iconv/gconv_dl.c

   1 /* Handle loading/unloading of shared object for transformation.
   2    Copyright (C) 1997, 1998, 1999, 2000 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 <assert.h>
  22 #include <dlfcn.h>
  23 #include <inttypes.h>
  24 #include <search.h>
  25 #include <stdlib.h>
  26 #include <string.h>
  27 #include <bits/libc-lock.h>
  28 #include <sys/param.h>
  29
  30 #include <gconv_int.h>
  31
  32
  33 #ifdef DEBUG
  34 /* For debugging purposes.  */
  35 static void print_all (void);
  36 #endif
  37
  38
  39 /* This is a tuning parameter.  If a transformation module is not used
  40    anymore it gets not immediately unloaded.  Instead we wait a certain
  41    number of load attempts for further modules.  If none of the
  42    subsequent load attempts name the same object it finally gets unloaded.
  43    Otherwise it is still available which hopefully is the frequent case.
  44    The following number is the number of unloading attempts we wait
  45    before unloading.  */
  46 #define TRIES_BEFORE_UNLOAD     2
  47
  48 /* Array of loaded objects.  This is shared by all threads so we have
  49    to use semaphores to access it.  */
  50 static void *loaded;
  51
  52 /* Comparison function for searching `loaded_object' tree.  */
  53 static int
  54 known_compare (const void *p1, const void *p2)
  55 {
  56   const struct __gconv_loaded_object *s1 =
  57     (const struct __gconv_loaded_object *) p1;
  58   const struct __gconv_loaded_object *s2 =
  59     (const struct __gconv_loaded_object *) p2;
  60
  61   return strcmp (s1->name, s2->name);
  62 }
  63
  64 /* Open the gconv database if necessary.  A non-negative return value
  65    means success.  */
  66 struct __gconv_loaded_object *
  67 internal_function
  68 __gconv_find_shlib (const char *name)
  69 {
  70   struct __gconv_loaded_object *found;
  71   void *keyp;
  72
  73   /* Search the tree of shared objects previously requested.  Data in
  74      the tree are `loaded_object' structures, whose first member is a
  75      `const char *', the lookup key.  The search returns a pointer to
  76      the tree node structure; the first member of the is a pointer to
  77      our structure (i.e. what will be a `loaded_object'); since the
  78      first member of that is the lookup key string, &FCT_NAME is close
  79      enough to a pointer to our structure to use as a lookup key that
  80      will be passed to `known_compare' (above).  */
  81
  82   keyp = __tfind (&name, &loaded, known_compare);
  83   if (keyp == NULL)
  84     {
  85       /* This name was not known before.  */
  86       found = malloc (sizeof (struct __gconv_loaded_object));
  87       if (found != NULL)
  88         {
  89           /* Point the tree node at this new structure.  */
  90           found->name = name;
  91           found->counter = -TRIES_BEFORE_UNLOAD - 1;
  92           found->handle = NULL;
  93
  94           if (__builtin_expect (__tsearch (found, &loaded, known_compare)
  95                                 == NULL, 0))
  96             {
  97               /* Something went wrong while inserting the entry.  */
  98               free (found);
  99               found = NULL;
 100             }
 101         }
 102     }
 103   else
 104     found = *(struct __gconv_loaded_object **) keyp;
 105
 106   /* Try to load the shared object if the usage count is 0.  This
 107      implies that if the shared object is not loadable, the handle is
 108      NULL and the usage count > 0.  */
 109   if (found != NULL)
 110     {
 111       if (found->counter < -TRIES_BEFORE_UNLOAD)
 112         {
 113           found->handle = __libc_dlopen (found->name);
 114           if (found->handle != NULL)
 115             {
 116               found->fct = __libc_dlsym (found->handle, "gconv");
 117               if (found->fct == NULL)
 118                 {
 119                   /* Argh, no conversion function.  There is something
 120                      wrong here.  */
 121                   __gconv_release_shlib (found);
 122                   found = NULL;
 123                 }
 124               else
 125                 {
 126                   found->init_fct = __libc_dlsym (found->handle, "gconv_init");
 127                   found->end_fct = __libc_dlsym (found->handle, "gconv_end");
 128
 129                   /* We have succeeded in loading the shared object.  */
 130                   found->counter = 1;
 131                 }
 132             }
 133           else
 134             /* Error while loading the shared object.  */
 135             found = NULL;
 136         }
 137       else if (found->handle != NULL)
 138         found->counter = MAX (found->counter + 1, 1);
 139     }
 140
 141   return found;
 142 }
 143
 144
 145 /* This is very ugly but the tsearch functions provide no way to pass
 146    information to the walker function.  So we use a global variable.
 147    It is MT safe since we use a lock.  */
 148 static struct __gconv_loaded_object *release_handle;
 149
 150 static void
 151 do_release_shlib (const void *nodep, VISIT value, int level)
 152 {
 153   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 154
 155   if (value != preorder && value != leaf)
 156     return;
 157
 158   if (obj == release_handle)
 159     {
 160       /* This is the object we want to unload.  Now decrement the
 161          reference counter.  */
 162       assert (obj->counter > 0);
 163       --obj->counter;
 164     }
 165   else if (obj->counter <= 0)
 166     {
 167       if (--obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
 168         {
 169           /* Unload the shared object.  */
 170           __libc_dlclose (obj->handle);
 171           obj->handle = NULL;
 172         }
 173     }
 174 }
 175
 176
 177 /* Notify system that a shared object is not longer needed.  */
 178 int
 179 internal_function
 180 __gconv_release_shlib (struct __gconv_loaded_object *handle)
 181 {
 182   /* Urgh, this is ugly but we have no other possibility.  */
 183   release_handle = handle;
 184
 185   /* Process all entries.  Please note that we also visit entries
 186      with release counts <= 0.  This way we can finally unload them
 187      if necessary.  */
 188   __twalk (loaded, do_release_shlib);
 189
 190   return __GCONV_OK;
 191 }
 192
 193
 194 /* We run this if we debug the memory allocation.  */
 195 static void
 196 do_release_all (void *nodep)
 197 {
 198   struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;
 199
 200   /* Unload the shared object.  */
 201   if (obj->handle != NULL)
 202     __libc_dlclose (obj->handle);
 203
 204   free (obj);
 205 }
 206
 207 static void __attribute__ ((unused))
 208 free_mem (void)
 209 {
 210   __tdestroy (loaded, do_release_all);
 211 }
 212 text_set_element (__libc_subfreeres, free_mem);
 213
 214
 215 #ifdef DEBUG
 216 static void
 217 do_print (const void *nodep, VISIT value, int level)
 218 {
 219   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 220
 221   printf ("%10s: \"%s\", %d\n",
 222           value == leaf ? "leaf" :
 223           value == preorder ? "preorder" :
 224           value == postorder ? "postorder" : "endorder",
 225           obj->name, obj->counter);
 226 }
 227
 228 static void
 229 print_all (void)
 230 {
 231   __twalk (loaded, do_print);
 232 }
 233 #endif