1	// SPDX-License-Identifier: GPL-2.0-or-later
2	/* Generic associative array implementation.
3	*
4	* See Documentation/core-api/assoc_array.rst for information.
5	*
6	* Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
7	* Written by David Howells (dhowells@redhat.com)
8	*/
9	//#define DEBUG
10	#include <linux/rcupdate.h>
11	#include <linux/slab.h>
12	#include <linux/err.h>
13	#include <linux/assoc_array_priv.h>
14
15	/*
16	* Iterate over an associative array. The caller must hold the RCU read lock
17	* or better.
18	*/
19	static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root,
20	const struct assoc_array_ptr *stop,
21	int (*iterator)(const void *leaf,
22	void *iterator_data),
23	void *iterator_data)
24	{
25	const struct assoc_array_shortcut *shortcut;
26	const struct assoc_array_node *node;
27	const struct assoc_array_ptr *cursor, *ptr, *parent;
28	unsigned long has_meta;
29	int slot, ret;
30
31	cursor = root;
32
33	begin_node:
34	if (assoc_array_ptr_is_shortcut(x: cursor)) {
35	/* Descend through a shortcut */
36	shortcut = assoc_array_ptr_to_shortcut(x: cursor);
37	cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */
38	}
39
40	node = assoc_array_ptr_to_node(x: cursor);
41	slot = 0;
42
43	/* We perform two passes of each node.
44	*
45	* The first pass does all the leaves in this node. This means we
46	* don't miss any leaves if the node is split up by insertion whilst
47	* we're iterating over the branches rooted here (we may, however, see
48	* some leaves twice).
49	*/
50	has_meta = 0;
51	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
52	ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
53	has_meta |= (unsigned long)ptr;
54	if (ptr && assoc_array_ptr_is_leaf(x: ptr)) {
55	/* We need a barrier between the read of the pointer,
56	* which is supplied by the above READ_ONCE().
57	*/
58	/* Invoke the callback */
59	ret = iterator(assoc_array_ptr_to_leaf(x: ptr),
60	iterator_data);
61	if (ret)
62	return ret;
63	}
64	}
65
66	/* The second pass attends to all the metadata pointers. If we follow
67	* one of these we may find that we don't come back here, but rather go
68	* back to a replacement node with the leaves in a different layout.
69	*
70	* We are guaranteed to make progress, however, as the slot number for
71	* a particular portion of the key space cannot change - and we
72	* continue at the back pointer + 1.
73	*/
74	if (!(has_meta & ASSOC_ARRAY_PTR_META_TYPE))
75	goto finished_node;
76	slot = 0;
77
78	continue_node:
79	node = assoc_array_ptr_to_node(x: cursor);
80	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
81	ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
82	if (assoc_array_ptr_is_meta(x: ptr)) {
83	cursor = ptr;
84	goto begin_node;
85	}
86	}
87
88	finished_node:
89	/* Move up to the parent (may need to skip back over a shortcut) */
90	parent = READ_ONCE(node->back_pointer); /* Address dependency. */
91	slot = node->parent_slot;
92	if (parent == stop)
93	return 0;
94
95	if (assoc_array_ptr_is_shortcut(x: parent)) {
96	shortcut = assoc_array_ptr_to_shortcut(x: parent);
97	cursor = parent;
98	parent = READ_ONCE(shortcut->back_pointer); /* Address dependency. */
99	slot = shortcut->parent_slot;
100	if (parent == stop)
101	return 0;
102	}
103
104	/* Ascend to next slot in parent node */
105	cursor = parent;
106	slot++;
107	goto continue_node;
108	}
109
110	/**
111	* assoc_array_iterate - Pass all objects in the array to a callback
112	* @array: The array to iterate over.
113	* @iterator: The callback function.
114	* @iterator_data: Private data for the callback function.
115	*
116	* Iterate over all the objects in an associative array. Each one will be
117	* presented to the iterator function.
118	*
119	* If the array is being modified concurrently with the iteration then it is
120	* possible that some objects in the array will be passed to the iterator
121	* callback more than once - though every object should be passed at least
122	* once. If this is undesirable then the caller must lock against modification
123	* for the duration of this function.
124	*
125	* The function will return 0 if no objects were in the array or else it will
126	* return the result of the last iterator function called. Iteration stops
127	* immediately if any call to the iteration function results in a non-zero
128	* return.
129	*
130	* The caller should hold the RCU read lock or better if concurrent
131	* modification is possible.
132	*/
133	int assoc_array_iterate(const struct assoc_array *array,
134	int (*iterator)(const void *object,
135	void *iterator_data),
136	void *iterator_data)
137	{
138	struct assoc_array_ptr *root = READ_ONCE(array->root); /* Address dependency. */
139
140	if (!root)
141	return 0;
142	return assoc_array_subtree_iterate(root, NULL, iterator, iterator_data);
143	}
144
145	enum assoc_array_walk_status {
146	assoc_array_walk_tree_empty,
147	assoc_array_walk_found_terminal_node,
148	assoc_array_walk_found_wrong_shortcut,
149	};
150
151	struct assoc_array_walk_result {
152	struct {
153	struct assoc_array_node *node; /* Node in which leaf might be found */
154	int level;
155	int slot;
156	} terminal_node;
157	struct {
158	struct assoc_array_shortcut *shortcut;
159	int level;
160	int sc_level;
161	unsigned long sc_segments;
162	unsigned long dissimilarity;
163	} wrong_shortcut;
164	};
165
166	/*
167	* Navigate through the internal tree looking for the closest node to the key.
168	*/
169	static enum assoc_array_walk_status
170	assoc_array_walk(const struct assoc_array *array,
171	const struct assoc_array_ops *ops,
172	const void *index_key,
173	struct assoc_array_walk_result *result)
174	{
175	struct assoc_array_shortcut *shortcut;
176	struct assoc_array_node *node;
177	struct assoc_array_ptr *cursor, *ptr;
178	unsigned long sc_segments, dissimilarity;
179	unsigned long segments;
180	int level, sc_level, next_sc_level;
181	int slot;
182
183	pr_devel("-->%s()\n", __func__);
184
185	cursor = READ_ONCE(array->root); /* Address dependency. */
186	if (!cursor)
187	return assoc_array_walk_tree_empty;
188
189	level = 0;
190
191	/* Use segments from the key for the new leaf to navigate through the
192	* internal tree, skipping through nodes and shortcuts that are on
193	* route to the destination. Eventually we'll come to a slot that is
194	* either empty or contains a leaf at which point we've found a node in
195	* which the leaf we're looking for might be found or into which it
196	* should be inserted.
197	*/
198	jumped:
199	segments = ops->get_key_chunk(index_key, level);
200	pr_devel("segments[%d]: %lx\n", level, segments);
201
202	if (assoc_array_ptr_is_shortcut(x: cursor))
203	goto follow_shortcut;
204
205	consider_node:
206	node = assoc_array_ptr_to_node(x: cursor);
207	slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
208	slot &= ASSOC_ARRAY_FAN_MASK;
209	ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
210
211	pr_devel("consider slot %x [ix=%d type=%lu]\n",
212	slot, level, (unsigned long)ptr & 3);
213
214	if (!assoc_array_ptr_is_meta(x: ptr)) {
215	/* The node doesn't have a node/shortcut pointer in the slot
216	* corresponding to the index key that we have to follow.
217	*/
218	result->terminal_node.node = node;
219	result->terminal_node.level = level;
220	result->terminal_node.slot = slot;
221	pr_devel("<--%s() = terminal_node\n", __func__);
222	return assoc_array_walk_found_terminal_node;
223	}
224
225	if (assoc_array_ptr_is_node(x: ptr)) {
226	/* There is a pointer to a node in the slot corresponding to
227	* this index key segment, so we need to follow it.
228	*/
229	cursor = ptr;
230	level += ASSOC_ARRAY_LEVEL_STEP;
231	if ((level & ASSOC_ARRAY_KEY_CHUNK_MASK) != 0)
232	goto consider_node;
233	goto jumped;
234	}
235
236	/* There is a shortcut in the slot corresponding to the index key
237	* segment. We follow the shortcut if its partial index key matches
238	* this leaf's. Otherwise we need to split the shortcut.
239	*/
240	cursor = ptr;
241	follow_shortcut:
242	shortcut = assoc_array_ptr_to_shortcut(x: cursor);
243	pr_devel("shortcut to %d\n", shortcut->skip_to_level);
244	sc_level = level + ASSOC_ARRAY_LEVEL_STEP;
245	BUG_ON(sc_level > shortcut->skip_to_level);
246
247	do {
248	/* Check the leaf against the shortcut's index key a word at a
249	* time, trimming the final word (the shortcut stores the index
250	* key completely from the root to the shortcut's target).
251	*/
252	if ((sc_level & ASSOC_ARRAY_KEY_CHUNK_MASK) == 0)
253	segments = ops->get_key_chunk(index_key, sc_level);
254
255	sc_segments = shortcut->index_key[sc_level >> ASSOC_ARRAY_KEY_CHUNK_SHIFT];
256	dissimilarity = segments ^ sc_segments;
257
258	if (round_up(sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE) > shortcut->skip_to_level) {
259	/* Trim segments that are beyond the shortcut */
260	int shift = shortcut->skip_to_level & ASSOC_ARRAY_KEY_CHUNK_MASK;
261	dissimilarity &= ~(ULONG_MAX << shift);
262	next_sc_level = shortcut->skip_to_level;
263	} else {
264	next_sc_level = sc_level + ASSOC_ARRAY_KEY_CHUNK_SIZE;
265	next_sc_level = round_down(next_sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
266	}
267
268	if (dissimilarity != 0) {
269	/* This shortcut points elsewhere */
270	result->wrong_shortcut.shortcut = shortcut;
271	result->wrong_shortcut.level = level;
272	result->wrong_shortcut.sc_level = sc_level;
273	result->wrong_shortcut.sc_segments = sc_segments;
274	result->wrong_shortcut.dissimilarity = dissimilarity;
275	return assoc_array_walk_found_wrong_shortcut;
276	}
277
278	sc_level = next_sc_level;
279	} while (sc_level < shortcut->skip_to_level);
280
281	/* The shortcut matches the leaf's index to this point. */
282	cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */
283	if (((level ^ sc_level) & ~ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) {
284	level = sc_level;
285	goto jumped;
286	} else {
287	level = sc_level;
288	goto consider_node;
289	}
290	}
291
292	/**
293	* assoc_array_find - Find an object by index key
294	* @array: The associative array to search.
295	* @ops: The operations to use.
296	* @index_key: The key to the object.
297	*
298	* Find an object in an associative array by walking through the internal tree
299	* to the node that should contain the object and then searching the leaves
300	* there. NULL is returned if the requested object was not found in the array.
301	*
302	* The caller must hold the RCU read lock or better.
303	*/
304	void *assoc_array_find(const struct assoc_array *array,
305	const struct assoc_array_ops *ops,
306	const void *index_key)
307	{
308	struct assoc_array_walk_result result;
309	const struct assoc_array_node *node;
310	const struct assoc_array_ptr *ptr;
311	const void *leaf;
312	int slot;
313
314	if (assoc_array_walk(array, ops, index_key, result: &result) !=
315	assoc_array_walk_found_terminal_node)
316	return NULL;
317
318	node = result.terminal_node.node;
319
320	/* If the target key is available to us, it's has to be pointed to by
321	* the terminal node.
322	*/
323	for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
324	ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */
325	if (ptr && assoc_array_ptr_is_leaf(x: ptr)) {
326	/* We need a barrier between the read of the pointer
327	* and dereferencing the pointer - but only if we are
328	* actually going to dereference it.
329	*/
330	leaf = assoc_array_ptr_to_leaf(x: ptr);
331	if (ops->compare_object(leaf, index_key))
332	return (void *)leaf;
333	}
334	}
335
336	return NULL;
337	}
338
339	/*
340	* Destructively iterate over an associative array. The caller must prevent
341	* other simultaneous accesses.
342	*/
343	static void assoc_array_destroy_subtree(struct assoc_array_ptr *root,
344	const struct assoc_array_ops *ops)
345	{
346	struct assoc_array_shortcut *shortcut;
347	struct assoc_array_node *node;
348	struct assoc_array_ptr *cursor, *parent = NULL;
349	int slot = -1;
350
351	pr_devel("-->%s()\n", __func__);
352
353	cursor = root;
354	if (!cursor) {
355	pr_devel("empty\n");
356	return;
357	}
358
359	move_to_meta:
360	if (assoc_array_ptr_is_shortcut(x: cursor)) {
361	/* Descend through a shortcut */
362	pr_devel("[%d] shortcut\n", slot);
363	BUG_ON(!assoc_array_ptr_is_shortcut(cursor));
364	shortcut = assoc_array_ptr_to_shortcut(x: cursor);
365	BUG_ON(shortcut->back_pointer != parent);
366	BUG_ON(slot != -1 && shortcut->parent_slot != slot);
367	parent = cursor;
368	cursor = shortcut->next_node;
369	slot = -1;
370	BUG_ON(!assoc_array_ptr_is_node(cursor));
371	}
372
373	pr_devel("[%d] node\n", slot);
374	node = assoc_array_ptr_to_node(x: cursor);
375	BUG_ON(node->back_pointer != parent);
376	BUG_ON(slot != -1 && node->parent_slot != slot);
377	slot = 0;
378
379	continue_node:
380	pr_devel("Node %p [back=%p]\n", node, node->back_pointer);
381	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
382	struct assoc_array_ptr *ptr = node->slots[slot];
383	if (!ptr)
384	continue;
385	if (assoc_array_ptr_is_meta(x: ptr)) {
386	parent = cursor;
387	cursor = ptr;
388	goto move_to_meta;
389	}
390
391	if (ops) {
392	pr_devel("[%d] free leaf\n", slot);
393	ops->free_object(assoc_array_ptr_to_leaf(x: ptr));
394	}
395	}
396
397	parent = node->back_pointer;
398	slot = node->parent_slot;
399	pr_devel("free node\n");
400	kfree(objp: node);
401	if (!parent)
402	return; /* Done */
403
404	/* Move back up to the parent (may need to free a shortcut on
405	* the way up) */
406	if (assoc_array_ptr_is_shortcut(x: parent)) {
407	shortcut = assoc_array_ptr_to_shortcut(x: parent);
408	BUG_ON(shortcut->next_node != cursor);
409	cursor = parent;
410	parent = shortcut->back_pointer;
411	slot = shortcut->parent_slot;
412	pr_devel("free shortcut\n");
413	kfree(objp: shortcut);
414	if (!parent)
415	return;
416
417	BUG_ON(!assoc_array_ptr_is_node(parent));
418	}
419
420	/* Ascend to next slot in parent node */
421	pr_devel("ascend to %p[%d]\n", parent, slot);
422	cursor = parent;
423	node = assoc_array_ptr_to_node(x: cursor);
424	slot++;
425	goto continue_node;
426	}
427
428	/**
429	* assoc_array_destroy - Destroy an associative array
430	* @array: The array to destroy.
431	* @ops: The operations to use.
432	*
433	* Discard all metadata and free all objects in an associative array. The
434	* array will be empty and ready to use again upon completion. This function
435	* cannot fail.
436	*
437	* The caller must prevent all other accesses whilst this takes place as no
438	* attempt is made to adjust pointers gracefully to permit RCU readlock-holding
439	* accesses to continue. On the other hand, no memory allocation is required.
440	*/
441	void assoc_array_destroy(struct assoc_array *array,
442	const struct assoc_array_ops *ops)
443	{
444	assoc_array_destroy_subtree(root: array->root, ops);
445	array->root = NULL;
446	}
447
448	/*
449	* Handle insertion into an empty tree.
450	*/
451	static bool assoc_array_insert_in_empty_tree(struct assoc_array_edit *edit)
452	{
453	struct assoc_array_node *new_n0;
454
455	pr_devel("-->%s()\n", __func__);
456
457	new_n0 = kzalloc(size: sizeof(struct assoc_array_node), GFP_KERNEL);
458	if (!new_n0)
459	return false;
460
461	edit->new_meta[0] = assoc_array_node_to_ptr(p: new_n0);
462	edit->leaf_p = &new_n0->slots[0];
463	edit->adjust_count_on = new_n0;
464	edit->set[0].ptr = &edit->array->root;
465	edit->set[0].to = assoc_array_node_to_ptr(p: new_n0);
466
467	pr_devel("<--%s() = ok [no root]\n", __func__);
468	return true;
469	}
470
471	/*
472	* Handle insertion into a terminal node.
473	*/
474	static bool assoc_array_insert_into_terminal_node(struct assoc_array_edit *edit,
475	const struct assoc_array_ops *ops,
476	const void *index_key,
477	struct assoc_array_walk_result *result)
478	{
479	struct assoc_array_shortcut *shortcut, *new_s0;
480	struct assoc_array_node *node, *new_n0, *new_n1, *side;
481	struct assoc_array_ptr *ptr;
482	unsigned long dissimilarity, base_seg, blank;
483	size_t keylen;
484	bool have_meta;
485	int level, diff;
486	int slot, next_slot, free_slot, i, j;
487
488	node = result->terminal_node.node;
489	level = result->terminal_node.level;
490	edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = result->terminal_node.slot;
491
492	pr_devel("-->%s()\n", __func__);
493
494	/* We arrived at a node which doesn't have an onward node or shortcut
495	* pointer that we have to follow. This means that (a) the leaf we
496	* want must go here (either by insertion or replacement) or (b) we
497	* need to split this node and insert in one of the fragments.
498	*/
499	free_slot = -1;
500
501	/* Firstly, we have to check the leaves in this node to see if there's
502	* a matching one we should replace in place.
503	*/
504	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
505	ptr = node->slots[i];
506	if (!ptr) {
507	free_slot = i;
508	continue;
509	}
510	if (assoc_array_ptr_is_leaf(x: ptr) &&
511	ops->compare_object(assoc_array_ptr_to_leaf(x: ptr),
512	index_key)) {
513	pr_devel("replace in slot %d\n", i);
514	edit->leaf_p = &node->slots[i];
515	edit->dead_leaf = node->slots[i];
516	pr_devel("<--%s() = ok [replace]\n", __func__);
517	return true;
518	}
519	}
520
521	/* If there is a free slot in this node then we can just insert the
522	* leaf here.
523	*/
524	if (free_slot >= 0) {
525	pr_devel("insert in free slot %d\n", free_slot);
526	edit->leaf_p = &node->slots[free_slot];
527	edit->adjust_count_on = node;
528	pr_devel("<--%s() = ok [insert]\n", __func__);
529	return true;
530	}
531
532	/* The node has no spare slots - so we're either going to have to split
533	* it or insert another node before it.
534	*
535	* Whatever, we're going to need at least two new nodes - so allocate
536	* those now. We may also need a new shortcut, but we deal with that
537	* when we need it.
538	*/
539	new_n0 = kzalloc(size: sizeof(struct assoc_array_node), GFP_KERNEL);
540	if (!new_n0)
541	return false;
542	edit->new_meta[0] = assoc_array_node_to_ptr(p: new_n0);
543	new_n1 = kzalloc(size: sizeof(struct assoc_array_node), GFP_KERNEL);
544	if (!new_n1)
545	return false;
546	edit->new_meta[1] = assoc_array_node_to_ptr(p: new_n1);
547
548	/* We need to find out how similar the leaves are. */
549	pr_devel("no spare slots\n");
550	have_meta = false;
551	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
552	ptr = node->slots[i];
553	if (assoc_array_ptr_is_meta(x: ptr)) {
554	edit->segment_cache[i] = 0xff;
555	have_meta = true;
556	continue;
557	}
558	base_seg = ops->get_object_key_chunk(
559	assoc_array_ptr_to_leaf(x: ptr), level);
560	base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
561	edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
562	}
563
564	if (have_meta) {
565	pr_devel("have meta\n");
566	goto split_node;
567	}
568
569	/* The node contains only leaves */
570	dissimilarity = 0;
571	base_seg = edit->segment_cache[0];
572	for (i = 1; i < ASSOC_ARRAY_FAN_OUT; i++)
573	dissimilarity |= edit->segment_cache[i] ^ base_seg;
574
575	pr_devel("only leaves; dissimilarity=%lx\n", dissimilarity);
576
577	if ((dissimilarity & ASSOC_ARRAY_FAN_MASK) == 0) {
578	/* The old leaves all cluster in the same slot. We will need
579	* to insert a shortcut if the new node wants to cluster with them.
580	*/
581	if ((edit->segment_cache[ASSOC_ARRAY_FAN_OUT] ^ base_seg) == 0)
582	goto all_leaves_cluster_together;
583
584	/* Otherwise all the old leaves cluster in the same slot, but
585	* the new leaf wants to go into a different slot - so we
586	* create a new node (n0) to hold the new leaf and a pointer to
587	* a new node (n1) holding all the old leaves.
588	*
589	* This can be done by falling through to the node splitting
590	* path.
591	*/
592	pr_devel("present leaves cluster but not new leaf\n");
593	}
594
595	split_node:
596	pr_devel("split node\n");
597
598	/* We need to split the current node. The node must contain anything
599	* from a single leaf (in the one leaf case, this leaf will cluster
600	* with the new leaf) and the rest meta-pointers, to all leaves, some
601	* of which may cluster.
602	*
603	* It won't contain the case in which all the current leaves plus the
604	* new leaves want to cluster in the same slot.
605	*
606	* We need to expel at least two leaves out of a set consisting of the
607	* leaves in the node and the new leaf. The current meta pointers can
608	* just be copied as they shouldn't cluster with any of the leaves.
609	*
610	* We need a new node (n0) to replace the current one and a new node to
611	* take the expelled nodes (n1).
612	*/
613	edit->set[0].to = assoc_array_node_to_ptr(p: new_n0);
614	new_n0->back_pointer = node->back_pointer;
615	new_n0->parent_slot = node->parent_slot;
616	new_n1->back_pointer = assoc_array_node_to_ptr(p: new_n0);
617	new_n1->parent_slot = -1; /* Need to calculate this */
618
619	do_split_node:
620	pr_devel("do_split_node\n");
621
622	new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
623	new_n1->nr_leaves_on_branch = 0;
624
625	/* Begin by finding two matching leaves. There have to be at least two
626	* that match - even if there are meta pointers - because any leaf that
627	* would match a slot with a meta pointer in it must be somewhere
628	* behind that meta pointer and cannot be here. Further, given N
629	* remaining leaf slots, we now have N+1 leaves to go in them.
630	*/
631	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
632	slot = edit->segment_cache[i];
633	if (slot != 0xff)
634	for (j = i + 1; j < ASSOC_ARRAY_FAN_OUT + 1; j++)
635	if (edit->segment_cache[j] == slot)
636	goto found_slot_for_multiple_occupancy;
637	}
638	found_slot_for_multiple_occupancy:
639	pr_devel("same slot: %x %x [%02x]\n", i, j, slot);
640	BUG_ON(i >= ASSOC_ARRAY_FAN_OUT);
641	BUG_ON(j >= ASSOC_ARRAY_FAN_OUT + 1);
642	BUG_ON(slot >= ASSOC_ARRAY_FAN_OUT);
643
644	new_n1->parent_slot = slot;
645
646	/* Metadata pointers cannot change slot */
647	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
648	if (assoc_array_ptr_is_meta(x: node->slots[i]))
649	new_n0->slots[i] = node->slots[i];
650	else
651	new_n0->slots[i] = NULL;
652	BUG_ON(new_n0->slots[slot] != NULL);
653	new_n0->slots[slot] = assoc_array_node_to_ptr(p: new_n1);
654
655	/* Filter the leaf pointers between the new nodes */
656	free_slot = -1;
657	next_slot = 0;
658	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
659	if (assoc_array_ptr_is_meta(x: node->slots[i]))
660	continue;
661	if (edit->segment_cache[i] == slot) {
662	new_n1->slots[next_slot++] = node->slots[i];
663	new_n1->nr_leaves_on_branch++;
664	} else {
665	do {
666	free_slot++;
667	} while (new_n0->slots[free_slot] != NULL);
668	new_n0->slots[free_slot] = node->slots[i];
669	}
670	}
671
672	pr_devel("filtered: f=%x n=%x\n", free_slot, next_slot);
673
674	if (edit->segment_cache[ASSOC_ARRAY_FAN_OUT] != slot) {
675	do {
676	free_slot++;
677	} while (new_n0->slots[free_slot] != NULL);
678	edit->leaf_p = &new_n0->slots[free_slot];
679	edit->adjust_count_on = new_n0;
680	} else {
681	edit->leaf_p = &new_n1->slots[next_slot++];
682	edit->adjust_count_on = new_n1;
683	}
684
685	BUG_ON(next_slot <= 1);
686
687	edit->set_backpointers_to = assoc_array_node_to_ptr(p: new_n0);
688	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
689	if (edit->segment_cache[i] == 0xff) {
690	ptr = node->slots[i];
691	BUG_ON(assoc_array_ptr_is_leaf(ptr));
692	if (assoc_array_ptr_is_node(x: ptr)) {
693	side = assoc_array_ptr_to_node(x: ptr);
694	edit->set_backpointers[i] = &side->back_pointer;
695	} else {
696	shortcut = assoc_array_ptr_to_shortcut(x: ptr);
697	edit->set_backpointers[i] = &shortcut->back_pointer;
698	}
699	}
700	}
701
702	ptr = node->back_pointer;
703	if (!ptr)
704	edit->set[0].ptr = &edit->array->root;
705	else if (assoc_array_ptr_is_node(x: ptr))
706	edit->set[0].ptr = &assoc_array_ptr_to_node(x: ptr)->slots[node->parent_slot];
707	else
708	edit->set[0].ptr = &assoc_array_ptr_to_shortcut(x: ptr)->next_node;
709	edit->excised_meta[0] = assoc_array_node_to_ptr(p: node);
710	pr_devel("<--%s() = ok [split node]\n", __func__);
711	return true;
712
713	all_leaves_cluster_together:
714	/* All the leaves, new and old, want to cluster together in this node
715	* in the same slot, so we have to replace this node with a shortcut to
716	* skip over the identical parts of the key and then place a pair of
717	* nodes, one inside the other, at the end of the shortcut and
718	* distribute the keys between them.
719	*
720	* Firstly we need to work out where the leaves start diverging as a
721	* bit position into their keys so that we know how big the shortcut
722	* needs to be.
723	*
724	* We only need to make a single pass of N of the N+1 leaves because if
725	* any keys differ between themselves at bit X then at least one of
726	* them must also differ with the base key at bit X or before.
727	*/
728	pr_devel("all leaves cluster together\n");
729	diff = INT_MAX;
730	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
731	int x = ops->diff_objects(assoc_array_ptr_to_leaf(x: node->slots[i]),
732	index_key);
733	if (x < diff) {
734	BUG_ON(x < 0);
735	diff = x;
736	}
737	}
738	BUG_ON(diff == INT_MAX);
739	BUG_ON(diff < level + ASSOC_ARRAY_LEVEL_STEP);
740
741	keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
742	keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
743
744	new_s0 = kzalloc(struct_size(new_s0, index_key, keylen), GFP_KERNEL);
745	if (!new_s0)
746	return false;
747	edit->new_meta[2] = assoc_array_shortcut_to_ptr(p: new_s0);
748
749	edit->set[0].to = assoc_array_shortcut_to_ptr(p: new_s0);
750	new_s0->back_pointer = node->back_pointer;
751	new_s0->parent_slot = node->parent_slot;
752	new_s0->next_node = assoc_array_node_to_ptr(p: new_n0);
753	new_n0->back_pointer = assoc_array_shortcut_to_ptr(p: new_s0);
754	new_n0->parent_slot = 0;
755	new_n1->back_pointer = assoc_array_node_to_ptr(p: new_n0);
756	new_n1->parent_slot = -1; /* Need to calculate this */
757
758	new_s0->skip_to_level = level = diff & ~ASSOC_ARRAY_LEVEL_STEP_MASK;
759	pr_devel("skip_to_level = %d [diff %d]\n", level, diff);
760	BUG_ON(level <= 0);
761
762	for (i = 0; i < keylen; i++)
763	new_s0->index_key[i] =
764	ops->get_key_chunk(index_key, i * ASSOC_ARRAY_KEY_CHUNK_SIZE);
765
766	if (level & ASSOC_ARRAY_KEY_CHUNK_MASK) {
767	blank = ULONG_MAX << (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
768	pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, level, blank);
769	new_s0->index_key[keylen - 1] &= ~blank;
770	}
771
772	/* This now reduces to a node splitting exercise for which we'll need
773	* to regenerate the disparity table.
774	*/
775	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
776	ptr = node->slots[i];
777	base_seg = ops->get_object_key_chunk(assoc_array_ptr_to_leaf(x: ptr),
778	level);
779	base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
780	edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK;
781	}
782
783	base_seg = ops->get_key_chunk(index_key, level);
784	base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK;
785	edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = base_seg & ASSOC_ARRAY_FAN_MASK;
786	goto do_split_node;
787	}
788
789	/*
790	* Handle insertion into the middle of a shortcut.
791	*/
792	static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
793	const struct assoc_array_ops *ops,
794	struct assoc_array_walk_result *result)
795	{
796	struct assoc_array_shortcut *shortcut, *new_s0, *new_s1;
797	struct assoc_array_node *node, *new_n0, *side;
798	unsigned long sc_segments, dissimilarity, blank;
799	size_t keylen;
800	int level, sc_level, diff;
801	int sc_slot;
802
803	shortcut = result->wrong_shortcut.shortcut;
804	level = result->wrong_shortcut.level;
805	sc_level = result->wrong_shortcut.sc_level;
806	sc_segments = result->wrong_shortcut.sc_segments;
807	dissimilarity = result->wrong_shortcut.dissimilarity;
808
809	pr_devel("-->%s(ix=%d dis=%lx scix=%d)\n",
810	__func__, level, dissimilarity, sc_level);
811
812	/* We need to split a shortcut and insert a node between the two
813	* pieces. Zero-length pieces will be dispensed with entirely.
814	*
815	* First of all, we need to find out in which level the first
816	* difference was.
817	*/
818	diff = __ffs(dissimilarity);
819	diff &= ~ASSOC_ARRAY_LEVEL_STEP_MASK;
820	diff += sc_level & ~ASSOC_ARRAY_KEY_CHUNK_MASK;
821	pr_devel("diff=%d\n", diff);
822
823	if (!shortcut->back_pointer) {
824	edit->set[0].ptr = &edit->array->root;
825	} else if (assoc_array_ptr_is_node(x: shortcut->back_pointer)) {
826	node = assoc_array_ptr_to_node(x: shortcut->back_pointer);
827	edit->set[0].ptr = &node->slots[shortcut->parent_slot];
828	} else {
829	BUG();
830	}
831
832	edit->excised_meta[0] = assoc_array_shortcut_to_ptr(p: shortcut);
833
834	/* Create a new node now since we're going to need it anyway */
835	new_n0 = kzalloc(size: sizeof(struct assoc_array_node), GFP_KERNEL);
836	if (!new_n0)
837	return false;
838	edit->new_meta[0] = assoc_array_node_to_ptr(p: new_n0);
839	edit->adjust_count_on = new_n0;
840
841	/* Insert a new shortcut before the new node if this segment isn't of
842	* zero length - otherwise we just connect the new node directly to the
843	* parent.
844	*/
845	level += ASSOC_ARRAY_LEVEL_STEP;
846	if (diff > level) {
847	pr_devel("pre-shortcut %d...%d\n", level, diff);
848	keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
849	keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
850
851	new_s0 = kzalloc(struct_size(new_s0, index_key, keylen),
852	GFP_KERNEL);
853	if (!new_s0)
854	return false;
855	edit->new_meta[1] = assoc_array_shortcut_to_ptr(p: new_s0);
856	edit->set[0].to = assoc_array_shortcut_to_ptr(p: new_s0);
857	new_s0->back_pointer = shortcut->back_pointer;
858	new_s0->parent_slot = shortcut->parent_slot;
859	new_s0->next_node = assoc_array_node_to_ptr(p: new_n0);
860	new_s0->skip_to_level = diff;
861
862	new_n0->back_pointer = assoc_array_shortcut_to_ptr(p: new_s0);
863	new_n0->parent_slot = 0;
864
865	memcpy(new_s0->index_key, shortcut->index_key,
866	flex_array_size(new_s0, index_key, keylen));
867
868	blank = ULONG_MAX << (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
869	pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, diff, blank);
870	new_s0->index_key[keylen - 1] &= ~blank;
871	} else {
872	pr_devel("no pre-shortcut\n");
873	edit->set[0].to = assoc_array_node_to_ptr(p: new_n0);
874	new_n0->back_pointer = shortcut->back_pointer;
875	new_n0->parent_slot = shortcut->parent_slot;
876	}
877
878	side = assoc_array_ptr_to_node(x: shortcut->next_node);
879	new_n0->nr_leaves_on_branch = side->nr_leaves_on_branch;
880
881	/* We need to know which slot in the new node is going to take a
882	* metadata pointer.
883	*/
884	sc_slot = sc_segments >> (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
885	sc_slot &= ASSOC_ARRAY_FAN_MASK;
886
887	pr_devel("new slot %lx >> %d -> %d\n",
888	sc_segments, diff & ASSOC_ARRAY_KEY_CHUNK_MASK, sc_slot);
889
890	/* Determine whether we need to follow the new node with a replacement
891	* for the current shortcut. We could in theory reuse the current
892	* shortcut if its parent slot number doesn't change - but that's a
893	* 1-in-16 chance so not worth expending the code upon.
894	*/
895	level = diff + ASSOC_ARRAY_LEVEL_STEP;
896	if (level < shortcut->skip_to_level) {
897	pr_devel("post-shortcut %d...%d\n", level, shortcut->skip_to_level);
898	keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
899	keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
900
901	new_s1 = kzalloc(struct_size(new_s1, index_key, keylen),
902	GFP_KERNEL);
903	if (!new_s1)
904	return false;
905	edit->new_meta[2] = assoc_array_shortcut_to_ptr(p: new_s1);
906
907	new_s1->back_pointer = assoc_array_node_to_ptr(p: new_n0);
908	new_s1->parent_slot = sc_slot;
909	new_s1->next_node = shortcut->next_node;
910	new_s1->skip_to_level = shortcut->skip_to_level;
911
912	new_n0->slots[sc_slot] = assoc_array_shortcut_to_ptr(p: new_s1);
913
914	memcpy(new_s1->index_key, shortcut->index_key,
915	flex_array_size(new_s1, index_key, keylen));
916
917	edit->set[1].ptr = &side->back_pointer;
918	edit->set[1].to = assoc_array_shortcut_to_ptr(p: new_s1);
919	} else {
920	pr_devel("no post-shortcut\n");
921
922	/* We don't have to replace the pointed-to node as long as we
923	* use memory barriers to make sure the parent slot number is
924	* changed before the back pointer (the parent slot number is
925	* irrelevant to the old parent shortcut).
926	*/
927	new_n0->slots[sc_slot] = shortcut->next_node;
928	edit->set_parent_slot[0].p = &side->parent_slot;
929	edit->set_parent_slot[0].to = sc_slot;
930	edit->set[1].ptr = &side->back_pointer;
931	edit->set[1].to = assoc_array_node_to_ptr(p: new_n0);
932	}
933
934	/* Install the new leaf in a spare slot in the new node. */
935	if (sc_slot == 0)
936	edit->leaf_p = &new_n0->slots[1];
937	else
938	edit->leaf_p = &new_n0->slots[0];
939
940	pr_devel("<--%s() = ok [split shortcut]\n", __func__);
941	return edit;
942	}
943
944	/**
945	* assoc_array_insert - Script insertion of an object into an associative array
946	* @array: The array to insert into.
947	* @ops: The operations to use.
948	* @index_key: The key to insert at.
949	* @object: The object to insert.
950	*
951	* Precalculate and preallocate a script for the insertion or replacement of an
952	* object in an associative array. This results in an edit script that can
953	* either be applied or cancelled.
954	*
955	* The function returns a pointer to an edit script or -ENOMEM.
956	*
957	* The caller should lock against other modifications and must continue to hold
958	* the lock until assoc_array_apply_edit() has been called.
959	*
960	* Accesses to the tree may take place concurrently with this function,
961	* provided they hold the RCU read lock.
962	*/
963	struct assoc_array_edit *assoc_array_insert(struct assoc_array *array,
964	const struct assoc_array_ops *ops,
965	const void *index_key,
966	void *object)
967	{
968	struct assoc_array_walk_result result;
969	struct assoc_array_edit *edit;
970
971	pr_devel("-->%s()\n", __func__);
972
973	/* The leaf pointer we're given must not have the bottom bit set as we
974	* use those for type-marking the pointer. NULL pointers are also not
975	* allowed as they indicate an empty slot but we have to allow them
976	* here as they can be updated later.
977	*/
978	BUG_ON(assoc_array_ptr_is_meta(object));
979
980	edit = kzalloc(size: sizeof(struct assoc_array_edit), GFP_KERNEL);
981	if (!edit)
982	return ERR_PTR(error: -ENOMEM);
983	edit->array = array;
984	edit->ops = ops;
985	edit->leaf = assoc_array_leaf_to_ptr(p: object);
986	edit->adjust_count_by = 1;
987
988	switch (assoc_array_walk(array, ops, index_key, result: &result)) {
989	case assoc_array_walk_tree_empty:
990	/* Allocate a root node if there isn't one yet */
991	if (!assoc_array_insert_in_empty_tree(edit))
992	goto enomem;
993	return edit;
994
995	case assoc_array_walk_found_terminal_node:
996	/* We found a node that doesn't have a node/shortcut pointer in
997	* the slot corresponding to the index key that we have to
998	* follow.
999	*/
1000	if (!assoc_array_insert_into_terminal_node(edit, ops, index_key,
1001	result: &result))
1002	goto enomem;
1003	return edit;
1004
1005	case assoc_array_walk_found_wrong_shortcut:
1006	/* We found a shortcut that didn't match our key in a slot we
1007	* needed to follow.
1008	*/
1009	if (!assoc_array_insert_mid_shortcut(edit, ops, result: &result))
1010	goto enomem;
1011	return edit;
1012	}
1013
1014	enomem:
1015	/* Clean up after an out of memory error */
1016	pr_devel("enomem\n");
1017	assoc_array_cancel_edit(edit);
1018	return ERR_PTR(error: -ENOMEM);
1019	}
1020
1021	/**
1022	* assoc_array_insert_set_object - Set the new object pointer in an edit script
1023	* @edit: The edit script to modify.
1024	* @object: The object pointer to set.
1025	*
1026	* Change the object to be inserted in an edit script. The object pointed to
1027	* by the old object is not freed. This must be done prior to applying the
1028	* script.
1029	*/
1030	void assoc_array_insert_set_object(struct assoc_array_edit *edit, void *object)
1031	{
1032	BUG_ON(!object);
1033	edit->leaf = assoc_array_leaf_to_ptr(p: object);
1034	}
1035
1036	struct assoc_array_delete_collapse_context {
1037	struct assoc_array_node *node;
1038	const void *skip_leaf;
1039	int slot;
1040	};
1041
1042	/*
1043	* Subtree collapse to node iterator.
1044	*/
1045	static int assoc_array_delete_collapse_iterator(const void *leaf,
1046	void *iterator_data)
1047	{
1048	struct assoc_array_delete_collapse_context *collapse = iterator_data;
1049
1050	if (leaf == collapse->skip_leaf)
1051	return 0;
1052
1053	BUG_ON(collapse->slot >= ASSOC_ARRAY_FAN_OUT);
1054
1055	collapse->node->slots[collapse->slot++] = assoc_array_leaf_to_ptr(p: leaf);
1056	return 0;
1057	}
1058
1059	/**
1060	* assoc_array_delete - Script deletion of an object from an associative array
1061	* @array: The array to search.
1062	* @ops: The operations to use.
1063	* @index_key: The key to the object.
1064	*
1065	* Precalculate and preallocate a script for the deletion of an object from an
1066	* associative array. This results in an edit script that can either be
1067	* applied or cancelled.
1068	*
1069	* The function returns a pointer to an edit script if the object was found,
1070	* NULL if the object was not found or -ENOMEM.
1071	*
1072	* The caller should lock against other modifications and must continue to hold
1073	* the lock until assoc_array_apply_edit() has been called.
1074	*
1075	* Accesses to the tree may take place concurrently with this function,
1076	* provided they hold the RCU read lock.
1077	*/
1078	struct assoc_array_edit *assoc_array_delete(struct assoc_array *array,
1079	const struct assoc_array_ops *ops,
1080	const void *index_key)
1081	{
1082	struct assoc_array_delete_collapse_context collapse;
1083	struct assoc_array_walk_result result;
1084	struct assoc_array_node *node, *new_n0;
1085	struct assoc_array_edit *edit;
1086	struct assoc_array_ptr *ptr;
1087	bool has_meta;
1088	int slot, i;
1089
1090	pr_devel("-->%s()\n", __func__);
1091
1092	edit = kzalloc(size: sizeof(struct assoc_array_edit), GFP_KERNEL);
1093	if (!edit)
1094	return ERR_PTR(error: -ENOMEM);
1095	edit->array = array;
1096	edit->ops = ops;
1097	edit->adjust_count_by = -1;
1098
1099	switch (assoc_array_walk(array, ops, index_key, result: &result)) {
1100	case assoc_array_walk_found_terminal_node:
1101	/* We found a node that should contain the leaf we've been
1102	* asked to remove - *if* it's in the tree.
1103	*/
1104	pr_devel("terminal_node\n");
1105	node = result.terminal_node.node;
1106
1107	for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1108	ptr = node->slots[slot];
1109	if (ptr &&
1110	assoc_array_ptr_is_leaf(x: ptr) &&
1111	ops->compare_object(assoc_array_ptr_to_leaf(x: ptr),
1112	index_key))
1113	goto found_leaf;
1114	}
1115	fallthrough;
1116	case assoc_array_walk_tree_empty:
1117	case assoc_array_walk_found_wrong_shortcut:
1118	default:
1119	assoc_array_cancel_edit(edit);
1120	pr_devel("not found\n");
1121	return NULL;
1122	}
1123
1124	found_leaf:
1125	BUG_ON(array->nr_leaves_on_tree <= 0);
1126
1127	/* In the simplest form of deletion we just clear the slot and release
1128	* the leaf after a suitable interval.
1129	*/
1130	edit->dead_leaf = node->slots[slot];
1131	edit->set[0].ptr = &node->slots[slot];
1132	edit->set[0].to = NULL;
1133	edit->adjust_count_on = node;
1134
1135	/* If that concludes erasure of the last leaf, then delete the entire
1136	* internal array.
1137	*/
1138	if (array->nr_leaves_on_tree == 1) {
1139	edit->set[1].ptr = &array->root;
1140	edit->set[1].to = NULL;
1141	edit->adjust_count_on = NULL;
1142	edit->excised_subtree = array->root;
1143	pr_devel("all gone\n");
1144	return edit;
1145	}
1146
1147	/* However, we'd also like to clear up some metadata blocks if we
1148	* possibly can.
1149	*
1150	* We go for a simple algorithm of: if this node has FAN_OUT or fewer
1151	* leaves in it, then attempt to collapse it - and attempt to
1152	* recursively collapse up the tree.
1153	*
1154	* We could also try and collapse in partially filled subtrees to take
1155	* up space in this node.
1156	*/
1157	if (node->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1158	struct assoc_array_node *parent, *grandparent;
1159	struct assoc_array_ptr *ptr;
1160
1161	/* First of all, we need to know if this node has metadata so
1162	* that we don't try collapsing if all the leaves are already
1163	* here.
1164	*/
1165	has_meta = false;
1166	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1167	ptr = node->slots[i];
1168	if (assoc_array_ptr_is_meta(x: ptr)) {
1169	has_meta = true;
1170	break;
1171	}
1172	}
1173
1174	pr_devel("leaves: %ld [m=%d]\n",
1175	node->nr_leaves_on_branch - 1, has_meta);
1176
1177	/* Look further up the tree to see if we can collapse this node
1178	* into a more proximal node too.
1179	*/
1180	parent = node;
1181	collapse_up:
1182	pr_devel("collapse subtree: %ld\n", parent->nr_leaves_on_branch);
1183
1184	ptr = parent->back_pointer;
1185	if (!ptr)
1186	goto do_collapse;
1187	if (assoc_array_ptr_is_shortcut(x: ptr)) {
1188	struct assoc_array_shortcut *s = assoc_array_ptr_to_shortcut(x: ptr);
1189	ptr = s->back_pointer;
1190	if (!ptr)
1191	goto do_collapse;
1192	}
1193
1194	grandparent = assoc_array_ptr_to_node(x: ptr);
1195	if (grandparent->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) {
1196	parent = grandparent;
1197	goto collapse_up;
1198	}
1199
1200	do_collapse:
1201	/* There's no point collapsing if the original node has no meta
1202	* pointers to discard and if we didn't merge into one of that
1203	* node's ancestry.
1204	*/
1205	if (has_meta || parent != node) {
1206	node = parent;
1207
1208	/* Create a new node to collapse into */
1209	new_n0 = kzalloc(size: sizeof(struct assoc_array_node), GFP_KERNEL);
1210	if (!new_n0)
1211	goto enomem;
1212	edit->new_meta[0] = assoc_array_node_to_ptr(p: new_n0);
1213
1214	new_n0->back_pointer = node->back_pointer;
1215	new_n0->parent_slot = node->parent_slot;
1216	new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch;
1217	edit->adjust_count_on = new_n0;
1218
1219	collapse.node = new_n0;
1220	collapse.skip_leaf = assoc_array_ptr_to_leaf(x: edit->dead_leaf);
1221	collapse.slot = 0;
1222	assoc_array_subtree_iterate(root: assoc_array_node_to_ptr(p: node),
1223	stop: node->back_pointer,
1224	iterator: assoc_array_delete_collapse_iterator,
1225	iterator_data: &collapse);
1226	pr_devel("collapsed %d,%lu\n", collapse.slot, new_n0->nr_leaves_on_branch);
1227	BUG_ON(collapse.slot != new_n0->nr_leaves_on_branch - 1);
1228
1229	if (!node->back_pointer) {
1230	edit->set[1].ptr = &array->root;
1231	} else if (assoc_array_ptr_is_leaf(x: node->back_pointer)) {
1232	BUG();
1233	} else if (assoc_array_ptr_is_node(x: node->back_pointer)) {
1234	struct assoc_array_node *p =
1235	assoc_array_ptr_to_node(x: node->back_pointer);
1236	edit->set[1].ptr = &p->slots[node->parent_slot];
1237	} else if (assoc_array_ptr_is_shortcut(x: node->back_pointer)) {
1238	struct assoc_array_shortcut *s =
1239	assoc_array_ptr_to_shortcut(x: node->back_pointer);
1240	edit->set[1].ptr = &s->next_node;
1241	}
1242	edit->set[1].to = assoc_array_node_to_ptr(p: new_n0);
1243	edit->excised_subtree = assoc_array_node_to_ptr(p: node);
1244	}
1245	}
1246
1247	return edit;
1248
1249	enomem:
1250	/* Clean up after an out of memory error */
1251	pr_devel("enomem\n");
1252	assoc_array_cancel_edit(edit);
1253	return ERR_PTR(error: -ENOMEM);
1254	}
1255
1256	/**
1257	* assoc_array_clear - Script deletion of all objects from an associative array
1258	* @array: The array to clear.
1259	* @ops: The operations to use.
1260	*
1261	* Precalculate and preallocate a script for the deletion of all the objects
1262	* from an associative array. This results in an edit script that can either
1263	* be applied or cancelled.
1264	*
1265	* The function returns a pointer to an edit script if there are objects to be
1266	* deleted, NULL if there are no objects in the array or -ENOMEM.
1267	*
1268	* The caller should lock against other modifications and must continue to hold
1269	* the lock until assoc_array_apply_edit() has been called.
1270	*
1271	* Accesses to the tree may take place concurrently with this function,
1272	* provided they hold the RCU read lock.
1273	*/
1274	struct assoc_array_edit *assoc_array_clear(struct assoc_array *array,
1275	const struct assoc_array_ops *ops)
1276	{
1277	struct assoc_array_edit *edit;
1278
1279	pr_devel("-->%s()\n", __func__);
1280
1281	if (!array->root)
1282	return NULL;
1283
1284	edit = kzalloc(size: sizeof(struct assoc_array_edit), GFP_KERNEL);
1285	if (!edit)
1286	return ERR_PTR(error: -ENOMEM);
1287	edit->array = array;
1288	edit->ops = ops;
1289	edit->set[1].ptr = &array->root;
1290	edit->set[1].to = NULL;
1291	edit->excised_subtree = array->root;
1292	edit->ops_for_excised_subtree = ops;
1293	pr_devel("all gone\n");
1294	return edit;
1295	}
1296
1297	/*
1298	* Handle the deferred destruction after an applied edit.
1299	*/
1300	static void assoc_array_rcu_cleanup(struct rcu_head *head)
1301	{
1302	struct assoc_array_edit *edit =
1303	container_of(head, struct assoc_array_edit, rcu);
1304	int i;
1305
1306	pr_devel("-->%s()\n", __func__);
1307
1308	if (edit->dead_leaf)
1309	edit->ops->free_object(assoc_array_ptr_to_leaf(x: edit->dead_leaf));
1310	for (i = 0; i < ARRAY_SIZE(edit->excised_meta); i++)
1311	if (edit->excised_meta[i])
1312	kfree(objp: assoc_array_ptr_to_node(x: edit->excised_meta[i]));
1313
1314	if (edit->excised_subtree) {
1315	BUG_ON(assoc_array_ptr_is_leaf(edit->excised_subtree));
1316	if (assoc_array_ptr_is_node(x: edit->excised_subtree)) {
1317	struct assoc_array_node *n =
1318	assoc_array_ptr_to_node(x: edit->excised_subtree);
1319	n->back_pointer = NULL;
1320	} else {
1321	struct assoc_array_shortcut *s =
1322	assoc_array_ptr_to_shortcut(x: edit->excised_subtree);
1323	s->back_pointer = NULL;
1324	}
1325	assoc_array_destroy_subtree(root: edit->excised_subtree,
1326	ops: edit->ops_for_excised_subtree);
1327	}
1328
1329	kfree(objp: edit);
1330	}
1331
1332	/**
1333	* assoc_array_apply_edit - Apply an edit script to an associative array
1334	* @edit: The script to apply.
1335	*
1336	* Apply an edit script to an associative array to effect an insertion,
1337	* deletion or clearance. As the edit script includes preallocated memory,
1338	* this is guaranteed not to fail.
1339	*
1340	* The edit script, dead objects and dead metadata will be scheduled for
1341	* destruction after an RCU grace period to permit those doing read-only
1342	* accesses on the array to continue to do so under the RCU read lock whilst
1343	* the edit is taking place.
1344	*/
1345	void assoc_array_apply_edit(struct assoc_array_edit *edit)
1346	{
1347	struct assoc_array_shortcut *shortcut;
1348	struct assoc_array_node *node;
1349	struct assoc_array_ptr *ptr;
1350	int i;
1351
1352	pr_devel("-->%s()\n", __func__);
1353
1354	smp_wmb();
1355	if (edit->leaf_p)
1356	*edit->leaf_p = edit->leaf;
1357
1358	smp_wmb();
1359	for (i = 0; i < ARRAY_SIZE(edit->set_parent_slot); i++)
1360	if (edit->set_parent_slot[i].p)
1361	*edit->set_parent_slot[i].p = edit->set_parent_slot[i].to;
1362
1363	smp_wmb();
1364	for (i = 0; i < ARRAY_SIZE(edit->set_backpointers); i++)
1365	if (edit->set_backpointers[i])
1366	*edit->set_backpointers[i] = edit->set_backpointers_to;
1367
1368	smp_wmb();
1369	for (i = 0; i < ARRAY_SIZE(edit->set); i++)
1370	if (edit->set[i].ptr)
1371	*edit->set[i].ptr = edit->set[i].to;
1372
1373	if (edit->array->root == NULL) {
1374	edit->array->nr_leaves_on_tree = 0;
1375	} else if (edit->adjust_count_on) {
1376	node = edit->adjust_count_on;
1377	for (;;) {
1378	node->nr_leaves_on_branch += edit->adjust_count_by;
1379
1380	ptr = node->back_pointer;
1381	if (!ptr)
1382	break;
1383	if (assoc_array_ptr_is_shortcut(x: ptr)) {
1384	shortcut = assoc_array_ptr_to_shortcut(x: ptr);
1385	ptr = shortcut->back_pointer;
1386	if (!ptr)
1387	break;
1388	}
1389	BUG_ON(!assoc_array_ptr_is_node(ptr));
1390	node = assoc_array_ptr_to_node(x: ptr);
1391	}
1392
1393	edit->array->nr_leaves_on_tree += edit->adjust_count_by;
1394	}
1395
1396	call_rcu(head: &edit->rcu, func: assoc_array_rcu_cleanup);
1397	}
1398
1399	/**
1400	* assoc_array_cancel_edit - Discard an edit script.
1401	* @edit: The script to discard.
1402	*
1403	* Free an edit script and all the preallocated data it holds without making
1404	* any changes to the associative array it was intended for.
1405	*
1406	* NOTE! In the case of an insertion script, this does _not_ release the leaf
1407	* that was to be inserted. That is left to the caller.
1408	*/
1409	void assoc_array_cancel_edit(struct assoc_array_edit *edit)
1410	{
1411	struct assoc_array_ptr *ptr;
1412	int i;
1413
1414	pr_devel("-->%s()\n", __func__);
1415
1416	/* Clean up after an out of memory error */
1417	for (i = 0; i < ARRAY_SIZE(edit->new_meta); i++) {
1418	ptr = edit->new_meta[i];
1419	if (ptr) {
1420	if (assoc_array_ptr_is_node(x: ptr))
1421	kfree(objp: assoc_array_ptr_to_node(x: ptr));
1422	else
1423	kfree(objp: assoc_array_ptr_to_shortcut(x: ptr));
1424	}
1425	}
1426	kfree(objp: edit);
1427	}
1428
1429	/**
1430	* assoc_array_gc - Garbage collect an associative array.
1431	* @array: The array to clean.
1432	* @ops: The operations to use.
1433	* @iterator: A callback function to pass judgement on each object.
1434	* @iterator_data: Private data for the callback function.
1435	*
1436	* Collect garbage from an associative array and pack down the internal tree to
1437	* save memory.
1438	*
1439	* The iterator function is asked to pass judgement upon each object in the
1440	* array. If it returns false, the object is discard and if it returns true,
1441	* the object is kept. If it returns true, it must increment the object's
1442	* usage count (or whatever it needs to do to retain it) before returning.
1443	*
1444	* This function returns 0 if successful or -ENOMEM if out of memory. In the
1445	* latter case, the array is not changed.
1446	*
1447	* The caller should lock against other modifications and must continue to hold
1448	* the lock until assoc_array_apply_edit() has been called.
1449	*
1450	* Accesses to the tree may take place concurrently with this function,
1451	* provided they hold the RCU read lock.
1452	*/
1453	int assoc_array_gc(struct assoc_array *array,
1454	const struct assoc_array_ops *ops,
1455	bool (*iterator)(void *object, void *iterator_data),
1456	void *iterator_data)
1457	{
1458	struct assoc_array_shortcut *shortcut, *new_s;
1459	struct assoc_array_node *node, *new_n;
1460	struct assoc_array_edit *edit;
1461	struct assoc_array_ptr *cursor, *ptr;
1462	struct assoc_array_ptr *new_root, *new_parent, **new_ptr_pp;
1463	unsigned long nr_leaves_on_tree;
1464	bool retained;
1465	int keylen, slot, nr_free, next_slot, i;
1466
1467	pr_devel("-->%s()\n", __func__);
1468
1469	if (!array->root)
1470	return 0;
1471
1472	edit = kzalloc(size: sizeof(struct assoc_array_edit), GFP_KERNEL);
1473	if (!edit)
1474	return -ENOMEM;
1475	edit->array = array;
1476	edit->ops = ops;
1477	edit->ops_for_excised_subtree = ops;
1478	edit->set[0].ptr = &array->root;
1479	edit->excised_subtree = array->root;
1480
1481	new_root = new_parent = NULL;
1482	new_ptr_pp = &new_root;
1483	cursor = array->root;
1484
1485	descend:
1486	/* If this point is a shortcut, then we need to duplicate it and
1487	* advance the target cursor.
1488	*/
1489	if (assoc_array_ptr_is_shortcut(x: cursor)) {
1490	shortcut = assoc_array_ptr_to_shortcut(x: cursor);
1491	keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
1492	keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
1493	new_s = kmalloc(struct_size(new_s, index_key, keylen),
1494	GFP_KERNEL);
1495	if (!new_s)
1496	goto enomem;
1497	pr_devel("dup shortcut %p -> %p\n", shortcut, new_s);
1498	memcpy(new_s, shortcut, struct_size(new_s, index_key, keylen));
1499	new_s->back_pointer = new_parent;
1500	new_s->parent_slot = shortcut->parent_slot;
1501	*new_ptr_pp = new_parent = assoc_array_shortcut_to_ptr(p: new_s);
1502	new_ptr_pp = &new_s->next_node;
1503	cursor = shortcut->next_node;
1504	}
1505
1506	/* Duplicate the node at this position */
1507	node = assoc_array_ptr_to_node(x: cursor);
1508	new_n = kzalloc(size: sizeof(struct assoc_array_node), GFP_KERNEL);
1509	if (!new_n)
1510	goto enomem;
1511	pr_devel("dup node %p -> %p\n", node, new_n);
1512	new_n->back_pointer = new_parent;
1513	new_n->parent_slot = node->parent_slot;
1514	*new_ptr_pp = new_parent = assoc_array_node_to_ptr(p: new_n);
1515	new_ptr_pp = NULL;
1516	slot = 0;
1517
1518	continue_node:
1519	/* Filter across any leaves and gc any subtrees */
1520	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1521	ptr = node->slots[slot];
1522	if (!ptr)
1523	continue;
1524
1525	if (assoc_array_ptr_is_leaf(x: ptr)) {
1526	if (iterator(assoc_array_ptr_to_leaf(x: ptr),
1527	iterator_data))
1528	/* The iterator will have done any reference
1529	* counting on the object for us.
1530	*/
1531	new_n->slots[slot] = ptr;
1532	continue;
1533	}
1534
1535	new_ptr_pp = &new_n->slots[slot];
1536	cursor = ptr;
1537	goto descend;
1538	}
1539
1540	retry_compress:
1541	pr_devel("-- compress node %p --\n", new_n);
1542
1543	/* Count up the number of empty slots in this node and work out the
1544	* subtree leaf count.
1545	*/
1546	new_n->nr_leaves_on_branch = 0;
1547	nr_free = 0;
1548	for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1549	ptr = new_n->slots[slot];
1550	if (!ptr)
1551	nr_free++;
1552	else if (assoc_array_ptr_is_leaf(x: ptr))
1553	new_n->nr_leaves_on_branch++;
1554	}
1555	pr_devel("free=%d, leaves=%lu\n", nr_free, new_n->nr_leaves_on_branch);
1556
1557	/* See what we can fold in */
1558	retained = false;
1559	next_slot = 0;
1560	for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
1561	struct assoc_array_shortcut *s;
1562	struct assoc_array_node *child;
1563
1564	ptr = new_n->slots[slot];
1565	if (!ptr || assoc_array_ptr_is_leaf(x: ptr))
1566	continue;
1567
1568	s = NULL;
1569	if (assoc_array_ptr_is_shortcut(x: ptr)) {
1570	s = assoc_array_ptr_to_shortcut(x: ptr);
1571	ptr = s->next_node;
1572	}
1573
1574	child = assoc_array_ptr_to_node(x: ptr);
1575	new_n->nr_leaves_on_branch += child->nr_leaves_on_branch;
1576
1577	if (child->nr_leaves_on_branch <= nr_free + 1) {
1578	/* Fold the child node into this one */
1579	pr_devel("[%d] fold node %lu/%d [nx %d]\n",
1580	slot, child->nr_leaves_on_branch, nr_free + 1,
1581	next_slot);
1582
1583	/* We would already have reaped an intervening shortcut
1584	* on the way back up the tree.
1585	*/
1586	BUG_ON(s);
1587
1588	new_n->slots[slot] = NULL;
1589	nr_free++;
1590	if (slot < next_slot)
1591	next_slot = slot;
1592	for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) {
1593	struct assoc_array_ptr *p = child->slots[i];
1594	if (!p)
1595	continue;
1596	BUG_ON(assoc_array_ptr_is_meta(p));
1597	while (new_n->slots[next_slot])
1598	next_slot++;
1599	BUG_ON(next_slot >= ASSOC_ARRAY_FAN_OUT);
1600	new_n->slots[next_slot++] = p;
1601	nr_free--;
1602	}
1603	kfree(objp: child);
1604	} else {
1605	pr_devel("[%d] retain node %lu/%d [nx %d]\n",
1606	slot, child->nr_leaves_on_branch, nr_free + 1,
1607	next_slot);
1608	retained = true;
1609	}
1610	}
1611
1612	if (retained && new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) {
1613	pr_devel("internal nodes remain despite enough space, retrying\n");
1614	goto retry_compress;
1615	}
1616	pr_devel("after: %lu\n", new_n->nr_leaves_on_branch);
1617
1618	nr_leaves_on_tree = new_n->nr_leaves_on_branch;
1619
1620	/* Excise this node if it is singly occupied by a shortcut */
1621	if (nr_free == ASSOC_ARRAY_FAN_OUT - 1) {
1622	for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++)
1623	if ((ptr = new_n->slots[slot]))
1624	break;
1625
1626	if (assoc_array_ptr_is_meta(x: ptr) &&
1627	assoc_array_ptr_is_shortcut(x: ptr)) {
1628	pr_devel("excise node %p with 1 shortcut\n", new_n);
1629	new_s = assoc_array_ptr_to_shortcut(x: ptr);
1630	new_parent = new_n->back_pointer;
1631	slot = new_n->parent_slot;
1632	kfree(objp: new_n);
1633	if (!new_parent) {
1634	new_s->back_pointer = NULL;
1635	new_s->parent_slot = 0;
1636	new_root = ptr;
1637	goto gc_complete;
1638	}
1639
1640	if (assoc_array_ptr_is_shortcut(x: new_parent)) {
1641	/* We can discard any preceding shortcut also */
1642	struct assoc_array_shortcut *s =
1643	assoc_array_ptr_to_shortcut(x: new_parent);
1644
1645	pr_devel("excise preceding shortcut\n");
1646
1647	new_parent = new_s->back_pointer = s->back_pointer;
1648	slot = new_s->parent_slot = s->parent_slot;
1649	kfree(objp: s);
1650	if (!new_parent) {
1651	new_s->back_pointer = NULL;
1652	new_s->parent_slot = 0;
1653	new_root = ptr;
1654	goto gc_complete;
1655	}
1656	}
1657
1658	new_s->back_pointer = new_parent;
1659	new_s->parent_slot = slot;
1660	new_n = assoc_array_ptr_to_node(x: new_parent);
1661	new_n->slots[slot] = ptr;
1662	goto ascend_old_tree;
1663	}
1664	}
1665
1666	/* Excise any shortcuts we might encounter that point to nodes that
1667	* only contain leaves.
1668	*/
1669	ptr = new_n->back_pointer;
1670	if (!ptr)
1671	goto gc_complete;
1672
1673	if (assoc_array_ptr_is_shortcut(x: ptr)) {
1674	new_s = assoc_array_ptr_to_shortcut(x: ptr);
1675	new_parent = new_s->back_pointer;
1676	slot = new_s->parent_slot;
1677
1678	if (new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) {
1679	struct assoc_array_node *n;
1680
1681	pr_devel("excise shortcut\n");
1682	new_n->back_pointer = new_parent;
1683	new_n->parent_slot = slot;
1684	kfree(objp: new_s);
1685	if (!new_parent) {
1686	new_root = assoc_array_node_to_ptr(p: new_n);
1687	goto gc_complete;
1688	}
1689
1690	n = assoc_array_ptr_to_node(x: new_parent);
1691	n->slots[slot] = assoc_array_node_to_ptr(p: new_n);
1692	}
1693	} else {
1694	new_parent = ptr;
1695	}
1696	new_n = assoc_array_ptr_to_node(x: new_parent);
1697
1698	ascend_old_tree:
1699	ptr = node->back_pointer;
1700	if (assoc_array_ptr_is_shortcut(x: ptr)) {
1701	shortcut = assoc_array_ptr_to_shortcut(x: ptr);
1702	slot = shortcut->parent_slot;
1703	cursor = shortcut->back_pointer;
1704	if (!cursor)
1705	goto gc_complete;
1706	} else {
1707	slot = node->parent_slot;
1708	cursor = ptr;
1709	}
1710	BUG_ON(!cursor);
1711	node = assoc_array_ptr_to_node(x: cursor);
1712	slot++;
1713	goto continue_node;
1714
1715	gc_complete:
1716	edit->set[0].to = new_root;
1717	assoc_array_apply_edit(edit);
1718	array->nr_leaves_on_tree = nr_leaves_on_tree;
1719	return 0;
1720
1721	enomem:
1722	pr_devel("enomem\n");
1723	assoc_array_destroy_subtree(root: new_root, ops: edit->ops);
1724	kfree(objp: edit);
1725	return -ENOMEM;
1726	}
1727