iconv/gconv_dl.c

   1 /* Handle loading/unloading of shared object for transformation.
   2    Copyright (C) 1997, 1998, 1999 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include <dlfcn.h>
  22 #include <inttypes.h>
  23 #include <search.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <bits/libc-lock.h>
  27 #include <sys/param.h>
  28
  29 #include <gconv_int.h>
  30
  31 /* This is a tuning parameter.  If a transformation module is not used
  32    anymore it gets not immediately unloaded.  Instead we wait a certain
  33    number of load attempts for further modules.  If none of the
  34    subsequent load attempts name the same object it finally gets unloaded.
  35    Otherwise it is still available which hopefully is the frequent case.
  36    The following number is the number of unloading attempts we wait
  37    before unloading.  */
  38 #define TRIES_BEFORE_UNLOAD     2
  39
  40 /* Array of loaded objects.  This is shared by all threads so we have
  41    to use semaphores to access it.  */
  42 static void *loaded;
  43
  44 /* Comparison function for searching `loaded_object' tree.  */
  45 static int
  46 known_compare (const void *p1, const void *p2)
  47 {
  48   const struct __gconv_loaded_object *s1 =
  49     (const struct __gconv_loaded_object *) p1;
  50   const struct __gconv_loaded_object *s2 =
  51     (const struct __gconv_loaded_object *) p2;
  52
  53   return (intptr_t) s1->handle - (intptr_t) s2->handle;
  54 }
  55
  56 /* Open the gconv database if necessary.  A non-negative return value
  57    means success.  */
  58 struct __gconv_loaded_object *
  59 internal_function
  60 __gconv_find_shlib (const char *name)
  61 {
  62   struct __gconv_loaded_object *found;
  63   void *keyp;
  64
  65   /* Search the tree of shared objects previously requested.  Data in
  66      the tree are `loaded_object' structures, whose first member is a
  67      `const char *', the lookup key.  The search returns a pointer to
  68      the tree node structure; the first member of the is a pointer to
  69      our structure (i.e. what will be a `loaded_object'); since the
  70      first member of that is the lookup key string, &FCT_NAME is close
  71      enough to a pointer to our structure to use as a lookup key that
  72      will be passed to `known_compare' (above).  */
  73
  74   keyp = __tfind (&name, &loaded, known_compare);
  75   if (keyp == NULL)
  76     {
  77       /* This name was not known before.  */
  78       found = malloc (sizeof (struct __gconv_loaded_object));
  79       if (found != NULL)
  80         {
  81           /* Point the tree node at this new structure.  */
  82           found->name = name;
  83           found->counter = -TRIES_BEFORE_UNLOAD - 1;
  84           found->handle = NULL;
  85
  86           if (__tsearch (found, &loaded, known_compare) == NULL)
  87             {
  88               /* Something went wrong while inserting the entry.  */
  89               free (found);
  90               found = NULL;
  91             }
  92         }
  93     }
  94   else
  95     found = *(struct __gconv_loaded_object **) keyp;
  96
  97   /* Try to load the shared object if the usage count is 0.  This
  98      implies that if the shared object is not loadable, the handle is
  99      NULL and the usage count > 0.  */
 100   if (found != NULL)
 101     {
 102       if (found->counter < -TRIES_BEFORE_UNLOAD)
 103         {
 104           found->handle = __libc_dlopen (found->name);
 105           if (found->handle != NULL)
 106             {
 107               found->fct = __libc_dlsym (found->handle, "gconv");
 108               if (found->fct == NULL)
 109                 {
 110                   /* Argh, no conversion function.  There is something
 111                      wrong here.  */
 112                   __gconv_release_shlib (found);
 113                   found = NULL;
 114                 }
 115               else
 116                 {
 117                   found->init_fct = __libc_dlsym (found->handle, "gconv_init");
 118                   found->end_fct = __libc_dlsym (found->handle, "gconv_end");
 119
 120                   /* We have succeeded in loading the shared object.  */
 121                   found->counter = 1;
 122                 }
 123             }
 124           else
 125             /* Error while loading the shared object.  */
 126             found = NULL;
 127         }
 128       else if (found->handle != NULL)
 129         found->counter = MAX (found->counter + 1, 1);
 130     }
 131
 132   return found;
 133 }
 134
 135
 136 /* This is very ugly but the tsearch functions provide no way to pass
 137    information to the walker function.  So we use a global variable.
 138    It is MT safe since we use a lock.  */
 139 static struct __gconv_loaded_object *release_handle;
 140
 141 static void
 142 do_release_shlib (const void *nodep, VISIT value, int level)
 143 {
 144   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 145
 146   if (value != preorder && value != leaf)
 147     return;
 148
 149   if (obj == release_handle)
 150     /* This is the object we want to unload.  Now set the release
 151        counter to zero.  */
 152     obj->counter = 0;
 153   else if (obj->counter <= 0)
 154     {
 155       if (--obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
 156         {
 157           /* Unload the shared object.  */
 158           __libc_dlclose (obj->handle);
 159           obj->handle = NULL;
 160         }
 161     }
 162 }
 163
 164
 165 /* Notify system that a shared object is not longer needed.  */
 166 int
 167 internal_function
 168 __gconv_release_shlib (struct __gconv_loaded_object *handle)
 169 {
 170   /* Urgh, this is ugly but we have no other possibility.  */
 171   release_handle = handle;
 172
 173   /* Process all entries.  Please note that we also visit entries
 174      with release counts <= 0.  This way we can finally unload them
 175      if necessary.  */
 176   __twalk (loaded, do_release_shlib);
 177
 178   return __GCONV_OK;
 179 }
 180
 181
 182 /* We run this if we debug the memory allocation.  */
 183 static void
 184 do_release_all (void *nodep)
 185 {
 186   struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;
 187
 188   /* Unload the shared object.  */
 189   if (obj->handle != NULL)
 190     __libc_dlclose (obj->handle);
 191
 192   free (obj);
 193 }
 194
 195 static void __attribute__ ((unused))
 196 free_mem (void)
 197 {
 198   __tdestroy (loaded, do_release_all);
 199 }
 200 text_set_element (__libc_subfreeres, free_mem);