glibc/sysdeps/generic/setenv.c

/* Copyright (C) 1992, 95, 96, 97, 98, 99 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

/* Issues:

   1. putenv must not use setenv since the string provided by the user
      must be used, not a copy

   2. a common function should determine the place where to insert the
      new entry and if necessary take care of extending the array

   3. It must be kept track of whether an entry was inserted via putenv
      or setenv.  In the former case the entry must not be put into
      the search tree since removing it could mean it will not be
      available anymore (e.g., when allocated on the stack)

      To handle this an array parallel to the __environ array must specify
      whether the entry was added via putenv or not
*/

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <errno.h>
#if !_LIBC
# if !defined errno && !defined HAVE_ERRNO_DECL
extern int errno;
# endif
# define __set_errno(ev) ((errno) = (ev))
#endif

#if _LIBC || HAVE_STDLIB_H
# include <stdlib.h>
#endif
#if _LIBC || HAVE_STRING_H
# include <string.h>
#endif
#if _LIBC || HAVE_UNISTD_H
# include <unistd.h>
#endif

#if !_LIBC
# define __environ	environ
# ifndef HAVE_ENVIRON_DECL
extern char **environ;
# endif
#endif

#if _LIBC
/* This lock protects against simultaneous modifications of `environ'.  */
# include <bits/libc-lock.h>
__libc_lock_define_initialized (static, envlock)
# define LOCK	__libc_lock_lock (envlock)
# define UNLOCK	__libc_lock_unlock (envlock)
#else
# define LOCK
# define UNLOCK
#endif

/* In the GNU C library we must keep the namespace clean.  */
#ifdef _LIBC
# define setenv __setenv
# define unsetenv __unsetenv
# define clearenv __clearenv
# define tfind __tfind
# define tsearch __tsearch
#endif

/* In the GNU C library implementation we try to be more clever and
   allow arbitrary many changes of the environment given that the used
   values are from a small set.  Outside glibc this will eat up all
   memory after a while.  */
#if defined _LIBC || (defined HAVE_SEARCH_H && defined HAVE_TSEARCH \
		      && defined __GNUC__)
# define USE_TSEARCH	1
# include <search.h>

/* This is a pointer to the root of the search tree with the known
   values.  */
static void *known_values;

# define KNOWN_VALUE(Str) \
  ({									      \
    void *value = tfind (Str, &known_values, (__compar_fn_t) strcmp);	      \
    value != NULL ? *(char **) value : NULL;				      \
  })
# define STORE_VALUE(Str) \
  tsearch (Str, &known_values, (__compar_fn_t) strcmp)

#else
# undef USE_TSEARCH

# define KNOWN_VALUE(Str) NULL
# define STORE_VALUE(Str) do { } while (0)

#endif


/* If this variable is not a null pointer we allocated the current
   environment.  */
static char **last_environ;


int
setenv (name, value, replace)
     const char *name;
     const char *value;
     int replace;
{
  register char **ep;
  register size_t size;
  const size_t namelen = strlen (name);
  const size_t vallen = strlen (value) + 1;

  LOCK;

  size = 0;
  if (__environ != NULL)
    {
      for (ep = __environ; *ep != NULL; ++ep)
	if (!strncmp (*ep, name, namelen) && (*ep)[namelen] == '=')
	  break;
	else
	  ++size;
    }

  if (__environ == NULL || *ep == NULL)
    {
      char **new_environ;
#ifdef USE_TSEARCH
      char *new_value;
#endif

      /* We allocated this space; we can extend it.  */
      new_environ = (char **) realloc (last_environ,
				       (size + 2) * sizeof (char *));
      if (new_environ == NULL)
	{
	  UNLOCK;
	  return -1;
	}

      /* See whether the value is already known.  */
#ifdef USE_TSEARCH
      new_value = alloca (namelen + 1 + vallen);
# ifdef _LIBC
      __mempcpy (__mempcpy (__mempcpy (new_value, name, namelen), "=", 1),
		 value, vallen);
# else
      memcpy (new_value, name, namelen);
      new_value[namelen] = '=';
      memcpy (&new_value[namelen + 1], value, vallen);
# endif

      new_environ[size] = KNOWN_VALUE (new_value);
      if (new_environ[size] == NULL)
#endif
	{
	  new_environ[size] = malloc (namelen + 1 + vallen);
	  if (new_environ[size] == NULL)
	    {
	      __set_errno (ENOMEM);
	      UNLOCK;
	      return -1;
	    }

#ifdef USE_TSEARCH
	  memcpy (new_environ[size], new_value, namelen + 1 + vallen);
#else
	  memcpy (new_environ[size], name, namelen);
	  new_environ[size][namelen] = '=';
	  memcpy (&new_environ[size][namelen + 1], value, vallen);
#endif
	}

      if (__environ != last_environ)
	memcpy ((char *) new_environ, (char *) __environ,
		size * sizeof (char *));

      new_environ[size + 1] = NULL;

      last_environ = __environ = new_environ;
    }
  else if (replace)
    {
      char *new_value;
      char *np;

      /* The existing string is too short; malloc a new one.  */
#ifdef USE_TSEARCH
      new_value = alloca (namelen + 1 + vallen);
# ifdef _LIBC
      __mempcpy (__mempcpy (__mempcpy (new_value, name, namelen), "=", 1),
		 value, vallen);
# else
      memcpy (new_value, name, namelen);
      new_value[namelen] = '=';
      memcpy (&new_value[namelen + 1], value, vallen);
# endif

      np = KNOWN_VALUE (new_value);
      if (np == NULL)
#endif
	{
	  np = malloc (namelen + 1 + vallen);
	  if (np == NULL)
	    {
	      UNLOCK;
	      return -1;
	    }

#ifdef USE_TSEARCH
	  memcpy (np, new_value, namelen + 1 + vallen);
#else
	  memcpy (np, name, namelen);
	  np[namelen] = '=';
	  memcpy (&np[namelen + 1], value, vallen);
#endif
	}

      /* Keep the old value around.  */
      STORE_VALUE (*ep);
      *ep = np;
    }

  UNLOCK;

  return 0;
}

void
unsetenv (name)
     const char *name;
{
  const size_t len = strlen (name);
  char **ep;

  LOCK;

  for (ep = __environ; *ep != NULL; ++ep)
    if (!strncmp (*ep, name, len) && (*ep)[len] == '=')
      {
	/* Found it.  Remove this pointer by moving later ones back.  */
	char **dp = ep;

	/* Store the value so that we can reuse it later.  */
	STORE_VALUE (*ep);

	do
	  dp[0] = dp[1];
	while (*dp++);
	/* Continue the loop in case NAME appears again.  */
      }

  UNLOCK;
}

/* The `clearenv' was planned to be added to POSIX.1 but probably
   never made it.  Nevertheless the POSIX.9 standard (POSIX bindings
   for Fortran 77) requires this function.  */
int
clearenv ()
{
  LOCK;

  if (__environ == last_environ && __environ != NULL)
    {
      /* We allocated this environment so we can free it.  Store all the
         strings.  */
      char **ep = __environ;
      while (*ep != NULL)
	STORE_VALUE (*ep++);

      free (__environ);
      last_environ = NULL;
    }

  /* Clear the environment pointer removes the whole environment.  */
  __environ = NULL;

  UNLOCK;

  return 0;
}
#ifdef _LIBC
# undef setenv
# undef unsetenv
# undef clearenv
weak_alias (__setenv, setenv)
weak_alias (__unsetenv, unsetenv)
weak_alias (__clearenv, clearenv)
#endif