel@tonic-gate 			environ_gen++;
2647c478bd9Sstevel@tonic-gate 
2657c478bd9Sstevel@tonic-gate 			lmutex_unlock(&update_lock);
2667c478bd9Sstevel@tonic-gate 			return (0);
2677c478bd9Sstevel@tonic-gate 		}
2687c478bd9Sstevel@tonic-gate 
2697c478bd9Sstevel@tonic-gate 		/*
270*59f081edSraf 		 * There is no room. Attempt to allocate a new _environ list
2717c478bd9Sstevel@tonic-gate 		 * which is at least double the size of the current one. See
2727c478bd9Sstevel@tonic-gate 		 * comment above concerning locking and malloc() etc.
2737c478bd9Sstevel@tonic-gate 		 */
2747c478bd9Sstevel@tonic-gate 		new_size = environ_size * 2;
2757c478bd9Sstevel@tonic-gate 		if (new_size < MIN_ENV_SIZE)
2767c478bd9Sstevel@tonic-gate 			new_size = MIN_ENV_SIZE;
2777c478bd9Sstevel@tonic-gate 
2787c478bd9Sstevel@tonic-gate 		old_gen = environ_gen;
2797c478bd9Sstevel@tonic-gate 		lmutex_unlock(&update_lock);
2807c478bd9Sstevel@tonic-gate 
2817c478bd9Sstevel@tonic-gate 		new_chunk = malloc(sizeof (chunk_t) +
2827c478bd9Sstevel@tonic-gate 		    new_size * sizeof (char *));
2837c478bd9Sstevel@tonic-gate 		if (new_chunk == NULL) {
2847c478bd9Sstevel@tonic-gate 			errno = ENOMEM;
2857c478bd9Sstevel@tonic-gate 			return (-1);
2867c478bd9Sstevel@tonic-gate 		}
2877c478bd9Sstevel@tonic-gate 
2887c478bd9Sstevel@tonic-gate 		lmutex_lock(&update_lock);
2897c478bd9Sstevel@tonic-gate 
2907c478bd9Sstevel@tonic-gate 		/*
2917c478bd9Sstevel@tonic-gate 		 * If no other thread added or removed names while the lock
2927c478bd9Sstevel@tonic-gate 		 * was dropped, it is time to break out of this loop.
2937c478bd9Sstevel@tonic-gate 		 */
2947c478bd9Sstevel@tonic-gate 		if (environ_gen == old_gen)
2957c478bd9Sstevel@tonic-gate 			break;
2967c478bd9Sstevel@tonic-gate 
2977c478bd9Sstevel@tonic-gate 		/*
2987c478bd9Sstevel@tonic-gate 		 * At least one name has been added or removed, so we need to
2997c478bd9Sstevel@tonic-gate 		 * try again. It is very likely that we will find sufficient
3007c478bd9Sstevel@tonic-gate 		 * space the next time around.
3017c478bd9Sstevel@tonic-gate 		 */
3027c478bd9Sstevel@tonic-gate 		lmutex_unlock(&update_lock);
3037c478bd9Sstevel@tonic-gate 		free(new_chunk);
3047c478bd9Sstevel@tonic-gate 		lmutex_lock(&update_lock);
3057c478bd9Sstevel@tonic-gate 	}
3067c478bd9Sstevel@tonic-gate 
3077c478bd9Sstevel@tonic-gate 	/* Add the new chunk to chunk_list to hide potential future leak. */
3087c478bd9Sstevel@tonic-gate 	new_chunk->next = chunk_list;
3097c478bd9Sstevel@tonic-gate 	chunk_list = new_chunk;
3107c478bd9Sstevel@tonic-gate 
311*59f081edSraf 	/* Copy the old _environ list into the top of the new _environ list. */
3127c478bd9Sstevel@tonic-gate 	new_base = (const char **)(new_chunk + 1);
3137c478bd9Sstevel@tonic-gate 	new_environ = &new_base[(new_size - 1) - environ_size];
3147c478bd9Sstevel@tonic-gate 	(void) memcpy(new_environ, my_environ, environ_size * sizeof (char *));
3157c478bd9Sstevel@tonic-gate 
316*59f081edSraf 	/* Insert the new entry at the bottom of the new _environ list. */
3177c478bd9Sstevel@tonic-gate 	new_environ[-1] = string;
3187c478bd9Sstevel@tonic-gate 	new_environ--;
3197c478bd9Sstevel@tonic-gate 
320*59f081edSraf 	/* Ensure that the new _environ list is visible to all. */
3217c478bd9Sstevel@tonic-gate 	membar_producer();
3227c478bd9Sstevel@tonic-gate 
323*59f081edSraf 	/* Make the switch (dropping the old _environ list on the floor). */
3247c478bd9Sstevel@tonic-gate 	environ_base = new_base;
3257c478bd9Sstevel@tonic-gate 	my_environ = new_environ;
326*59f081edSraf 	_environ = my_environ;
3277c478bd9Sstevel@tonic-gate 	environ_size = new_size;
3287c478bd9Sstevel@tonic-gate 
3297c478bd9Sstevel@tonic-gate 	/* We've added a name, so bump the generation number. */
3307c478bd9Sstevel@tonic-gate 	environ_gen++;
3317c478bd9Sstevel@tonic-gate 
3327c478bd9Sstevel@tonic-gate 	lmutex_unlock(&update_lock);
3337c478bd9Sstevel@tonic-gate 	return (0);
3347c478bd9Sstevel@tonic-gate }
3357c478bd9Sstevel@tonic-gate 
3367c478bd9Sstevel@tonic-gate /*
3377c478bd9Sstevel@tonic-gate  * All the work for putenv() is done in addtoenv().
3387c478bd9Sstevel@tonic-gate  */
3397c478bd9Sstevel@tonic-gate int
3407c478bd9Sstevel@tonic-gate putenv(char *string)
3417c478bd9Sstevel@tonic-gate {
3427c478bd9Sstevel@tonic-gate 	return (addtoenv(string, 1));
3437c478bd9Sstevel@tonic-gate }
3447c478bd9Sstevel@tonic-gate 
3457c478bd9Sstevel@tonic-gate /*
3467c478bd9Sstevel@tonic-gate  * setenv() is a little more complex than putenv() because we have to allocate
347*59f081edSraf  * and construct an _environ entry on behalf of the caller. The bulk of the
3487c478bd9Sstevel@tonic-gate  * work is still done in addtoenv().
3497c478bd9Sstevel@tonic-gate  */
3507c478bd9Sstevel@tonic-gate 
3517c478bd9Sstevel@tonic-gate int
3527c478bd9Sstevel@tonic-gate setenv(const char *envname, const char *envval, int overwrite)
3537c478bd9Sstevel@tonic-gate {
3547c478bd9Sstevel@tonic-gate 	chunk_t			*new_chunk;
3557c478bd9Sstevel@tonic-gate 	char			*new_string;
3567c478bd9Sstevel@tonic-gate 	size_t			name_len;
3577c478bd9Sstevel@tonic-gate 	size_t			val_len;
3587c478bd9Sstevel@tonic-gate 	int			res;
3597c478bd9Sstevel@tonic-gate 
3607c478bd9Sstevel@tonic-gate 	if (envname == NULL || *envname == 0 || strchr(envname, '=') != NULL) {
3617c478bd9Sstevel@tonic-gate 		errno = EINVAL;
3627c478bd9Sstevel@tonic-gate 		return (-1);
3637c478bd9Sstevel@tonic-gate 	}
3647c478bd9Sstevel@tonic-gate 
3657c478bd9Sstevel@tonic-gate 	name_len = strlen(envname);
3667c478bd9Sstevel@tonic-gate 	val_len = strlen(envval);
3677c478bd9Sstevel@tonic-gate 
3687c478bd9Sstevel@tonic-gate 	new_chunk = malloc(sizeof (chunk_t) + name_len + val_len + 2);
3697c478bd9Sstevel@tonic-gate 	if (new_chunk == NULL) {
3707c478bd9Sstevel@tonic-gate 		errno = ENOMEM;
3717c478bd9Sstevel@tonic-gate 		return (-1);
3727c478bd9Sstevel@tonic-gate 	}
3737c478bd9Sstevel@tonic-gate 	new_string = (char *)(new_chunk + 1);
3747c478bd9Sstevel@tonic-gate 
3757c478bd9Sstevel@tonic-gate 	(void) memcpy(new_string, envname, name_len);
3767c478bd9Sstevel@tonic-gate 	new_string[name_len] = '=';
3777c478bd9Sstevel@tonic-gate 	(void) memcpy(new_string + name_len + 1, envval, val_len);
3787c478bd9Sstevel@tonic-gate 	new_string[name_len + 1 + val_len] = 0;
3797c478bd9Sstevel@tonic-gate 
3807c478bd9Sstevel@tonic-gate 	if ((res = addtoenv(new_string, overwrite)) < 0) {
3817c478bd9Sstevel@tonic-gate 		free(new_chunk);
3827c478bd9Sstevel@tonic-gate 		if (res == -2) {
3837c478bd9Sstevel@tonic-gate 			/* The name already existed, but not an error. */
3847c478bd9Sstevel@tonic-gate 			return (0);
3857c478bd9Sstevel@tonic-gate 		} else {
3867c478bd9Sstevel@tonic-gate 			/* i.e. res == -1 which means only one thing. */
3877c478bd9Sstevel@tonic-gate 			errno = ENOMEM;
3887c478bd9Sstevel@tonic-gate 			return (-1);
3897c478bd9Sstevel@tonic-gate 		}
3907c478bd9Sstevel@tonic-gate 	}
3917c478bd9Sstevel@tonic-gate 
3927c478bd9Sstevel@tonic-gate 	/* Hide potential leak of new_string. */
3937c478bd9Sstevel@tonic-gate 	lmutex_lock(&update_lock);
3947c478bd9Sstevel@tonic-gate 	new_chunk->next = chunk_list;
3957c478bd9Sstevel@tonic-gate 	chunk_list = new_chunk;
3967c478bd9Sstevel@tonic-gate 	lmutex_unlock(&update_lock);
3977c478bd9Sstevel@tonic-gate 
3987c478bd9Sstevel@tonic-gate 	return (0);
3997c478bd9Sstevel@tonic-gate }
4007c478bd9Sstevel@tonic-gate 
4017c478bd9Sstevel@tonic-gate /*
402*59f081edSraf  * unsetenv() is tricky because we need to compress the _environ list in a way
4037c478bd9Sstevel@tonic-gate  * which supports a lockless getenv(). The approach here is to move the first
4047c478bd9Sstevel@tonic-gate  * entry from the enrivon list into the space occupied by the entry to be
405*59f081edSraf  * deleted, and then to increment _environ. This has the added advantage of
406*59f081edSraf  * making _any_ incremental linear search of the _environ list consistent (i.e.
4077c478bd9Sstevel@tonic-gate  * we will not break any naughty apps which read the list without our help).
4087c478bd9Sstevel@tonic-gate  */
4097c478bd9Sstevel@tonic-gate int
4107c478bd9Sstevel@tonic-gate unsetenv(const char *name)
4117c478bd9Sstevel@tonic-gate {
4127c478bd9Sstevel@tonic-gate 	const char		**p;
4137c478bd9Sstevel@tonic-gate 	char			*value;
4147c478bd9Sstevel@tonic-gate 
4157c478bd9Sstevel@tonic-gate 	if (name == NULL || *name == 0 || strchr(name, '=') != NULL) {
4167c478bd9Sstevel@tonic-gate 		errno = EINVAL;
4177c478bd9Sstevel@tonic-gate 		return (-1);
4187c478bd9Sstevel@tonic-gate 	}
4197c478bd9Sstevel@tonic-gate 
420cb620785Sraf 	initenv();
4217c478bd9Sstevel@tonic-gate 
4227c478bd9Sstevel@tonic-gate 	lmutex_lock(&update_lock);
4237c478bd9Sstevel@tonic-gate 
4247c478bd9Sstevel@tonic-gate 	/*
4257c478bd9Sstevel@tonic-gate 	 * Find the target, overwrite it with the first entry, increment the
426*59f081edSraf 	 * _environ pointer.
4277c478bd9Sstevel@tonic-gate 	 */
4287c478bd9Sstevel@tonic-gate 	if ((p = findenv(my_environ, name, 1, &value)) != NULL) {
4297c478bd9Sstevel@tonic-gate 		/* Overwrite target with the first entry. */
4307c478bd9Sstevel@tonic-gate 		*p = my_environ[0];
4317c478bd9Sstevel@tonic-gate 
4327c478bd9Sstevel@tonic-gate 		/* Ensure that the moved entry is visible to all.  */
4337c478bd9Sstevel@tonic-gate 		membar_producer();
4347c478bd9Sstevel@tonic-gate 
435*59f081edSraf 		/* Shrink the _environ list. */
4367c478bd9Sstevel@tonic-gate 		my_environ++;
437*59f081edSraf 		_environ = my_environ;
4387c478bd9Sstevel@tonic-gate 
4397c478bd9Sstevel@tonic-gate 		/* Make sure addtoenv() knows that we've removed a name. */
4407c478bd9Sstevel@tonic-gate 		environ_gen++;
4417c478bd9Sstevel@tonic-gate 	}
4427c478bd9Sstevel@tonic-gate 
4437c478bd9Sstevel@tonic-gate 	lmutex_unlock(&update_lock);
4447c478bd9Sstevel@tonic-gate 	return (0);
4457c478bd9Sstevel@tonic-gate }
4467c478bd9Sstevel@tonic-gate 
4477c478bd9Sstevel@tonic-gate /*
4487c478bd9Sstevel@tonic-gate  * At last, a lockless implementation of getenv()!
4497c478bd9Sstevel@tonic-gate  */
4507c478bd9Sstevel@tonic-gate char *
4517c478bd9Sstevel@tonic-gate getenv(const char *name)
4527c478bd9Sstevel@tonic-gate {
4537c478bd9Sstevel@tonic-gate 	char			*value;
4547c478bd9Sstevel@tonic-gate 
455cb620785Sraf 	initenv();
4567c478bd9Sstevel@tonic-gate 
457*59f081edSraf 	if (findenv(_environ, name, 1, &value) != NULL)
4587c478bd9Sstevel@tonic-gate 		return (value);
4597c478bd9Sstevel@tonic-gate 
4607c478bd9Sstevel@tonic-gate 	return (NULL);
4617c478bd9Sstevel@tonic-gate }
462