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TOMOYO Linux Cross Reference
Linux/lib/assoc_array.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /* Generic associative array implementation.
  3  *
  4  * See Documentation/core-api/assoc_array.rst for information.
  5  *
  6  * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
  7  * Written by David Howells (dhowells@redhat.com)
  8  */
  9 //#define DEBUG
 10 #include <linux/rcupdate.h>
 11 #include <linux/slab.h>
 12 #include <linux/err.h>
 13 #include <linux/assoc_array_priv.h>
 14 
 15 /*
 16  * Iterate over an associative array.  The caller must hold the RCU read lock
 17  * or better.
 18  */
 19 static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root,
 20                                        const struct assoc_array_ptr *stop,
 21                                        int (*iterator)(const void *leaf,
 22                                                        void *iterator_data),
 23                                        void *iterator_data)
 24 {
 25         const struct assoc_array_shortcut *shortcut;
 26         const struct assoc_array_node *node;
 27         const struct assoc_array_ptr *cursor, *ptr, *parent;
 28         unsigned long has_meta;
 29         int slot, ret;
 30 
 31         cursor = root;
 32 
 33 begin_node:
 34         if (assoc_array_ptr_is_shortcut(cursor)) {
 35                 /* Descend through a shortcut */
 36                 shortcut = assoc_array_ptr_to_shortcut(cursor);
 37                 cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */
 38         }
 39 
 40         node = assoc_array_ptr_to_node(cursor);
 41         slot = 0;
 42 
 43         /* We perform two passes of each node.
 44          *
 45          * The first pass does all the leaves in this node.  This means we
 46          * don't miss any leaves if the node is split up by insertion whilst
 47          * we're iterating over the branches rooted here (we may, however, see
 48          * some leaves twice).
 49          */
 50         has_meta = 0;
 51         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
 52                 ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
 53                 has_meta |= (unsigned long)ptr;
 54                 if (ptr && assoc_array_ptr_is_leaf(ptr)) {
 55                         /* We need a barrier between the read of the pointer,
 56                          * which is supplied by the above READ_ONCE().
 57                          */
 58                         /* Invoke the callback */
 59                         ret = iterator(assoc_array_ptr_to_leaf(ptr),
 60                                        iterator_data);
 61                         if (ret)
 62                                 return ret;
 63                 }
 64         }
 65 
 66         /* The second pass attends to all the metadata pointers.  If we follow
 67          * one of these we may find that we don't come back here, but rather go
 68          * back to a replacement node with the leaves in a different layout.
 69          *
 70          * We are guaranteed to make progress, however, as the slot number for
 71          * a particular portion of the key space cannot change - and we
 72          * continue at the back pointer + 1.
 73          */
 74         if (!(has_meta & ASSOC_ARRAY_PTR_META_TYPE))
 75                 goto finished_node;
 76         slot = 0;
 77 
 78 continue_node:
 79         node = assoc_array_ptr_to_node(cursor);
 80         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
 81                 ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
 82                 if (assoc_array_ptr_is_meta(ptr)) {
 83                         cursor = ptr;
 84                         goto begin_node;
 85                 }
 86         }
 87 
 88 finished_node:
 89         /* Move up to the parent (may need to skip back over a shortcut) */
 90         parent = READ_ONCE(node->back_pointer); /* Address dependency. */
 91         slot = node->parent_slot;
 92         if (parent == stop)
 93                 return 0;
 94 
 95         if (assoc_array_ptr_is_shortcut(parent)) {
 96                 shortcut = assoc_array_ptr_to_shortcut(parent);
 97                 cursor = parent;
 98                 parent = READ_ONCE(shortcut->back_pointer); /* Address dependency. */
 99                 slot = shortcut->parent_slot;
100                 if (parent == stop)
101                         return 0;
102         }
103 
104         /* Ascend to next slot in parent node */
105         cursor = parent;
106         slot++;
107         goto continue_node;
108 }
109 
110 /**
111  * assoc_array_iterate - Pass all objects in the array to a callback
112  * @array: The array to iterate over.
113  * @iterator: The callback function.
114  * @iterator_data: Private data for the callback function.
115  *
116  * Iterate over all the objects in an associative array.  Each one will be
117  * presented to the iterator function.
118  *
119  * If the array is being modified concurrently with the iteration then it is
120  * possible that some objects in the array will be passed to the iterator
121  * callback more than once - though every object should be passed at least
122  * once.  If this is undesirable then the caller must lock against modification
123  * for the duration of this function.
124  *
125  * The function will return 0 if no objects were in the array or else it will
126  * return the result of the last iterator function called.  Iteration stops
127  * immediately if any call to the iteration function results in a non-zero
128  * return.
129  *
130  * The caller should hold the RCU read lock or better if concurrent
131  * modification is possible.
132  */
133 int assoc_array_iterate(const struct assoc_array *array,
134                         int (*iterator)(const void *object,
135                                         void *iterator_data),
136                         void *iterator_data)
137 {
138         struct assoc_array_ptr *root = READ_ONCE(array->root); /* Address dependency. */
139 
140         if (!root)
141                 return 0;
142         return assoc_array_subtree_iterate(root, NULL, iterator, iterator_data);
143 }
144 
145 enum assoc_array_walk_status {
146         assoc_array_walk_tree_empty,
147         assoc_array_walk_found_terminal_node,
148         assoc_array_walk_found_wrong_shortcut,
149 };
150 
151 struct assoc_array_walk_result {
152         struct {
153                 struct assoc_array_node *node;  /* Node in which leaf might be found */
154                 int             level;
155                 int             slot;
156         } terminal_node;
157         struct {
158                 struct assoc_array_shortcut *shortcut;
159                 int             level;
160                 int             sc_level;
161                 unsigned long   sc_segments;
162                 unsigned long   dissimilarity;
163         } wrong_shortcut;
164 };
165 
166 /*
167  * Navigate through the internal tree looking for the closest node to the key.
168  */
169 static enum assoc_array_walk_status
170 assoc_array_walk(const struct assoc_array *array,
171                  const struct assoc_array_ops *ops,
172                  const void *index_key,
173                  struct assoc_array_walk_result *result)
174 {
175         struct assoc_array_shortcut *shortcut;
176         struct assoc_array_node *node;
177         struct assoc_array_ptr *cursor, *ptr;
178         unsigned long sc_segments, dissimilarity;
179         unsigned long segments;
180         int level, sc_level, next_sc_level;
181         int slot;
182 
183         pr_devel("-->%s()\n", __func__);
184 
185         cursor = READ_ONCE(array->root);  /* Address dependency. */
186         if (!cursor)
187                 return assoc_array_walk_tree_empty;
188 
189         level = 0;
190 
191         /* Use segments from the key for the new leaf to navigate through the
192          * internal tree, skipping through nodes and shortcuts that are on
193          * route to the destination.  Eventually we'll come to a slot that is
194          * either empty or contains a leaf at which point we've found a node in
195          * which the leaf we're looking for might be found or into which it
196          * should be inserted.
197          */
198 jumped:
199         segments = ops->get_key_chunk(index_key, level);
200         pr_devel("segments[%d]: %lx\n", level, segments);
201 
202         if (assoc_array_ptr_is_shortcut(cursor))
203                 goto follow_shortcut;
204 
205 consider_node:
206         node = assoc_array_ptr_to_node(cursor);
207         slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
208         slot &= ASSOC_ARRAY_FAN_MASK;
209         ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
210 
211         pr_devel("consider slot %x [ix=%d type=%lu]\n",
212                  slot, level, (unsigned long)ptr & 3);
213 
214         if (!assoc_array_ptr_is_meta(ptr)) {
215                 /* The node doesn't have a node/shortcut pointer in the slot
216                  * corresponding to the index key that we have to follow.
217                  */
218                 result->terminal_node.node = node;
219                 result->terminal_node.level = level;
220                 result->terminal_node.slot = slot;
221                 pr_devel("<--%s() = terminal_node\n", __func__);
222                 return assoc_array_walk_found_terminal_node;
223         }
224 
225         if (assoc_array_ptr_is_node(ptr)) {
226                 /* There is a pointer to a node in the slot corresponding to
227                  * this index key segment, so we need to follow it.
228                  */
229                 cursor = ptr;
230                 level += ASSOC_ARRAY_LEVEL_STEP;
231                 if ((level & ASSOC_ARRAY_KEY_CHUNK_MASK) != 0)
232                         goto consider_node;
233                 goto jumped;
234         }
235 
236         /* There is a shortcut in the slot corresponding to the index key
237          * segment.  We follow the shortcut if its partial index key matches
238          * this leaf's.  Otherwise we need to split the shortcut.
239          */
240         cursor = ptr;
241 follow_shortcut:
242         shortcut = assoc_array_ptr_to_shortcut(cursor);
243         pr_devel("shortcut to %d\n", shortcut->skip_to_level);
244         sc_level = level + ASSOC_ARRAY_LEVEL_STEP;
245         BUG_ON(sc_level > shortcut->skip_to_level);
246 
247         do {
248                 /* Check the leaf against the shortcut's index key a word at a
249                  * time, trimming the final word (the shortcut stores the index
250                  * key completely from the root to the shortcut's target).
251                  */
252                 if ((sc_level & ASSOC_ARRAY_KEY_CHUNK_MASK) == 0)
253                         segments = ops->get_key_chunk(index_key, sc_level);
254 
255                 sc_segments = shortcut->index_key[sc_level >> ASSOC_ARRAY_KEY_CHUNK_SHIFT];
256                 dissimilarity = segments ^ sc_segments;
257 
258                 if (round_up(sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE) > shortcut->skip_to_level) {
259                         /* Trim segments that are beyond the shortcut */
260                         int shift = shortcut->skip_to_level & ASSOC_ARRAY_KEY_CHUNK_MASK;
261                         dissimilarity &= ~(ULONG_MAX << shift);
262                         next_sc_level = shortcut->skip_to_level;
263                 } else {
264                         next_sc_level = sc_level + ASSOC_ARRAY_KEY_CHUNK_SIZE;
265                         next_sc_level = round_down(next_sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
266                 }
267 
268                 if (dissimilarity != 0) {
269                         /* This shortcut points elsewhere */
270                         result->wrong_shortcut.shortcut = shortcut;
271                         result->wrong_shortcut.level = level;
272                         result->wrong_shortcut.sc_level = sc_level;
273                         result->wrong_shortcut.sc_segments = sc_segments;
274                         result->wrong_shortcut.dissimilarity = dissimilarity;
275                         return assoc_array_walk_found_wrong_shortcut;
276                 }
277 
278                 sc_level = next_sc_level;
279         } while (sc_level < shortcut->skip_to_level);
280 
281         /* The shortcut matches the leaf's index to this point. */
282         cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */
283         if (((level ^ sc_level) & ~ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) {
284                 level = sc_level;
285                 goto jumped;
286         } else {
287                 level = sc_level;
288                 goto consider_node;
289         }
290 }
291 
292 /**
293  * assoc_array_find - Find an object by index key
294  * @array: The associative array to search.
295  * @ops: The operations to use.
296  * @index_key: The key to the object.
297  *
298  * Find an object in an associative array by walking through the internal tree
299  * to the node that should contain the object and then searching the leaves
300  * there.  NULL is returned if the requested object was not found in the array.
301  *
302  * The caller must hold the RCU read lock or better.
303  */
304 void *assoc_array_find(const struct assoc_array *array,
305                        const struct assoc_array_ops *ops,
306                        const void *index_key)
307 {
308         struct assoc_array_walk_result result;
309         const struct assoc_array_node *node;
310         const struct assoc_array_ptr *ptr;
311         const void *leaf;
312         int slot;
313 
314         if (assoc_array_walk(array, ops, index_key, &result) !=
315             assoc_array_walk_found_terminal_node)
316                 return NULL;
317 
318         node = result.terminal_node.node;
319 
320         /* If the target key is available to us, it's has to be pointed to by
321          * the terminal node.
322          */
323         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
324                 ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
325                 if (ptr && assoc_array_ptr_is_leaf(ptr)) {
326                         /* We need a barrier between the read of the pointer
327                          * and dereferencing the pointer - but only if we are
328                          * actually going to dereference it.
329                          */
330                         leaf = assoc_array_ptr_to_leaf(ptr);
331                         if (ops->compare_object(leaf, index_key))
332                                 return (void *)leaf;
333                 }
334         }
335 
336         return NULL;
337 }
338 
339 /*
340  * Destructively iterate over an associative array.  The caller must prevent
341  * other simultaneous accesses.
342  */
343 static void assoc_array_destroy_subtree(struct assoc_array_ptr *root,
344                                         const struct assoc_array_ops *ops)
345 {
346         struct assoc_array_shortcut *shortcut;
347         struct assoc_array_node *node;
348         struct assoc_array_ptr *cursor, *parent = NULL;
349         int slot = -1;
350 
351         pr_devel("-->%s()\n", __func__);
352 
353         cursor = root;
354         if (!cursor) {
355                 pr_devel("empty\n");
356                 return;
357         }
358 
359 move_to_meta:
360         if (assoc_array_ptr_is_shortcut(cursor)) {
361                 /* Descend through a shortcut */
362                 pr_devel("[%d] shortcut\n", slot);
363                 BUG_ON(!assoc_array_ptr_is_shortcut(cursor));
364                 shortcut = assoc_array_ptr_to_shortcut(cursor);
365                 BUG_ON(shortcut->back_pointer != parent);
366                 BUG_ON(slot != -1 && shortcut->parent_slot != slot);
367                 parent = cursor;
368                 cursor = shortcut->next_node;
369                 slot = -1;
370                 BUG_ON(!assoc_array_ptr_is_node(cursor));
371         }
372 
373         pr_devel("[%d] node\n", slot);
374         node = assoc_array_ptr_to_node(cursor);
375         BUG_ON(node->back_pointer != parent);
376         BUG_ON(slot != -1 && node->parent_slot != slot);
377         slot = 0;
378 
379 continue_node:
380         pr_devel("Node %p [back=%p]\n", node, node->back_pointer);
381         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
382                 struct assoc_array_ptr *ptr = node->slots[slot];
383                 if (!ptr)
384                         continue;
385                 if (assoc_array_ptr_is_meta(ptr)) {
386                         parent = cursor;
387                         cursor = ptr;
388                         goto move_to_meta;
389                 }
390 
391                 if (ops) {
392                         pr_devel("[%d] free leaf\n", slot);
393                         ops->free_object(assoc_array_ptr_to_leaf(ptr));
394                 }
395         }
396 
397         parent = node->back_pointer;
398         slot = node->parent_slot;
399         pr_devel("free node\n");
400         kfree(node);
401         if (!parent)
402                 return; /* Done */
403 
404         /* Move back up to the parent (may need to free a shortcut on
405          * the way up) */
406         if (assoc_array_ptr_is_shortcut(parent)) {
407                 shortcut = assoc_array_ptr_to_shortcut(parent);
408                 BUG_ON(shortcut->next_node != cursor);
409                 cursor = parent;
410                 parent = shortcut->back_pointer;
411                 slot = shortcut->parent_slot;
412                 pr_devel("free shortcut\n");
413                 kfree(shortcut);
414                 if (!parent)
415                         return;
416 
417                 BUG_ON(!assoc_array_ptr_is_node(parent));
418         }
419 
420         /* Ascend to next slot in parent node */
421         pr_devel("ascend to %p[%d]\n", parent, slot);
422         cursor = parent;
423         node = assoc_array_ptr_to_node(cursor);
424         slot++;
425         goto continue_node;
426 }
427 
428 /**
429  * assoc_array_destroy - Destroy an associative array
430  * @array: The array to destroy.
431  * @ops: The operations to use.
432  *
433  * Discard all metadata and free all objects in an associative array.  The
434  * array will be empty and ready to use again upon completion.  This function
435  * cannot fail.
436  *
437  * The caller must prevent all other accesses whilst this takes place as no
438  * attempt is made to adjust pointers gracefully to permit RCU readlock-holding
439  * accesses to continue.  On the other hand, no memory allocation is required.
440  */
441 void assoc_array_destroy(struct assoc_array *array,
442                          const struct assoc_array_ops *ops)
443 {
444         assoc_array_destroy_subtree(array->root, ops);
445         array->root = NULL;
446 }
447 
448 /*
449  * Handle insertion into an empty tree.
450  */
451 static bool assoc_array_insert_in_empty_tree(struct assoc_array_edit *edit)
452 {
453         struct assoc_array_node *new_n0;
454 
455         pr_devel("-->%s()\n", __func__);
456 
457         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
458         if (!new_n0)
459                 return false;
460 
461         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
462         edit->leaf_p = &new_n0->slots[0];
463         edit->adjust_count_on = new_n0;
464         edit->set[0].ptr = &edit->array->root;
465         edit->set[0].to = assoc_array_node_to_ptr(new_n0);
466 
467         pr_devel("<--%s() = ok [no root]\n", __func__);
468         return true;
469 }
470 
471 /*
472  * Handle insertion into a terminal node.
473  */
474 static bool assoc_array_insert_into_terminal_node(struct assoc_array_edit *edit,
475                                                   const struct assoc_array_ops *ops,
476                                                   const void *index_key,
477                                                   struct assoc_array_walk_result *result)
478 {
479         struct assoc_array_shortcut *shortcut, *new_s0;
480         struct assoc_array_node *node, *new_n0, *new_n1, *side;
481         struct assoc_array_ptr *ptr;
482         unsigned long dissimilarity, base_seg, blank;
483         size_t keylen;
484         bool have_meta;
485         int level, diff;
486         int slot, next_slot, free_slot, i, j;
487 
488         node    = result->terminal_node.node;
489         level   = result->terminal_node.level;
490         edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = result->terminal_node.slot;
491 
492         pr_devel("-->%s()\n", __func__);
493 
494         /* We arrived at a node which doesn't have an onward node or shortcut
495          * pointer that we have to follow.  This means that (a) the leaf we
496          * want must go here (either by insertion or replacement) or (b) we
497          * need to split this node and insert in one of the fragments.
498          */
499         free_slot = -1;
500 
501         /* Firstly, we have to check the leaves in this node to see if there's
502          * a matching one we should replace in place.
503          */
504         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
505                 ptr = node->slots[i];
506                 if (!ptr) {
507                         free_slot = i;
508                         continue;
509                 }
510                 if (assoc_array_ptr_is_leaf(ptr) &&
511                     ops->compare_object(assoc_array_ptr_to_leaf(ptr),
512                                         index_key)) {
513                         pr_devel("replace in slot %d\n", i);
514                         edit->leaf_p = &node->slots[i];
515                         edit->dead_leaf = node->slots[i];
516                         pr_devel("<--%s() = ok [replace]\n", __func__);
517                         return true;
518                 }
519         }
520 
521         /* If there is a free slot in this node then we can just insert the
522          * leaf here.
523          */
524         if (free_slot >= 0) {
525                 pr_devel("insert in free slot %d\n", free_slot);
526                 edit->leaf_p = &node->slots[free_slot];
527                 edit->adjust_count_on = node;
528                 pr_devel("<--%s() = ok [insert]\n", __func__);
529                 return true;
530         }
531 
532         /* The node has no spare slots - so we're either going to have to split
533          * it or insert another node before it.
534          *
535          * Whatever, we're going to need at least two new nodes - so allocate
536          * those now.  We may also need a new shortcut, but we deal with that
537          * when we need it.
538          */
539         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
540         if (!new_n0)
541                 return false;
542         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
543         new_n1 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
544         if (!new_n1)
545                 return false;
546         edit->new_meta[1] = assoc_array_node_to_ptr(new_n1);
547 
548         /* We need to find out how similar the leaves are. */
549         pr_devel("no spare slots\n");
550         have_meta = false;
551         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
552                 ptr = node->slots[i];
553                 if (assoc_array_ptr_is_meta(ptr)) {
554                         edit->segment_cache[i] = 0xff;
555                         have_meta = true;
556                         continue;
557                 }
558                 base_seg = ops->get_object_key_chunk(
559                         assoc_array_ptr_to_leaf(ptr), level);
560                 base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
561                 edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
562         }
563 
564         if (have_meta) {
565                 pr_devel("have meta\n");
566                 goto split_node;
567         }
568 
569         /* The node contains only leaves */
570         dissimilarity = 0;
571         base_seg = edit->segment_cache[0];
572         for (i = 1; i < ASSOC_ARRAY_FAN_OUT; i++)
573                 dissimilarity |= edit->segment_cache[i] ^ base_seg;
574 
575         pr_devel("only leaves; dissimilarity=%lx\n", dissimilarity);
576 
577         if ((dissimilarity & ASSOC_ARRAY_FAN_MASK) == 0) {
578                 /* The old leaves all cluster in the same slot.  We will need
579                  * to insert a shortcut if the new node wants to cluster with them.
580                  */
581                 if ((edit->segment_cache[ASSOC_ARRAY_FAN_OUT] ^ base_seg) == 0)
582                         goto all_leaves_cluster_together;
583 
584                 /* Otherwise all the old leaves cluster in the same slot, but
585                  * the new leaf wants to go into a different slot - so we
586                  * create a new node (n0) to hold the new leaf and a pointer to
587                  * a new node (n1) holding all the old leaves.
588                  *
589                  * This can be done by falling through to the node splitting
590                  * path.
591                  */
592                 pr_devel("present leaves cluster but not new leaf\n");
593         }
594 
595 split_node:
596         pr_devel("split node\n");
597 
598         /* We need to split the current node.  The node must contain anything
599          * from a single leaf (in the one leaf case, this leaf will cluster
600          * with the new leaf) and the rest meta-pointers, to all leaves, some
601          * of which may cluster.
602          *
603          * It won't contain the case in which all the current leaves plus the
604          * new leaves want to cluster in the same slot.
605          *
606          * We need to expel at least two leaves out of a set consisting of the
607          * leaves in the node and the new leaf.  The current meta pointers can
608          * just be copied as they shouldn't cluster with any of the leaves.
609          *
610          * We need a new node (n0) to replace the current one and a new node to
611          * take the expelled nodes (n1).
612          */
613         edit->set[0].to = assoc_array_node_to_ptr(new_n0);
614         new_n0->back_pointer = node->back_pointer;
615         new_n0->parent_slot = node->parent_slot;
616         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
617         new_n1->parent_slot = -1; /* Need to calculate this */
618 
619 do_split_node:
620         pr_devel("do_split_node\n");
621 
622         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
623         new_n1->nr_leaves_on_branch = 0;
624 
625         /* Begin by finding two matching leaves.  There have to be at least two
626          * that match - even if there are meta pointers - because any leaf that
627          * would match a slot with a meta pointer in it must be somewhere
628          * behind that meta pointer and cannot be here.  Further, given N
629          * remaining leaf slots, we now have N+1 leaves to go in them.
630          */
631         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
632                 slot = edit->segment_cache[i];
633                 if (slot != 0xff)
634                         for (j = i + 1; j < ASSOC_ARRAY_FAN_OUT + 1; j++)
635                                 if (edit->segment_cache[j] == slot)
636                                         goto found_slot_for_multiple_occupancy;
637         }
638 found_slot_for_multiple_occupancy:
639         pr_devel("same slot: %x %x [%02x]\n", i, j, slot);
640         BUG_ON(i >= ASSOC_ARRAY_FAN_OUT);
641         BUG_ON(j >= ASSOC_ARRAY_FAN_OUT + 1);
642         BUG_ON(slot >= ASSOC_ARRAY_FAN_OUT);
643 
644         new_n1->parent_slot = slot;
645 
646         /* Metadata pointers cannot change slot */
647         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
648                 if (assoc_array_ptr_is_meta(node->slots[i]))
649                         new_n0->slots[i] = node->slots[i];
650                 else
651                         new_n0->slots[i] = NULL;
652         BUG_ON(new_n0->slots[slot] != NULL);
653         new_n0->slots[slot] = assoc_array_node_to_ptr(new_n1);
654 
655         /* Filter the leaf pointers between the new nodes */
656         free_slot = -1;
657         next_slot = 0;
658         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
659                 if (assoc_array_ptr_is_meta(node->slots[i]))
660                         continue;
661                 if (edit->segment_cache[i] == slot) {
662                         new_n1->slots[next_slot++] = node->slots[i];
663                         new_n1->nr_leaves_on_branch++;
664                 } else {
665                         do {
666                                 free_slot++;
667                         } while (new_n0->slots[free_slot] != NULL);
668                         new_n0->slots[free_slot] = node->slots[i];
669                 }
670         }
671 
672         pr_devel("filtered: f=%x n=%x\n", free_slot, next_slot);
673 
674         if (edit->segment_cache[ASSOC_ARRAY_FAN_OUT] != slot) {
675                 do {
676                         free_slot++;
677                 } while (new_n0->slots[free_slot] != NULL);
678                 edit->leaf_p = &new_n0->slots[free_slot];
679                 edit->adjust_count_on = new_n0;
680         } else {
681                 edit->leaf_p = &new_n1->slots[next_slot++];
682                 edit->adjust_count_on = new_n1;
683         }
684 
685         BUG_ON(next_slot <= 1);
686 
687         edit->set_backpointers_to = assoc_array_node_to_ptr(new_n0);
688         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
689                 if (edit->segment_cache[i] == 0xff) {
690                         ptr = node->slots[i];
691                         BUG_ON(assoc_array_ptr_is_leaf(ptr));
692                         if (assoc_array_ptr_is_node(ptr)) {
693                                 side = assoc_array_ptr_to_node(ptr);
694                                 edit->set_backpointers[i] = &side->back_pointer;
695                         } else {
696                                 shortcut = assoc_array_ptr_to_shortcut(ptr);
697                                 edit->set_backpointers[i] = &shortcut->back_pointer;
698                         }
699                 }
700         }
701 
702         ptr = node->back_pointer;
703         if (!ptr)
704                 edit->set[0].ptr = &edit->array->root;
705         else if (assoc_array_ptr_is_node(ptr))
706                 edit->set[0].ptr = &assoc_array_ptr_to_node(ptr)->slots[node->parent_slot];
707         else
708                 edit->set[0].ptr = &assoc_array_ptr_to_shortcut(ptr)->next_node;
709         edit->excised_meta[0] = assoc_array_node_to_ptr(node);
710         pr_devel("<--%s() = ok [split node]\n", __func__);
711         return true;
712 
713 all_leaves_cluster_together:
714         /* All the leaves, new and old, want to cluster together in this node
715          * in the same slot, so we have to replace this node with a shortcut to
716          * skip over the identical parts of the key and then place a pair of
717          * nodes, one inside the other, at the end of the shortcut and
718          * distribute the keys between them.
719          *
720          * Firstly we need to work out where the leaves start diverging as a
721          * bit position into their keys so that we know how big the shortcut
722          * needs to be.
723          *
724          * We only need to make a single pass of N of the N+1 leaves because if
725          * any keys differ between themselves at bit X then at least one of
726          * them must also differ with the base key at bit X or before.
727          */
728         pr_devel("all leaves cluster together\n");
729         diff = INT_MAX;
730         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
731                 int x = ops->diff_objects(assoc_array_ptr_to_leaf(node->slots[i]),
732                                           index_key);
733                 if (x < diff) {
734                         BUG_ON(x < 0);
735                         diff = x;
736                 }
737         }
738         BUG_ON(diff == INT_MAX);
739         BUG_ON(diff < level + ASSOC_ARRAY_LEVEL_STEP);
740 
741         keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
742         keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
743 
744         new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
745                          keylen * sizeof(unsigned long), GFP_KERNEL);
746         if (!new_s0)
747                 return false;
748         edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s0);
749 
750         edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
751         new_s0->back_pointer = node->back_pointer;
752         new_s0->parent_slot = node->parent_slot;
753         new_s0->next_node = assoc_array_node_to_ptr(new_n0);
754         new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
755         new_n0->parent_slot = 0;
756         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
757         new_n1->parent_slot = -1; /* Need to calculate this */
758 
759         new_s0->skip_to_level = level = diff & ~ASSOC_ARRAY_LEVEL_STEP_MASK;
760         pr_devel("skip_to_level = %d [diff %d]\n", level, diff);
761         BUG_ON(level <= 0);
762 
763         for (i = 0; i < keylen; i++)
764                 new_s0->index_key[i] =
765                         ops->get_key_chunk(index_key, i * ASSOC_ARRAY_KEY_CHUNK_SIZE);
766 
767         if (level & ASSOC_ARRAY_KEY_CHUNK_MASK) {
768                 blank = ULONG_MAX << (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
769                 pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, level, blank);
770                 new_s0->index_key[keylen - 1] &= ~blank;
771         }
772 
773         /* This now reduces to a node splitting exercise for which we'll need
774          * to regenerate the disparity table.
775          */
776         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
777                 ptr = node->slots[i];
778                 base_seg = ops->get_object_key_chunk(assoc_array_ptr_to_leaf(ptr),
779                                                      level);
780                 base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
781                 edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
782         }
783 
784         base_seg = ops->get_key_chunk(index_key, level);
785         base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
786         edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = base_seg & ASSOC_ARRAY_FAN_MASK;
787         goto do_split_node;
788 }
789 
790 /*
791  * Handle insertion into the middle of a shortcut.
792  */
793 static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
794                                             const struct assoc_array_ops *ops,
795                                             struct assoc_array_walk_result *result)
796 {
797         struct assoc_array_shortcut *shortcut, *new_s0, *new_s1;
798         struct assoc_array_node *node, *new_n0, *side;
799         unsigned long sc_segments, dissimilarity, blank;
800         size_t keylen;
801         int level, sc_level, diff;
802         int sc_slot;
803 
804         shortcut        = result->wrong_shortcut.shortcut;
805         level           = result->wrong_shortcut.level;
806         sc_level        = result->wrong_shortcut.sc_level;
807         sc_segments     = result->wrong_shortcut.sc_segments;
808         dissimilarity   = result->wrong_shortcut.dissimilarity;
809 
810         pr_devel("-->%s(ix=%d dis=%lx scix=%d)\n",
811                  __func__, level, dissimilarity, sc_level);
812 
813         /* We need to split a shortcut and insert a node between the two
814          * pieces.  Zero-length pieces will be dispensed with entirely.
815          *
816          * First of all, we need to find out in which level the first
817          * difference was.
818          */
819         diff = __ffs(dissimilarity);
820         diff &= ~ASSOC_ARRAY_LEVEL_STEP_MASK;
821         diff += sc_level & ~ASSOC_ARRAY_KEY_CHUNK_MASK;
822         pr_devel("diff=%d\n", diff);
823 
824         if (!shortcut->back_pointer) {
825                 edit->set[0].ptr = &edit->array->root;
826         } else if (assoc_array_ptr_is_node(shortcut->back_pointer)) {
827                 node = assoc_array_ptr_to_node(shortcut->back_pointer);
828                 edit->set[0].ptr = &node->slots[shortcut->parent_slot];
829         } else {
830                 BUG();
831         }
832 
833         edit->excised_meta[0] = assoc_array_shortcut_to_ptr(shortcut);
834 
835         /* Create a new node now since we're going to need it anyway */
836         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
837         if (!new_n0)
838                 return false;
839         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
840         edit->adjust_count_on = new_n0;
841 
842         /* Insert a new shortcut before the new node if this segment isn't of
843          * zero length - otherwise we just connect the new node directly to the
844          * parent.
845          */
846         level += ASSOC_ARRAY_LEVEL_STEP;
847         if (diff > level) {
848                 pr_devel("pre-shortcut %d...%d\n", level, diff);
849                 keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
850                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
851 
852                 new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
853                                  keylen * sizeof(unsigned long), GFP_KERNEL);
854                 if (!new_s0)
855                         return false;
856                 edit->new_meta[1] = assoc_array_shortcut_to_ptr(new_s0);
857                 edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
858                 new_s0->back_pointer = shortcut->back_pointer;
859                 new_s0->parent_slot = shortcut->parent_slot;
860                 new_s0->next_node = assoc_array_node_to_ptr(new_n0);
861                 new_s0->skip_to_level = diff;
862 
863                 new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
864                 new_n0->parent_slot = 0;
865 
866                 memcpy(new_s0->index_key, shortcut->index_key,
867                        keylen * sizeof(unsigned long));
868 
869                 blank = ULONG_MAX << (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
870                 pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, diff, blank);
871                 new_s0->index_key[keylen - 1] &= ~blank;
872         } else {
873                 pr_devel("no pre-shortcut\n");
874                 edit->set[0].to = assoc_array_node_to_ptr(new_n0);
875                 new_n0->back_pointer = shortcut->back_pointer;
876                 new_n0->parent_slot = shortcut->parent_slot;
877         }
878 
879         side = assoc_array_ptr_to_node(shortcut->next_node);
880         new_n0->nr_leaves_on_branch = side->nr_leaves_on_branch;
881 
882         /* We need to know which slot in the new node is going to take a
883          * metadata pointer.
884          */
885         sc_slot = sc_segments >> (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
886         sc_slot &= ASSOC_ARRAY_FAN_MASK;
887 
888         pr_devel("new slot %lx >> %d -> %d\n",
889                  sc_segments, diff & ASSOC_ARRAY_KEY_CHUNK_MASK, sc_slot);
890 
891         /* Determine whether we need to follow the new node with a replacement
892          * for the current shortcut.  We could in theory reuse the current
893          * shortcut if its parent slot number doesn't change - but that's a
894          * 1-in-16 chance so not worth expending the code upon.
895          */
896         level = diff + ASSOC_ARRAY_LEVEL_STEP;
897         if (level < shortcut->skip_to_level) {
898                 pr_devel("post-shortcut %d...%d\n", level, shortcut->skip_to_level);
899                 keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
900                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
901 
902                 new_s1 = kzalloc(sizeof(struct assoc_array_shortcut) +
903                                  keylen * sizeof(unsigned long), GFP_KERNEL);
904                 if (!new_s1)
905                         return false;
906                 edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s1);
907 
908                 new_s1->back_pointer = assoc_array_node_to_ptr(new_n0);
909                 new_s1->parent_slot = sc_slot;
910                 new_s1->next_node = shortcut->next_node;
911                 new_s1->skip_to_level = shortcut->skip_to_level;
912 
913                 new_n0->slots[sc_slot] = assoc_array_shortcut_to_ptr(new_s1);
914 
915                 memcpy(new_s1->index_key, shortcut->index_key,
916                        keylen * sizeof(unsigned long));
917 
918                 edit->set[1].ptr = &side->back_pointer;
919                 edit->set[1].to = assoc_array_shortcut_to_ptr(new_s1);
920         } else {
921                 pr_devel("no post-shortcut\n");
922 
923                 /* We don't have to replace the pointed-to node as long as we
924                  * use memory barriers to make sure the parent slot number is
925                  * changed before the back pointer (the parent slot number is
926                  * irrelevant to the old parent shortcut).
927                  */
928                 new_n0->slots[sc_slot] = shortcut->next_node;
929                 edit->set_parent_slot[0].p = &side->parent_slot;
930                 edit->set_parent_slot[0].to = sc_slot;
931                 edit->set[1].ptr = &side->back_pointer;
932                 edit->set[1].to = assoc_array_node_to_ptr(new_n0);
933         }
934 
935         /* Install the new leaf in a spare slot in the new node. */
936         if (sc_slot == 0)
937                 edit->leaf_p = &new_n0->slots[1];
938         else
939                 edit->leaf_p = &new_n0->slots[0];
940 
941         pr_devel("<--%s() = ok [split shortcut]\n", __func__);
942         return edit;
943 }
944 
945 /**
946  * assoc_array_insert - Script insertion of an object into an associative array
947  * @array: The array to insert into.
948  * @ops: The operations to use.
949  * @index_key: The key to insert at.
950  * @object: The object to insert.
951  *
952  * Precalculate and preallocate a script for the insertion or replacement of an
953  * object in an associative array.  This results in an edit script that can
954  * either be applied or cancelled.
955  *
956  * The function returns a pointer to an edit script or -ENOMEM.
957  *
958  * The caller should lock against other modifications and must continue to hold
959  * the lock until assoc_array_apply_edit() has been called.
960  *
961  * Accesses to the tree may take place concurrently with this function,
962  * provided they hold the RCU read lock.
963  */
964 struct assoc_array_edit *assoc_array_insert(struct assoc_array *array,
965                                             const struct assoc_array_ops *ops,
966                                             const void *index_key,
967                                             void *object)
968 {
969         struct assoc_array_walk_result result;
970         struct assoc_array_edit *edit;
971 
972         pr_devel("-->%s()\n", __func__);
973 
974         /* The leaf pointer we're given must not have the bottom bit set as we
975          * use those for type-marking the pointer.  NULL pointers are also not
976          * allowed as they indicate an empty slot but we have to allow them
977          * here as they can be updated later.
978          */
979         BUG_ON(assoc_array_ptr_is_meta(object));
980 
981         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
982         if (!edit)
983                 return ERR_PTR(-ENOMEM);
984         edit->array = array;
985         edit->ops = ops;
986         edit->leaf = assoc_array_leaf_to_ptr(object);
987         edit->adjust_count_by = 1;
988 
989         switch (assoc_array_walk(array, ops, index_key, &result)) {
990         case assoc_array_walk_tree_empty:
991                 /* Allocate a root node if there isn't one yet */
992                 if (!assoc_array_insert_in_empty_tree(edit))
993                         goto enomem;
994                 return edit;
995 
996         case assoc_array_walk_found_terminal_node:
997                 /* We found a node that doesn't have a node/shortcut pointer in
998                  * the slot corresponding to the index key that we have to
999                  * follow.
1000                  */
1001                 if (!assoc_array_insert_into_terminal_node(edit, ops, index_key,
1002                                                            &result))
1003                         goto enomem;
1004                 return edit;
1005 
1006         case assoc_array_walk_found_wrong_shortcut:
1007                 /* We found a shortcut that didn't match our key in a slot we
1008                  * needed to follow.
1009                  */
1010                 if (!assoc_array_insert_mid_shortcut(edit, ops, &result))
1011                         goto enomem;
1012                 return edit;
1013         }
1014 
1015 enomem:
1016         /* Clean up after an out of memory error */
1017         pr_devel("enomem\n");
1018         assoc_array_cancel_edit(edit);
1019         return ERR_PTR(-ENOMEM);
1020 }
1021 
1022 /**
1023  * assoc_array_insert_set_object - Set the new object pointer in an edit script
1024  * @edit: The edit script to modify.
1025  * @object: The object pointer to set.
1026  *
1027  * Change the object to be inserted in an edit script.  The object pointed to
1028  * by the old object is not freed.  This must be done prior to applying the
1029  * script.
1030  */
1031 void assoc_array_insert_set_object(struct assoc_array_edit *edit, void *object)
1032 {
1033         BUG_ON(!object);
1034         edit->leaf = assoc_array_leaf_to_ptr(object);
1035 }
1036 
1037 struct assoc_array_delete_collapse_context {
1038         struct assoc_array_node *node;
1039         const void              *skip_leaf;
1040         int                     slot;
1041 };
1042 
1043 /*
1044  * Subtree collapse to node iterator.
1045  */
1046 static int assoc_array_delete_collapse_iterator(const void *leaf,
1047                                                 void *iterator_data)
1048 {
1049         struct assoc_array_delete_collapse_context *collapse = iterator_data;
1050 
1051         if (leaf == collapse->skip_leaf)
1052                 return 0;
1053 
1054         BUG_ON(collapse->slot >= ASSOC_ARRAY_FAN_OUT);
1055 
1056         collapse->node->slots[collapse->slot++] = assoc_array_leaf_to_ptr(leaf);
1057         return 0;
1058 }
1059 
1060 /**
1061  * assoc_array_delete - Script deletion of an object from an associative array
1062  * @array: The array to search.
1063  * @ops: The operations to use.
1064  * @index_key: The key to the object.
1065  *
1066  * Precalculate and preallocate a script for the deletion of an object from an
1067  * associative array.  This results in an edit script that can either be
1068  * applied or cancelled.
1069  *
1070  * The function returns a pointer to an edit script if the object was found,
1071  * NULL if the object was not found or -ENOMEM.
1072  *
1073  * The caller should lock against other modifications and must continue to hold
1074  * the lock until assoc_array_apply_edit() has been called.
1075  *
1076  * Accesses to the tree may take place concurrently with this function,
1077  * provided they hold the RCU read lock.
1078  */
1079 struct assoc_array_edit *assoc_array_delete(struct assoc_array *array,
1080                                             const struct assoc_array_ops *ops,
1081                                             const void *index_key)
1082 {
1083         struct assoc_array_delete_collapse_context collapse;
1084         struct assoc_array_walk_result result;
1085         struct assoc_array_node *node, *new_n0;
1086         struct assoc_array_edit *edit;
1087         struct assoc_array_ptr *ptr;
1088         bool has_meta;
1089         int slot, i;
1090 
1091         pr_devel("-->%s()\n", __func__);
1092 
1093         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1094         if (!edit)
1095                 return ERR_PTR(-ENOMEM);
1096         edit->array = array;
1097         edit->ops = ops;
1098         edit->adjust_count_by = -1;
1099 
1100         switch (assoc_array_walk(array, ops, index_key, &result)) {
1101         case assoc_array_walk_found_terminal_node:
1102                 /* We found a node that should contain the leaf we've been
1103                  * asked to remove - *if* it's in the tree.
1104                  */
1105                 pr_devel("terminal_node\n");
1106                 node = result.terminal_node.node;
1107 
1108                 for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1109                         ptr = node->slots[slot];
1110                         if (ptr &&
1111                             assoc_array_ptr_is_leaf(ptr) &&
1112                             ops->compare_object(assoc_array_ptr_to_leaf(ptr),
1113                                                 index_key))
1114                                 goto found_leaf;
1115                 }
1116                 /* fall through */
1117         case assoc_array_walk_tree_empty:
1118         case assoc_array_walk_found_wrong_shortcut:
1119         default:
1120                 assoc_array_cancel_edit(edit);
1121                 pr_devel("not found\n");
1122                 return NULL;
1123         }
1124 
1125 found_leaf:
1126         BUG_ON(array->nr_leaves_on_tree <= 0);
1127 
1128         /* In the simplest form of deletion we just clear the slot and release
1129          * the leaf after a suitable interval.
1130          */
1131         edit->dead_leaf = node->slots[slot];
1132         edit->set[0].ptr = &node->slots[slot];
1133         edit->set[0].to = NULL;
1134         edit->adjust_count_on = node;
1135 
1136         /* If that concludes erasure of the last leaf, then delete the entire
1137          * internal array.
1138          */
1139         if (array->nr_leaves_on_tree == 1) {
1140                 edit->set[1].ptr = &array->root;
1141                 edit->set[1].to = NULL;
1142                 edit->adjust_count_on = NULL;
1143                 edit->excised_subtree = array->root;
1144                 pr_devel("all gone\n");
1145                 return edit;
1146         }
1147 
1148         /* However, we'd also like to clear up some metadata blocks if we
1149          * possibly can.
1150          *
1151          * We go for a simple algorithm of: if this node has FAN_OUT or fewer
1152          * leaves in it, then attempt to collapse it - and attempt to
1153          * recursively collapse up the tree.
1154          *
1155          * We could also try and collapse in partially filled subtrees to take
1156          * up space in this node.
1157          */
1158         if (node->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1159                 struct assoc_array_node *parent, *grandparent;
1160                 struct assoc_array_ptr *ptr;
1161 
1162                 /* First of all, we need to know if this node has metadata so
1163                  * that we don't try collapsing if all the leaves are already
1164                  * here.
1165                  */
1166                 has_meta = false;
1167                 for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1168                         ptr = node->slots[i];
1169                         if (assoc_array_ptr_is_meta(ptr)) {
1170                                 has_meta = true;
1171                                 break;
1172                         }
1173                 }
1174 
1175                 pr_devel("leaves: %ld [m=%d]\n",
1176                          node->nr_leaves_on_branch - 1, has_meta);
1177 
1178                 /* Look further up the tree to see if we can collapse this node
1179                  * into a more proximal node too.
1180                  */
1181                 parent = node;
1182         collapse_up:
1183                 pr_devel("collapse subtree: %ld\n", parent->nr_leaves_on_branch);
1184 
1185                 ptr = parent->back_pointer;
1186                 if (!ptr)
1187                         goto do_collapse;
1188                 if (assoc_array_ptr_is_shortcut(ptr)) {
1189                         struct assoc_array_shortcut *s = assoc_array_ptr_to_shortcut(ptr);
1190                         ptr = s->back_pointer;
1191                         if (!ptr)
1192                                 goto do_collapse;
1193                 }
1194 
1195                 grandparent = assoc_array_ptr_to_node(ptr);
1196                 if (grandparent->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1197                         parent = grandparent;
1198                         goto collapse_up;
1199                 }
1200 
1201         do_collapse:
1202                 /* There's no point collapsing if the original node has no meta
1203                  * pointers to discard and if we didn't merge into one of that
1204                  * node's ancestry.
1205                  */
1206                 if (has_meta || parent != node) {
1207                         node = parent;
1208 
1209                         /* Create a new node to collapse into */
1210                         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1211                         if (!new_n0)
1212                                 goto enomem;
1213                         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
1214 
1215                         new_n0->back_pointer = node->back_pointer;
1216                         new_n0->parent_slot = node->parent_slot;
1217                         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
1218                         edit->adjust_count_on = new_n0;
1219 
1220                         collapse.node = new_n0;
1221                         collapse.skip_leaf = assoc_array_ptr_to_leaf(edit->dead_leaf);
1222                         collapse.slot = 0;
1223                         assoc_array_subtree_iterate(assoc_array_node_to_ptr(node),
1224                                                     node->back_pointer,
1225                                                     assoc_array_delete_collapse_iterator,
1226                                                     &collapse);
1227                         pr_devel("collapsed %d,%lu\n", collapse.slot, new_n0->nr_leaves_on_branch);
1228                         BUG_ON(collapse.slot != new_n0->nr_leaves_on_branch - 1);
1229 
1230                         if (!node->back_pointer) {
1231                                 edit->set[1].ptr = &array->root;
1232                         } else if (assoc_array_ptr_is_leaf(node->back_pointer)) {
1233                                 BUG();
1234                         } else if (assoc_array_ptr_is_node(node->back_pointer)) {
1235                                 struct assoc_array_node *p =
1236                                         assoc_array_ptr_to_node(node->back_pointer);
1237                                 edit->set[1].ptr = &p->slots[node->parent_slot];
1238                         } else if (assoc_array_ptr_is_shortcut(node->back_pointer)) {
1239                                 struct assoc_array_shortcut *s =
1240                                         assoc_array_ptr_to_shortcut(node->back_pointer);
1241                                 edit->set[1].ptr = &s->next_node;
1242                         }
1243                         edit->set[1].to = assoc_array_node_to_ptr(new_n0);
1244                         edit->excised_subtree = assoc_array_node_to_ptr(node);
1245                 }
1246         }
1247 
1248         return edit;
1249 
1250 enomem:
1251         /* Clean up after an out of memory error */
1252         pr_devel("enomem\n");
1253         assoc_array_cancel_edit(edit);
1254         return ERR_PTR(-ENOMEM);
1255 }
1256 
1257 /**
1258  * assoc_array_clear - Script deletion of all objects from an associative array
1259  * @array: The array to clear.
1260  * @ops: The operations to use.
1261  *
1262  * Precalculate and preallocate a script for the deletion of all the objects
1263  * from an associative array.  This results in an edit script that can either
1264  * be applied or cancelled.
1265  *
1266  * The function returns a pointer to an edit script if there are objects to be
1267  * deleted, NULL if there are no objects in the array or -ENOMEM.
1268  *
1269  * The caller should lock against other modifications and must continue to hold
1270  * the lock until assoc_array_apply_edit() has been called.
1271  *
1272  * Accesses to the tree may take place concurrently with this function,
1273  * provided they hold the RCU read lock.
1274  */
1275 struct assoc_array_edit *assoc_array_clear(struct assoc_array *array,
1276                                            const struct assoc_array_ops *ops)
1277 {
1278         struct assoc_array_edit *edit;
1279 
1280         pr_devel("-->%s()\n", __func__);
1281 
1282         if (!array->root)
1283                 return NULL;
1284 
1285         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1286         if (!edit)
1287                 return ERR_PTR(-ENOMEM);
1288         edit->array = array;
1289         edit->ops = ops;
1290         edit->set[1].ptr = &array->root;
1291         edit->set[1].to = NULL;
1292         edit->excised_subtree = array->root;
1293         edit->ops_for_excised_subtree = ops;
1294         pr_devel("all gone\n");
1295         return edit;
1296 }
1297 
1298 /*
1299  * Handle the deferred destruction after an applied edit.
1300  */
1301 static void assoc_array_rcu_cleanup(struct rcu_head *head)
1302 {
1303         struct assoc_array_edit *edit =
1304                 container_of(head, struct assoc_array_edit, rcu);
1305         int i;
1306 
1307         pr_devel("-->%s()\n", __func__);
1308 
1309         if (edit->dead_leaf)
1310                 edit->ops->free_object(assoc_array_ptr_to_leaf(edit->dead_leaf));
1311         for (i = 0; i < ARRAY_SIZE(edit->excised_meta); i++)
1312                 if (edit->excised_meta[i])
1313                         kfree(assoc_array_ptr_to_node(edit->excised_meta[i]));
1314 
1315         if (edit->excised_subtree) {
1316                 BUG_ON(assoc_array_ptr_is_leaf(edit->excised_subtree));
1317                 if (assoc_array_ptr_is_node(edit->excised_subtree)) {
1318                         struct assoc_array_node *n =
1319                                 assoc_array_ptr_to_node(edit->excised_subtree);
1320                         n->back_pointer = NULL;
1321                 } else {
1322                         struct assoc_array_shortcut *s =
1323                                 assoc_array_ptr_to_shortcut(edit->excised_subtree);
1324                         s->back_pointer = NULL;
1325                 }
1326                 assoc_array_destroy_subtree(edit->excised_subtree,
1327                                             edit->ops_for_excised_subtree);
1328         }
1329 
1330         kfree(edit);
1331 }
1332 
1333 /**
1334  * assoc_array_apply_edit - Apply an edit script to an associative array
1335  * @edit: The script to apply.
1336  *
1337  * Apply an edit script to an associative array to effect an insertion,
1338  * deletion or clearance.  As the edit script includes preallocated memory,
1339  * this is guaranteed not to fail.
1340  *
1341  * The edit script, dead objects and dead metadata will be scheduled for
1342  * destruction after an RCU grace period to permit those doing read-only
1343  * accesses on the array to continue to do so under the RCU read lock whilst
1344  * the edit is taking place.
1345  */
1346 void assoc_array_apply_edit(struct assoc_array_edit *edit)
1347 {
1348         struct assoc_array_shortcut *shortcut;
1349         struct assoc_array_node *node;
1350         struct assoc_array_ptr *ptr;
1351         int i;
1352 
1353         pr_devel("-->%s()\n", __func__);
1354 
1355         smp_wmb();
1356         if (edit->leaf_p)
1357                 *edit->leaf_p = edit->leaf;
1358 
1359         smp_wmb();
1360         for (i = 0; i < ARRAY_SIZE(edit->set_parent_slot); i++)
1361                 if (edit->set_parent_slot[i].p)
1362                         *edit->set_parent_slot[i].p = edit->set_parent_slot[i].to;
1363 
1364         smp_wmb();
1365         for (i = 0; i < ARRAY_SIZE(edit->set_backpointers); i++)
1366                 if (edit->set_backpointers[i])
1367                         *edit->set_backpointers[i] = edit->set_backpointers_to;
1368 
1369         smp_wmb();
1370         for (i = 0; i < ARRAY_SIZE(edit->set); i++)
1371                 if (edit->set[i].ptr)
1372                         *edit->set[i].ptr = edit->set[i].to;
1373 
1374         if (edit->array->root == NULL) {
1375                 edit->array->nr_leaves_on_tree = 0;
1376         } else if (edit->adjust_count_on) {
1377                 node = edit->adjust_count_on;
1378                 for (;;) {
1379                         node->nr_leaves_on_branch += edit->adjust_count_by;
1380 
1381                         ptr = node->back_pointer;
1382                         if (!ptr)
1383                                 break;
1384                         if (assoc_array_ptr_is_shortcut(ptr)) {
1385                                 shortcut = assoc_array_ptr_to_shortcut(ptr);
1386                                 ptr = shortcut->back_pointer;
1387                                 if (!ptr)
1388                                         break;
1389                         }
1390                         BUG_ON(!assoc_array_ptr_is_node(ptr));
1391                         node = assoc_array_ptr_to_node(ptr);
1392                 }
1393 
1394                 edit->array->nr_leaves_on_tree += edit->adjust_count_by;
1395         }
1396 
1397         call_rcu(&edit->rcu, assoc_array_rcu_cleanup);
1398 }
1399 
1400 /**
1401  * assoc_array_cancel_edit - Discard an edit script.
1402  * @edit: The script to discard.
1403  *
1404  * Free an edit script and all the preallocated data it holds without making
1405  * any changes to the associative array it was intended for.
1406  *
1407  * NOTE!  In the case of an insertion script, this does _not_ release the leaf
1408  * that was to be inserted.  That is left to the caller.
1409  */
1410 void assoc_array_cancel_edit(struct assoc_array_edit *edit)
1411 {
1412         struct assoc_array_ptr *ptr;
1413         int i;
1414 
1415         pr_devel("-->%s()\n", __func__);
1416 
1417         /* Clean up after an out of memory error */
1418         for (i = 0; i < ARRAY_SIZE(edit->new_meta); i++) {
1419                 ptr = edit->new_meta[i];
1420                 if (ptr) {
1421                         if (assoc_array_ptr_is_node(ptr))
1422                                 kfree(assoc_array_ptr_to_node(ptr));
1423                         else
1424                                 kfree(assoc_array_ptr_to_shortcut(ptr));
1425                 }
1426         }
1427         kfree(edit);
1428 }
1429 
1430 /**
1431  * assoc_array_gc - Garbage collect an associative array.
1432  * @array: The array to clean.
1433  * @ops: The operations to use.
1434  * @iterator: A callback function to pass judgement on each object.
1435  * @iterator_data: Private data for the callback function.
1436  *
1437  * Collect garbage from an associative array and pack down the internal tree to
1438  * save memory.
1439  *
1440  * The iterator function is asked to pass judgement upon each object in the
1441  * array.  If it returns false, the object is discard and if it returns true,
1442  * the object is kept.  If it returns true, it must increment the object's
1443  * usage count (or whatever it needs to do to retain it) before returning.
1444  *
1445  * This function returns 0 if successful or -ENOMEM if out of memory.  In the
1446  * latter case, the array is not changed.
1447  *
1448  * The caller should lock against other modifications and must continue to hold
1449  * the lock until assoc_array_apply_edit() has been called.
1450  *
1451  * Accesses to the tree may take place concurrently with this function,
1452  * provided they hold the RCU read lock.
1453  */
1454 int assoc_array_gc(struct assoc_array *array,
1455                    const struct assoc_array_ops *ops,
1456                    bool (*iterator)(void *object, void *iterator_data),
1457                    void *iterator_data)
1458 {
1459         struct assoc_array_shortcut *shortcut, *new_s;
1460         struct assoc_array_node *node, *new_n;
1461         struct assoc_array_edit *edit;
1462         struct assoc_array_ptr *cursor, *ptr;
1463         struct assoc_array_ptr *new_root, *new_parent, **new_ptr_pp;
1464         unsigned long nr_leaves_on_tree;
1465         int keylen, slot, nr_free, next_slot, i;
1466 
1467         pr_devel("-->%s()\n", __func__);
1468 
1469         if (!array->root)
1470                 return 0;
1471 
1472         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1473         if (!edit)
1474                 return -ENOMEM;
1475         edit->array = array;
1476         edit->ops = ops;
1477         edit->ops_for_excised_subtree = ops;
1478         edit->set[0].ptr = &array->root;
1479         edit->excised_subtree = array->root;
1480 
1481         new_root = new_parent = NULL;
1482         new_ptr_pp = &new_root;
1483         cursor = array->root;
1484 
1485 descend:
1486         /* If this point is a shortcut, then we need to duplicate it and
1487          * advance the target cursor.
1488          */
1489         if (assoc_array_ptr_is_shortcut(cursor)) {
1490                 shortcut = assoc_array_ptr_to_shortcut(cursor);
1491                 keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
1492                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
1493                 new_s = kmalloc(sizeof(struct assoc_array_shortcut) +
1494                                 keylen * sizeof(unsigned long), GFP_KERNEL);
1495                 if (!new_s)
1496                         goto enomem;
1497                 pr_devel("dup shortcut %p -> %p\n", shortcut, new_s);
1498                 memcpy(new_s, shortcut, (sizeof(struct assoc_array_shortcut) +
1499                                          keylen * sizeof(unsigned long)));
1500                 new_s->back_pointer = new_parent;
1501                 new_s->parent_slot = shortcut->parent_slot;
1502                 *new_ptr_pp = new_parent = assoc_array_shortcut_to_ptr(new_s);
1503                 new_ptr_pp = &new_s->next_node;
1504                 cursor = shortcut->next_node;
1505         }
1506 
1507         /* Duplicate the node at this position */
1508         node = assoc_array_ptr_to_node(cursor);
1509         new_n = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1510         if (!new_n)
1511                 goto enomem;
1512         pr_devel("dup node %p -> %p\n", node, new_n);
1513         new_n->back_pointer = new_parent;
1514         new_n->parent_slot = node->parent_slot;
1515         *new_ptr_pp = new_parent = assoc_array_node_to_ptr(new_n);
1516         new_ptr_pp = NULL;
1517         slot = 0;
1518 
1519 continue_node:
1520         /* Filter across any leaves and gc any subtrees */
1521         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1522                 ptr = node->slots[slot];
1523                 if (!ptr)
1524                         continue;
1525 
1526                 if (assoc_array_ptr_is_leaf(ptr)) {
1527                         if (iterator(assoc_array_ptr_to_leaf(ptr),
1528                                      iterator_data))
1529                                 /* The iterator will have done any reference
1530                                  * counting on the object for us.
1531                                  */
1532                                 new_n->slots[slot] = ptr;
1533                         continue;
1534                 }
1535 
1536                 new_ptr_pp = &new_n->slots[slot];
1537                 cursor = ptr;
1538                 goto descend;
1539         }
1540 
1541         pr_devel("-- compress node %p --\n", new_n);
1542 
1543         /* Count up the number of empty slots in this node and work out the
1544          * subtree leaf count.
1545          */
1546         new_n->nr_leaves_on_branch = 0;
1547         nr_free = 0;
1548         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1549                 ptr = new_n->slots[slot];
1550                 if (!ptr)
1551                         nr_free++;
1552                 else if (assoc_array_ptr_is_leaf(ptr))
1553                         new_n->nr_leaves_on_branch++;
1554         }
1555         pr_devel("free=%d, leaves=%lu\n", nr_free, new_n->nr_leaves_on_branch);
1556 
1557         /* See what we can fold in */
1558         next_slot = 0;
1559         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1560                 struct assoc_array_shortcut *s;
1561                 struct assoc_array_node *child;
1562 
1563                 ptr = new_n->slots[slot];
1564                 if (!ptr || assoc_array_ptr_is_leaf(ptr))
1565                         continue;
1566 
1567                 s = NULL;
1568                 if (assoc_array_ptr_is_shortcut(ptr)) {
1569                         s = assoc_array_ptr_to_shortcut(ptr);
1570                         ptr = s->next_node;
1571                 }
1572 
1573                 child = assoc_array_ptr_to_node(ptr);
1574                 new_n->nr_leaves_on_branch += child->nr_leaves_on_branch;
1575 
1576                 if (child->nr_leaves_on_branch <= nr_free + 1) {
1577                         /* Fold the child node into this one */
1578                         pr_devel("[%d] fold node %lu/%d [nx %d]\n",
1579                                  slot, child->nr_leaves_on_branch, nr_free + 1,
1580                                  next_slot);
1581 
1582                         /* We would already have reaped an intervening shortcut
1583                          * on the way back up the tree.
1584                          */
1585                         BUG_ON(s);
1586 
1587                         new_n->slots[slot] = NULL;
1588                         nr_free++;
1589                         if (slot < next_slot)
1590                                 next_slot = slot;
1591                         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1592                                 struct assoc_array_ptr *p = child->slots[i];
1593                                 if (!p)
1594                                         continue;
1595                                 BUG_ON(assoc_array_ptr_is_meta(p));
1596                                 while (new_n->slots[next_slot])
1597                                         next_slot++;
1598                                 BUG_ON(next_slot >= ASSOC_ARRAY_FAN_OUT);
1599                                 new_n->slots[next_slot++] = p;
1600                                 nr_free--;
1601                         }
1602                         kfree(child);
1603                 } else {
1604                         pr_devel("[%d] retain node %lu/%d [nx %d]\n",
1605                                  slot, child->nr_leaves_on_branch, nr_free + 1,
1606                                  next_slot);
1607                 }
1608         }
1609 
1610         pr_devel("after: %lu\n", new_n->nr_leaves_on_branch);
1611 
1612         nr_leaves_on_tree = new_n->nr_leaves_on_branch;
1613 
1614         /* Excise this node if it is singly occupied by a shortcut */
1615         if (nr_free == ASSOC_ARRAY_FAN_OUT - 1) {
1616                 for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++)
1617                         if ((ptr = new_n->slots[slot]))
1618                                 break;
1619 
1620                 if (assoc_array_ptr_is_meta(ptr) &&
1621                     assoc_array_ptr_is_shortcut(ptr)) {
1622                         pr_devel("excise node %p with 1 shortcut\n", new_n);
1623                         new_s = assoc_array_ptr_to_shortcut(ptr);
1624                         new_parent = new_n->back_pointer;
1625                         slot = new_n->parent_slot;
1626                         kfree(new_n);
1627                         if (!new_parent) {
1628                                 new_s->back_pointer = NULL;
1629                                 new_s->parent_slot = 0;
1630                                 new_root = ptr;
1631                                 goto gc_complete;
1632                         }
1633 
1634                         if (assoc_array_ptr_is_shortcut(new_parent)) {
1635                                 /* We can discard any preceding shortcut also */
1636                                 struct assoc_array_shortcut *s =
1637                                         assoc_array_ptr_to_shortcut(new_parent);
1638 
1639                                 pr_devel("excise preceding shortcut\n");
1640 
1641                                 new_parent = new_s->back_pointer = s->back_pointer;
1642                                 slot = new_s->parent_slot = s->parent_slot;
1643                                 kfree(s);
1644                                 if (!new_parent) {
1645                                         new_s->back_pointer = NULL;
1646                                         new_s->parent_slot = 0;
1647                                         new_root = ptr;
1648                                         goto gc_complete;
1649                                 }
1650                         }
1651 
1652                         new_s->back_pointer = new_parent;
1653                         new_s->parent_slot = slot;
1654                         new_n = assoc_array_ptr_to_node(new_parent);
1655                         new_n->slots[slot] = ptr;
1656                         goto ascend_old_tree;
1657                 }
1658         }
1659 
1660         /* Excise any shortcuts we might encounter that point to nodes that
1661          * only contain leaves.
1662          */
1663         ptr = new_n->back_pointer;
1664         if (!ptr)
1665                 goto gc_complete;
1666 
1667         if (assoc_array_ptr_is_shortcut(ptr)) {
1668                 new_s = assoc_array_ptr_to_shortcut(ptr);
1669                 new_parent = new_s->back_pointer;
1670                 slot = new_s->parent_slot;
1671 
1672                 if (new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) {
1673                         struct assoc_array_node *n;
1674 
1675                         pr_devel("excise shortcut\n");
1676                         new_n->back_pointer = new_parent;
1677                         new_n->parent_slot = slot;
1678                         kfree(new_s);
1679                         if (!new_parent) {
1680                                 new_root = assoc_array_node_to_ptr(new_n);
1681                                 goto gc_complete;
1682                         }
1683 
1684                         n = assoc_array_ptr_to_node(new_parent);
1685                         n->slots[slot] = assoc_array_node_to_ptr(new_n);
1686                 }
1687         } else {
1688                 new_parent = ptr;
1689         }
1690         new_n = assoc_array_ptr_to_node(new_parent);
1691 
1692 ascend_old_tree:
1693         ptr = node->back_pointer;
1694         if (assoc_array_ptr_is_shortcut(ptr)) {
1695                 shortcut = assoc_array_ptr_to_shortcut(ptr);
1696                 slot = shortcut->parent_slot;
1697                 cursor = shortcut->back_pointer;
1698                 if (!cursor)
1699                         goto gc_complete;
1700         } else {
1701                 slot = node->parent_slot;
1702                 cursor = ptr;
1703         }
1704         BUG_ON(!cursor);
1705         node = assoc_array_ptr_to_node(cursor);
1706         slot++;
1707         goto continue_node;
1708 
1709 gc_complete:
1710         edit->set[0].to = new_root;
1711         assoc_array_apply_edit(edit);
1712         array->nr_leaves_on_tree = nr_leaves_on_tree;
1713         return 0;
1714 
1715 enomem:
1716         pr_devel("enomem\n");
1717         assoc_array_destroy_subtree(new_root, edit->ops);
1718         kfree(edit);
1719         return -ENOMEM;
1720 }
1721 

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