epan/plugins.c

   1 /* plugins.c
   2  * plugin routines
   3  *
   4  * $Id: plugins.c,v 1.52 2002/05/05 00:34:11 guy Exp $
   5  *
   6  * Ethereal - Network traffic analyzer
   7  * By Gerald Combs <gerald@ethereal.com>
   8  * Copyright 1999 Gerald Combs
   9  *
  10  * This program is free software; you can redistribute it and/or
  11  * modify it under the terms of the GNU General Public License
  12  * as published by the Free Software Foundation; either version 2
  13  * of the License, or (at your option) any later version.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  * GNU General Public License for more details.
  19  *
  20  * You should have received a copy of the GNU General Public License
  21  * along with this program; if not, write to the Free Software
  22  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  23  */
  24
  25 #ifdef HAVE_CONFIG_H
  26 # include "config.h"
  27 #endif
  28
  29 #include "plugins.h"
  30
  31 #ifdef HAVE_PLUGINS
  32
  33 #include <time.h>
  34
  35 #ifdef HAVE_DIRENT_H
  36 #include <dirent.h>
  37 #endif
  38
  39 #ifdef HAVE_DIRECT_H
  40 #include <direct.h>
  41 #endif
  42
  43 #include <string.h>
  44 #include <stdlib.h>
  45 #include <errno.h>
  46
  47 #ifdef HAVE_SYS_STAT_H
  48 #include <sys/stat.h>
  49 #endif
  50
  51 #ifdef HAVE_SYS_TYPES_H
  52 #include <sys/types.h>
  53 #endif
  54
  55 #ifdef HAVE_UNISTD_H
  56 #include <unistd.h>
  57 #endif
  58
  59 #include "filesystem.h"
  60
  61 #include "prefs.h"
  62
  63 #ifdef PLUGINS_NEED_ADDRESS_TABLE
  64 #include "conversation.h"
  65 #include "packet-giop.h"
  66 #include "packet-tpkt.h"
  67 #include "packet-tcp.h"
  68 #include "plugins/plugin_table.h"
  69 static plugin_address_table_t   patable;
  70 #endif
  71
  72 /* linked list of all plugins */
  73 plugin *plugin_list;
  74
  75 #ifndef WIN32
  76 static gchar std_plug_dir[] = "/usr/lib/ethereal/plugins/" VERSION;
  77 static gchar local_plug_dir[] = "/usr/local/lib/ethereal/plugins/" VERSION;
  78 #endif
  79 static gchar *user_plug_dir = NULL;
  80
  81 #define PLUGINS_DIR_NAME        "plugins"
  82
  83 /*
  84  * add a new plugin to the list
  85  * returns :
  86  * - 0 : OK
  87  * - ENOMEM : memory allocation problem
  88  * - EEXIST : the same plugin (i.e. name/version) was already registered.
  89  */
  90 static int
  91 add_plugin(void *handle, gchar *name, gchar *version,
  92            void (*reg_handoff)(void))
  93 {
  94     plugin *new_plug, *pt_plug;
  95
  96     pt_plug = plugin_list;
  97     if (!pt_plug) /* the list is empty */
  98     {
  99         new_plug = (plugin *)g_malloc(sizeof(plugin));
 100         if (new_plug == NULL) return ENOMEM;
 101         plugin_list = new_plug;
 102     }
 103     else
 104     {
 105         while (1)
 106         {
 107             /* check if the same name/version is already registered */
 108             if (!strcmp(pt_plug->name, name) &&
 109                 !strcmp(pt_plug->version, version))
 110             {
 111                 return EEXIST;
 112             }
 113
 114             /* we found the last plugin in the list */
 115             if (pt_plug->next == NULL) break;
 116
 117             pt_plug = pt_plug->next;
 118         }
 119         new_plug = (plugin *)g_malloc(sizeof(plugin));
 120         if (new_plug == NULL) return ENOMEM;
 121         pt_plug->next = new_plug;
 122     }
 123
 124     new_plug->handle = handle;
 125     new_plug->name = name;
 126     new_plug->version = version;
 127     new_plug->reg_handoff = reg_handoff;
 128     new_plug->next = NULL;
 129     return 0;
 130 }
 131
 132 /*
 133  * XXX - when we remove support for old-style plugins (which we should
 134  * probably do eventually, as all plugins should be written as new-style
 135  * ones), we may want to have "init_plugins()" merely save a pointer
 136  * to the plugin's "init" routine, just as we save a pointer to its
 137  * "reg_handoff" routine, and have a "register_all_plugins()" routine
 138  * to go through the list of plugins and call all of them.
 139  *
 140  * Then we'd have "epan_init()", or perhaps even something higher up
 141  * in the call tree, call "init_plugins()", and have "proto_init()"
 142  * call "register_all_plugins()" right after calling "register_all_protocols()";
 143  * this might be a bit cleaner.
 144  */
 145 static void
 146 plugins_scan_dir(const char *dirname)
 147 {
 148 #define FILENAME_LEN    1024
 149     gchar         *hack_path;       /* pathname used to construct lt_lib_ext */
 150     gchar         *lt_lib_ext;      /* extension for loadable modules */
 151     DIR           *dir;             /* scanned directory */
 152     struct dirent *file;            /* current file */
 153     gchar          filename[FILENAME_LEN];   /* current file name */
 154     GModule       *handle;          /* handle returned by dlopen */
 155     gchar         *name;
 156     gchar         *version;
 157     void         (*init)(void *);
 158     void         (*reg_handoff)(void);
 159     gchar         *dot;
 160     int            cr;
 161
 162     /*
 163      * We find the extension used on this platform for loadable modules
 164      * by the sneaky hack of calling "g_module_build_path" to build
 165      * the pathname for a module with an empty directory name and
 166      * empty module name, and then search for the last "." and use
 167      * everything from the last "." on.
 168      *
 169      * GLib 2.0 will probably define G_MODULE_SUFFIX as the extension
 170      * to use, but that's not checked into the GLib CVS tree yet,
 171      * and we can't use it on systems that don't have GLib 2.0.
 172      */
 173     hack_path = g_module_build_path("", "");
 174     lt_lib_ext = strrchr(hack_path, '.');
 175     if (lt_lib_ext == NULL)
 176     {
 177         /*
 178          * Does this mean there *is* no extension?  Assume so.
 179          *
 180          * XXX - the code below assumes that all loadable modules have
 181          * an extension....
 182          */
 183         lt_lib_ext = "";
 184     }
 185
 186     if ((dir = opendir(dirname)) != NULL)
 187     {
 188         while ((file = readdir(dir)) != NULL)
 189         {
 190             /* don't try to open "." and ".." */
 191             if (!(strcmp(file->d_name, "..") &&
 192                   strcmp(file->d_name, "."))) continue;
 193
 194             /* skip anything but files with lt_lib_ext */
 195             dot = strrchr(file->d_name, '.');
 196             if (dot == NULL || strcmp(dot, lt_lib_ext) != 0) continue;
 197
 198             snprintf(filename, FILENAME_LEN, "%s" G_DIR_SEPARATOR_S "%s",
 199                 dirname, file->d_name);
 200             if ((handle = g_module_open(filename, 0)) == NULL) continue;
 201             name = (gchar *)file->d_name;
 202             if (g_module_symbol(handle, "version", (gpointer*)&version) == FALSE)
 203             {
 204                 g_warning("The plugin %s has no version symbol", name);
 205                 g_module_close(handle);
 206                 continue;
 207             }
 208
 209             /*
 210              * Old-style dissectors don't have a "plugin_reg_handoff()"
 211              * routine; we no longer support them.
 212              *
 213              * New-style dissectors have one, because, otherwise, there's
 214              * no way for them to arrange that they ever be called.
 215              */
 216             if (g_module_symbol(handle, "plugin_reg_handoff",
 217                                          (gpointer*)&reg_handoff))
 218             {
 219                 /*
 220                  * We require it to have a "plugin_init()" routine.
 221                  */
 222                 if (!g_module_symbol(handle, "plugin_init", (gpointer*)&init))
 223                 {
 224                     g_warning("The plugin %s has a plugin_reg_handoff symbol but no plugin_init routine", name);
 225                     g_module_close(handle);
 226                     continue;
 227                 }
 228
 229                 /*
 230                  * We have a "plugin_reg_handoff()" routine, so we don't
 231                  * need the protocol, filter string, or dissector pointer.
 232                  */
 233                 if ((cr = add_plugin(handle, g_strdup(file->d_name), version,
 234                                      reg_handoff)))
 235                 {
 236                     if (cr == EEXIST)
 237                         fprintf(stderr, "The plugin %s, version %s\n"
 238                             "was found in multiple directories\n", name, version);
 239                     else
 240                         fprintf(stderr, "Memory allocation problem\n"
 241                             "when processing plugin %s, version %s\n",
 242                             name, version);
 243                     g_module_close(handle);
 244                     continue;
 245                 }
 246
 247                 /*
 248                  * Call its init routine.
 249                  */
 250 #ifdef PLUGINS_NEED_ADDRESS_TABLE
 251                 init(&patable);
 252 #else
 253                 init(NULL);
 254 #endif
 255             }
 256             else
 257             {
 258                 /*
 259                  * This is an old-style dissector; warn that it won't
 260                  * be used, as those aren't supported.
 261                  */
 262                 fprintf(stderr,
 263                     "The plugin %s, version %s is an old-style plugin;\n"
 264                     "Those are no longer supported.\n", name, version);
 265             }
 266         }
 267         closedir(dir);
 268     }
 269     g_free(hack_path);
 270 }
 271
 272 /*
 273  * init plugins
 274  */
 275 void
 276 init_plugins(const char *plugin_dir)
 277 {
 278 #ifdef WIN32
 279     const char *datafile_dir;
 280     char *install_plugin_dir;
 281 #else
 282     struct stat std_dir_stat, local_dir_stat, plugin_dir_stat;
 283 #endif
 284
 285     if (plugin_list == NULL)      /* ensure init_plugins is only run once */
 286     {
 287 #ifdef PLUGINS_NEED_ADDRESS_TABLE
 288         /* Intialize address table */
 289         patable.p_check_col                     = check_col;
 290         patable.p_col_clear                     = col_clear;
 291         patable.p_col_add_fstr                  = col_add_fstr;
 292         patable.p_col_append_fstr               = col_append_fstr;
 293         patable.p_col_prepend_fstr              = col_prepend_fstr;
 294         patable.p_col_add_str                   = col_add_str;
 295         patable.p_col_append_str                = col_append_str;
 296         patable.p_col_set_str                   = col_set_str;
 297
 298         patable.p_register_init_routine         = register_init_routine;
 299         patable.p_register_postseq_cleanup_routine      = register_postseq_cleanup_routine;
 300
 301         patable.p_match_strval                  = match_strval;
 302         patable.p_val_to_str                    = val_to_str;
 303
 304         patable.p_conversation_new              = conversation_new;
 305         patable.p_find_conversation             = find_conversation;
 306         patable.p_conversation_set_dissector    = conversation_set_dissector;
 307
 308         patable.p_proto_register_protocol       = proto_register_protocol;
 309         patable.p_proto_register_field_array    = proto_register_field_array;
 310         patable.p_proto_register_subtree_array  = proto_register_subtree_array;
 311
 312         patable.p_dissector_add                 = dissector_add;
 313         patable.p_dissector_delete              = dissector_delete;
 314         patable.p_dissector_add_handle          = dissector_add_handle;
 315
 316         patable.p_heur_dissector_add            = heur_dissector_add;
 317
 318         patable.p_register_dissector            = register_dissector;
 319         patable.p_find_dissector                = find_dissector;
 320         patable.p_create_dissector_handle       = create_dissector_handle;
 321         patable.p_call_dissector                = call_dissector;
 322
 323         patable.p_tcp_dissect_pdus              = tcp_dissect_pdus;
 324
 325         patable.p_proto_is_protocol_enabled     = proto_is_protocol_enabled;
 326
 327         patable.p_proto_item_get_len            = proto_item_get_len;
 328         patable.p_proto_item_set_len            = proto_item_set_len;
 329         patable.p_proto_item_set_text           = proto_item_set_text;
 330         patable.p_proto_item_append_text        = proto_item_append_text;
 331         patable.p_proto_item_add_subtree        = proto_item_add_subtree;
 332         patable.p_proto_tree_add_item           = proto_tree_add_item;
 333         patable.p_proto_tree_add_item_hidden    = proto_tree_add_item_hidden;
 334         patable.p_proto_tree_add_protocol_format = proto_tree_add_protocol_format;
 335         patable.p_proto_tree_add_bytes          = proto_tree_add_bytes;
 336         patable.p_proto_tree_add_bytes_hidden   = proto_tree_add_bytes_hidden;
 337         patable.p_proto_tree_add_bytes_format   = proto_tree_add_bytes_format;
 338         patable.p_proto_tree_add_time           = proto_tree_add_time;
 339         patable.p_proto_tree_add_time_hidden    = proto_tree_add_time_hidden;
 340         patable.p_proto_tree_add_time_format    = proto_tree_add_time_format;
 341         patable.p_proto_tree_add_ipxnet         = proto_tree_add_ipxnet;
 342         patable.p_proto_tree_add_ipxnet_hidden  = proto_tree_add_ipxnet_hidden;
 343         patable.p_proto_tree_add_ipxnet_format  = proto_tree_add_ipxnet_format;
 344         patable.p_proto_tree_add_ipv4           = proto_tree_add_ipv4;
 345         patable.p_proto_tree_add_ipv4_hidden    = proto_tree_add_ipv4_hidden;
 346         patable.p_proto_tree_add_ipv4_format    = proto_tree_add_ipv4_format;
 347         patable.p_proto_tree_add_ipv6           = proto_tree_add_ipv6;
 348         patable.p_proto_tree_add_ipv6_hidden    = proto_tree_add_ipv6_hidden;
 349         patable.p_proto_tree_add_ipv6_format    = proto_tree_add_ipv6_format;
 350         patable.p_proto_tree_add_ether          = proto_tree_add_ether;
 351         patable.p_proto_tree_add_ether_hidden   = proto_tree_add_ether_hidden;
 352         patable.p_proto_tree_add_ether_format   = proto_tree_add_ether_format;
 353         patable.p_proto_tree_add_string         = proto_tree_add_string;
 354         patable.p_proto_tree_add_string_hidden  = proto_tree_add_string_hidden;
 355         patable.p_proto_tree_add_string_format  = proto_tree_add_string_format;
 356         patable.p_proto_tree_add_boolean        = proto_tree_add_boolean;
 357         patable.p_proto_tree_add_boolean_hidden = proto_tree_add_boolean_hidden;
 358         patable.p_proto_tree_add_boolean_format = proto_tree_add_boolean_format;
 359         patable.p_proto_tree_add_double         = proto_tree_add_double;
 360         patable.p_proto_tree_add_double_hidden  = proto_tree_add_double_hidden;
 361         patable.p_proto_tree_add_double_format  = proto_tree_add_double_format;
 362         patable.p_proto_tree_add_uint           = proto_tree_add_uint;
 363         patable.p_proto_tree_add_uint_hidden    = proto_tree_add_uint_hidden;
 364         patable.p_proto_tree_add_uint_format    = proto_tree_add_uint_format;
 365         patable.p_proto_tree_add_int            = proto_tree_add_int;
 366         patable.p_proto_tree_add_int_hidden     = proto_tree_add_int_hidden;
 367         patable.p_proto_tree_add_int_format     = proto_tree_add_int_format;
 368         patable.p_proto_tree_add_text           = proto_tree_add_text;
 369
 370         patable.p_tvb_new_subset                = tvb_new_subset;
 371         patable.p_tvb_set_free_cb               = tvb_set_free_cb;
 372         patable.p_tvb_set_child_real_data_tvbuff = tvb_set_child_real_data_tvbuff;
 373         patable.p_tvb_new_real_data             = tvb_new_real_data;
 374
 375         patable.p_tvb_length                    = tvb_length;
 376         patable.p_tvb_length_remaining          = tvb_length_remaining;
 377         patable.p_tvb_bytes_exist               = tvb_bytes_exist;
 378         patable.p_tvb_offset_exists             = tvb_offset_exists;
 379         patable.p_tvb_reported_length           = tvb_reported_length;
 380         patable.p_tvb_reported_length_remaining = tvb_reported_length_remaining;
 381
 382         patable.p_tvb_get_guint8                = tvb_get_guint8;
 383
 384         patable.p_tvb_get_ntohs                 = tvb_get_ntohs;
 385         patable.p_tvb_get_ntoh24                = tvb_get_ntoh24;
 386         patable.p_tvb_get_ntohl                 = tvb_get_ntohl;
 387
 388         patable.p_tvb_get_letohs                = tvb_get_letohs;
 389         patable.p_tvb_get_letoh24               = tvb_get_letoh24;
 390         patable.p_tvb_get_letohl                = tvb_get_letohl;
 391
 392         patable.p_tvb_memcpy                    = tvb_memcpy;
 393         patable.p_tvb_memdup                    = tvb_memdup;
 394
 395         patable.p_tvb_get_ptr                   = tvb_get_ptr;
 396
 397         patable.p_tvb_find_guint8               = tvb_find_guint8;
 398         patable.p_tvb_pbrk_guint8               = tvb_pbrk_guint8;
 399
 400         patable.p_tvb_strnlen                   = tvb_strnlen;
 401
 402         patable.p_tvb_format_text               = tvb_format_text;
 403
 404         patable.p_tvb_get_nstringz              = tvb_get_nstringz;
 405         patable.p_tvb_get_nstringz0             = tvb_get_nstringz0;
 406
 407         patable.p_tvb_find_line_end             = tvb_find_line_end;
 408         patable.p_tvb_find_line_end_unquoted    = tvb_find_line_end_unquoted;
 409
 410         patable.p_tvb_strneql                   = tvb_strneql;
 411         patable.p_tvb_strncaseeql               = tvb_strncaseeql;
 412
 413         patable.p_tvb_bytes_to_str              = tvb_bytes_to_str;
 414
 415         patable.p_prefs_register_protocol       = prefs_register_protocol;
 416         patable.p_prefs_register_uint_preference = prefs_register_uint_preference;
 417         patable.p_prefs_register_bool_preference = prefs_register_bool_preference;
 418         patable.p_prefs_register_enum_preference = prefs_register_enum_preference;
 419         patable.p_prefs_register_string_preference = prefs_register_string_preference;
 420
 421         patable.p_register_giop_user            = register_giop_user;
 422         patable.p_is_big_endian                 = is_big_endian;
 423         patable.p_get_CDR_encap_info            = get_CDR_encap_info;
 424
 425         patable.p_get_CDR_any                   = get_CDR_any;
 426         patable.p_get_CDR_boolean               = get_CDR_boolean;
 427         patable.p_get_CDR_char                  = get_CDR_char;
 428         patable.p_get_CDR_double                = get_CDR_double;
 429         patable.p_get_CDR_enum                  = get_CDR_enum;
 430         patable.p_get_CDR_fixed                 = get_CDR_fixed;
 431         patable.p_get_CDR_float                 = get_CDR_float;
 432         patable.p_get_CDR_interface             = get_CDR_interface;
 433         patable.p_get_CDR_long                  = get_CDR_long;
 434         patable.p_get_CDR_object                = get_CDR_object;
 435         patable.p_get_CDR_octet                 = get_CDR_octet;
 436         patable.p_get_CDR_octet_seq             = get_CDR_octet_seq;
 437         patable.p_get_CDR_short                 = get_CDR_short;
 438         patable.p_get_CDR_string                = get_CDR_string;
 439         patable.p_get_CDR_typeCode              = get_CDR_typeCode;
 440         patable.p_get_CDR_ulong                 = get_CDR_ulong;
 441         patable.p_get_CDR_ushort                = get_CDR_ushort;
 442         patable.p_get_CDR_wchar                 = get_CDR_wchar;
 443         patable.p_get_CDR_wstring               = get_CDR_wstring;
 444
 445         patable.p_is_tpkt                       = is_tpkt;
 446         patable.p_dissect_tpkt_encap            = dissect_tpkt_encap;
 447
 448         patable.p_set_actual_length             = set_actual_length;
 449         patable.p_decode_boolean_bitfield       = decode_boolean_bitfield;
 450         patable.p_decode_numeric_bitfield       = decode_numeric_bitfield;
 451         patable.p_decode_enumerated_bitfield    = decode_enumerated_bitfield;
 452 #endif
 453
 454 #ifdef WIN32
 455         /*
 456          * On Windows, the data file directory is the installation
 457          * directory; the plugins are stored under it.
 458          *
 459          * Assume we're running the installed version of Ethereal;
 460          * on Windows, the data file directory is the directory
 461          * in which the Ethereal binary resides.
 462          */
 463         datafile_dir = get_datafile_dir();
 464         install_plugin_dir = g_malloc(strlen(datafile_dir) + strlen("plugins") +
 465             strlen(VERSION) + 3);
 466         sprintf(install_plugin_dir, "%s\\plugins\\%s", datafile_dir, VERSION);
 467
 468         /*
 469          * Make sure that pathname refers to a directory.
 470          */
 471         if (test_for_directory(install_plugin_dir) != EISDIR) {
 472                 /*
 473                  * Either it doesn't refer to a directory or it
 474                  * refers to something that doesn't exist.
 475                  *
 476                  * Assume that means we're running, for example,
 477                  * a version of Ethereal we've built in a source
 478                  * directory, and fall back on the default
 479                  * installation directory, so you can put the plugins
 480                  * somewhere so they can be used with this version
 481                  * of Ethereal.
 482                  *
 483                  * XXX - should we, instead, have the Windows build
 484                  * procedure create a subdirectory of the "plugins"
 485                  * source directory, and copy the plugin DLLs there,
 486                  * so that you use the plugins from the build tree?
 487                  */
 488                 install_plugin_dir =
 489                     g_strdup("C:\\Program Files\\Ethereal\\plugins\\" VERSION);
 490         }
 491
 492         /*
 493          * Scan that directory.
 494          */
 495         plugins_scan_dir(install_plugin_dir);
 496         g_free(install_plugin_dir);
 497 #else
 498         /*
 499          * XXX - why not just scan "plugin_dir"?  That's where we
 500          * installed the plugins; if Ethereal isn't installed under
 501          * "/usr" or "/usr/local", why should we search for its plugins
 502          * there?
 503          */
 504         plugins_scan_dir(std_plug_dir);
 505         plugins_scan_dir(local_plug_dir);
 506         if ((strcmp(std_plug_dir, plugin_dir) != 0) &&
 507                 (strcmp(local_plug_dir, plugin_dir) != 0))
 508         {
 509             if (stat(plugin_dir, &plugin_dir_stat) == 0)
 510             {
 511                 /* check if plugin_dir is really different from std_dir and
 512                  * local_dir if they exist ! */
 513                 if (stat(std_plug_dir, &std_dir_stat) == 0)
 514                 {
 515                     if (stat(local_plug_dir, &local_dir_stat) == 0)
 516                     {
 517                         if ((plugin_dir_stat.st_dev != std_dir_stat.st_dev ||
 518                                     plugin_dir_stat.st_ino != std_dir_stat.st_ino) &&
 519                                 (plugin_dir_stat.st_dev != local_dir_stat.st_dev ||
 520                                  plugin_dir_stat.st_ino != local_dir_stat.st_ino))
 521                             plugins_scan_dir(plugin_dir);
 522                     }
 523                     else
 524                     {
 525                         if ((plugin_dir_stat.st_dev != std_dir_stat.st_dev ||
 526                                     plugin_dir_stat.st_ino != std_dir_stat.st_ino))
 527                             plugins_scan_dir(plugin_dir);
 528                     }
 529                 }
 530                 else if (stat(local_plug_dir, &local_dir_stat) == 0)
 531                 {
 532                     if ((plugin_dir_stat.st_dev != local_dir_stat.st_dev ||
 533                                 plugin_dir_stat.st_ino != local_dir_stat.st_ino))
 534                         plugins_scan_dir(plugin_dir);
 535                 }
 536                 else plugins_scan_dir(plugin_dir);
 537             }
 538         }
 539 #endif
 540         if (!user_plug_dir)
 541             user_plug_dir = get_persconffile_path(PLUGINS_DIR_NAME, FALSE);
 542         plugins_scan_dir(user_plug_dir);
 543     }
 544 }
 545
 546 void
 547 register_all_plugin_handoffs(void)
 548 {
 549   plugin *pt_plug;
 550
 551   /*
 552    * For all new-style plugins, call the register-handoff routine.
 553    * This is called from "proto_init()"; it must be called after
 554    * "register_all_protocols()" and "init_plugins()" are called,
 555    * in case one plugin registers itself either with a built-in
 556    * dissector or with another plugin; we must first register all
 557    * dissectors, whether built-in or plugin, so their dissector tables
 558    * are initialized, and only then register all handoffs.
 559    *
 560    * We treat those protocols as always being enabled; they should
 561    * use the standard mechanism for enabling/disabling protocols, not
 562    * the plugin-specific mechanism.
 563    */
 564   for (pt_plug = plugin_list; pt_plug != NULL; pt_plug = pt_plug->next)
 565     (pt_plug->reg_handoff)();
 566 }
 567 #endif