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TOMOYO Linux Cross Reference
Linux/lib/assoc_array.c

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  1 /* Generic associative array implementation.
  2  *
  3  * See Documentation/assoc_array.txt for information.
  4  *
  5  * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
  6  * Written by David Howells (dhowells@redhat.com)
  7  *
  8  * This program is free software; you can redistribute it and/or
  9  * modify it under the terms of the GNU General Public Licence
 10  * as published by the Free Software Foundation; either version
 11  * 2 of the Licence, or (at your option) any later version.
 12  */
 13 //#define DEBUG
 14 #include <linux/rcupdate.h>
 15 #include <linux/slab.h>
 16 #include <linux/err.h>
 17 #include <linux/assoc_array_priv.h>
 18 
 19 /*
 20  * Iterate over an associative array.  The caller must hold the RCU read lock
 21  * or better.
 22  */
 23 static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root,
 24                                        const struct assoc_array_ptr *stop,
 25                                        int (*iterator)(const void *leaf,
 26                                                        void *iterator_data),
 27                                        void *iterator_data)
 28 {
 29         const struct assoc_array_shortcut *shortcut;
 30         const struct assoc_array_node *node;
 31         const struct assoc_array_ptr *cursor, *ptr, *parent;
 32         unsigned long has_meta;
 33         int slot, ret;
 34 
 35         cursor = root;
 36 
 37 begin_node:
 38         if (assoc_array_ptr_is_shortcut(cursor)) {
 39                 /* Descend through a shortcut */
 40                 shortcut = assoc_array_ptr_to_shortcut(cursor);
 41                 smp_read_barrier_depends();
 42                 cursor = ACCESS_ONCE(shortcut->next_node);
 43         }
 44 
 45         node = assoc_array_ptr_to_node(cursor);
 46         smp_read_barrier_depends();
 47         slot = 0;
 48 
 49         /* We perform two passes of each node.
 50          *
 51          * The first pass does all the leaves in this node.  This means we
 52          * don't miss any leaves if the node is split up by insertion whilst
 53          * we're iterating over the branches rooted here (we may, however, see
 54          * some leaves twice).
 55          */
 56         has_meta = 0;
 57         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
 58                 ptr = ACCESS_ONCE(node->slots[slot]);
 59                 has_meta |= (unsigned long)ptr;
 60                 if (ptr && assoc_array_ptr_is_leaf(ptr)) {
 61                         /* We need a barrier between the read of the pointer
 62                          * and dereferencing the pointer - but only if we are
 63                          * actually going to dereference it.
 64                          */
 65                         smp_read_barrier_depends();
 66 
 67                         /* Invoke the callback */
 68                         ret = iterator(assoc_array_ptr_to_leaf(ptr),
 69                                        iterator_data);
 70                         if (ret)
 71                                 return ret;
 72                 }
 73         }
 74 
 75         /* The second pass attends to all the metadata pointers.  If we follow
 76          * one of these we may find that we don't come back here, but rather go
 77          * back to a replacement node with the leaves in a different layout.
 78          *
 79          * We are guaranteed to make progress, however, as the slot number for
 80          * a particular portion of the key space cannot change - and we
 81          * continue at the back pointer + 1.
 82          */
 83         if (!(has_meta & ASSOC_ARRAY_PTR_META_TYPE))
 84                 goto finished_node;
 85         slot = 0;
 86 
 87 continue_node:
 88         node = assoc_array_ptr_to_node(cursor);
 89         smp_read_barrier_depends();
 90 
 91         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
 92                 ptr = ACCESS_ONCE(node->slots[slot]);
 93                 if (assoc_array_ptr_is_meta(ptr)) {
 94                         cursor = ptr;
 95                         goto begin_node;
 96                 }
 97         }
 98 
 99 finished_node:
100         /* Move up to the parent (may need to skip back over a shortcut) */
101         parent = ACCESS_ONCE(node->back_pointer);
102         slot = node->parent_slot;
103         if (parent == stop)
104                 return 0;
105 
106         if (assoc_array_ptr_is_shortcut(parent)) {
107                 shortcut = assoc_array_ptr_to_shortcut(parent);
108                 smp_read_barrier_depends();
109                 cursor = parent;
110                 parent = ACCESS_ONCE(shortcut->back_pointer);
111                 slot = shortcut->parent_slot;
112                 if (parent == stop)
113                         return 0;
114         }
115 
116         /* Ascend to next slot in parent node */
117         cursor = parent;
118         slot++;
119         goto continue_node;
120 }
121 
122 /**
123  * assoc_array_iterate - Pass all objects in the array to a callback
124  * @array: The array to iterate over.
125  * @iterator: The callback function.
126  * @iterator_data: Private data for the callback function.
127  *
128  * Iterate over all the objects in an associative array.  Each one will be
129  * presented to the iterator function.
130  *
131  * If the array is being modified concurrently with the iteration then it is
132  * possible that some objects in the array will be passed to the iterator
133  * callback more than once - though every object should be passed at least
134  * once.  If this is undesirable then the caller must lock against modification
135  * for the duration of this function.
136  *
137  * The function will return 0 if no objects were in the array or else it will
138  * return the result of the last iterator function called.  Iteration stops
139  * immediately if any call to the iteration function results in a non-zero
140  * return.
141  *
142  * The caller should hold the RCU read lock or better if concurrent
143  * modification is possible.
144  */
145 int assoc_array_iterate(const struct assoc_array *array,
146                         int (*iterator)(const void *object,
147                                         void *iterator_data),
148                         void *iterator_data)
149 {
150         struct assoc_array_ptr *root = ACCESS_ONCE(array->root);
151 
152         if (!root)
153                 return 0;
154         return assoc_array_subtree_iterate(root, NULL, iterator, iterator_data);
155 }
156 
157 enum assoc_array_walk_status {
158         assoc_array_walk_tree_empty,
159         assoc_array_walk_found_terminal_node,
160         assoc_array_walk_found_wrong_shortcut,
161 };
162 
163 struct assoc_array_walk_result {
164         struct {
165                 struct assoc_array_node *node;  /* Node in which leaf might be found */
166                 int             level;
167                 int             slot;
168         } terminal_node;
169         struct {
170                 struct assoc_array_shortcut *shortcut;
171                 int             level;
172                 int             sc_level;
173                 unsigned long   sc_segments;
174                 unsigned long   dissimilarity;
175         } wrong_shortcut;
176 };
177 
178 /*
179  * Navigate through the internal tree looking for the closest node to the key.
180  */
181 static enum assoc_array_walk_status
182 assoc_array_walk(const struct assoc_array *array,
183                  const struct assoc_array_ops *ops,
184                  const void *index_key,
185                  struct assoc_array_walk_result *result)
186 {
187         struct assoc_array_shortcut *shortcut;
188         struct assoc_array_node *node;
189         struct assoc_array_ptr *cursor, *ptr;
190         unsigned long sc_segments, dissimilarity;
191         unsigned long segments;
192         int level, sc_level, next_sc_level;
193         int slot;
194 
195         pr_devel("-->%s()\n", __func__);
196 
197         cursor = ACCESS_ONCE(array->root);
198         if (!cursor)
199                 return assoc_array_walk_tree_empty;
200 
201         level = 0;
202 
203         /* Use segments from the key for the new leaf to navigate through the
204          * internal tree, skipping through nodes and shortcuts that are on
205          * route to the destination.  Eventually we'll come to a slot that is
206          * either empty or contains a leaf at which point we've found a node in
207          * which the leaf we're looking for might be found or into which it
208          * should be inserted.
209          */
210 jumped:
211         segments = ops->get_key_chunk(index_key, level);
212         pr_devel("segments[%d]: %lx\n", level, segments);
213 
214         if (assoc_array_ptr_is_shortcut(cursor))
215                 goto follow_shortcut;
216 
217 consider_node:
218         node = assoc_array_ptr_to_node(cursor);
219         smp_read_barrier_depends();
220 
221         slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
222         slot &= ASSOC_ARRAY_FAN_MASK;
223         ptr = ACCESS_ONCE(node->slots[slot]);
224 
225         pr_devel("consider slot %x [ix=%d type=%lu]\n",
226                  slot, level, (unsigned long)ptr & 3);
227 
228         if (!assoc_array_ptr_is_meta(ptr)) {
229                 /* The node doesn't have a node/shortcut pointer in the slot
230                  * corresponding to the index key that we have to follow.
231                  */
232                 result->terminal_node.node = node;
233                 result->terminal_node.level = level;
234                 result->terminal_node.slot = slot;
235                 pr_devel("<--%s() = terminal_node\n", __func__);
236                 return assoc_array_walk_found_terminal_node;
237         }
238 
239         if (assoc_array_ptr_is_node(ptr)) {
240                 /* There is a pointer to a node in the slot corresponding to
241                  * this index key segment, so we need to follow it.
242                  */
243                 cursor = ptr;
244                 level += ASSOC_ARRAY_LEVEL_STEP;
245                 if ((level & ASSOC_ARRAY_KEY_CHUNK_MASK) != 0)
246                         goto consider_node;
247                 goto jumped;
248         }
249 
250         /* There is a shortcut in the slot corresponding to the index key
251          * segment.  We follow the shortcut if its partial index key matches
252          * this leaf's.  Otherwise we need to split the shortcut.
253          */
254         cursor = ptr;
255 follow_shortcut:
256         shortcut = assoc_array_ptr_to_shortcut(cursor);
257         smp_read_barrier_depends();
258         pr_devel("shortcut to %d\n", shortcut->skip_to_level);
259         sc_level = level + ASSOC_ARRAY_LEVEL_STEP;
260         BUG_ON(sc_level > shortcut->skip_to_level);
261 
262         do {
263                 /* Check the leaf against the shortcut's index key a word at a
264                  * time, trimming the final word (the shortcut stores the index
265                  * key completely from the root to the shortcut's target).
266                  */
267                 if ((sc_level & ASSOC_ARRAY_KEY_CHUNK_MASK) == 0)
268                         segments = ops->get_key_chunk(index_key, sc_level);
269 
270                 sc_segments = shortcut->index_key[sc_level >> ASSOC_ARRAY_KEY_CHUNK_SHIFT];
271                 dissimilarity = segments ^ sc_segments;
272 
273                 if (round_up(sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE) > shortcut->skip_to_level) {
274                         /* Trim segments that are beyond the shortcut */
275                         int shift = shortcut->skip_to_level & ASSOC_ARRAY_KEY_CHUNK_MASK;
276                         dissimilarity &= ~(ULONG_MAX << shift);
277                         next_sc_level = shortcut->skip_to_level;
278                 } else {
279                         next_sc_level = sc_level + ASSOC_ARRAY_KEY_CHUNK_SIZE;
280                         next_sc_level = round_down(next_sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
281                 }
282 
283                 if (dissimilarity != 0) {
284                         /* This shortcut points elsewhere */
285                         result->wrong_shortcut.shortcut = shortcut;
286                         result->wrong_shortcut.level = level;
287                         result->wrong_shortcut.sc_level = sc_level;
288                         result->wrong_shortcut.sc_segments = sc_segments;
289                         result->wrong_shortcut.dissimilarity = dissimilarity;
290                         return assoc_array_walk_found_wrong_shortcut;
291                 }
292 
293                 sc_level = next_sc_level;
294         } while (sc_level < shortcut->skip_to_level);
295 
296         /* The shortcut matches the leaf's index to this point. */
297         cursor = ACCESS_ONCE(shortcut->next_node);
298         if (((level ^ sc_level) & ~ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) {
299                 level = sc_level;
300                 goto jumped;
301         } else {
302                 level = sc_level;
303                 goto consider_node;
304         }
305 }
306 
307 /**
308  * assoc_array_find - Find an object by index key
309  * @array: The associative array to search.
310  * @ops: The operations to use.
311  * @index_key: The key to the object.
312  *
313  * Find an object in an associative array by walking through the internal tree
314  * to the node that should contain the object and then searching the leaves
315  * there.  NULL is returned if the requested object was not found in the array.
316  *
317  * The caller must hold the RCU read lock or better.
318  */
319 void *assoc_array_find(const struct assoc_array *array,
320                        const struct assoc_array_ops *ops,
321                        const void *index_key)
322 {
323         struct assoc_array_walk_result result;
324         const struct assoc_array_node *node;
325         const struct assoc_array_ptr *ptr;
326         const void *leaf;
327         int slot;
328 
329         if (assoc_array_walk(array, ops, index_key, &result) !=
330             assoc_array_walk_found_terminal_node)
331                 return NULL;
332 
333         node = result.terminal_node.node;
334         smp_read_barrier_depends();
335 
336         /* If the target key is available to us, it's has to be pointed to by
337          * the terminal node.
338          */
339         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
340                 ptr = ACCESS_ONCE(node->slots[slot]);
341                 if (ptr && assoc_array_ptr_is_leaf(ptr)) {
342                         /* We need a barrier between the read of the pointer
343                          * and dereferencing the pointer - but only if we are
344                          * actually going to dereference it.
345                          */
346                         leaf = assoc_array_ptr_to_leaf(ptr);
347                         smp_read_barrier_depends();
348                         if (ops->compare_object(leaf, index_key))
349                                 return (void *)leaf;
350                 }
351         }
352 
353         return NULL;
354 }
355 
356 /*
357  * Destructively iterate over an associative array.  The caller must prevent
358  * other simultaneous accesses.
359  */
360 static void assoc_array_destroy_subtree(struct assoc_array_ptr *root,
361                                         const struct assoc_array_ops *ops)
362 {
363         struct assoc_array_shortcut *shortcut;
364         struct assoc_array_node *node;
365         struct assoc_array_ptr *cursor, *parent = NULL;
366         int slot = -1;
367 
368         pr_devel("-->%s()\n", __func__);
369 
370         cursor = root;
371         if (!cursor) {
372                 pr_devel("empty\n");
373                 return;
374         }
375 
376 move_to_meta:
377         if (assoc_array_ptr_is_shortcut(cursor)) {
378                 /* Descend through a shortcut */
379                 pr_devel("[%d] shortcut\n", slot);
380                 BUG_ON(!assoc_array_ptr_is_shortcut(cursor));
381                 shortcut = assoc_array_ptr_to_shortcut(cursor);
382                 BUG_ON(shortcut->back_pointer != parent);
383                 BUG_ON(slot != -1 && shortcut->parent_slot != slot);
384                 parent = cursor;
385                 cursor = shortcut->next_node;
386                 slot = -1;
387                 BUG_ON(!assoc_array_ptr_is_node(cursor));
388         }
389 
390         pr_devel("[%d] node\n", slot);
391         node = assoc_array_ptr_to_node(cursor);
392         BUG_ON(node->back_pointer != parent);
393         BUG_ON(slot != -1 && node->parent_slot != slot);
394         slot = 0;
395 
396 continue_node:
397         pr_devel("Node %p [back=%p]\n", node, node->back_pointer);
398         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
399                 struct assoc_array_ptr *ptr = node->slots[slot];
400                 if (!ptr)
401                         continue;
402                 if (assoc_array_ptr_is_meta(ptr)) {
403                         parent = cursor;
404                         cursor = ptr;
405                         goto move_to_meta;
406                 }
407 
408                 if (ops) {
409                         pr_devel("[%d] free leaf\n", slot);
410                         ops->free_object(assoc_array_ptr_to_leaf(ptr));
411                 }
412         }
413 
414         parent = node->back_pointer;
415         slot = node->parent_slot;
416         pr_devel("free node\n");
417         kfree(node);
418         if (!parent)
419                 return; /* Done */
420 
421         /* Move back up to the parent (may need to free a shortcut on
422          * the way up) */
423         if (assoc_array_ptr_is_shortcut(parent)) {
424                 shortcut = assoc_array_ptr_to_shortcut(parent);
425                 BUG_ON(shortcut->next_node != cursor);
426                 cursor = parent;
427                 parent = shortcut->back_pointer;
428                 slot = shortcut->parent_slot;
429                 pr_devel("free shortcut\n");
430                 kfree(shortcut);
431                 if (!parent)
432                         return;
433 
434                 BUG_ON(!assoc_array_ptr_is_node(parent));
435         }
436 
437         /* Ascend to next slot in parent node */
438         pr_devel("ascend to %p[%d]\n", parent, slot);
439         cursor = parent;
440         node = assoc_array_ptr_to_node(cursor);
441         slot++;
442         goto continue_node;
443 }
444 
445 /**
446  * assoc_array_destroy - Destroy an associative array
447  * @array: The array to destroy.
448  * @ops: The operations to use.
449  *
450  * Discard all metadata and free all objects in an associative array.  The
451  * array will be empty and ready to use again upon completion.  This function
452  * cannot fail.
453  *
454  * The caller must prevent all other accesses whilst this takes place as no
455  * attempt is made to adjust pointers gracefully to permit RCU readlock-holding
456  * accesses to continue.  On the other hand, no memory allocation is required.
457  */
458 void assoc_array_destroy(struct assoc_array *array,
459                          const struct assoc_array_ops *ops)
460 {
461         assoc_array_destroy_subtree(array->root, ops);
462         array->root = NULL;
463 }
464 
465 /*
466  * Handle insertion into an empty tree.
467  */
468 static bool assoc_array_insert_in_empty_tree(struct assoc_array_edit *edit)
469 {
470         struct assoc_array_node *new_n0;
471 
472         pr_devel("-->%s()\n", __func__);
473 
474         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
475         if (!new_n0)
476                 return false;
477 
478         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
479         edit->leaf_p = &new_n0->slots[0];
480         edit->adjust_count_on = new_n0;
481         edit->set[0].ptr = &edit->array->root;
482         edit->set[0].to = assoc_array_node_to_ptr(new_n0);
483 
484         pr_devel("<--%s() = ok [no root]\n", __func__);
485         return true;
486 }
487 
488 /*
489  * Handle insertion into a terminal node.
490  */
491 static bool assoc_array_insert_into_terminal_node(struct assoc_array_edit *edit,
492                                                   const struct assoc_array_ops *ops,
493                                                   const void *index_key,
494                                                   struct assoc_array_walk_result *result)
495 {
496         struct assoc_array_shortcut *shortcut, *new_s0;
497         struct assoc_array_node *node, *new_n0, *new_n1, *side;
498         struct assoc_array_ptr *ptr;
499         unsigned long dissimilarity, base_seg, blank;
500         size_t keylen;
501         bool have_meta;
502         int level, diff;
503         int slot, next_slot, free_slot, i, j;
504 
505         node    = result->terminal_node.node;
506         level   = result->terminal_node.level;
507         edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = result->terminal_node.slot;
508 
509         pr_devel("-->%s()\n", __func__);
510 
511         /* We arrived at a node which doesn't have an onward node or shortcut
512          * pointer that we have to follow.  This means that (a) the leaf we
513          * want must go here (either by insertion or replacement) or (b) we
514          * need to split this node and insert in one of the fragments.
515          */
516         free_slot = -1;
517 
518         /* Firstly, we have to check the leaves in this node to see if there's
519          * a matching one we should replace in place.
520          */
521         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
522                 ptr = node->slots[i];
523                 if (!ptr) {
524                         free_slot = i;
525                         continue;
526                 }
527                 if (ops->compare_object(assoc_array_ptr_to_leaf(ptr), index_key)) {
528                         pr_devel("replace in slot %d\n", i);
529                         edit->leaf_p = &node->slots[i];
530                         edit->dead_leaf = node->slots[i];
531                         pr_devel("<--%s() = ok [replace]\n", __func__);
532                         return true;
533                 }
534         }
535 
536         /* If there is a free slot in this node then we can just insert the
537          * leaf here.
538          */
539         if (free_slot >= 0) {
540                 pr_devel("insert in free slot %d\n", free_slot);
541                 edit->leaf_p = &node->slots[free_slot];
542                 edit->adjust_count_on = node;
543                 pr_devel("<--%s() = ok [insert]\n", __func__);
544                 return true;
545         }
546 
547         /* The node has no spare slots - so we're either going to have to split
548          * it or insert another node before it.
549          *
550          * Whatever, we're going to need at least two new nodes - so allocate
551          * those now.  We may also need a new shortcut, but we deal with that
552          * when we need it.
553          */
554         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
555         if (!new_n0)
556                 return false;
557         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
558         new_n1 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
559         if (!new_n1)
560                 return false;
561         edit->new_meta[1] = assoc_array_node_to_ptr(new_n1);
562 
563         /* We need to find out how similar the leaves are. */
564         pr_devel("no spare slots\n");
565         have_meta = false;
566         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
567                 ptr = node->slots[i];
568                 if (assoc_array_ptr_is_meta(ptr)) {
569                         edit->segment_cache[i] = 0xff;
570                         have_meta = true;
571                         continue;
572                 }
573                 base_seg = ops->get_object_key_chunk(
574                         assoc_array_ptr_to_leaf(ptr), level);
575                 base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
576                 edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
577         }
578 
579         if (have_meta) {
580                 pr_devel("have meta\n");
581                 goto split_node;
582         }
583 
584         /* The node contains only leaves */
585         dissimilarity = 0;
586         base_seg = edit->segment_cache[0];
587         for (i = 1; i < ASSOC_ARRAY_FAN_OUT; i++)
588                 dissimilarity |= edit->segment_cache[i] ^ base_seg;
589 
590         pr_devel("only leaves; dissimilarity=%lx\n", dissimilarity);
591 
592         if ((dissimilarity & ASSOC_ARRAY_FAN_MASK) == 0) {
593                 /* The old leaves all cluster in the same slot.  We will need
594                  * to insert a shortcut if the new node wants to cluster with them.
595                  */
596                 if ((edit->segment_cache[ASSOC_ARRAY_FAN_OUT] ^ base_seg) == 0)
597                         goto all_leaves_cluster_together;
598 
599                 /* Otherwise we can just insert a new node ahead of the old
600                  * one.
601                  */
602                 goto present_leaves_cluster_but_not_new_leaf;
603         }
604 
605 split_node:
606         pr_devel("split node\n");
607 
608         /* We need to split the current node; we know that the node doesn't
609          * simply contain a full set of leaves that cluster together (it
610          * contains meta pointers and/or non-clustering leaves).
611          *
612          * We need to expel at least two leaves out of a set consisting of the
613          * leaves in the node and the new leaf.
614          *
615          * We need a new node (n0) to replace the current one and a new node to
616          * take the expelled nodes (n1).
617          */
618         edit->set[0].to = assoc_array_node_to_ptr(new_n0);
619         new_n0->back_pointer = node->back_pointer;
620         new_n0->parent_slot = node->parent_slot;
621         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
622         new_n1->parent_slot = -1; /* Need to calculate this */
623 
624 do_split_node:
625         pr_devel("do_split_node\n");
626 
627         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
628         new_n1->nr_leaves_on_branch = 0;
629 
630         /* Begin by finding two matching leaves.  There have to be at least two
631          * that match - even if there are meta pointers - because any leaf that
632          * would match a slot with a meta pointer in it must be somewhere
633          * behind that meta pointer and cannot be here.  Further, given N
634          * remaining leaf slots, we now have N+1 leaves to go in them.
635          */
636         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
637                 slot = edit->segment_cache[i];
638                 if (slot != 0xff)
639                         for (j = i + 1; j < ASSOC_ARRAY_FAN_OUT + 1; j++)
640                                 if (edit->segment_cache[j] == slot)
641                                         goto found_slot_for_multiple_occupancy;
642         }
643 found_slot_for_multiple_occupancy:
644         pr_devel("same slot: %x %x [%02x]\n", i, j, slot);
645         BUG_ON(i >= ASSOC_ARRAY_FAN_OUT);
646         BUG_ON(j >= ASSOC_ARRAY_FAN_OUT + 1);
647         BUG_ON(slot >= ASSOC_ARRAY_FAN_OUT);
648 
649         new_n1->parent_slot = slot;
650 
651         /* Metadata pointers cannot change slot */
652         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
653                 if (assoc_array_ptr_is_meta(node->slots[i]))
654                         new_n0->slots[i] = node->slots[i];
655                 else
656                         new_n0->slots[i] = NULL;
657         BUG_ON(new_n0->slots[slot] != NULL);
658         new_n0->slots[slot] = assoc_array_node_to_ptr(new_n1);
659 
660         /* Filter the leaf pointers between the new nodes */
661         free_slot = -1;
662         next_slot = 0;
663         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
664                 if (assoc_array_ptr_is_meta(node->slots[i]))
665                         continue;
666                 if (edit->segment_cache[i] == slot) {
667                         new_n1->slots[next_slot++] = node->slots[i];
668                         new_n1->nr_leaves_on_branch++;
669                 } else {
670                         do {
671                                 free_slot++;
672                         } while (new_n0->slots[free_slot] != NULL);
673                         new_n0->slots[free_slot] = node->slots[i];
674                 }
675         }
676 
677         pr_devel("filtered: f=%x n=%x\n", free_slot, next_slot);
678 
679         if (edit->segment_cache[ASSOC_ARRAY_FAN_OUT] != slot) {
680                 do {
681                         free_slot++;
682                 } while (new_n0->slots[free_slot] != NULL);
683                 edit->leaf_p = &new_n0->slots[free_slot];
684                 edit->adjust_count_on = new_n0;
685         } else {
686                 edit->leaf_p = &new_n1->slots[next_slot++];
687                 edit->adjust_count_on = new_n1;
688         }
689 
690         BUG_ON(next_slot <= 1);
691 
692         edit->set_backpointers_to = assoc_array_node_to_ptr(new_n0);
693         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
694                 if (edit->segment_cache[i] == 0xff) {
695                         ptr = node->slots[i];
696                         BUG_ON(assoc_array_ptr_is_leaf(ptr));
697                         if (assoc_array_ptr_is_node(ptr)) {
698                                 side = assoc_array_ptr_to_node(ptr);
699                                 edit->set_backpointers[i] = &side->back_pointer;
700                         } else {
701                                 shortcut = assoc_array_ptr_to_shortcut(ptr);
702                                 edit->set_backpointers[i] = &shortcut->back_pointer;
703                         }
704                 }
705         }
706 
707         ptr = node->back_pointer;
708         if (!ptr)
709                 edit->set[0].ptr = &edit->array->root;
710         else if (assoc_array_ptr_is_node(ptr))
711                 edit->set[0].ptr = &assoc_array_ptr_to_node(ptr)->slots[node->parent_slot];
712         else
713                 edit->set[0].ptr = &assoc_array_ptr_to_shortcut(ptr)->next_node;
714         edit->excised_meta[0] = assoc_array_node_to_ptr(node);
715         pr_devel("<--%s() = ok [split node]\n", __func__);
716         return true;
717 
718 present_leaves_cluster_but_not_new_leaf:
719         /* All the old leaves cluster in the same slot, but the new leaf wants
720          * to go into a different slot, so we create a new node to hold the new
721          * leaf and a pointer to a new node holding all the old leaves.
722          */
723         pr_devel("present leaves cluster but not new leaf\n");
724 
725         new_n0->back_pointer = node->back_pointer;
726         new_n0->parent_slot = node->parent_slot;
727         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
728         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
729         new_n1->parent_slot = edit->segment_cache[0];
730         new_n1->nr_leaves_on_branch = node->nr_leaves_on_branch;
731         edit->adjust_count_on = new_n0;
732 
733         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
734                 new_n1->slots[i] = node->slots[i];
735 
736         new_n0->slots[edit->segment_cache[0]] = assoc_array_node_to_ptr(new_n0);
737         edit->leaf_p = &new_n0->slots[edit->segment_cache[ASSOC_ARRAY_FAN_OUT]];
738 
739         edit->set[0].ptr = &assoc_array_ptr_to_node(node->back_pointer)->slots[node->parent_slot];
740         edit->set[0].to = assoc_array_node_to_ptr(new_n0);
741         edit->excised_meta[0] = assoc_array_node_to_ptr(node);
742         pr_devel("<--%s() = ok [insert node before]\n", __func__);
743         return true;
744 
745 all_leaves_cluster_together:
746         /* All the leaves, new and old, want to cluster together in this node
747          * in the same slot, so we have to replace this node with a shortcut to
748          * skip over the identical parts of the key and then place a pair of
749          * nodes, one inside the other, at the end of the shortcut and
750          * distribute the keys between them.
751          *
752          * Firstly we need to work out where the leaves start diverging as a
753          * bit position into their keys so that we know how big the shortcut
754          * needs to be.
755          *
756          * We only need to make a single pass of N of the N+1 leaves because if
757          * any keys differ between themselves at bit X then at least one of
758          * them must also differ with the base key at bit X or before.
759          */
760         pr_devel("all leaves cluster together\n");
761         diff = INT_MAX;
762         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
763                 int x = ops->diff_objects(assoc_array_ptr_to_leaf(node->slots[i]),
764                                           index_key);
765                 if (x < diff) {
766                         BUG_ON(x < 0);
767                         diff = x;
768                 }
769         }
770         BUG_ON(diff == INT_MAX);
771         BUG_ON(diff < level + ASSOC_ARRAY_LEVEL_STEP);
772 
773         keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
774         keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
775 
776         new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
777                          keylen * sizeof(unsigned long), GFP_KERNEL);
778         if (!new_s0)
779                 return false;
780         edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s0);
781 
782         edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
783         new_s0->back_pointer = node->back_pointer;
784         new_s0->parent_slot = node->parent_slot;
785         new_s0->next_node = assoc_array_node_to_ptr(new_n0);
786         new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
787         new_n0->parent_slot = 0;
788         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
789         new_n1->parent_slot = -1; /* Need to calculate this */
790 
791         new_s0->skip_to_level = level = diff & ~ASSOC_ARRAY_LEVEL_STEP_MASK;
792         pr_devel("skip_to_level = %d [diff %d]\n", level, diff);
793         BUG_ON(level <= 0);
794 
795         for (i = 0; i < keylen; i++)
796                 new_s0->index_key[i] =
797                         ops->get_key_chunk(index_key, i * ASSOC_ARRAY_KEY_CHUNK_SIZE);
798 
799         blank = ULONG_MAX << (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
800         pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, level, blank);
801         new_s0->index_key[keylen - 1] &= ~blank;
802 
803         /* This now reduces to a node splitting exercise for which we'll need
804          * to regenerate the disparity table.
805          */
806         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
807                 ptr = node->slots[i];
808                 base_seg = ops->get_object_key_chunk(assoc_array_ptr_to_leaf(ptr),
809                                                      level);
810                 base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
811                 edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
812         }
813 
814         base_seg = ops->get_key_chunk(index_key, level);
815         base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
816         edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = base_seg & ASSOC_ARRAY_FAN_MASK;
817         goto do_split_node;
818 }
819 
820 /*
821  * Handle insertion into the middle of a shortcut.
822  */
823 static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
824                                             const struct assoc_array_ops *ops,
825                                             struct assoc_array_walk_result *result)
826 {
827         struct assoc_array_shortcut *shortcut, *new_s0, *new_s1;
828         struct assoc_array_node *node, *new_n0, *side;
829         unsigned long sc_segments, dissimilarity, blank;
830         size_t keylen;
831         int level, sc_level, diff;
832         int sc_slot;
833 
834         shortcut        = result->wrong_shortcut.shortcut;
835         level           = result->wrong_shortcut.level;
836         sc_level        = result->wrong_shortcut.sc_level;
837         sc_segments     = result->wrong_shortcut.sc_segments;
838         dissimilarity   = result->wrong_shortcut.dissimilarity;
839 
840         pr_devel("-->%s(ix=%d dis=%lx scix=%d)\n",
841                  __func__, level, dissimilarity, sc_level);
842 
843         /* We need to split a shortcut and insert a node between the two
844          * pieces.  Zero-length pieces will be dispensed with entirely.
845          *
846          * First of all, we need to find out in which level the first
847          * difference was.
848          */
849         diff = __ffs(dissimilarity);
850         diff &= ~ASSOC_ARRAY_LEVEL_STEP_MASK;
851         diff += sc_level & ~ASSOC_ARRAY_KEY_CHUNK_MASK;
852         pr_devel("diff=%d\n", diff);
853 
854         if (!shortcut->back_pointer) {
855                 edit->set[0].ptr = &edit->array->root;
856         } else if (assoc_array_ptr_is_node(shortcut->back_pointer)) {
857                 node = assoc_array_ptr_to_node(shortcut->back_pointer);
858                 edit->set[0].ptr = &node->slots[shortcut->parent_slot];
859         } else {
860                 BUG();
861         }
862 
863         edit->excised_meta[0] = assoc_array_shortcut_to_ptr(shortcut);
864 
865         /* Create a new node now since we're going to need it anyway */
866         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
867         if (!new_n0)
868                 return false;
869         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
870         edit->adjust_count_on = new_n0;
871 
872         /* Insert a new shortcut before the new node if this segment isn't of
873          * zero length - otherwise we just connect the new node directly to the
874          * parent.
875          */
876         level += ASSOC_ARRAY_LEVEL_STEP;
877         if (diff > level) {
878                 pr_devel("pre-shortcut %d...%d\n", level, diff);
879                 keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
880                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
881 
882                 new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
883                                  keylen * sizeof(unsigned long), GFP_KERNEL);
884                 if (!new_s0)
885                         return false;
886                 edit->new_meta[1] = assoc_array_shortcut_to_ptr(new_s0);
887                 edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
888                 new_s0->back_pointer = shortcut->back_pointer;
889                 new_s0->parent_slot = shortcut->parent_slot;
890                 new_s0->next_node = assoc_array_node_to_ptr(new_n0);
891                 new_s0->skip_to_level = diff;
892 
893                 new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
894                 new_n0->parent_slot = 0;
895 
896                 memcpy(new_s0->index_key, shortcut->index_key,
897                        keylen * sizeof(unsigned long));
898 
899                 blank = ULONG_MAX << (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
900                 pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, diff, blank);
901                 new_s0->index_key[keylen - 1] &= ~blank;
902         } else {
903                 pr_devel("no pre-shortcut\n");
904                 edit->set[0].to = assoc_array_node_to_ptr(new_n0);
905                 new_n0->back_pointer = shortcut->back_pointer;
906                 new_n0->parent_slot = shortcut->parent_slot;
907         }
908 
909         side = assoc_array_ptr_to_node(shortcut->next_node);
910         new_n0->nr_leaves_on_branch = side->nr_leaves_on_branch;
911 
912         /* We need to know which slot in the new node is going to take a
913          * metadata pointer.
914          */
915         sc_slot = sc_segments >> (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
916         sc_slot &= ASSOC_ARRAY_FAN_MASK;
917 
918         pr_devel("new slot %lx >> %d -> %d\n",
919                  sc_segments, diff & ASSOC_ARRAY_KEY_CHUNK_MASK, sc_slot);
920 
921         /* Determine whether we need to follow the new node with a replacement
922          * for the current shortcut.  We could in theory reuse the current
923          * shortcut if its parent slot number doesn't change - but that's a
924          * 1-in-16 chance so not worth expending the code upon.
925          */
926         level = diff + ASSOC_ARRAY_LEVEL_STEP;
927         if (level < shortcut->skip_to_level) {
928                 pr_devel("post-shortcut %d...%d\n", level, shortcut->skip_to_level);
929                 keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
930                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
931 
932                 new_s1 = kzalloc(sizeof(struct assoc_array_shortcut) +
933                                  keylen * sizeof(unsigned long), GFP_KERNEL);
934                 if (!new_s1)
935                         return false;
936                 edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s1);
937 
938                 new_s1->back_pointer = assoc_array_node_to_ptr(new_n0);
939                 new_s1->parent_slot = sc_slot;
940                 new_s1->next_node = shortcut->next_node;
941                 new_s1->skip_to_level = shortcut->skip_to_level;
942 
943                 new_n0->slots[sc_slot] = assoc_array_shortcut_to_ptr(new_s1);
944 
945                 memcpy(new_s1->index_key, shortcut->index_key,
946                        keylen * sizeof(unsigned long));
947 
948                 edit->set[1].ptr = &side->back_pointer;
949                 edit->set[1].to = assoc_array_shortcut_to_ptr(new_s1);
950         } else {
951                 pr_devel("no post-shortcut\n");
952 
953                 /* We don't have to replace the pointed-to node as long as we
954                  * use memory barriers to make sure the parent slot number is
955                  * changed before the back pointer (the parent slot number is
956                  * irrelevant to the old parent shortcut).
957                  */
958                 new_n0->slots[sc_slot] = shortcut->next_node;
959                 edit->set_parent_slot[0].p = &side->parent_slot;
960                 edit->set_parent_slot[0].to = sc_slot;
961                 edit->set[1].ptr = &side->back_pointer;
962                 edit->set[1].to = assoc_array_node_to_ptr(new_n0);
963         }
964 
965         /* Install the new leaf in a spare slot in the new node. */
966         if (sc_slot == 0)
967                 edit->leaf_p = &new_n0->slots[1];
968         else
969                 edit->leaf_p = &new_n0->slots[0];
970 
971         pr_devel("<--%s() = ok [split shortcut]\n", __func__);
972         return edit;
973 }
974 
975 /**
976  * assoc_array_insert - Script insertion of an object into an associative array
977  * @array: The array to insert into.
978  * @ops: The operations to use.
979  * @index_key: The key to insert at.
980  * @object: The object to insert.
981  *
982  * Precalculate and preallocate a script for the insertion or replacement of an
983  * object in an associative array.  This results in an edit script that can
984  * either be applied or cancelled.
985  *
986  * The function returns a pointer to an edit script or -ENOMEM.
987  *
988  * The caller should lock against other modifications and must continue to hold
989  * the lock until assoc_array_apply_edit() has been called.
990  *
991  * Accesses to the tree may take place concurrently with this function,
992  * provided they hold the RCU read lock.
993  */
994 struct assoc_array_edit *assoc_array_insert(struct assoc_array *array,
995                                             const struct assoc_array_ops *ops,
996                                             const void *index_key,
997                                             void *object)
998 {
999         struct assoc_array_walk_result result;
1000         struct assoc_array_edit *edit;
1001 
1002         pr_devel("-->%s()\n", __func__);
1003 
1004         /* The leaf pointer we're given must not have the bottom bit set as we
1005          * use those for type-marking the pointer.  NULL pointers are also not
1006          * allowed as they indicate an empty slot but we have to allow them
1007          * here as they can be updated later.
1008          */
1009         BUG_ON(assoc_array_ptr_is_meta(object));
1010 
1011         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1012         if (!edit)
1013                 return ERR_PTR(-ENOMEM);
1014         edit->array = array;
1015         edit->ops = ops;
1016         edit->leaf = assoc_array_leaf_to_ptr(object);
1017         edit->adjust_count_by = 1;
1018 
1019         switch (assoc_array_walk(array, ops, index_key, &result)) {
1020         case assoc_array_walk_tree_empty:
1021                 /* Allocate a root node if there isn't one yet */
1022                 if (!assoc_array_insert_in_empty_tree(edit))
1023                         goto enomem;
1024                 return edit;
1025 
1026         case assoc_array_walk_found_terminal_node:
1027                 /* We found a node that doesn't have a node/shortcut pointer in
1028                  * the slot corresponding to the index key that we have to
1029                  * follow.
1030                  */
1031                 if (!assoc_array_insert_into_terminal_node(edit, ops, index_key,
1032                                                            &result))
1033                         goto enomem;
1034                 return edit;
1035 
1036         case assoc_array_walk_found_wrong_shortcut:
1037                 /* We found a shortcut that didn't match our key in a slot we
1038                  * needed to follow.
1039                  */
1040                 if (!assoc_array_insert_mid_shortcut(edit, ops, &result))
1041                         goto enomem;
1042                 return edit;
1043         }
1044 
1045 enomem:
1046         /* Clean up after an out of memory error */
1047         pr_devel("enomem\n");
1048         assoc_array_cancel_edit(edit);
1049         return ERR_PTR(-ENOMEM);
1050 }
1051 
1052 /**
1053  * assoc_array_insert_set_object - Set the new object pointer in an edit script
1054  * @edit: The edit script to modify.
1055  * @object: The object pointer to set.
1056  *
1057  * Change the object to be inserted in an edit script.  The object pointed to
1058  * by the old object is not freed.  This must be done prior to applying the
1059  * script.
1060  */
1061 void assoc_array_insert_set_object(struct assoc_array_edit *edit, void *object)
1062 {
1063         BUG_ON(!object);
1064         edit->leaf = assoc_array_leaf_to_ptr(object);
1065 }
1066 
1067 struct assoc_array_delete_collapse_context {
1068         struct assoc_array_node *node;
1069         const void              *skip_leaf;
1070         int                     slot;
1071 };
1072 
1073 /*
1074  * Subtree collapse to node iterator.
1075  */
1076 static int assoc_array_delete_collapse_iterator(const void *leaf,
1077                                                 void *iterator_data)
1078 {
1079         struct assoc_array_delete_collapse_context *collapse = iterator_data;
1080 
1081         if (leaf == collapse->skip_leaf)
1082                 return 0;
1083 
1084         BUG_ON(collapse->slot >= ASSOC_ARRAY_FAN_OUT);
1085 
1086         collapse->node->slots[collapse->slot++] = assoc_array_leaf_to_ptr(leaf);
1087         return 0;
1088 }
1089 
1090 /**
1091  * assoc_array_delete - Script deletion of an object from an associative array
1092  * @array: The array to search.
1093  * @ops: The operations to use.
1094  * @index_key: The key to the object.
1095  *
1096  * Precalculate and preallocate a script for the deletion of an object from an
1097  * associative array.  This results in an edit script that can either be
1098  * applied or cancelled.
1099  *
1100  * The function returns a pointer to an edit script if the object was found,
1101  * NULL if the object was not found or -ENOMEM.
1102  *
1103  * The caller should lock against other modifications and must continue to hold
1104  * the lock until assoc_array_apply_edit() has been called.
1105  *
1106  * Accesses to the tree may take place concurrently with this function,
1107  * provided they hold the RCU read lock.
1108  */
1109 struct assoc_array_edit *assoc_array_delete(struct assoc_array *array,
1110                                             const struct assoc_array_ops *ops,
1111                                             const void *index_key)
1112 {
1113         struct assoc_array_delete_collapse_context collapse;
1114         struct assoc_array_walk_result result;
1115         struct assoc_array_node *node, *new_n0;
1116         struct assoc_array_edit *edit;
1117         struct assoc_array_ptr *ptr;
1118         bool has_meta;
1119         int slot, i;
1120 
1121         pr_devel("-->%s()\n", __func__);
1122 
1123         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1124         if (!edit)
1125                 return ERR_PTR(-ENOMEM);
1126         edit->array = array;
1127         edit->ops = ops;
1128         edit->adjust_count_by = -1;
1129 
1130         switch (assoc_array_walk(array, ops, index_key, &result)) {
1131         case assoc_array_walk_found_terminal_node:
1132                 /* We found a node that should contain the leaf we've been
1133                  * asked to remove - *if* it's in the tree.
1134                  */
1135                 pr_devel("terminal_node\n");
1136                 node = result.terminal_node.node;
1137 
1138                 for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1139                         ptr = node->slots[slot];
1140                         if (ptr &&
1141                             assoc_array_ptr_is_leaf(ptr) &&
1142                             ops->compare_object(assoc_array_ptr_to_leaf(ptr),
1143                                                 index_key))
1144                                 goto found_leaf;
1145                 }
1146         case assoc_array_walk_tree_empty:
1147         case assoc_array_walk_found_wrong_shortcut:
1148         default:
1149                 assoc_array_cancel_edit(edit);
1150                 pr_devel("not found\n");
1151                 return NULL;
1152         }
1153 
1154 found_leaf:
1155         BUG_ON(array->nr_leaves_on_tree <= 0);
1156 
1157         /* In the simplest form of deletion we just clear the slot and release
1158          * the leaf after a suitable interval.
1159          */
1160         edit->dead_leaf = node->slots[slot];
1161         edit->set[0].ptr = &node->slots[slot];
1162         edit->set[0].to = NULL;
1163         edit->adjust_count_on = node;
1164 
1165         /* If that concludes erasure of the last leaf, then delete the entire
1166          * internal array.
1167          */
1168         if (array->nr_leaves_on_tree == 1) {
1169                 edit->set[1].ptr = &array->root;
1170                 edit->set[1].to = NULL;
1171                 edit->adjust_count_on = NULL;
1172                 edit->excised_subtree = array->root;
1173                 pr_devel("all gone\n");
1174                 return edit;
1175         }
1176 
1177         /* However, we'd also like to clear up some metadata blocks if we
1178          * possibly can.
1179          *
1180          * We go for a simple algorithm of: if this node has FAN_OUT or fewer
1181          * leaves in it, then attempt to collapse it - and attempt to
1182          * recursively collapse up the tree.
1183          *
1184          * We could also try and collapse in partially filled subtrees to take
1185          * up space in this node.
1186          */
1187         if (node->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1188                 struct assoc_array_node *parent, *grandparent;
1189                 struct assoc_array_ptr *ptr;
1190 
1191                 /* First of all, we need to know if this node has metadata so
1192                  * that we don't try collapsing if all the leaves are already
1193                  * here.
1194                  */
1195                 has_meta = false;
1196                 for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1197                         ptr = node->slots[i];
1198                         if (assoc_array_ptr_is_meta(ptr)) {
1199                                 has_meta = true;
1200                                 break;
1201                         }
1202                 }
1203 
1204                 pr_devel("leaves: %ld [m=%d]\n",
1205                          node->nr_leaves_on_branch - 1, has_meta);
1206 
1207                 /* Look further up the tree to see if we can collapse this node
1208                  * into a more proximal node too.
1209                  */
1210                 parent = node;
1211         collapse_up:
1212                 pr_devel("collapse subtree: %ld\n", parent->nr_leaves_on_branch);
1213 
1214                 ptr = parent->back_pointer;
1215                 if (!ptr)
1216                         goto do_collapse;
1217                 if (assoc_array_ptr_is_shortcut(ptr)) {
1218                         struct assoc_array_shortcut *s = assoc_array_ptr_to_shortcut(ptr);
1219                         ptr = s->back_pointer;
1220                         if (!ptr)
1221                                 goto do_collapse;
1222                 }
1223 
1224                 grandparent = assoc_array_ptr_to_node(ptr);
1225                 if (grandparent->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1226                         parent = grandparent;
1227                         goto collapse_up;
1228                 }
1229 
1230         do_collapse:
1231                 /* There's no point collapsing if the original node has no meta
1232                  * pointers to discard and if we didn't merge into one of that
1233                  * node's ancestry.
1234                  */
1235                 if (has_meta || parent != node) {
1236                         node = parent;
1237 
1238                         /* Create a new node to collapse into */
1239                         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1240                         if (!new_n0)
1241                                 goto enomem;
1242                         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
1243 
1244                         new_n0->back_pointer = node->back_pointer;
1245                         new_n0->parent_slot = node->parent_slot;
1246                         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
1247                         edit->adjust_count_on = new_n0;
1248 
1249                         collapse.node = new_n0;
1250                         collapse.skip_leaf = assoc_array_ptr_to_leaf(edit->dead_leaf);
1251                         collapse.slot = 0;
1252                         assoc_array_subtree_iterate(assoc_array_node_to_ptr(node),
1253                                                     node->back_pointer,
1254                                                     assoc_array_delete_collapse_iterator,
1255                                                     &collapse);
1256                         pr_devel("collapsed %d,%lu\n", collapse.slot, new_n0->nr_leaves_on_branch);
1257                         BUG_ON(collapse.slot != new_n0->nr_leaves_on_branch - 1);
1258 
1259                         if (!node->back_pointer) {
1260                                 edit->set[1].ptr = &array->root;
1261                         } else if (assoc_array_ptr_is_leaf(node->back_pointer)) {
1262                                 BUG();
1263                         } else if (assoc_array_ptr_is_node(node->back_pointer)) {
1264                                 struct assoc_array_node *p =
1265                                         assoc_array_ptr_to_node(node->back_pointer);
1266                                 edit->set[1].ptr = &p->slots[node->parent_slot];
1267                         } else if (assoc_array_ptr_is_shortcut(node->back_pointer)) {
1268                                 struct assoc_array_shortcut *s =
1269                                         assoc_array_ptr_to_shortcut(node->back_pointer);
1270                                 edit->set[1].ptr = &s->next_node;
1271                         }
1272                         edit->set[1].to = assoc_array_node_to_ptr(new_n0);
1273                         edit->excised_subtree = assoc_array_node_to_ptr(node);
1274                 }
1275         }
1276 
1277         return edit;
1278 
1279 enomem:
1280         /* Clean up after an out of memory error */
1281         pr_devel("enomem\n");
1282         assoc_array_cancel_edit(edit);
1283         return ERR_PTR(-ENOMEM);
1284 }
1285 
1286 /**
1287  * assoc_array_clear - Script deletion of all objects from an associative array
1288  * @array: The array to clear.
1289  * @ops: The operations to use.
1290  *
1291  * Precalculate and preallocate a script for the deletion of all the objects
1292  * from an associative array.  This results in an edit script that can either
1293  * be applied or cancelled.
1294  *
1295  * The function returns a pointer to an edit script if there are objects to be
1296  * deleted, NULL if there are no objects in the array or -ENOMEM.
1297  *
1298  * The caller should lock against other modifications and must continue to hold
1299  * the lock until assoc_array_apply_edit() has been called.
1300  *
1301  * Accesses to the tree may take place concurrently with this function,
1302  * provided they hold the RCU read lock.
1303  */
1304 struct assoc_array_edit *assoc_array_clear(struct assoc_array *array,
1305                                            const struct assoc_array_ops *ops)
1306 {
1307         struct assoc_array_edit *edit;
1308 
1309         pr_devel("-->%s()\n", __func__);
1310 
1311         if (!array->root)
1312                 return NULL;
1313 
1314         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1315         if (!edit)
1316                 return ERR_PTR(-ENOMEM);
1317         edit->array = array;
1318         edit->ops = ops;
1319         edit->set[1].ptr = &array->root;
1320         edit->set[1].to = NULL;
1321         edit->excised_subtree = array->root;
1322         edit->ops_for_excised_subtree = ops;
1323         pr_devel("all gone\n");
1324         return edit;
1325 }
1326 
1327 /*
1328  * Handle the deferred destruction after an applied edit.
1329  */
1330 static void assoc_array_rcu_cleanup(struct rcu_head *head)
1331 {
1332         struct assoc_array_edit *edit =
1333                 container_of(head, struct assoc_array_edit, rcu);
1334         int i;
1335 
1336         pr_devel("-->%s()\n", __func__);
1337 
1338         if (edit->dead_leaf)
1339                 edit->ops->free_object(assoc_array_ptr_to_leaf(edit->dead_leaf));
1340         for (i = 0; i < ARRAY_SIZE(edit->excised_meta); i++)
1341                 if (edit->excised_meta[i])
1342                         kfree(assoc_array_ptr_to_node(edit->excised_meta[i]));
1343 
1344         if (edit->excised_subtree) {
1345                 BUG_ON(assoc_array_ptr_is_leaf(edit->excised_subtree));
1346                 if (assoc_array_ptr_is_node(edit->excised_subtree)) {
1347                         struct assoc_array_node *n =
1348                                 assoc_array_ptr_to_node(edit->excised_subtree);
1349                         n->back_pointer = NULL;
1350                 } else {
1351                         struct assoc_array_shortcut *s =
1352                                 assoc_array_ptr_to_shortcut(edit->excised_subtree);
1353                         s->back_pointer = NULL;
1354                 }
1355                 assoc_array_destroy_subtree(edit->excised_subtree,
1356                                             edit->ops_for_excised_subtree);
1357         }
1358 
1359         kfree(edit);
1360 }
1361 
1362 /**
1363  * assoc_array_apply_edit - Apply an edit script to an associative array
1364  * @edit: The script to apply.
1365  *
1366  * Apply an edit script to an associative array to effect an insertion,
1367  * deletion or clearance.  As the edit script includes preallocated memory,
1368  * this is guaranteed not to fail.
1369  *
1370  * The edit script, dead objects and dead metadata will be scheduled for
1371  * destruction after an RCU grace period to permit those doing read-only
1372  * accesses on the array to continue to do so under the RCU read lock whilst
1373  * the edit is taking place.
1374  */
1375 void assoc_array_apply_edit(struct assoc_array_edit *edit)
1376 {
1377         struct assoc_array_shortcut *shortcut;
1378         struct assoc_array_node *node;
1379         struct assoc_array_ptr *ptr;
1380         int i;
1381 
1382         pr_devel("-->%s()\n", __func__);
1383 
1384         smp_wmb();
1385         if (edit->leaf_p)
1386                 *edit->leaf_p = edit->leaf;
1387 
1388         smp_wmb();
1389         for (i = 0; i < ARRAY_SIZE(edit->set_parent_slot); i++)
1390                 if (edit->set_parent_slot[i].p)
1391                         *edit->set_parent_slot[i].p = edit->set_parent_slot[i].to;
1392 
1393         smp_wmb();
1394         for (i = 0; i < ARRAY_SIZE(edit->set_backpointers); i++)
1395                 if (edit->set_backpointers[i])
1396                         *edit->set_backpointers[i] = edit->set_backpointers_to;
1397 
1398         smp_wmb();
1399         for (i = 0; i < ARRAY_SIZE(edit->set); i++)
1400                 if (edit->set[i].ptr)
1401                         *edit->set[i].ptr = edit->set[i].to;
1402 
1403         if (edit->array->root == NULL) {
1404                 edit->array->nr_leaves_on_tree = 0;
1405         } else if (edit->adjust_count_on) {
1406                 node = edit->adjust_count_on;
1407                 for (;;) {
1408                         node->nr_leaves_on_branch += edit->adjust_count_by;
1409 
1410                         ptr = node->back_pointer;
1411                         if (!ptr)
1412                                 break;
1413                         if (assoc_array_ptr_is_shortcut(ptr)) {
1414                                 shortcut = assoc_array_ptr_to_shortcut(ptr);
1415                                 ptr = shortcut->back_pointer;
1416                                 if (!ptr)
1417                                         break;
1418                         }
1419                         BUG_ON(!assoc_array_ptr_is_node(ptr));
1420                         node = assoc_array_ptr_to_node(ptr);
1421                 }
1422 
1423                 edit->array->nr_leaves_on_tree += edit->adjust_count_by;
1424         }
1425 
1426         call_rcu(&edit->rcu, assoc_array_rcu_cleanup);
1427 }
1428 
1429 /**
1430  * assoc_array_cancel_edit - Discard an edit script.
1431  * @edit: The script to discard.
1432  *
1433  * Free an edit script and all the preallocated data it holds without making
1434  * any changes to the associative array it was intended for.
1435  *
1436  * NOTE!  In the case of an insertion script, this does _not_ release the leaf
1437  * that was to be inserted.  That is left to the caller.
1438  */
1439 void assoc_array_cancel_edit(struct assoc_array_edit *edit)
1440 {
1441         struct assoc_array_ptr *ptr;
1442         int i;
1443 
1444         pr_devel("-->%s()\n", __func__);
1445 
1446         /* Clean up after an out of memory error */
1447         for (i = 0; i < ARRAY_SIZE(edit->new_meta); i++) {
1448                 ptr = edit->new_meta[i];
1449                 if (ptr) {
1450                         if (assoc_array_ptr_is_node(ptr))
1451                                 kfree(assoc_array_ptr_to_node(ptr));
1452                         else
1453                                 kfree(assoc_array_ptr_to_shortcut(ptr));
1454                 }
1455         }
1456         kfree(edit);
1457 }
1458 
1459 /**
1460  * assoc_array_gc - Garbage collect an associative array.
1461  * @array: The array to clean.
1462  * @ops: The operations to use.
1463  * @iterator: A callback function to pass judgement on each object.
1464  * @iterator_data: Private data for the callback function.
1465  *
1466  * Collect garbage from an associative array and pack down the internal tree to
1467  * save memory.
1468  *
1469  * The iterator function is asked to pass judgement upon each object in the
1470  * array.  If it returns false, the object is discard and if it returns true,
1471  * the object is kept.  If it returns true, it must increment the object's
1472  * usage count (or whatever it needs to do to retain it) before returning.
1473  *
1474  * This function returns 0 if successful or -ENOMEM if out of memory.  In the
1475  * latter case, the array is not changed.
1476  *
1477  * The caller should lock against other modifications and must continue to hold
1478  * the lock until assoc_array_apply_edit() has been called.
1479  *
1480  * Accesses to the tree may take place concurrently with this function,
1481  * provided they hold the RCU read lock.
1482  */
1483 int assoc_array_gc(struct assoc_array *array,
1484                    const struct assoc_array_ops *ops,
1485                    bool (*iterator)(void *object, void *iterator_data),
1486                    void *iterator_data)
1487 {
1488         struct assoc_array_shortcut *shortcut, *new_s;
1489         struct assoc_array_node *node, *new_n;
1490         struct assoc_array_edit *edit;
1491         struct assoc_array_ptr *cursor, *ptr;
1492         struct assoc_array_ptr *new_root, *new_parent, **new_ptr_pp;
1493         unsigned long nr_leaves_on_tree;
1494         int keylen, slot, nr_free, next_slot, i;
1495 
1496         pr_devel("-->%s()\n", __func__);
1497 
1498         if (!array->root)
1499                 return 0;
1500 
1501         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1502         if (!edit)
1503                 return -ENOMEM;
1504         edit->array = array;
1505         edit->ops = ops;
1506         edit->ops_for_excised_subtree = ops;
1507         edit->set[0].ptr = &array->root;
1508         edit->excised_subtree = array->root;
1509 
1510         new_root = new_parent = NULL;
1511         new_ptr_pp = &new_root;
1512         cursor = array->root;
1513 
1514 descend:
1515         /* If this point is a shortcut, then we need to duplicate it and
1516          * advance the target cursor.
1517          */
1518         if (assoc_array_ptr_is_shortcut(cursor)) {
1519                 shortcut = assoc_array_ptr_to_shortcut(cursor);
1520                 keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
1521                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
1522                 new_s = kmalloc(sizeof(struct assoc_array_shortcut) +
1523                                 keylen * sizeof(unsigned long), GFP_KERNEL);
1524                 if (!new_s)
1525                         goto enomem;
1526                 pr_devel("dup shortcut %p -> %p\n", shortcut, new_s);
1527                 memcpy(new_s, shortcut, (sizeof(struct assoc_array_shortcut) +
1528                                          keylen * sizeof(unsigned long)));
1529                 new_s->back_pointer = new_parent;
1530                 new_s->parent_slot = shortcut->parent_slot;
1531                 *new_ptr_pp = new_parent = assoc_array_shortcut_to_ptr(new_s);
1532                 new_ptr_pp = &new_s->next_node;
1533                 cursor = shortcut->next_node;
1534         }
1535 
1536         /* Duplicate the node at this position */
1537         node = assoc_array_ptr_to_node(cursor);
1538         new_n = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1539         if (!new_n)
1540                 goto enomem;
1541         pr_devel("dup node %p -> %p\n", node, new_n);
1542         new_n->back_pointer = new_parent;
1543         new_n->parent_slot = node->parent_slot;
1544         *new_ptr_pp = new_parent = assoc_array_node_to_ptr(new_n);
1545         new_ptr_pp = NULL;
1546         slot = 0;
1547 
1548 continue_node:
1549         /* Filter across any leaves and gc any subtrees */
1550         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1551                 ptr = node->slots[slot];
1552                 if (!ptr)
1553                         continue;
1554 
1555                 if (assoc_array_ptr_is_leaf(ptr)) {
1556                         if (iterator(assoc_array_ptr_to_leaf(ptr),
1557                                      iterator_data))
1558                                 /* The iterator will have done any reference
1559                                  * counting on the object for us.
1560                                  */
1561                                 new_n->slots[slot] = ptr;
1562                         continue;
1563                 }
1564 
1565                 new_ptr_pp = &new_n->slots[slot];
1566                 cursor = ptr;
1567                 goto descend;
1568         }
1569 
1570         pr_devel("-- compress node %p --\n", new_n);
1571 
1572         /* Count up the number of empty slots in this node and work out the
1573          * subtree leaf count.
1574          */
1575         new_n->nr_leaves_on_branch = 0;
1576         nr_free = 0;
1577         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1578                 ptr = new_n->slots[slot];
1579                 if (!ptr)
1580                         nr_free++;
1581                 else if (assoc_array_ptr_is_leaf(ptr))
1582                         new_n->nr_leaves_on_branch++;
1583         }
1584         pr_devel("free=%d, leaves=%lu\n", nr_free, new_n->nr_leaves_on_branch);
1585 
1586         /* See what we can fold in */
1587         next_slot = 0;
1588         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1589                 struct assoc_array_shortcut *s;
1590                 struct assoc_array_node *child;
1591 
1592                 ptr = new_n->slots[slot];
1593                 if (!ptr || assoc_array_ptr_is_leaf(ptr))
1594                         continue;
1595 
1596                 s = NULL;
1597                 if (assoc_array_ptr_is_shortcut(ptr)) {
1598                         s = assoc_array_ptr_to_shortcut(ptr);
1599                         ptr = s->next_node;
1600                 }
1601 
1602                 child = assoc_array_ptr_to_node(ptr);
1603                 new_n->nr_leaves_on_branch += child->nr_leaves_on_branch;
1604 
1605                 if (child->nr_leaves_on_branch <= nr_free + 1) {
1606                         /* Fold the child node into this one */
1607                         pr_devel("[%d] fold node %lu/%d [nx %d]\n",
1608                                  slot, child->nr_leaves_on_branch, nr_free + 1,
1609                                  next_slot);
1610 
1611                         /* We would already have reaped an intervening shortcut
1612                          * on the way back up the tree.
1613                          */
1614                         BUG_ON(s);
1615 
1616                         new_n->slots[slot] = NULL;
1617                         nr_free++;
1618                         if (slot < next_slot)
1619                                 next_slot = slot;
1620                         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1621                                 struct assoc_array_ptr *p = child->slots[i];
1622                                 if (!p)
1623                                         continue;
1624                                 BUG_ON(assoc_array_ptr_is_meta(p));
1625                                 while (new_n->slots[next_slot])
1626                                         next_slot++;
1627                                 BUG_ON(next_slot >= ASSOC_ARRAY_FAN_OUT);
1628                                 new_n->slots[next_slot++] = p;
1629                                 nr_free--;
1630                         }
1631                         kfree(child);
1632                 } else {
1633                         pr_devel("[%d] retain node %lu/%d [nx %d]\n",
1634                                  slot, child->nr_leaves_on_branch, nr_free + 1,
1635                                  next_slot);
1636                 }
1637         }
1638 
1639         pr_devel("after: %lu\n", new_n->nr_leaves_on_branch);
1640 
1641         nr_leaves_on_tree = new_n->nr_leaves_on_branch;
1642 
1643         /* Excise this node if it is singly occupied by a shortcut */
1644         if (nr_free == ASSOC_ARRAY_FAN_OUT - 1) {
1645                 for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++)
1646                         if ((ptr = new_n->slots[slot]))
1647                                 break;
1648 
1649                 if (assoc_array_ptr_is_meta(ptr) &&
1650                     assoc_array_ptr_is_shortcut(ptr)) {
1651                         pr_devel("excise node %p with 1 shortcut\n", new_n);
1652                         new_s = assoc_array_ptr_to_shortcut(ptr);
1653                         new_parent = new_n->back_pointer;
1654                         slot = new_n->parent_slot;
1655                         kfree(new_n);
1656                         if (!new_parent) {
1657                                 new_s->back_pointer = NULL;
1658                                 new_s->parent_slot = 0;
1659                                 new_root = ptr;
1660                                 goto gc_complete;
1661                         }
1662 
1663                         if (assoc_array_ptr_is_shortcut(new_parent)) {
1664                                 /* We can discard any preceding shortcut also */
1665                                 struct assoc_array_shortcut *s =
1666                                         assoc_array_ptr_to_shortcut(new_parent);
1667 
1668                                 pr_devel("excise preceding shortcut\n");
1669 
1670                                 new_parent = new_s->back_pointer = s->back_pointer;
1671                                 slot = new_s->parent_slot = s->parent_slot;
1672                                 kfree(s);
1673                                 if (!new_parent) {
1674                                         new_s->back_pointer = NULL;
1675                                         new_s->parent_slot = 0;
1676                                         new_root = ptr;
1677                                         goto gc_complete;
1678                                 }
1679                         }
1680 
1681                         new_s->back_pointer = new_parent;
1682                         new_s->parent_slot = slot;
1683                         new_n = assoc_array_ptr_to_node(new_parent);
1684                         new_n->slots[slot] = ptr;
1685                         goto ascend_old_tree;
1686                 }
1687         }
1688 
1689         /* Excise any shortcuts we might encounter that point to nodes that
1690          * only contain leaves.
1691          */
1692         ptr = new_n->back_pointer;
1693         if (!ptr)
1694                 goto gc_complete;
1695 
1696         if (assoc_array_ptr_is_shortcut(ptr)) {
1697                 new_s = assoc_array_ptr_to_shortcut(ptr);
1698                 new_parent = new_s->back_pointer;
1699                 slot = new_s->parent_slot;
1700 
1701                 if (new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) {
1702                         struct assoc_array_node *n;
1703 
1704                         pr_devel("excise shortcut\n");
1705                         new_n->back_pointer = new_parent;
1706                         new_n->parent_slot = slot;
1707                         kfree(new_s);
1708                         if (!new_parent) {
1709                                 new_root = assoc_array_node_to_ptr(new_n);
1710                                 goto gc_complete;
1711                         }
1712 
1713                         n = assoc_array_ptr_to_node(new_parent);
1714                         n->slots[slot] = assoc_array_node_to_ptr(new_n);
1715                 }
1716         } else {
1717                 new_parent = ptr;
1718         }
1719         new_n = assoc_array_ptr_to_node(new_parent);
1720 
1721 ascend_old_tree:
1722         ptr = node->back_pointer;
1723         if (assoc_array_ptr_is_shortcut(ptr)) {
1724                 shortcut = assoc_array_ptr_to_shortcut(ptr);
1725                 slot = shortcut->parent_slot;
1726                 cursor = shortcut->back_pointer;
1727                 if (!cursor)
1728                         goto gc_complete;
1729         } else {
1730                 slot = node->parent_slot;
1731                 cursor = ptr;
1732         }
1733         BUG_ON(!cursor);
1734         node = assoc_array_ptr_to_node(cursor);
1735         slot++;
1736         goto continue_node;
1737 
1738 gc_complete:
1739         edit->set[0].to = new_root;
1740         assoc_array_apply_edit(edit);
1741         array->nr_leaves_on_tree = nr_leaves_on_tree;
1742         return 0;
1743 
1744 enomem:
1745         pr_devel("enomem\n");
1746         assoc_array_destroy_subtree(new_root, edit->ops);
1747         kfree(edit);
1748         return -ENOMEM;
1749 }
1750 

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