sys/vfs/hammer/hammer_cursor.c

   1 /*
   2  * Copyright (c) 2007 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@backplane.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  * $DragonFly: src/sys/vfs/hammer/hammer_cursor.c,v 1.15 2008/01/24 02:14:45 dillon Exp $
  35  */
  36
  37 /*
  38  * HAMMER B-Tree index - cursor support routines
  39  */
  40 #include "hammer.h"
  41
  42 static int hammer_load_cursor_parent(hammer_cursor_t cursor);
  43 static int hammer_load_cursor_parent_local(hammer_cursor_t cursor);
  44 static int hammer_load_cursor_parent_cluster(hammer_cursor_t cursor);
  45
  46 /*
  47  * Initialize a fresh cursor using the B-Tree node cache.  If the cache
  48  * is not available initialize a fresh cursor at the root of the root
  49  * cluster.
  50  */
  51 int
  52 hammer_init_cursor_hmp(hammer_cursor_t cursor, struct hammer_node **cache,
  53                        hammer_mount_t hmp)
  54 {
  55         hammer_cluster_t cluster;
  56         hammer_node_t node;
  57         int error;
  58
  59         bzero(cursor, sizeof(*cursor));
  60
  61         /*
  62          * Step 1 - acquire a locked node from the cache if possible
  63          */
  64         if (cache && *cache) {
  65                 node = hammer_ref_node_safe(hmp, cache, &error);
  66                 if (error == 0) {
  67                         hammer_lock_sh(&node->lock);
  68                         if (node->flags & HAMMER_NODE_DELETED) {
  69                                 hammer_unlock(&node->lock);
  70                                 hammer_rel_node(node);
  71                                 node = NULL;
  72                         }
  73                 }
  74         } else {
  75                 node = NULL;
  76         }
  77
  78         /*
  79          * Step 2 - If we couldn't get a node from the cache, get
  80          * the one from the root of the root cluster.
  81          */
  82         while (node == NULL) {
  83                 cluster = hammer_get_root_cluster(hmp, &error);
  84                 if (error)
  85                         break;
  86                 node = hammer_get_node(cluster,
  87                                        cluster->ondisk->clu_btree_root,
  88                                        &error);
  89                 hammer_rel_cluster(cluster, 0);
  90                 if (error)
  91                         break;
  92                 hammer_lock_sh(&node->lock);
  93                 if (node->flags & HAMMER_NODE_DELETED) {
  94                         hammer_unlock(&node->lock);
  95                         hammer_rel_node(node);
  96                         node = NULL;
  97                 }
  98         }
  99
 100         /*
 101          * Step 3 - finish initializing the cursor by acquiring the parent
 102          */
 103         cursor->node = node;
 104         if (error == 0)
 105                 error = hammer_load_cursor_parent(cursor);
 106         KKASSERT(error == 0);
 107         return(error);
 108 }
 109
 110 /*
 111  * Initialize a fresh cursor at the root of the specified cluster and
 112  * limit operations to within the cluster.
 113  *
 114  * NOTE: cursor->parent will be set to NULL to avoid referencing B-Tree
 115  * nodes in other clusters.
 116  */
 117 int
 118 hammer_init_cursor_cluster(hammer_cursor_t cursor, hammer_cluster_t cluster)
 119 {
 120         int error;
 121
 122         bzero(cursor, sizeof(*cursor));
 123         cursor->flags |= HAMMER_CURSOR_INCLUSTER;
 124         cursor->node = hammer_get_node(cluster,
 125                                        cluster->ondisk->clu_btree_root,
 126                                        &error);
 127         if (error == 0)
 128                 hammer_lock_sh(&cursor->node->lock);
 129         cursor->left_bound = &cluster->ondisk->clu_btree_beg;
 130         cursor->right_bound = &cluster->ondisk->clu_btree_end;
 131         KKASSERT(error == 0);
 132         return(error);
 133 }
 134
 135 /*
 136  * We are finished with a cursor.  We NULL out various fields as sanity
 137  * check, in case the structure is inappropriately used afterwords.
 138  */
 139 void
 140 hammer_done_cursor(hammer_cursor_t cursor)
 141 {
 142         if (cursor->parent) {
 143                 hammer_unlock(&cursor->parent->lock);
 144                 hammer_rel_node(cursor->parent);
 145                 cursor->parent = NULL;
 146         }
 147         if (cursor->node) {
 148                 hammer_unlock(&cursor->node->lock);
 149                 hammer_rel_node(cursor->node);
 150                 cursor->node = NULL;
 151         }
 152         if (cursor->data_buffer) {
 153                 hammer_rel_buffer(cursor->data_buffer, 0);
 154                 cursor->data_buffer = NULL;
 155         }
 156         if (cursor->record_buffer) {
 157                 hammer_rel_buffer(cursor->record_buffer, 0);
 158                 cursor->record_buffer = NULL;
 159         }
 160         if (cursor->ip)
 161                 hammer_mem_done(cursor);
 162
 163         /*
 164          * If we deadlocked this node will be referenced.  Do a quick
 165          * lock/unlock to wait for the deadlock condition to clear.
 166          */
 167         if (cursor->deadlk_node) {
 168                 hammer_lock_ex(&cursor->deadlk_node->lock);
 169                 hammer_unlock(&cursor->deadlk_node->lock);
 170                 hammer_rel_node(cursor->deadlk_node);
 171                 cursor->deadlk_node = NULL;
 172         }
 173
 174         cursor->data = NULL;
 175         cursor->record = NULL;
 176         cursor->left_bound = NULL;
 177         cursor->right_bound = NULL;
 178 }
 179
 180 /*
 181  * Upgrade cursor->node and cursor->parent to exclusive locks.  This
 182  * function can return EDEADLK.
 183  *
 184  * If we fail to upgrade the lock and cursor->deadlk_node is NULL,
 185  * we add another reference to the node that failed and set
 186  * cursor->deadlk_node so hammer_done_cursor() can block on it.
 187  */
 188 int
 189 hammer_cursor_upgrade(hammer_cursor_t cursor)
 190 {
 191         int error;
 192
 193         if (hammer_lock_held(&cursor->node->lock) < 0) {
 194                 error = hammer_lock_upgrade(&cursor->node->lock);
 195                 if (error && cursor->deadlk_node == NULL) {
 196                         cursor->deadlk_node = cursor->node;
 197                         hammer_ref_node(cursor->deadlk_node);
 198                 }
 199         } else {
 200                 error = 0;
 201         }
 202         if (cursor->parent && hammer_lock_held(&cursor->parent->lock) < 0) {
 203                 error = hammer_lock_upgrade(&cursor->parent->lock);
 204                 if (error && cursor->deadlk_node == NULL) {
 205                         cursor->deadlk_node = cursor->parent;
 206                         hammer_ref_node(cursor->deadlk_node);
 207                 }
 208         } else {
 209                 error = 0;
 210         }
 211         return(error);
 212 }
 213
 214 /*
 215  * Downgrade cursor->node and cursor->parent to shared locks.  This
 216  * function can return EDEADLK.
 217  */
 218 void
 219 hammer_cursor_downgrade(hammer_cursor_t cursor)
 220 {
 221         if (hammer_lock_held(&cursor->node->lock) > 0)
 222                 hammer_lock_downgrade(&cursor->node->lock);
 223         if (cursor->parent && hammer_lock_held(&cursor->parent->lock) > 0)
 224                 hammer_lock_downgrade(&cursor->parent->lock);
 225 }
 226
 227
 228 #if 0
 229
 230 /*
 231  * Acquire the parent B-Tree node of the specified node, returning a
 232  * referenced but unlocked node.  NULL can be returned with *errorp == 0
 233  * if node is the root node of the root cluster.
 234  */
 235 static
 236 hammer_node_t
 237 hammer_get_parent_node(hammer_node_t node, int *errorp)
 238 {
 239         hammer_cluster_t cluster;
 240         hammer_node_t parent;
 241
 242         cluster = node->cluster;
 243         if (node->ondisk->parent) {
 244                 /*
 245                  * Local parent
 246                  */
 247                 parent = hammer_get_node(cluster, node->ondisk->parent, errorp);
 248         } else if (cluster->ondisk->clu_btree_parent_vol_no >= 0) {
 249                 /*
 250                  * At cluster root, locate node in parent cluster
 251                  */
 252                 hammer_cluster_ondisk_t ondisk;
 253                 hammer_cluster_t pcluster;
 254                 hammer_volume_t pvolume;
 255                 int32_t clu_no;
 256                 int32_t vol_no;
 257
 258                 ondisk = cluster->ondisk;
 259                 vol_no = ondisk->clu_btree_parent_vol_no;
 260                 clu_no = ondisk->clu_btree_parent_clu_no;
 261
 262                 /*
 263                  * Acquire the node from (volume, cluster, offset)
 264                  */
 265                 pvolume = hammer_get_volume(cluster->volume->hmp, vol_no,
 266                                             errorp);
 267                 if (*errorp)
 268                         return (NULL);
 269                 pcluster = hammer_get_cluster(pvolume, clu_no, errorp, 0);
 270                 hammer_rel_volume(pvolume, 0);
 271                 if (*errorp)
 272                         return (NULL);
 273                 parent = hammer_get_node(pcluster,
 274                                          ondisk->clu_btree_parent_offset,
 275                                          errorp);
 276                 hammer_rel_cluster(pcluster, 0);
 277         } else {
 278                 /*
 279                  * At root of root cluster, there is no parent.
 280                  */
 281                 KKASSERT(cluster->ondisk->clu_btree_parent_vol_no == -1);
 282                 parent = NULL;
 283                 *errorp = 0;
 284         }
 285         return(parent);
 286 }
 287
 288 #endif
 289
 290 /*
 291  * Load the parent of cursor->node into cursor->parent.  There are several
 292  * cases.  (1) The parent is in the current cluster.  (2) We are at the
 293  * root of the cluster and the parent is in another cluster.  (3) We are at
 294  * the root of the root cluster.
 295  *
 296  * If HAMMER_CURSOR_INCLUSTER is set and we are at the root of the cluster,
 297  * we do not access the parent cluster at all and make the cursor look like
 298  * its at the root.
 299  */
 300 static
 301 int
 302 hammer_load_cursor_parent(hammer_cursor_t cursor)
 303 {
 304         hammer_cluster_t cluster;
 305         int error;
 306
 307         cluster = cursor->node->cluster;
 308
 309         if (cursor->node->ondisk->parent) {
 310                 error = hammer_load_cursor_parent_local(cursor);
 311         } else if (cluster->ondisk->clu_btree_parent_vol_no >= 0 &&
 312                    ((cursor->flags & HAMMER_CURSOR_INCLUSTER) == 0)
 313         ) {
 314                 error = hammer_load_cursor_parent_cluster(cursor);
 315         } else {
 316                 cursor->parent = NULL;
 317                 cursor->parent_index = 0;
 318                 cursor->left_bound = &cluster->ondisk->clu_btree_beg;
 319                 cursor->right_bound = &cluster->ondisk->clu_btree_end;
 320                 error = 0;
 321         }
 322         return(error);
 323 }
 324
 325 static
 326 int
 327 hammer_load_cursor_parent_local(hammer_cursor_t cursor)
 328 {
 329         hammer_node_t node;
 330         hammer_node_t parent;
 331         hammer_btree_elm_t elm;
 332         int error;
 333         int i;
 334
 335         node = cursor->node;
 336         parent = hammer_get_node(node->cluster, node->ondisk->parent, &error);
 337         if (error)
 338                 return(error);
 339         elm = NULL;
 340         for (i = 0; i < parent->ondisk->count; ++i) {
 341                 elm = &parent->ondisk->elms[i];
 342                 if (parent->ondisk->elms[i].internal.subtree_offset ==
 343                     node->node_offset) {
 344                         break;
 345                 }
 346         }
 347         if (i == parent->ondisk->count)
 348                 panic("Bad B-Tree link: parent %p node %p\n", parent, node);
 349         KKASSERT(i != parent->ondisk->count);
 350         cursor->parent = parent;
 351         cursor->parent_index = i;
 352         cursor->left_bound = &elm[0].internal.base;
 353         cursor->right_bound = &elm[1].internal.base;
 354
 355         hammer_lock_sh(&parent->lock);
 356         return(error);
 357 }
 358
 359 static
 360 int
 361 hammer_load_cursor_parent_cluster(hammer_cursor_t cursor)
 362 {
 363         hammer_cluster_ondisk_t ondisk;
 364         hammer_cluster_t pcluster;
 365         hammer_cluster_t ccluster;
 366         hammer_volume_t volume;
 367         hammer_node_t node;
 368         hammer_node_t parent;
 369         hammer_btree_elm_t elm;
 370         int32_t clu_no;
 371         int32_t vol_no;
 372         int error;
 373         int i;
 374
 375         node = cursor->node;
 376         ccluster = node->cluster;
 377         ondisk = ccluster->ondisk;
 378         vol_no = ondisk->clu_btree_parent_vol_no;
 379         clu_no = ondisk->clu_btree_parent_clu_no;
 380
 381         /*
 382          * Acquire the node from (volume, cluster, offset).  This should
 383          * be a leaf node containing the HAMMER_BTREE_TYPE_SPIKE_END element.
 384          */
 385         volume = hammer_get_volume(ccluster->volume->hmp, vol_no, &error);
 386         if (error)
 387                 return (error);
 388         pcluster = hammer_get_cluster(volume, clu_no, &error, 0);
 389         hammer_rel_volume(volume, 0);
 390         if (error)
 391                 return (error);
 392         parent = hammer_get_node(pcluster, ondisk->clu_btree_parent_offset,
 393                                  &error);
 394         hammer_rel_cluster(pcluster, 0);
 395         if (error)
 396                 return (error);
 397         KKASSERT(parent->ondisk->type == HAMMER_BTREE_TYPE_LEAF);
 398
 399         /*
 400          * Ok, we have the node.  Locate the inter-cluster element
 401          */
 402         elm = NULL;
 403         for (i = 0; i < parent->ondisk->count; ++i) {
 404                 elm = &parent->ondisk->elms[i];
 405
 406                 if (elm->leaf.base.btype == HAMMER_BTREE_TYPE_SPIKE_END &&
 407                     elm->leaf.spike_clu_no == cursor->node->cluster->clu_no) {
 408                         break;
 409                 }
 410         }
 411         KKASSERT(i != parent->ondisk->count);
 412         KKASSERT(i && elm[-1].leaf.base.btype == HAMMER_BTREE_TYPE_SPIKE_BEG);
 413         cursor->parent = parent;
 414         cursor->parent_index = i;
 415         cursor->left_bound = &ccluster->ondisk->clu_btree_beg;
 416         cursor->right_bound = &ccluster->ondisk->clu_btree_end;
 417
 418         KKASSERT(hammer_btree_cmp(&elm[-1].leaf.base,
 419                  &ccluster->ondisk->clu_btree_beg) == 0);
 420             /*
 421              * spike_end is an inclusive boundary and will != clu_btree_end
 422         KKASSERT(hammer_btree_cmp(cursor->right_bound,
 423                  &ccluster->ondisk->clu_btree_end) >= 0);
 424             */
 425
 426         hammer_lock_sh(&parent->lock);
 427         return(0);
 428 }
 429
 430 /*
 431  * Cursor up to our parent node.  Return ENOENT if we are at the root of
 432  * the root cluster.
 433  *
 434  * If doing a nonblocking cursor-up and we are unable to acquire the lock,
 435  * the cursor remains unchanged.
 436  */
 437 int
 438 hammer_cursor_up(hammer_cursor_t cursor)
 439 {
 440         int error;
 441
 442         hammer_cursor_downgrade(cursor);
 443
 444         /*
 445          * Set the node to its parent.  If the parent is NULL we are at
 446          * the root of the root cluster and return ENOENT.
 447          */
 448         hammer_unlock(&cursor->node->lock);
 449         hammer_rel_node(cursor->node);
 450         cursor->node = cursor->parent;
 451         cursor->index = cursor->parent_index;
 452         cursor->parent = NULL;
 453         cursor->parent_index = 0;
 454
 455         if (cursor->node == NULL) {
 456                 error = ENOENT;
 457         } else if ((cursor->flags & HAMMER_CURSOR_INCLUSTER) &&
 458                    cursor->node->ondisk->parent == 0
 459         ) {
 460                 error = ENOENT;
 461         } else {
 462                 error = hammer_load_cursor_parent(cursor);
 463         }
 464         return(error);
 465 }
 466
 467 /*
 468  * Set the cursor to the root of the current cursor's cluster.
 469  */
 470 int
 471 hammer_cursor_toroot(hammer_cursor_t cursor)
 472 {
 473         hammer_cluster_t cluster;
 474         int error;
 475
 476         /*
 477          * Already at root of cluster?
 478          */
 479         if (cursor->node->ondisk->parent == 0)
 480                 return (0);
 481
 482         hammer_cursor_downgrade(cursor);
 483
 484         /*
 485          * Parent is root of cluster?
 486          */
 487         if (cursor->parent->ondisk->parent == 0)
 488                 return (hammer_cursor_up(cursor));
 489
 490         /*
 491          * Ok, reload the cursor with the root of the cluster, then
 492          * locate its parent.
 493          */
 494         cluster = cursor->node->cluster;
 495         error = hammer_ref_cluster(cluster);
 496         if (error)
 497                 return (error);
 498
 499         hammer_unlock(&cursor->parent->lock);
 500         hammer_rel_node(cursor->parent);
 501         hammer_unlock(&cursor->node->lock);
 502         hammer_rel_node(cursor->node);
 503         cursor->parent = NULL;
 504         cursor->parent_index = 0;
 505
 506         cursor->node = hammer_get_node(cluster, cluster->ondisk->clu_btree_root,
 507                                        &error);
 508         cursor->index = 0;
 509         hammer_lock_sh(&cursor->node->lock);
 510         hammer_rel_cluster(cluster, 0);
 511         if (error == 0)
 512                 error = hammer_load_cursor_parent(cursor);
 513         return(error);
 514 }
 515
 516 /*
 517  * Cursor down through the current node, which must be an internal node.
 518  *
 519  * This routine adjusts the cursor and sets index to 0.
 520  */
 521 int
 522 hammer_cursor_down(hammer_cursor_t cursor)
 523 {
 524         hammer_node_t node;
 525         hammer_btree_elm_t elm;
 526         hammer_volume_t volume;
 527         hammer_cluster_t cluster;
 528         int32_t vol_no;
 529         int32_t clu_no;
 530         int error;
 531
 532         /*
 533          * The current node becomes the current parent
 534          */
 535         hammer_cursor_downgrade(cursor);
 536         node = cursor->node;
 537         KKASSERT(cursor->index >= 0 && cursor->index < node->ondisk->count);
 538         if (cursor->parent) {
 539                 hammer_unlock(&cursor->parent->lock);
 540                 hammer_rel_node(cursor->parent);
 541         }
 542         cursor->parent = node;
 543         cursor->parent_index = cursor->index;
 544         cursor->node = NULL;
 545         cursor->index = 0;
 546
 547         /*
 548          * Extract element to push into at (node,index), set bounds.
 549          */
 550         elm = &node->ondisk->elms[cursor->parent_index];
 551
 552         /*
 553          * Ok, push down into elm.  If elm specifies an internal or leaf
 554          * node the current node must be an internal node.  If elm specifies
 555          * a spike then the current node must be a leaf node.
 556          *
 557          * Cursoring down through a cluster transition when the INCLUSTER
 558          * flag is set is not legal.
 559          */
 560         switch(elm->base.btype) {
 561         case HAMMER_BTREE_TYPE_INTERNAL:
 562         case HAMMER_BTREE_TYPE_LEAF:
 563                 KKASSERT(node->ondisk->type == HAMMER_BTREE_TYPE_INTERNAL);
 564                 KKASSERT(elm->internal.subtree_offset != 0);
 565                 cursor->left_bound = &elm[0].internal.base;
 566                 cursor->right_bound = &elm[1].internal.base;
 567                 node = hammer_get_node(node->cluster,
 568                                        elm->internal.subtree_offset,
 569                                        &error);
 570                 if (error == 0) {
 571                         KKASSERT(elm->base.btype == node->ondisk->type);
 572                         if (node->ondisk->parent != cursor->parent->node_offset)
 573                                 panic("node %p %d vs %d\n", node, node->ondisk->parent, cursor->parent->node_offset);
 574                         KKASSERT(node->ondisk->parent == cursor->parent->node_offset);
 575                 }
 576                 break;
 577         case HAMMER_BTREE_TYPE_SPIKE_BEG:
 578                 /* case not supported yet */
 579                 KKASSERT(0);
 580                 KKASSERT(node->ondisk->type == HAMMER_BTREE_TYPE_LEAF);
 581                 KKASSERT(cursor->parent_index < node->ondisk->count - 1);
 582                 KKASSERT(elm[1].leaf.base.btype == HAMMER_BTREE_TYPE_SPIKE_END);
 583                 ++elm;
 584                 ++cursor->parent_index;
 585                 /* fall through */
 586         case HAMMER_BTREE_TYPE_SPIKE_END:
 587                 KKASSERT(node->ondisk->type == HAMMER_BTREE_TYPE_LEAF);
 588                 KKASSERT((cursor->flags & HAMMER_CURSOR_INCLUSTER) == 0);
 589                 vol_no = elm->leaf.spike_vol_no;
 590                 clu_no = elm->leaf.spike_clu_no;
 591                 volume = hammer_get_volume(node->cluster->volume->hmp,
 592                                            vol_no, &error);
 593                 KKASSERT(error != EINVAL);
 594                 if (error)
 595                         return(error);
 596                 cluster = hammer_get_cluster(volume, clu_no, &error, 0);
 597                 KKASSERT(error != EINVAL);
 598                 hammer_rel_volume(volume, 0);
 599                 if (error)
 600                         return(error);
 601                 KKASSERT(cluster->ondisk->clu_btree_parent_offset ==
 602                          cursor->parent->node_offset);
 603                 KKASSERT(cluster->ondisk->clu_btree_parent_clu_no ==
 604                          cursor->parent->cluster->clu_no);
 605
 606                 cursor->left_bound = &cluster->ondisk->clu_btree_beg;
 607                 cursor->right_bound = &cluster->ondisk->clu_btree_end;
 608                 node = hammer_get_node(cluster,
 609                                        cluster->ondisk->clu_btree_root,
 610                                        &error);
 611                 hammer_rel_cluster(cluster, 0);
 612                 break;
 613         default:
 614                 panic("hammer_cursor_down: illegal btype %02x (%c)\n",
 615                       elm->base.btype,
 616                       (elm->base.btype ? elm->base.btype : '?'));
 617                 break;
 618         }
 619         if (error == 0) {
 620                 hammer_lock_sh(&node->lock);
 621                 cursor->node = node;
 622                 cursor->index = 0;
 623         }
 624         return(error);
 625 }
 626