iconv/gconv_dl.c

   1 /* Handle loading/unloading of shared object for transformation.
   2    Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2004
   3    Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, write to the Free
  19    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20    02111-1307 USA.  */
  21
  22 #include <assert.h>
  23 #include <dlfcn.h>
  24 #include <inttypes.h>
  25 #include <search.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28 #include <bits/libc-lock.h>
  29 #include <sys/param.h>
  30
  31 #include <gconv_int.h>
  32
  33
  34 #ifdef DEBUG
  35 /* For debugging purposes.  */
  36 static void print_all (void);
  37 #endif
  38
  39
  40 /* This is a tuning parameter.  If a transformation module is not used
  41    anymore it gets not immediately unloaded.  Instead we wait a certain
  42    number of load attempts for further modules.  If none of the
  43    subsequent load attempts name the same object it finally gets unloaded.
  44    Otherwise it is still available which hopefully is the frequent case.
  45    The following number is the number of unloading attempts we wait
  46    before unloading.  */
  47 #define TRIES_BEFORE_UNLOAD     2
  48
  49 /* Array of loaded objects.  This is shared by all threads so we have
  50    to use semaphores to access it.  */
  51 static void *loaded;
  52
  53 /* Comparison function for searching `loaded_object' tree.  */
  54 static int
  55 known_compare (const void *p1, const void *p2)
  56 {
  57   const struct __gconv_loaded_object *s1 =
  58     (const struct __gconv_loaded_object *) p1;
  59   const struct __gconv_loaded_object *s2 =
  60     (const struct __gconv_loaded_object *) p2;
  61
  62   return strcmp (s1->name, s2->name);
  63 }
  64
  65 /* Open the gconv database if necessary.  A non-negative return value
  66    means success.  */
  67 struct __gconv_loaded_object *
  68 internal_function
  69 __gconv_find_shlib (const char *name)
  70 {
  71   struct __gconv_loaded_object *found;
  72   void *keyp;
  73
  74   /* Search the tree of shared objects previously requested.  Data in
  75      the tree are `loaded_object' structures, whose first member is a
  76      `const char *', the lookup key.  The search returns a pointer to
  77      the tree node structure; the first member of the is a pointer to
  78      our structure (i.e. what will be a `loaded_object'); since the
  79      first member of that is the lookup key string, &FCT_NAME is close
  80      enough to a pointer to our structure to use as a lookup key that
  81      will be passed to `known_compare' (above).  */
  82
  83   keyp = __tfind (&name, &loaded, known_compare);
  84   if (keyp == NULL)
  85     {
  86       /* This name was not known before.  */
  87       size_t namelen = strlen (name) + 1;
  88
  89       found = malloc (sizeof (struct __gconv_loaded_object) + namelen);
  90       if (found != NULL)
  91         {
  92           /* Point the tree node at this new structure.  */
  93           found->name = (char *) memcpy (found + 1, name, namelen);
  94           found->counter = -TRIES_BEFORE_UNLOAD - 1;
  95           found->handle = NULL;
  96
  97           if (__builtin_expect (__tsearch (found, &loaded, known_compare)
  98                                 == NULL, 0))
  99             {
 100               /* Something went wrong while inserting the entry.  */
 101               free (found);
 102               found = NULL;
 103             }
 104         }
 105     }
 106   else
 107     found = *(struct __gconv_loaded_object **) keyp;
 108
 109   /* Try to load the shared object if the usage count is 0.  This
 110      implies that if the shared object is not loadable, the handle is
 111      NULL and the usage count > 0.  */
 112   if (found != NULL)
 113     {
 114       if (found->counter < -TRIES_BEFORE_UNLOAD)
 115         {
 116           assert (found->handle == NULL);
 117           found->handle = __libc_dlopen (found->name);
 118           if (found->handle != NULL)
 119             {
 120               found->fct = __libc_dlsym (found->handle, "gconv");
 121               if (found->fct == NULL)
 122                 {
 123                   /* Argh, no conversion function.  There is something
 124                      wrong here.  */
 125                   __gconv_release_shlib (found);
 126                   found = NULL;
 127                 }
 128               else
 129                 {
 130                   found->init_fct = __libc_dlsym (found->handle, "gconv_init");
 131                   found->end_fct = __libc_dlsym (found->handle, "gconv_end");
 132
 133                   /* We have succeeded in loading the shared object.  */
 134                   found->counter = 1;
 135                 }
 136             }
 137           else
 138             /* Error while loading the shared object.  */
 139             found = NULL;
 140         }
 141       else if (found->handle != NULL)
 142         found->counter = MAX (found->counter + 1, 1);
 143     }
 144
 145   return found;
 146 }
 147
 148
 149 /* This is very ugly but the tsearch functions provide no way to pass
 150    information to the walker function.  So we use a global variable.
 151    It is MT safe since we use a lock.  */
 152 static struct __gconv_loaded_object *release_handle;
 153
 154 static void
 155 do_release_shlib (void *nodep, VISIT value, int level)
 156 {
 157   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 158
 159   if (value != preorder && value != leaf)
 160     return;
 161
 162   if (obj == release_handle)
 163     {
 164       /* This is the object we want to unload.  Now decrement the
 165          reference counter.  */
 166       assert (obj->counter > 0);
 167       --obj->counter;
 168     }
 169   else if (obj->counter <= 0 && obj->counter >= -TRIES_BEFORE_UNLOAD
 170            && --obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
 171     {
 172       /* Unload the shared object.  */
 173       __libc_dlclose (obj->handle);
 174       obj->handle = NULL;
 175     }
 176 }
 177
 178
 179 /* Notify system that a shared object is not longer needed.  */
 180 void
 181 internal_function
 182 __gconv_release_shlib (struct __gconv_loaded_object *handle)
 183 {
 184   /* Urgh, this is ugly but we have no other possibility.  */
 185   release_handle = handle;
 186
 187   /* Process all entries.  Please note that we also visit entries
 188      with release counts <= 0.  This way we can finally unload them
 189      if necessary.  */
 190   __twalk (loaded, (__action_fn_t) do_release_shlib);
 191 }
 192
 193
 194 /* We run this if we debug the memory allocation.  */
 195 static void __libc_freeres_fn_section
 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 libc_freeres_fn (free_mem)
 208 {
 209   __tdestroy (loaded, do_release_all);
 210   loaded = NULL;
 211 }
 212
 213
 214 #ifdef DEBUG
 215 static void
 216 do_print (const void *nodep, VISIT value, int level)
 217 {
 218   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 219
 220   printf ("%10s: \"%s\", %d\n",
 221           value == leaf ? "leaf" :
 222           value == preorder ? "preorder" :
 223           value == postorder ? "postorder" : "endorder",
 224           obj->name, obj->counter);
 225 }
 226
 227 static void
 228 print_all (void)
 229 {
 230   __twalk (loaded, do_print);
 231 }
 232 #endif