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Linux/lib/assoc_array.c

  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 (assoc_array_ptr_is_leaf(ptr) &&
528                     ops->compare_object(assoc_array_ptr_to_leaf(ptr),
529                                         index_key)) {
530                         pr_devel("replace in slot %d\n", i);
531                         edit->leaf_p = &node->slots[i];
532                         edit->dead_leaf = node->slots[i];
533                         pr_devel("<--%s() = ok [replace]\n", __func__);
534                         return true;
535                 }
536         }
537 
538         /* If there is a free slot in this node then we can just insert the
539          * leaf here.
540          */
541         if (free_slot >= 0) {
542                 pr_devel("insert in free slot %d\n", free_slot);
543                 edit->leaf_p = &node->slots[free_slot];
544                 edit->adjust_count_on = node;
545                 pr_devel("<--%s() = ok [insert]\n", __func__);
546                 return true;
547         }
548 
549         /* The node has no spare slots - so we're either going to have to split
550          * it or insert another node before it.
551          *
552          * Whatever, we're going to need at least two new nodes - so allocate
553          * those now.  We may also need a new shortcut, but we deal with that
554          * when we need it.
555          */
556         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
557         if (!new_n0)
558                 return false;
559         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
560         new_n1 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
561         if (!new_n1)
562                 return false;
563         edit->new_meta[1] = assoc_array_node_to_ptr(new_n1);
564 
565         /* We need to find out how similar the leaves are. */
566         pr_devel("no spare slots\n");
567         have_meta = false;
568         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
569                 ptr = node->slots[i];
570                 if (assoc_array_ptr_is_meta(ptr)) {
571                         edit->segment_cache[i] = 0xff;
572                         have_meta = true;
573                         continue;
574                 }
575                 base_seg = ops->get_object_key_chunk(
576                         assoc_array_ptr_to_leaf(ptr), level);
577                 base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
578                 edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
579         }
580 
581         if (have_meta) {
582                 pr_devel("have meta\n");
583                 goto split_node;
584         }
585 
586         /* The node contains only leaves */
587         dissimilarity = 0;
588         base_seg = edit->segment_cache[0];
589         for (i = 1; i < ASSOC_ARRAY_FAN_OUT; i++)
590                 dissimilarity |= edit->segment_cache[i] ^ base_seg;
591 
592         pr_devel("only leaves; dissimilarity=%lx\n", dissimilarity);
593 
594         if ((dissimilarity & ASSOC_ARRAY_FAN_MASK) == 0) {
595                 /* The old leaves all cluster in the same slot.  We will need
596                  * to insert a shortcut if the new node wants to cluster with them.
597                  */
598                 if ((edit->segment_cache[ASSOC_ARRAY_FAN_OUT] ^ base_seg) == 0)
599                         goto all_leaves_cluster_together;
600 
601                 /* Otherwise we can just insert a new node ahead of the old
602                  * one.
603                  */
604                 goto present_leaves_cluster_but_not_new_leaf;
605         }
606 
607 split_node:
608         pr_devel("split node\n");
609 
610         /* We need to split the current node; we know that the node doesn't
611          * simply contain a full set of leaves that cluster together (it
612          * contains meta pointers and/or non-clustering leaves).
613          *
614          * We need to expel at least two leaves out of a set consisting of the
615          * leaves in the node and the new leaf.
616          *
617          * We need a new node (n0) to replace the current one and a new node to
618          * take the expelled nodes (n1).
619          */
620         edit->set[0].to = assoc_array_node_to_ptr(new_n0);
621         new_n0->back_pointer = node->back_pointer;
622         new_n0->parent_slot = node->parent_slot;
623         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
624         new_n1->parent_slot = -1; /* Need to calculate this */
625 
626 do_split_node:
627         pr_devel("do_split_node\n");
628 
629         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
630         new_n1->nr_leaves_on_branch = 0;
631 
632         /* Begin by finding two matching leaves.  There have to be at least two
633          * that match - even if there are meta pointers - because any leaf that
634          * would match a slot with a meta pointer in it must be somewhere
635          * behind that meta pointer and cannot be here.  Further, given N
636          * remaining leaf slots, we now have N+1 leaves to go in them.
637          */
638         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
639                 slot = edit->segment_cache[i];
640                 if (slot != 0xff)
641                         for (j = i + 1; j < ASSOC_ARRAY_FAN_OUT + 1; j++)
642                                 if (edit->segment_cache[j] == slot)
643                                         goto found_slot_for_multiple_occupancy;
644         }
645 found_slot_for_multiple_occupancy:
646         pr_devel("same slot: %x %x [%02x]\n", i, j, slot);
647         BUG_ON(i >= ASSOC_ARRAY_FAN_OUT);
648         BUG_ON(j >= ASSOC_ARRAY_FAN_OUT + 1);
649         BUG_ON(slot >= ASSOC_ARRAY_FAN_OUT);
650 
651         new_n1->parent_slot = slot;
652 
653         /* Metadata pointers cannot change slot */
654         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
655                 if (assoc_array_ptr_is_meta(node->slots[i]))
656                         new_n0->slots[i] = node->slots[i];
657                 else
658                         new_n0->slots[i] = NULL;
659         BUG_ON(new_n0->slots[slot] != NULL);
660         new_n0->slots[slot] = assoc_array_node_to_ptr(new_n1);
661 
662         /* Filter the leaf pointers between the new nodes */
663         free_slot = -1;
664         next_slot = 0;
665         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
666                 if (assoc_array_ptr_is_meta(node->slots[i]))
667                         continue;
668                 if (edit->segment_cache[i] == slot) {
669                         new_n1->slots[next_slot++] = node->slots[i];
670                         new_n1->nr_leaves_on_branch++;
671                 } else {
672                         do {
673                                 free_slot++;
674                         } while (new_n0->slots[free_slot] != NULL);
675                         new_n0->slots[free_slot] = node->slots[i];
676                 }
677         }
678 
679         pr_devel("filtered: f=%x n=%x\n", free_slot, next_slot);
680 
681         if (edit->segment_cache[ASSOC_ARRAY_FAN_OUT] != slot) {
682                 do {
683                         free_slot++;
684                 } while (new_n0->slots[free_slot] != NULL);
685                 edit->leaf_p = &new_n0->slots[free_slot];
686                 edit->adjust_count_on = new_n0;
687         } else {
688                 edit->leaf_p = &new_n1->slots[next_slot++];
689                 edit->adjust_count_on = new_n1;
690         }
691 
692         BUG_ON(next_slot <= 1);
693 
694         edit->set_backpointers_to = assoc_array_node_to_ptr(new_n0);
695         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
696                 if (edit->segment_cache[i] == 0xff) {
697                         ptr = node->slots[i];
698                         BUG_ON(assoc_array_ptr_is_leaf(ptr));
699                         if (assoc_array_ptr_is_node(ptr)) {
700                                 side = assoc_array_ptr_to_node(ptr);
701                                 edit->set_backpointers[i] = &side->back_pointer;
702                         } else {
703                                 shortcut = assoc_array_ptr_to_shortcut(ptr);
704                                 edit->set_backpointers[i] = &shortcut->back_pointer;
705                         }
706                 }
707         }
708 
709         ptr = node->back_pointer;
710         if (!ptr)
711                 edit->set[0].ptr = &edit->array->root;
712         else if (assoc_array_ptr_is_node(ptr))
713                 edit->set[0].ptr = &assoc_array_ptr_to_node(ptr)->slots[node->parent_slot];
714         else
715                 edit->set[0].ptr = &assoc_array_ptr_to_shortcut(ptr)->next_node;
716         edit->excised_meta[0] = assoc_array_node_to_ptr(node);
717         pr_devel("<--%s() = ok [split node]\n", __func__);
718         return true;
719 
720 present_leaves_cluster_but_not_new_leaf:
721         /* All the old leaves cluster in the same slot, but the new leaf wants
722          * to go into a different slot, so we create a new node to hold the new
723          * leaf and a pointer to a new node holding all the old leaves.
724          */
725         pr_devel("present leaves cluster but not new leaf\n");
726 
727         new_n0->back_pointer = node->back_pointer;
728         new_n0->parent_slot = node->parent_slot;
729         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
730         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
731         new_n1->parent_slot = edit->segment_cache[0];
732         new_n1->nr_leaves_on_branch = node->nr_leaves_on_branch;
733         edit->adjust_count_on = new_n0;
734 
735         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
736                 new_n1->slots[i] = node->slots[i];
737 
738         new_n0->slots[edit->segment_cache[0]] = assoc_array_node_to_ptr(new_n0);
739         edit->leaf_p = &new_n0->slots[edit->segment_cache[ASSOC_ARRAY_FAN_OUT]];
740 
741         edit->set[0].ptr = &assoc_array_ptr_to_node(node->back_pointer)->slots[node->parent_slot];
742         edit->set[0].to = assoc_array_node_to_ptr(new_n0);
743         edit->excised_meta[0] = assoc_array_node_to_ptr(node);
744         pr_devel("<--%s() = ok [insert node before]\n", __func__);
745         return true;
746 
747 all_leaves_cluster_together:
748         /* All the leaves, new and old, want to cluster together in this node
749          * in the same slot, so we have to replace this node with a shortcut to
750          * skip over the identical parts of the key and then place a pair of
751          * nodes, one inside the other, at the end of the shortcut and
752          * distribute the keys between them.
753          *
754          * Firstly we need to work out where the leaves start diverging as a
755          * bit position into their keys so that we know how big the shortcut
756          * needs to be.
757          *
758          * We only need to make a single pass of N of the N+1 leaves because if
759          * any keys differ between themselves at bit X then at least one of
760          * them must also differ with the base key at bit X or before.
761          */
762         pr_devel("all leaves cluster together\n");
763         diff = INT_MAX;
764         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
765                 int x = ops->diff_objects(assoc_array_ptr_to_leaf(node->slots[i]),
766                                           index_key);
767                 if (x < diff) {
768                         BUG_ON(x < 0);
769                         diff = x;
770                 }
771         }
772         BUG_ON(diff == INT_MAX);
773         BUG_ON(diff < level + ASSOC_ARRAY_LEVEL_STEP);
774 
775         keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
776         keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
777 
778         new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
779                          keylen * sizeof(unsigned long), GFP_KERNEL);
780         if (!new_s0)
781                 return false;
782         edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s0);
783 
784         edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
785         new_s0->back_pointer = node->back_pointer;
786         new_s0->parent_slot = node->parent_slot;
787         new_s0->next_node = assoc_array_node_to_ptr(new_n0);
788         new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
789         new_n0->parent_slot = 0;
790         new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
791         new_n1->parent_slot = -1; /* Need to calculate this */
792 
793         new_s0->skip_to_level = level = diff & ~ASSOC_ARRAY_LEVEL_STEP_MASK;
794         pr_devel("skip_to_level = %d [diff %d]\n", level, diff);
795         BUG_ON(level <= 0);
796 
797         for (i = 0; i < keylen; i++)
798                 new_s0->index_key[i] =
799                         ops->get_key_chunk(index_key, i * ASSOC_ARRAY_KEY_CHUNK_SIZE);
800 
801         blank = ULONG_MAX << (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
802         pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, level, blank);
803         new_s0->index_key[keylen - 1] &= ~blank;
804 
805         /* This now reduces to a node splitting exercise for which we'll need
806          * to regenerate the disparity table.
807          */
808         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
809                 ptr = node->slots[i];
810                 base_seg = ops->get_object_key_chunk(assoc_array_ptr_to_leaf(ptr),
811                                                      level);
812                 base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
813                 edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
814         }
815 
816         base_seg = ops->get_key_chunk(index_key, level);
817         base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
818         edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = base_seg & ASSOC_ARRAY_FAN_MASK;
819         goto do_split_node;
820 }
821 
822 /*
823  * Handle insertion into the middle of a shortcut.
824  */
825 static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
826                                             const struct assoc_array_ops *ops,
827                                             struct assoc_array_walk_result *result)
828 {
829         struct assoc_array_shortcut *shortcut, *new_s0, *new_s1;
830         struct assoc_array_node *node, *new_n0, *side;
831         unsigned long sc_segments, dissimilarity, blank;
832         size_t keylen;
833         int level, sc_level, diff;
834         int sc_slot;
835 
836         shortcut        = result->wrong_shortcut.shortcut;
837         level           = result->wrong_shortcut.level;
838         sc_level        = result->wrong_shortcut.sc_level;
839         sc_segments     = result->wrong_shortcut.sc_segments;
840         dissimilarity   = result->wrong_shortcut.dissimilarity;
841 
842         pr_devel("-->%s(ix=%d dis=%lx scix=%d)\n",
843                  __func__, level, dissimilarity, sc_level);
844 
845         /* We need to split a shortcut and insert a node between the two
846          * pieces.  Zero-length pieces will be dispensed with entirely.
847          *
848          * First of all, we need to find out in which level the first
849          * difference was.
850          */
851         diff = __ffs(dissimilarity);
852         diff &= ~ASSOC_ARRAY_LEVEL_STEP_MASK;
853         diff += sc_level & ~ASSOC_ARRAY_KEY_CHUNK_MASK;
854         pr_devel("diff=%d\n", diff);
855 
856         if (!shortcut->back_pointer) {
857                 edit->set[0].ptr = &edit->array->root;
858         } else if (assoc_array_ptr_is_node(shortcut->back_pointer)) {
859                 node = assoc_array_ptr_to_node(shortcut->back_pointer);
860                 edit->set[0].ptr = &node->slots[shortcut->parent_slot];
861         } else {
862                 BUG();
863         }
864 
865         edit->excised_meta[0] = assoc_array_shortcut_to_ptr(shortcut);
866 
867         /* Create a new node now since we're going to need it anyway */
868         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
869         if (!new_n0)
870                 return false;
871         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
872         edit->adjust_count_on = new_n0;
873 
874         /* Insert a new shortcut before the new node if this segment isn't of
875          * zero length - otherwise we just connect the new node directly to the
876          * parent.
877          */
878         level += ASSOC_ARRAY_LEVEL_STEP;
879         if (diff > level) {
880                 pr_devel("pre-shortcut %d...%d\n", level, diff);
881                 keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
882                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
883 
884                 new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
885                                  keylen * sizeof(unsigned long), GFP_KERNEL);
886                 if (!new_s0)
887                         return false;
888                 edit->new_meta[1] = assoc_array_shortcut_to_ptr(new_s0);
889                 edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0);
890                 new_s0->back_pointer = shortcut->back_pointer;
891                 new_s0->parent_slot = shortcut->parent_slot;
892                 new_s0->next_node = assoc_array_node_to_ptr(new_n0);
893                 new_s0->skip_to_level = diff;
894 
895                 new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0);
896                 new_n0->parent_slot = 0;
897 
898                 memcpy(new_s0->index_key, shortcut->index_key,
899                        keylen * sizeof(unsigned long));
900 
901                 blank = ULONG_MAX << (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
902                 pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, diff, blank);
903                 new_s0->index_key[keylen - 1] &= ~blank;
904         } else {
905                 pr_devel("no pre-shortcut\n");
906                 edit->set[0].to = assoc_array_node_to_ptr(new_n0);
907                 new_n0->back_pointer = shortcut->back_pointer;
908                 new_n0->parent_slot = shortcut->parent_slot;
909         }
910 
911         side = assoc_array_ptr_to_node(shortcut->next_node);
912         new_n0->nr_leaves_on_branch = side->nr_leaves_on_branch;
913 
914         /* We need to know which slot in the new node is going to take a
915          * metadata pointer.
916          */
917         sc_slot = sc_segments >> (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
918         sc_slot &= ASSOC_ARRAY_FAN_MASK;
919 
920         pr_devel("new slot %lx >> %d -> %d\n",
921                  sc_segments, diff & ASSOC_ARRAY_KEY_CHUNK_MASK, sc_slot);
922 
923         /* Determine whether we need to follow the new node with a replacement
924          * for the current shortcut.  We could in theory reuse the current
925          * shortcut if its parent slot number doesn't change - but that's a
926          * 1-in-16 chance so not worth expending the code upon.
927          */
928         level = diff + ASSOC_ARRAY_LEVEL_STEP;
929         if (level < shortcut->skip_to_level) {
930                 pr_devel("post-shortcut %d...%d\n", level, shortcut->skip_to_level);
931                 keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
932                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
933 
934                 new_s1 = kzalloc(sizeof(struct assoc_array_shortcut) +
935                                  keylen * sizeof(unsigned long), GFP_KERNEL);
936                 if (!new_s1)
937                         return false;
938                 edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s1);
939 
940                 new_s1->back_pointer = assoc_array_node_to_ptr(new_n0);
941                 new_s1->parent_slot = sc_slot;
942                 new_s1->next_node = shortcut->next_node;
943                 new_s1->skip_to_level = shortcut->skip_to_level;
944 
945                 new_n0->slots[sc_slot] = assoc_array_shortcut_to_ptr(new_s1);
946 
947                 memcpy(new_s1->index_key, shortcut->index_key,
948                        keylen * sizeof(unsigned long));
949 
950                 edit->set[1].ptr = &side->back_pointer;
951                 edit->set[1].to = assoc_array_shortcut_to_ptr(new_s1);
952         } else {
953                 pr_devel("no post-shortcut\n");
954 
955                 /* We don't have to replace the pointed-to node as long as we
956                  * use memory barriers to make sure the parent slot number is
957                  * changed before the back pointer (the parent slot number is
958                  * irrelevant to the old parent shortcut).
959                  */
960                 new_n0->slots[sc_slot] = shortcut->next_node;
961                 edit->set_parent_slot[0].p = &side->parent_slot;
962                 edit->set_parent_slot[0].to = sc_slot;
963                 edit->set[1].ptr = &side->back_pointer;
964                 edit->set[1].to = assoc_array_node_to_ptr(new_n0);
965         }
966 
967         /* Install the new leaf in a spare slot in the new node. */
968         if (sc_slot == 0)
969                 edit->leaf_p = &new_n0->slots[1];
970         else
971                 edit->leaf_p = &new_n0->slots[0];
972 
973         pr_devel("<--%s() = ok [split shortcut]\n", __func__);
974         return edit;
975 }
976 
977 /**
978  * assoc_array_insert - Script insertion of an object into an associative array
979  * @array: The array to insert into.
980  * @ops: The operations to use.
981  * @index_key: The key to insert at.
982  * @object: The object to insert.
983  *
984  * Precalculate and preallocate a script for the insertion or replacement of an
985  * object in an associative array.  This results in an edit script that can
986  * either be applied or cancelled.
987  *
988  * The function returns a pointer to an edit script or -ENOMEM.
989  *
990  * The caller should lock against other modifications and must continue to hold
991  * the lock until assoc_array_apply_edit() has been called.
992  *
993  * Accesses to the tree may take place concurrently with this function,
994  * provided they hold the RCU read lock.
995  */
996 struct assoc_array_edit *assoc_array_insert(struct assoc_array *array,
997                                             const struct assoc_array_ops *ops,
998                                             const void *index_key,
999                                             void *object)
1000 {
1001         struct assoc_array_walk_result result;
1002         struct assoc_array_edit *edit;
1003 
1004         pr_devel("-->%s()\n", __func__);
1005 
1006         /* The leaf pointer we're given must not have the bottom bit set as we
1007          * use those for type-marking the pointer.  NULL pointers are also not
1008          * allowed as they indicate an empty slot but we have to allow them
1009          * here as they can be updated later.
1010          */
1011         BUG_ON(assoc_array_ptr_is_meta(object));
1012 
1013         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1014         if (!edit)
1015                 return ERR_PTR(-ENOMEM);
1016         edit->array = array;
1017         edit->ops = ops;
1018         edit->leaf = assoc_array_leaf_to_ptr(object);
1019         edit->adjust_count_by = 1;
1020 
1021         switch (assoc_array_walk(array, ops, index_key, &result)) {
1022         case assoc_array_walk_tree_empty:
1023                 /* Allocate a root node if there isn't one yet */
1024                 if (!assoc_array_insert_in_empty_tree(edit))
1025                         goto enomem;
1026                 return edit;
1027 
1028         case assoc_array_walk_found_terminal_node:
1029                 /* We found a node that doesn't have a node/shortcut pointer in
1030                  * the slot corresponding to the index key that we have to
1031                  * follow.
1032                  */
1033                 if (!assoc_array_insert_into_terminal_node(edit, ops, index_key,
1034                                                            &result))
1035                         goto enomem;
1036                 return edit;
1037 
1038         case assoc_array_walk_found_wrong_shortcut:
1039                 /* We found a shortcut that didn't match our key in a slot we
1040                  * needed to follow.
1041                  */
1042                 if (!assoc_array_insert_mid_shortcut(edit, ops, &result))
1043                         goto enomem;
1044                 return edit;
1045         }
1046 
1047 enomem:
1048         /* Clean up after an out of memory error */
1049         pr_devel("enomem\n");
1050         assoc_array_cancel_edit(edit);
1051         return ERR_PTR(-ENOMEM);
1052 }
1053 
1054 /**
1055  * assoc_array_insert_set_object - Set the new object pointer in an edit script
1056  * @edit: The edit script to modify.
1057  * @object: The object pointer to set.
1058  *
1059  * Change the object to be inserted in an edit script.  The object pointed to
1060  * by the old object is not freed.  This must be done prior to applying the
1061  * script.
1062  */
1063 void assoc_array_insert_set_object(struct assoc_array_edit *edit, void *object)
1064 {
1065         BUG_ON(!object);
1066         edit->leaf = assoc_array_leaf_to_ptr(object);
1067 }
1068 
1069 struct assoc_array_delete_collapse_context {
1070         struct assoc_array_node *node;
1071         const void              *skip_leaf;
1072         int                     slot;
1073 };
1074 
1075 /*
1076  * Subtree collapse to node iterator.
1077  */
1078 static int assoc_array_delete_collapse_iterator(const void *leaf,
1079                                                 void *iterator_data)
1080 {
1081         struct assoc_array_delete_collapse_context *collapse = iterator_data;
1082 
1083         if (leaf == collapse->skip_leaf)
1084                 return 0;
1085 
1086         BUG_ON(collapse->slot >= ASSOC_ARRAY_FAN_OUT);
1087 
1088         collapse->node->slots[collapse->slot++] = assoc_array_leaf_to_ptr(leaf);
1089         return 0;
1090 }
1091 
1092 /**
1093  * assoc_array_delete - Script deletion of an object from an associative array
1094  * @array: The array to search.
1095  * @ops: The operations to use.
1096  * @index_key: The key to the object.
1097  *
1098  * Precalculate and preallocate a script for the deletion of an object from an
1099  * associative array.  This results in an edit script that can either be
1100  * applied or cancelled.
1101  *
1102  * The function returns a pointer to an edit script if the object was found,
1103  * NULL if the object was not found or -ENOMEM.
1104  *
1105  * The caller should lock against other modifications and must continue to hold
1106  * the lock until assoc_array_apply_edit() has been called.
1107  *
1108  * Accesses to the tree may take place concurrently with this function,
1109  * provided they hold the RCU read lock.
1110  */
1111 struct assoc_array_edit *assoc_array_delete(struct assoc_array *array,
1112                                             const struct assoc_array_ops *ops,
1113                                             const void *index_key)
1114 {
1115         struct assoc_array_delete_collapse_context collapse;
1116         struct assoc_array_walk_result result;
1117         struct assoc_array_node *node, *new_n0;
1118         struct assoc_array_edit *edit;
1119         struct assoc_array_ptr *ptr;
1120         bool has_meta;
1121         int slot, i;
1122 
1123         pr_devel("-->%s()\n", __func__);
1124 
1125         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1126         if (!edit)
1127                 return ERR_PTR(-ENOMEM);
1128         edit->array = array;
1129         edit->ops = ops;
1130         edit->adjust_count_by = -1;
1131 
1132         switch (assoc_array_walk(array, ops, index_key, &result)) {
1133         case assoc_array_walk_found_terminal_node:
1134                 /* We found a node that should contain the leaf we've been
1135                  * asked to remove - *if* it's in the tree.
1136                  */
1137                 pr_devel("terminal_node\n");
1138                 node = result.terminal_node.node;
1139 
1140                 for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1141                         ptr = node->slots[slot];
1142                         if (ptr &&
1143                             assoc_array_ptr_is_leaf(ptr) &&
1144                             ops->compare_object(assoc_array_ptr_to_leaf(ptr),
1145                                                 index_key))
1146                                 goto found_leaf;
1147                 }
1148         case assoc_array_walk_tree_empty:
1149         case assoc_array_walk_found_wrong_shortcut:
1150         default:
1151                 assoc_array_cancel_edit(edit);
1152                 pr_devel("not found\n");
1153                 return NULL;
1154         }
1155 
1156 found_leaf:
1157         BUG_ON(array->nr_leaves_on_tree <= 0);
1158 
1159         /* In the simplest form of deletion we just clear the slot and release
1160          * the leaf after a suitable interval.
1161          */
1162         edit->dead_leaf = node->slots[slot];
1163         edit->set[0].ptr = &node->slots[slot];
1164         edit->set[0].to = NULL;
1165         edit->adjust_count_on = node;
1166 
1167         /* If that concludes erasure of the last leaf, then delete the entire
1168          * internal array.
1169          */
1170         if (array->nr_leaves_on_tree == 1) {
1171                 edit->set[1].ptr = &array->root;
1172                 edit->set[1].to = NULL;
1173                 edit->adjust_count_on = NULL;
1174                 edit->excised_subtree = array->root;
1175                 pr_devel("all gone\n");
1176                 return edit;
1177         }
1178 
1179         /* However, we'd also like to clear up some metadata blocks if we
1180          * possibly can.
1181          *
1182          * We go for a simple algorithm of: if this node has FAN_OUT or fewer
1183          * leaves in it, then attempt to collapse it - and attempt to
1184          * recursively collapse up the tree.
1185          *
1186          * We could also try and collapse in partially filled subtrees to take
1187          * up space in this node.
1188          */
1189         if (node->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1190                 struct assoc_array_node *parent, *grandparent;
1191                 struct assoc_array_ptr *ptr;
1192 
1193                 /* First of all, we need to know if this node has metadata so
1194                  * that we don't try collapsing if all the leaves are already
1195                  * here.
1196                  */
1197                 has_meta = false;
1198                 for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1199                         ptr = node->slots[i];
1200                         if (assoc_array_ptr_is_meta(ptr)) {
1201                                 has_meta = true;
1202                                 break;
1203                         }
1204                 }
1205 
1206                 pr_devel("leaves: %ld [m=%d]\n",
1207                          node->nr_leaves_on_branch - 1, has_meta);
1208 
1209                 /* Look further up the tree to see if we can collapse this node
1210                  * into a more proximal node too.
1211                  */
1212                 parent = node;
1213         collapse_up:
1214                 pr_devel("collapse subtree: %ld\n", parent->nr_leaves_on_branch);
1215 
1216                 ptr = parent->back_pointer;
1217                 if (!ptr)
1218                         goto do_collapse;
1219                 if (assoc_array_ptr_is_shortcut(ptr)) {
1220                         struct assoc_array_shortcut *s = assoc_array_ptr_to_shortcut(ptr);
1221                         ptr = s->back_pointer;
1222                         if (!ptr)
1223                                 goto do_collapse;
1224                 }
1225 
1226                 grandparent = assoc_array_ptr_to_node(ptr);
1227                 if (grandparent->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1228                         parent = grandparent;
1229                         goto collapse_up;
1230                 }
1231 
1232         do_collapse:
1233                 /* There's no point collapsing if the original node has no meta
1234                  * pointers to discard and if we didn't merge into one of that
1235                  * node's ancestry.
1236                  */
1237                 if (has_meta || parent != node) {
1238                         node = parent;
1239 
1240                         /* Create a new node to collapse into */
1241                         new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1242                         if (!new_n0)
1243                                 goto enomem;
1244                         edit->new_meta[0] = assoc_array_node_to_ptr(new_n0);
1245 
1246                         new_n0->back_pointer = node->back_pointer;
1247                         new_n0->parent_slot = node->parent_slot;
1248                         new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
1249                         edit->adjust_count_on = new_n0;
1250 
1251                         collapse.node = new_n0;
1252                         collapse.skip_leaf = assoc_array_ptr_to_leaf(edit->dead_leaf);
1253                         collapse.slot = 0;
1254                         assoc_array_subtree_iterate(assoc_array_node_to_ptr(node),
1255                                                     node->back_pointer,
1256                                                     assoc_array_delete_collapse_iterator,
1257                                                     &collapse);
1258                         pr_devel("collapsed %d,%lu\n", collapse.slot, new_n0->nr_leaves_on_branch);
1259                         BUG_ON(collapse.slot != new_n0->nr_leaves_on_branch - 1);
1260 
1261                         if (!node->back_pointer) {
1262                                 edit->set[1].ptr = &array->root;
1263                         } else if (assoc_array_ptr_is_leaf(node->back_pointer)) {
1264                                 BUG();
1265                         } else if (assoc_array_ptr_is_node(node->back_pointer)) {
1266                                 struct assoc_array_node *p =
1267                                         assoc_array_ptr_to_node(node->back_pointer);
1268                                 edit->set[1].ptr = &p->slots[node->parent_slot];
1269                         } else if (assoc_array_ptr_is_shortcut(node->back_pointer)) {
1270                                 struct assoc_array_shortcut *s =
1271                                         assoc_array_ptr_to_shortcut(node->back_pointer);
1272                                 edit->set[1].ptr = &s->next_node;
1273                         }
1274                         edit->set[1].to = assoc_array_node_to_ptr(new_n0);
1275                         edit->excised_subtree = assoc_array_node_to_ptr(node);
1276                 }
1277         }
1278 
1279         return edit;
1280 
1281 enomem:
1282         /* Clean up after an out of memory error */
1283         pr_devel("enomem\n");
1284         assoc_array_cancel_edit(edit);
1285         return ERR_PTR(-ENOMEM);
1286 }
1287 
1288 /**
1289  * assoc_array_clear - Script deletion of all objects from an associative array
1290  * @array: The array to clear.
1291  * @ops: The operations to use.
1292  *
1293  * Precalculate and preallocate a script for the deletion of all the objects
1294  * from an associative array.  This results in an edit script that can either
1295  * be applied or cancelled.
1296  *
1297  * The function returns a pointer to an edit script if there are objects to be
1298  * deleted, NULL if there are no objects in the array or -ENOMEM.
1299  *
1300  * The caller should lock against other modifications and must continue to hold
1301  * the lock until assoc_array_apply_edit() has been called.
1302  *
1303  * Accesses to the tree may take place concurrently with this function,
1304  * provided they hold the RCU read lock.
1305  */
1306 struct assoc_array_edit *assoc_array_clear(struct assoc_array *array,
1307                                            const struct assoc_array_ops *ops)
1308 {
1309         struct assoc_array_edit *edit;
1310 
1311         pr_devel("-->%s()\n", __func__);
1312 
1313         if (!array->root)
1314                 return NULL;
1315 
1316         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1317         if (!edit)
1318                 return ERR_PTR(-ENOMEM);
1319         edit->array = array;
1320         edit->ops = ops;
1321         edit->set[1].ptr = &array->root;
1322         edit->set[1].to = NULL;
1323         edit->excised_subtree = array->root;
1324         edit->ops_for_excised_subtree = ops;
1325         pr_devel("all gone\n");
1326         return edit;
1327 }
1328 
1329 /*
1330  * Handle the deferred destruction after an applied edit.
1331  */
1332 static void assoc_array_rcu_cleanup(struct rcu_head *head)
1333 {
1334         struct assoc_array_edit *edit =
1335                 container_of(head, struct assoc_array_edit, rcu);
1336         int i;
1337 
1338         pr_devel("-->%s()\n", __func__);
1339 
1340         if (edit->dead_leaf)
1341                 edit->ops->free_object(assoc_array_ptr_to_leaf(edit->dead_leaf));
1342         for (i = 0; i < ARRAY_SIZE(edit->excised_meta); i++)
1343                 if (edit->excised_meta[i])
1344                         kfree(assoc_array_ptr_to_node(edit->excised_meta[i]));
1345 
1346         if (edit->excised_subtree) {
1347                 BUG_ON(assoc_array_ptr_is_leaf(edit->excised_subtree));
1348                 if (assoc_array_ptr_is_node(edit->excised_subtree)) {
1349                         struct assoc_array_node *n =
1350                                 assoc_array_ptr_to_node(edit->excised_subtree);
1351                         n->back_pointer = NULL;
1352                 } else {
1353                         struct assoc_array_shortcut *s =
1354                                 assoc_array_ptr_to_shortcut(edit->excised_subtree);
1355                         s->back_pointer = NULL;
1356                 }
1357                 assoc_array_destroy_subtree(edit->excised_subtree,
1358                                             edit->ops_for_excised_subtree);
1359         }
1360 
1361         kfree(edit);
1362 }
1363 
1364 /**
1365  * assoc_array_apply_edit - Apply an edit script to an associative array
1366  * @edit: The script to apply.
1367  *
1368  * Apply an edit script to an associative array to effect an insertion,
1369  * deletion or clearance.  As the edit script includes preallocated memory,
1370  * this is guaranteed not to fail.
1371  *
1372  * The edit script, dead objects and dead metadata will be scheduled for
1373  * destruction after an RCU grace period to permit those doing read-only
1374  * accesses on the array to continue to do so under the RCU read lock whilst
1375  * the edit is taking place.
1376  */
1377 void assoc_array_apply_edit(struct assoc_array_edit *edit)
1378 {
1379         struct assoc_array_shortcut *shortcut;
1380         struct assoc_array_node *node;
1381         struct assoc_array_ptr *ptr;
1382         int i;
1383 
1384         pr_devel("-->%s()\n", __func__);
1385 
1386         smp_wmb();
1387         if (edit->leaf_p)
1388                 *edit->leaf_p = edit->leaf;
1389 
1390         smp_wmb();
1391         for (i = 0; i < ARRAY_SIZE(edit->set_parent_slot); i++)
1392                 if (edit->set_parent_slot[i].p)
1393                         *edit->set_parent_slot[i].p = edit->set_parent_slot[i].to;
1394 
1395         smp_wmb();
1396         for (i = 0; i < ARRAY_SIZE(edit->set_backpointers); i++)
1397                 if (edit->set_backpointers[i])
1398                         *edit->set_backpointers[i] = edit->set_backpointers_to;
1399 
1400         smp_wmb();
1401         for (i = 0; i < ARRAY_SIZE(edit->set); i++)
1402                 if (edit->set[i].ptr)
1403                         *edit->set[i].ptr = edit->set[i].to;
1404 
1405         if (edit->array->root == NULL) {
1406                 edit->array->nr_leaves_on_tree = 0;
1407         } else if (edit->adjust_count_on) {
1408                 node = edit->adjust_count_on;
1409                 for (;;) {
1410                         node->nr_leaves_on_branch += edit->adjust_count_by;
1411 
1412                         ptr = node->back_pointer;
1413                         if (!ptr)
1414                                 break;
1415                         if (assoc_array_ptr_is_shortcut(ptr)) {
1416                                 shortcut = assoc_array_ptr_to_shortcut(ptr);
1417                                 ptr = shortcut->back_pointer;
1418                                 if (!ptr)
1419                                         break;
1420                         }
1421                         BUG_ON(!assoc_array_ptr_is_node(ptr));
1422                         node = assoc_array_ptr_to_node(ptr);
1423                 }
1424 
1425                 edit->array->nr_leaves_on_tree += edit->adjust_count_by;
1426         }
1427 
1428         call_rcu(&edit->rcu, assoc_array_rcu_cleanup);
1429 }
1430 
1431 /**
1432  * assoc_array_cancel_edit - Discard an edit script.
1433  * @edit: The script to discard.
1434  *
1435  * Free an edit script and all the preallocated data it holds without making
1436  * any changes to the associative array it was intended for.
1437  *
1438  * NOTE!  In the case of an insertion script, this does _not_ release the leaf
1439  * that was to be inserted.  That is left to the caller.
1440  */
1441 void assoc_array_cancel_edit(struct assoc_array_edit *edit)
1442 {
1443         struct assoc_array_ptr *ptr;
1444         int i;
1445 
1446         pr_devel("-->%s()\n", __func__);
1447 
1448         /* Clean up after an out of memory error */
1449         for (i = 0; i < ARRAY_SIZE(edit->new_meta); i++) {
1450                 ptr = edit->new_meta[i];
1451                 if (ptr) {
1452                         if (assoc_array_ptr_is_node(ptr))
1453                                 kfree(assoc_array_ptr_to_node(ptr));
1454                         else
1455                                 kfree(assoc_array_ptr_to_shortcut(ptr));
1456                 }
1457         }
1458         kfree(edit);
1459 }
1460 
1461 /**
1462  * assoc_array_gc - Garbage collect an associative array.
1463  * @array: The array to clean.
1464  * @ops: The operations to use.
1465  * @iterator: A callback function to pass judgement on each object.
1466  * @iterator_data: Private data for the callback function.
1467  *
1468  * Collect garbage from an associative array and pack down the internal tree to
1469  * save memory.
1470  *
1471  * The iterator function is asked to pass judgement upon each object in the
1472  * array.  If it returns false, the object is discard and if it returns true,
1473  * the object is kept.  If it returns true, it must increment the object's
1474  * usage count (or whatever it needs to do to retain it) before returning.
1475  *
1476  * This function returns 0 if successful or -ENOMEM if out of memory.  In the
1477  * latter case, the array is not changed.
1478  *
1479  * The caller should lock against other modifications and must continue to hold
1480  * the lock until assoc_array_apply_edit() has been called.
1481  *
1482  * Accesses to the tree may take place concurrently with this function,
1483  * provided they hold the RCU read lock.
1484  */
1485 int assoc_array_gc(struct assoc_array *array,
1486                    const struct assoc_array_ops *ops,
1487                    bool (*iterator)(void *object, void *iterator_data),
1488                    void *iterator_data)
1489 {
1490         struct assoc_array_shortcut *shortcut, *new_s;
1491         struct assoc_array_node *node, *new_n;
1492         struct assoc_array_edit *edit;
1493         struct assoc_array_ptr *cursor, *ptr;
1494         struct assoc_array_ptr *new_root, *new_parent, **new_ptr_pp;
1495         unsigned long nr_leaves_on_tree;
1496         int keylen, slot, nr_free, next_slot, i;
1497 
1498         pr_devel("-->%s()\n", __func__);
1499 
1500         if (!array->root)
1501                 return 0;
1502 
1503         edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL);
1504         if (!edit)
1505                 return -ENOMEM;
1506         edit->array = array;
1507         edit->ops = ops;
1508         edit->ops_for_excised_subtree = ops;
1509         edit->set[0].ptr = &array->root;
1510         edit->excised_subtree = array->root;
1511 
1512         new_root = new_parent = NULL;
1513         new_ptr_pp = &new_root;
1514         cursor = array->root;
1515 
1516 descend:
1517         /* If this point is a shortcut, then we need to duplicate it and
1518          * advance the target cursor.
1519          */
1520         if (assoc_array_ptr_is_shortcut(cursor)) {
1521                 shortcut = assoc_array_ptr_to_shortcut(cursor);
1522                 keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
1523                 keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
1524                 new_s = kmalloc(sizeof(struct assoc_array_shortcut) +
1525                                 keylen * sizeof(unsigned long), GFP_KERNEL);
1526                 if (!new_s)
1527                         goto enomem;
1528                 pr_devel("dup shortcut %p -> %p\n", shortcut, new_s);
1529                 memcpy(new_s, shortcut, (sizeof(struct assoc_array_shortcut) +
1530                                          keylen * sizeof(unsigned long)));
1531                 new_s->back_pointer = new_parent;
1532                 new_s->parent_slot = shortcut->parent_slot;
1533                 *new_ptr_pp = new_parent = assoc_array_shortcut_to_ptr(new_s);
1534                 new_ptr_pp = &new_s->next_node;
1535                 cursor = shortcut->next_node;
1536         }
1537 
1538         /* Duplicate the node at this position */
1539         node = assoc_array_ptr_to_node(cursor);
1540         new_n = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL);
1541         if (!new_n)
1542                 goto enomem;
1543         pr_devel("dup node %p -> %p\n", node, new_n);
1544         new_n->back_pointer = new_parent;
1545         new_n->parent_slot = node->parent_slot;
1546         *new_ptr_pp = new_parent = assoc_array_node_to_ptr(new_n);
1547         new_ptr_pp = NULL;
1548         slot = 0;
1549 
1550 continue_node:
1551         /* Filter across any leaves and gc any subtrees */
1552         for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1553                 ptr = node->slots[slot];
1554                 if (!ptr)
1555                         continue;
1556 
1557                 if (assoc_array_ptr_is_leaf(ptr)) {
1558                         if (iterator(assoc_array_ptr_to_leaf(ptr),
1559                                      iterator_data))
1560                                 /* The iterator will have done any reference
1561                                  * counting on the object for us.
1562                                  */
1563                                 new_n->slots[slot] = ptr;
1564                         continue;
1565                 }
1566 
1567                 new_ptr_pp = &new_n->slots[slot];
1568                 cursor = ptr;
1569                 goto descend;
1570         }
1571 
1572         pr_devel("-- compress node %p --\n", new_n);
1573 
1574         /* Count up the number of empty slots in this node and work out the
1575          * subtree leaf count.
1576          */
1577         new_n->nr_leaves_on_branch = 0;
1578         nr_free = 0;
1579         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1580                 ptr = new_n->slots[slot];
1581                 if (!ptr)
1582                         nr_free++;
1583                 else if (assoc_array_ptr_is_leaf(ptr))
1584                         new_n->nr_leaves_on_branch++;
1585         }
1586         pr_devel("free=%d, leaves=%lu\n", nr_free, new_n->nr_leaves_on_branch);
1587 
1588         /* See what we can fold in */
1589         next_slot = 0;
1590         for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1591                 struct assoc_array_shortcut *s;
1592                 struct assoc_array_node *child;
1593 
1594                 ptr = new_n->slots[slot];
1595                 if (!ptr || assoc_array_ptr_is_leaf(ptr))
1596                         continue;
1597 
1598                 s = NULL;
1599                 if (assoc_array_ptr_is_shortcut(ptr)) {
1600                         s = assoc_array_ptr_to_shortcut(ptr);
1601                         ptr = s->next_node;
1602                 }
1603 
1604                 child = assoc_array_ptr_to_node(ptr);
1605                 new_n->nr_leaves_on_branch += child->nr_leaves_on_branch;
1606 
1607                 if (child->nr_leaves_on_branch <= nr_free + 1) {
1608                         /* Fold the child node into this one */
1609                         pr_devel("[%d] fold node %lu/%d [nx %d]\n",
1610                                  slot, child->nr_leaves_on_branch, nr_free + 1,
1611                                  next_slot);
1612 
1613                         /* We would already have reaped an intervening shortcut
1614                          * on the way back up the tree.
1615                          */
1616                         BUG_ON(s);
1617 
1618                         new_n->slots[slot] = NULL;
1619                         nr_free++;
1620                         if (slot < next_slot)
1621                                 next_slot = slot;
1622                         for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1623                                 struct assoc_array_ptr *p = child->slots[i];
1624                                 if (!p)
1625                                         continue;
1626                                 BUG_ON(assoc_array_ptr_is_meta(p));
1627                                 while (new_n->slots[next_slot])
1628                                         next_slot++;
1629                                 BUG_ON(next_slot >= ASSOC_ARRAY_FAN_OUT);
1630                                 new_n->slots[next_slot++] = p;
1631                                 nr_free--;
1632                         }
1633                         kfree(child);
1634                 } else {
1635                         pr_devel("[%d] retain node %lu/%d [nx %d]\n",
1636                                  slot, child->nr_leaves_on_branch, nr_free + 1,
1637                                  next_slot);
1638                 }
1639         }
1640 
1641         pr_devel("after: %lu\n", new_n->nr_leaves_on_branch);
1642 
1643         nr_leaves_on_tree = new_n->nr_leaves_on_branch;
1644 
1645         /* Excise this node if it is singly occupied by a shortcut */
1646         if (nr_free == ASSOC_ARRAY_FAN_OUT - 1) {
1647                 for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++)
1648                         if ((ptr = new_n->slots[slot]))
1649                                 break;
1650 
1651                 if (assoc_array_ptr_is_meta(ptr) &&
1652                     assoc_array_ptr_is_shortcut(ptr)) {
1653                         pr_devel("excise node %p with 1 shortcut\n", new_n);
1654                         new_s = assoc_array_ptr_to_shortcut(ptr);
1655                         new_parent = new_n->back_pointer;
1656                         slot = new_n->parent_slot;
1657                         kfree(new_n);
1658                         if (!new_parent) {
1659                                 new_s->back_pointer = NULL;
1660                                 new_s->parent_slot = 0;
1661                                 new_root = ptr;
1662                                 goto gc_complete;
1663                         }
1664 
1665                         if (assoc_array_ptr_is_shortcut(new_parent)) {
1666                                 /* We can discard any preceding shortcut also */
1667                                 struct assoc_array_shortcut *s =
1668                                         assoc_array_ptr_to_shortcut(new_parent);
1669 
1670                                 pr_devel("excise preceding shortcut\n");
1671 
1672                                 new_parent = new_s->back_pointer = s->back_pointer;
1673                                 slot = new_s->parent_slot = s->parent_slot;
1674                                 kfree(s);
1675                                 if (!new_parent) {
1676                                         new_s->back_pointer = NULL;
1677                                         new_s->parent_slot = 0;
1678                                         new_root = ptr;
1679                                         goto gc_complete;
1680                                 }
1681                         }
1682 
1683                         new_s->back_pointer = new_parent;
1684                         new_s->parent_slot = slot;
1685                         new_n = assoc_array_ptr_to_node(new_parent);
1686                         new_n->slots[slot] = ptr;
1687                         goto ascend_old_tree;
1688                 }
1689         }
1690 
1691         /* Excise any shortcuts we might encounter that point to nodes that
1692          * only contain leaves.
1693          */
1694         ptr = new_n->back_pointer;
1695         if (!ptr)
1696                 goto gc_complete;
1697 
1698         if (assoc_array_ptr_is_shortcut(ptr)) {
1699                 new_s = assoc_array_ptr_to_shortcut(ptr);
1700                 new_parent = new_s->back_pointer;
1701                 slot = new_s->parent_slot;
1702 
1703                 if (new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) {
1704                         struct assoc_array_node *n;
1705 
1706                         pr_devel("excise shortcut\n");
1707                         new_n->back_pointer = new_parent;
1708                         new_n->parent_slot = slot;
1709                         kfree(new_s);
1710                         if (!new_parent) {
1711                                 new_root = assoc_array_node_to_ptr(new_n);
1712                                 goto gc_complete;
1713                         }
1714 
1715                         n = assoc_array_ptr_to_node(new_parent);
1716                         n->slots[slot] = assoc_array_node_to_ptr(new_n);
1717                 }
1718         } else {
1719                 new_parent = ptr;
1720         }
1721         new_n = assoc_array_ptr_to_node(new_parent);
1722 
1723 ascend_old_tree:
1724         ptr = node->back_pointer;
1725         if (assoc_array_ptr_is_shortcut(ptr)) {
1726                 shortcut = assoc_array_ptr_to_shortcut(ptr);
1727                 slot = shortcut->parent_slot;
1728                 cursor = shortcut->back_pointer;
1729                 if (!cursor)
1730                         goto gc_complete;
1731         } else {
1732                 slot = node->parent_slot;
1733                 cursor = ptr;
1734         }
1735         BUG_ON(!cursor);
1736         node = assoc_array_ptr_to_node(cursor);
1737         slot++;
1738         goto continue_node;
1739 
1740 gc_complete:
1741         edit->set[0].to = new_root;
1742         assoc_array_apply_edit(edit);
1743         array->nr_leaves_on_tree = nr_leaves_on_tree;
1744         return 0;
1745 
1746 enomem:
1747         pr_devel("enomem\n");
1748         assoc_array_destroy_subtree(new_root, edit->ops);
1749         kfree(edit);
1750         return -ENOMEM;
1751 }
1752 

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