diff options
Diffstat (limited to 'lib/assoc_array.c')
| -rw-r--r-- | lib/assoc_array.c | 1728 |
1 files changed, 1728 insertions, 0 deletions
diff --git a/lib/assoc_array.c b/lib/assoc_array.c new file mode 100644 index 000000000..b537a8367 --- /dev/null +++ b/lib/assoc_array.c @@ -0,0 +1,1728 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* Generic associative array implementation. + * + * See Documentation/core-api/assoc_array.rst for information. + * + * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + */ +//#define DEBUG +#include <linux/rcupdate.h> +#include <linux/slab.h> +#include <linux/err.h> +#include <linux/assoc_array_priv.h> + +/* + * Iterate over an associative array. The caller must hold the RCU read lock + * or better. + */ +static int assoc_array_subtree_iterate(const struct assoc_array_ptr *root, + const struct assoc_array_ptr *stop, + int (*iterator)(const void *leaf, + void *iterator_data), + void *iterator_data) +{ + const struct assoc_array_shortcut *shortcut; + const struct assoc_array_node *node; + const struct assoc_array_ptr *cursor, *ptr, *parent; + unsigned long has_meta; + int slot, ret; + + cursor = root; + +begin_node: + if (assoc_array_ptr_is_shortcut(cursor)) { + /* Descend through a shortcut */ + shortcut = assoc_array_ptr_to_shortcut(cursor); + cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */ + } + + node = assoc_array_ptr_to_node(cursor); + slot = 0; + + /* We perform two passes of each node. + * + * The first pass does all the leaves in this node. This means we + * don't miss any leaves if the node is split up by insertion whilst + * we're iterating over the branches rooted here (we may, however, see + * some leaves twice). + */ + has_meta = 0; + for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ + has_meta |= (unsigned long)ptr; + if (ptr && assoc_array_ptr_is_leaf(ptr)) { + /* We need a barrier between the read of the pointer, + * which is supplied by the above READ_ONCE(). + */ + /* Invoke the callback */ + ret = iterator(assoc_array_ptr_to_leaf(ptr), + iterator_data); + if (ret) + return ret; + } + } + + /* The second pass attends to all the metadata pointers. If we follow + * one of these we may find that we don't come back here, but rather go + * back to a replacement node with the leaves in a different layout. + * + * We are guaranteed to make progress, however, as the slot number for + * a particular portion of the key space cannot change - and we + * continue at the back pointer + 1. + */ + if (!(has_meta & ASSOC_ARRAY_PTR_META_TYPE)) + goto finished_node; + slot = 0; + +continue_node: + node = assoc_array_ptr_to_node(cursor); + for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ + if (assoc_array_ptr_is_meta(ptr)) { + cursor = ptr; + goto begin_node; + } + } + +finished_node: + /* Move up to the parent (may need to skip back over a shortcut) */ + parent = READ_ONCE(node->back_pointer); /* Address dependency. */ + slot = node->parent_slot; + if (parent == stop) + return 0; + + if (assoc_array_ptr_is_shortcut(parent)) { + shortcut = assoc_array_ptr_to_shortcut(parent); + cursor = parent; + parent = READ_ONCE(shortcut->back_pointer); /* Address dependency. */ + slot = shortcut->parent_slot; + if (parent == stop) + return 0; + } + + /* Ascend to next slot in parent node */ + cursor = parent; + slot++; + goto continue_node; +} + +/** + * assoc_array_iterate - Pass all objects in the array to a callback + * @array: The array to iterate over. + * @iterator: The callback function. + * @iterator_data: Private data for the callback function. + * + * Iterate over all the objects in an associative array. Each one will be + * presented to the iterator function. + * + * If the array is being modified concurrently with the iteration then it is + * possible that some objects in the array will be passed to the iterator + * callback more than once - though every object should be passed at least + * once. If this is undesirable then the caller must lock against modification + * for the duration of this function. + * + * The function will return 0 if no objects were in the array or else it will + * return the result of the last iterator function called. Iteration stops + * immediately if any call to the iteration function results in a non-zero + * return. + * + * The caller should hold the RCU read lock or better if concurrent + * modification is possible. + */ +int assoc_array_iterate(const struct assoc_array *array, + int (*iterator)(const void *object, + void *iterator_data), + void *iterator_data) +{ + struct assoc_array_ptr *root = READ_ONCE(array->root); /* Address dependency. */ + + if (!root) + return 0; + return assoc_array_subtree_iterate(root, NULL, iterator, iterator_data); +} + +enum assoc_array_walk_status { + assoc_array_walk_tree_empty, + assoc_array_walk_found_terminal_node, + assoc_array_walk_found_wrong_shortcut, +}; + +struct assoc_array_walk_result { + struct { + struct assoc_array_node *node; /* Node in which leaf might be found */ + int level; + int slot; + } terminal_node; + struct { + struct assoc_array_shortcut *shortcut; + int level; + int sc_level; + unsigned long sc_segments; + unsigned long dissimilarity; + } wrong_shortcut; +}; + +/* + * Navigate through the internal tree looking for the closest node to the key. + */ +static enum assoc_array_walk_status +assoc_array_walk(const struct assoc_array *array, + const struct assoc_array_ops *ops, + const void *index_key, + struct assoc_array_walk_result *result) +{ + struct assoc_array_shortcut *shortcut; + struct assoc_array_node *node; + struct assoc_array_ptr *cursor, *ptr; + unsigned long sc_segments, dissimilarity; + unsigned long segments; + int level, sc_level, next_sc_level; + int slot; + + pr_devel("-->%s()\n", __func__); + + cursor = READ_ONCE(array->root); /* Address dependency. */ + if (!cursor) + return assoc_array_walk_tree_empty; + + level = 0; + + /* Use segments from the key for the new leaf to navigate through the + * internal tree, skipping through nodes and shortcuts that are on + * route to the destination. Eventually we'll come to a slot that is + * either empty or contains a leaf at which point we've found a node in + * which the leaf we're looking for might be found or into which it + * should be inserted. + */ +jumped: + segments = ops->get_key_chunk(index_key, level); + pr_devel("segments[%d]: %lx\n", level, segments); + + if (assoc_array_ptr_is_shortcut(cursor)) + goto follow_shortcut; + +consider_node: + node = assoc_array_ptr_to_node(cursor); + slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK); + slot &= ASSOC_ARRAY_FAN_MASK; + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ + + pr_devel("consider slot %x [ix=%d type=%lu]\n", + slot, level, (unsigned long)ptr & 3); + + if (!assoc_array_ptr_is_meta(ptr)) { + /* The node doesn't have a node/shortcut pointer in the slot + * corresponding to the index key that we have to follow. + */ + result->terminal_node.node = node; + result->terminal_node.level = level; + result->terminal_node.slot = slot; + pr_devel("<--%s() = terminal_node\n", __func__); + return assoc_array_walk_found_terminal_node; + } + + if (assoc_array_ptr_is_node(ptr)) { + /* There is a pointer to a node in the slot corresponding to + * this index key segment, so we need to follow it. + */ + cursor = ptr; + level += ASSOC_ARRAY_LEVEL_STEP; + if ((level & ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) + goto consider_node; + goto jumped; + } + + /* There is a shortcut in the slot corresponding to the index key + * segment. We follow the shortcut if its partial index key matches + * this leaf's. Otherwise we need to split the shortcut. + */ + cursor = ptr; +follow_shortcut: + shortcut = assoc_array_ptr_to_shortcut(cursor); + pr_devel("shortcut to %d\n", shortcut->skip_to_level); + sc_level = level + ASSOC_ARRAY_LEVEL_STEP; + BUG_ON(sc_level > shortcut->skip_to_level); + + do { + /* Check the leaf against the shortcut's index key a word at a + * time, trimming the final word (the shortcut stores the index + * key completely from the root to the shortcut's target). + */ + if ((sc_level & ASSOC_ARRAY_KEY_CHUNK_MASK) == 0) + segments = ops->get_key_chunk(index_key, sc_level); + + sc_segments = shortcut->index_key[sc_level >> ASSOC_ARRAY_KEY_CHUNK_SHIFT]; + dissimilarity = segments ^ sc_segments; + + if (round_up(sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE) > shortcut->skip_to_level) { + /* Trim segments that are beyond the shortcut */ + int shift = shortcut->skip_to_level & ASSOC_ARRAY_KEY_CHUNK_MASK; + dissimilarity &= ~(ULONG_MAX << shift); + next_sc_level = shortcut->skip_to_level; + } else { + next_sc_level = sc_level + ASSOC_ARRAY_KEY_CHUNK_SIZE; + next_sc_level = round_down(next_sc_level, ASSOC_ARRAY_KEY_CHUNK_SIZE); + } + + if (dissimilarity != 0) { + /* This shortcut points elsewhere */ + result->wrong_shortcut.shortcut = shortcut; + result->wrong_shortcut.level = level; + result->wrong_shortcut.sc_level = sc_level; + result->wrong_shortcut.sc_segments = sc_segments; + result->wrong_shortcut.dissimilarity = dissimilarity; + return assoc_array_walk_found_wrong_shortcut; + } + + sc_level = next_sc_level; + } while (sc_level < shortcut->skip_to_level); + + /* The shortcut matches the leaf's index to this point. */ + cursor = READ_ONCE(shortcut->next_node); /* Address dependency. */ + if (((level ^ sc_level) & ~ASSOC_ARRAY_KEY_CHUNK_MASK) != 0) { + level = sc_level; + goto jumped; + } else { + level = sc_level; + goto consider_node; + } +} + +/** + * assoc_array_find - Find an object by index key + * @array: The associative array to search. + * @ops: The operations to use. + * @index_key: The key to the object. + * + * Find an object in an associative array by walking through the internal tree + * to the node that should contain the object and then searching the leaves + * there. NULL is returned if the requested object was not found in the array. + * + * The caller must hold the RCU read lock or better. + */ +void *assoc_array_find(const struct assoc_array *array, + const struct assoc_array_ops *ops, + const void *index_key) +{ + struct assoc_array_walk_result result; + const struct assoc_array_node *node; + const struct assoc_array_ptr *ptr; + const void *leaf; + int slot; + + if (assoc_array_walk(array, ops, index_key, &result) != + assoc_array_walk_found_terminal_node) + return NULL; + + node = result.terminal_node.node; + + /* If the target key is available to us, it's has to be pointed to by + * the terminal node. + */ + for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) { + ptr = READ_ONCE(node->slots[slot]); /* Address dependency. */ + if (ptr && assoc_array_ptr_is_leaf(ptr)) { + /* We need a barrier between the read of the pointer + * and dereferencing the pointer - but only if we are + * actually going to dereference it. + */ + leaf = assoc_array_ptr_to_leaf(ptr); + if (ops->compare_object(leaf, index_key)) + return (void *)leaf; + } + } + + return NULL; +} + +/* + * Destructively iterate over an associative array. The caller must prevent + * other simultaneous accesses. + */ +static void assoc_array_destroy_subtree(struct assoc_array_ptr *root, + const struct assoc_array_ops *ops) +{ + struct assoc_array_shortcut *shortcut; + struct assoc_array_node *node; + struct assoc_array_ptr *cursor, *parent = NULL; + int slot = -1; + + pr_devel("-->%s()\n", __func__); + + cursor = root; + if (!cursor) { + pr_devel("empty\n"); + return; + } + +move_to_meta: + if (assoc_array_ptr_is_shortcut(cursor)) { + /* Descend through a shortcut */ + pr_devel("[%d] shortcut\n", slot); + BUG_ON(!assoc_array_ptr_is_shortcut(cursor)); + shortcut = assoc_array_ptr_to_shortcut(cursor); + BUG_ON(shortcut->back_pointer != parent); + BUG_ON(slot != -1 && shortcut->parent_slot != slot); + parent = cursor; + cursor = shortcut->next_node; + slot = -1; + BUG_ON(!assoc_array_ptr_is_node(cursor)); + } + + pr_devel("[%d] node\n", slot); + node = assoc_array_ptr_to_node(cursor); + BUG_ON(node->back_pointer != parent); + BUG_ON(slot != -1 && node->parent_slot != slot); + slot = 0; + +continue_node: + pr_devel("Node %p [back=%p]\n", node, node->back_pointer); + for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { + struct assoc_array_ptr *ptr = node->slots[slot]; + if (!ptr) + continue; + if (assoc_array_ptr_is_meta(ptr)) { + parent = cursor; + cursor = ptr; + goto move_to_meta; + } + + if (ops) { + pr_devel("[%d] free leaf\n", slot); + ops->free_object(assoc_array_ptr_to_leaf(ptr)); + } + } + + parent = node->back_pointer; + slot = node->parent_slot; + pr_devel("free node\n"); + kfree(node); + if (!parent) + return; /* Done */ + + /* Move back up to the parent (may need to free a shortcut on + * the way up) */ + if (assoc_array_ptr_is_shortcut(parent)) { + shortcut = assoc_array_ptr_to_shortcut(parent); + BUG_ON(shortcut->next_node != cursor); + cursor = parent; + parent = shortcut->back_pointer; + slot = shortcut->parent_slot; + pr_devel("free shortcut\n"); + kfree(shortcut); + if (!parent) + return; + + BUG_ON(!assoc_array_ptr_is_node(parent)); + } + + /* Ascend to next slot in parent node */ + pr_devel("ascend to %p[%d]\n", parent, slot); + cursor = parent; + node = assoc_array_ptr_to_node(cursor); + slot++; + goto continue_node; +} + +/** + * assoc_array_destroy - Destroy an associative array + * @array: The array to destroy. + * @ops: The operations to use. + * + * Discard all metadata and free all objects in an associative array. The + * array will be empty and ready to use again upon completion. This function + * cannot fail. + * + * The caller must prevent all other accesses whilst this takes place as no + * attempt is made to adjust pointers gracefully to permit RCU readlock-holding + * accesses to continue. On the other hand, no memory allocation is required. + */ +void assoc_array_destroy(struct assoc_array *array, + const struct assoc_array_ops *ops) +{ + assoc_array_destroy_subtree(array->root, ops); + array->root = NULL; +} + +/* + * Handle insertion into an empty tree. + */ +static bool assoc_array_insert_in_empty_tree(struct assoc_array_edit *edit) +{ + struct assoc_array_node *new_n0; + + pr_devel("-->%s()\n", __func__); + + new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL); + if (!new_n0) + return false; + + edit->new_meta[0] = assoc_array_node_to_ptr(new_n0); + edit->leaf_p = &new_n0->slots[0]; + edit->adjust_count_on = new_n0; + edit->set[0].ptr = &edit->array->root; + edit->set[0].to = assoc_array_node_to_ptr(new_n0); + + pr_devel("<--%s() = ok [no root]\n", __func__); + return true; +} + +/* + * Handle insertion into a terminal node. + */ +static bool assoc_array_insert_into_terminal_node(struct assoc_array_edit *edit, + const struct assoc_array_ops *ops, + const void *index_key, + struct assoc_array_walk_result *result) +{ + struct assoc_array_shortcut *shortcut, *new_s0; + struct assoc_array_node *node, *new_n0, *new_n1, *side; + struct assoc_array_ptr *ptr; + unsigned long dissimilarity, base_seg, blank; + size_t keylen; + bool have_meta; + int level, diff; + int slot, next_slot, free_slot, i, j; + + node = result->terminal_node.node; + level = result->terminal_node.level; + edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = result->terminal_node.slot; + + pr_devel("-->%s()\n", __func__); + + /* We arrived at a node which doesn't have an onward node or shortcut + * pointer that we have to follow. This means that (a) the leaf we + * want must go here (either by insertion or replacement) or (b) we + * need to split this node and insert in one of the fragments. + */ + free_slot = -1; + + /* Firstly, we have to check the leaves in this node to see if there's + * a matching one we should replace in place. + */ + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) { + ptr = node->slots[i]; + if (!ptr) { + free_slot = i; + continue; + } + if (assoc_array_ptr_is_leaf(ptr) && + ops->compare_object(assoc_array_ptr_to_leaf(ptr), + index_key)) { + pr_devel("replace in slot %d\n", i); + edit->leaf_p = &node->slots[i]; + edit->dead_leaf = node->slots[i]; + pr_devel("<--%s() = ok [replace]\n", __func__); + return true; + } + } + + /* If there is a free slot in this node then we can just insert the + * leaf here. + */ + if (free_slot >= 0) { + pr_devel("insert in free slot %d\n", free_slot); + edit->leaf_p = &node->slots[free_slot]; + edit->adjust_count_on = node; + pr_devel("<--%s() = ok [insert]\n", __func__); + return true; + } + + /* The node has no spare slots - so we're either going to have to split + * it or insert another node before it. + * + * Whatever, we're going to need at least two new nodes - so allocate + * those now. We may also need a new shortcut, but we deal with that + * when we need it. + */ + new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL); + if (!new_n0) + return false; + edit->new_meta[0] = assoc_array_node_to_ptr(new_n0); + new_n1 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL); + if (!new_n1) + return false; + edit->new_meta[1] = assoc_array_node_to_ptr(new_n1); + + /* We need to find out how similar the leaves are. */ + pr_devel("no spare slots\n"); + have_meta = false; + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) { + ptr = node->slots[i]; + if (assoc_array_ptr_is_meta(ptr)) { + edit->segment_cache[i] = 0xff; + have_meta = true; + continue; + } + base_seg = ops->get_object_key_chunk( + assoc_array_ptr_to_leaf(ptr), level); + base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK; + edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK; + } + + if (have_meta) { + pr_devel("have meta\n"); + goto split_node; + } + + /* The node contains only leaves */ + dissimilarity = 0; + base_seg = edit->segment_cache[0]; + for (i = 1; i < ASSOC_ARRAY_FAN_OUT; i++) + dissimilarity |= edit->segment_cache[i] ^ base_seg; + + pr_devel("only leaves; dissimilarity=%lx\n", dissimilarity); + + if ((dissimilarity & ASSOC_ARRAY_FAN_MASK) == 0) { + /* The old leaves all cluster in the same slot. We will need + * to insert a shortcut if the new node wants to cluster with them. + */ + if ((edit->segment_cache[ASSOC_ARRAY_FAN_OUT] ^ base_seg) == 0) + goto all_leaves_cluster_together; + + /* Otherwise all the old leaves cluster in the same slot, but + * the new leaf wants to go into a different slot - so we + * create a new node (n0) to hold the new leaf and a pointer to + * a new node (n1) holding all the old leaves. + * + * This can be done by falling through to the node splitting + * path. + */ + pr_devel("present leaves cluster but not new leaf\n"); + } + +split_node: + pr_devel("split node\n"); + + /* We need to split the current node. The node must contain anything + * from a single leaf (in the one leaf case, this leaf will cluster + * with the new leaf) and the rest meta-pointers, to all leaves, some + * of which may cluster. + * + * It won't contain the case in which all the current leaves plus the + * new leaves want to cluster in the same slot. + * + * We need to expel at least two leaves out of a set consisting of the + * leaves in the node and the new leaf. The current meta pointers can + * just be copied as they shouldn't cluster with any of the leaves. + * + * We need a new node (n0) to replace the current one and a new node to + * take the expelled nodes (n1). + */ + edit->set[0].to = assoc_array_node_to_ptr(new_n0); + new_n0->back_pointer = node->back_pointer; + new_n0->parent_slot = node->parent_slot; + new_n1->back_pointer = assoc_array_node_to_ptr(new_n0); + new_n1->parent_slot = -1; /* Need to calculate this */ + +do_split_node: + pr_devel("do_split_node\n"); + + new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch; + new_n1->nr_leaves_on_branch = 0; + + /* Begin by finding two matching leaves. There have to be at least two + * that match - even if there are meta pointers - because any leaf that + * would match a slot with a meta pointer in it must be somewhere + * behind that meta pointer and cannot be here. Further, given N + * remaining leaf slots, we now have N+1 leaves to go in them. + */ + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) { + slot = edit->segment_cache[i]; + if (slot != 0xff) + for (j = i + 1; j < ASSOC_ARRAY_FAN_OUT + 1; j++) + if (edit->segment_cache[j] == slot) + goto found_slot_for_multiple_occupancy; + } +found_slot_for_multiple_occupancy: + pr_devel("same slot: %x %x [%02x]\n", i, j, slot); + BUG_ON(i >= ASSOC_ARRAY_FAN_OUT); + BUG_ON(j >= ASSOC_ARRAY_FAN_OUT + 1); + BUG_ON(slot >= ASSOC_ARRAY_FAN_OUT); + + new_n1->parent_slot = slot; + + /* Metadata pointers cannot change slot */ + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) + if (assoc_array_ptr_is_meta(node->slots[i])) + new_n0->slots[i] = node->slots[i]; + else + new_n0->slots[i] = NULL; + BUG_ON(new_n0->slots[slot] != NULL); + new_n0->slots[slot] = assoc_array_node_to_ptr(new_n1); + + /* Filter the leaf pointers between the new nodes */ + free_slot = -1; + next_slot = 0; + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) { + if (assoc_array_ptr_is_meta(node->slots[i])) + continue; + if (edit->segment_cache[i] == slot) { + new_n1->slots[next_slot++] = node->slots[i]; + new_n1->nr_leaves_on_branch++; + } else { + do { + free_slot++; + } while (new_n0->slots[free_slot] != NULL); + new_n0->slots[free_slot] = node->slots[i]; + } + } + + pr_devel("filtered: f=%x n=%x\n", free_slot, next_slot); + + if (edit->segment_cache[ASSOC_ARRAY_FAN_OUT] != slot) { + do { + free_slot++; + } while (new_n0->slots[free_slot] != NULL); + edit->leaf_p = &new_n0->slots[free_slot]; + edit->adjust_count_on = new_n0; + } else { + edit->leaf_p = &new_n1->slots[next_slot++]; + edit->adjust_count_on = new_n1; + } + + BUG_ON(next_slot <= 1); + + edit->set_backpointers_to = assoc_array_node_to_ptr(new_n0); + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) { + if (edit->segment_cache[i] == 0xff) { + ptr = node->slots[i]; + BUG_ON(assoc_array_ptr_is_leaf(ptr)); + if (assoc_array_ptr_is_node(ptr)) { + side = assoc_array_ptr_to_node(ptr); + edit->set_backpointers[i] = &side->back_pointer; + } else { + shortcut = assoc_array_ptr_to_shortcut(ptr); + edit->set_backpointers[i] = &shortcut->back_pointer; + } + } + } + + ptr = node->back_pointer; + if (!ptr) + edit->set[0].ptr = &edit->array->root; + else if (assoc_array_ptr_is_node(ptr)) + edit->set[0].ptr = &assoc_array_ptr_to_node(ptr)->slots[node->parent_slot]; + else + edit->set[0].ptr = &assoc_array_ptr_to_shortcut(ptr)->next_node; + edit->excised_meta[0] = assoc_array_node_to_ptr(node); + pr_devel("<--%s() = ok [split node]\n", __func__); + return true; + +all_leaves_cluster_together: + /* All the leaves, new and old, want to cluster together in this node + * in the same slot, so we have to replace this node with a shortcut to + * skip over the identical parts of the key and then place a pair of + * nodes, one inside the other, at the end of the shortcut and + * distribute the keys between them. + * + * Firstly we need to work out where the leaves start diverging as a + * bit position into their keys so that we know how big the shortcut + * needs to be. + * + * We only need to make a single pass of N of the N+1 leaves because if + * any keys differ between themselves at bit X then at least one of + * them must also differ with the base key at bit X or before. + */ + pr_devel("all leaves cluster together\n"); + diff = INT_MAX; + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) { + int x = ops->diff_objects(assoc_array_ptr_to_leaf(node->slots[i]), + index_key); + if (x < diff) { + BUG_ON(x < 0); + diff = x; + } + } + BUG_ON(diff == INT_MAX); + BUG_ON(diff < level + ASSOC_ARRAY_LEVEL_STEP); + + keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE); + keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT; + + new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) + + keylen * sizeof(unsigned long), GFP_KERNEL); + if (!new_s0) + return false; + edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s0); + + edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0); + new_s0->back_pointer = node->back_pointer; + new_s0->parent_slot = node->parent_slot; + new_s0->next_node = assoc_array_node_to_ptr(new_n0); + new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0); + new_n0->parent_slot = 0; + new_n1->back_pointer = assoc_array_node_to_ptr(new_n0); + new_n1->parent_slot = -1; /* Need to calculate this */ + + new_s0->skip_to_level = level = diff & ~ASSOC_ARRAY_LEVEL_STEP_MASK; + pr_devel("skip_to_level = %d [diff %d]\n", level, diff); + BUG_ON(level <= 0); + + for (i = 0; i < keylen; i++) + new_s0->index_key[i] = + ops->get_key_chunk(index_key, i * ASSOC_ARRAY_KEY_CHUNK_SIZE); + + if (level & ASSOC_ARRAY_KEY_CHUNK_MASK) { + blank = ULONG_MAX << (level & ASSOC_ARRAY_KEY_CHUNK_MASK); + pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, level, blank); + new_s0->index_key[keylen - 1] &= ~blank; + } + + /* This now reduces to a node splitting exercise for which we'll need + * to regenerate the disparity table. + */ + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) { + ptr = node->slots[i]; + base_seg = ops->get_object_key_chunk(assoc_array_ptr_to_leaf(ptr), + level); + base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK; + edit->segment_cache[i] = base_seg & ASSOC_ARRAY_FAN_MASK; + } + + base_seg = ops->get_key_chunk(index_key, level); + base_seg >>= level & ASSOC_ARRAY_KEY_CHUNK_MASK; + edit->segment_cache[ASSOC_ARRAY_FAN_OUT] = base_seg & ASSOC_ARRAY_FAN_MASK; + goto do_split_node; +} + +/* + * Handle insertion into the middle of a shortcut. + */ +static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit, + const struct assoc_array_ops *ops, + struct assoc_array_walk_result *result) +{ + struct assoc_array_shortcut *shortcut, *new_s0, *new_s1; + struct assoc_array_node *node, *new_n0, *side; + unsigned long sc_segments, dissimilarity, blank; + size_t keylen; + int level, sc_level, diff; + int sc_slot; + + shortcut = result->wrong_shortcut.shortcut; + level = result->wrong_shortcut.level; + sc_level = result->wrong_shortcut.sc_level; + sc_segments = result->wrong_shortcut.sc_segments; + dissimilarity = result->wrong_shortcut.dissimilarity; + + pr_devel("-->%s(ix=%d dis=%lx scix=%d)\n", + __func__, level, dissimilarity, sc_level); + + /* We need to split a shortcut and insert a node between the two + * pieces. Zero-length pieces will be dispensed with entirely. + * + * First of all, we need to find out in which level the first + * difference was. + */ + diff = __ffs(dissimilarity); + diff &= ~ASSOC_ARRAY_LEVEL_STEP_MASK; + diff += sc_level & ~ASSOC_ARRAY_KEY_CHUNK_MASK; + pr_devel("diff=%d\n", diff); + + if (!shortcut->back_pointer) { + edit->set[0].ptr = &edit->array->root; + } else if (assoc_array_ptr_is_node(shortcut->back_pointer)) { + node = assoc_array_ptr_to_node(shortcut->back_pointer); + edit->set[0].ptr = &node->slots[shortcut->parent_slot]; + } else { + BUG(); + } + + edit->excised_meta[0] = assoc_array_shortcut_to_ptr(shortcut); + + /* Create a new node now since we're going to need it anyway */ + new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL); + if (!new_n0) + return false; + edit->new_meta[0] = assoc_array_node_to_ptr(new_n0); + edit->adjust_count_on = new_n0; + + /* Insert a new shortcut before the new node if this segment isn't of + * zero length - otherwise we just connect the new node directly to the + * parent. + */ + level += ASSOC_ARRAY_LEVEL_STEP; + if (diff > level) { + pr_devel("pre-shortcut %d...%d\n", level, diff); + keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE); + keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT; + + new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) + + keylen * sizeof(unsigned long), GFP_KERNEL); + if (!new_s0) + return false; + edit->new_meta[1] = assoc_array_shortcut_to_ptr(new_s0); + edit->set[0].to = assoc_array_shortcut_to_ptr(new_s0); + new_s0->back_pointer = shortcut->back_pointer; + new_s0->parent_slot = shortcut->parent_slot; + new_s0->next_node = assoc_array_node_to_ptr(new_n0); + new_s0->skip_to_level = diff; + + new_n0->back_pointer = assoc_array_shortcut_to_ptr(new_s0); + new_n0->parent_slot = 0; + + memcpy(new_s0->index_key, shortcut->index_key, + keylen * sizeof(unsigned long)); + + blank = ULONG_MAX << (diff & ASSOC_ARRAY_KEY_CHUNK_MASK); + pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, diff, blank); + new_s0->index_key[keylen - 1] &= ~blank; + } else { + pr_devel("no pre-shortcut\n"); + edit->set[0].to = assoc_array_node_to_ptr(new_n0); + new_n0->back_pointer = shortcut->back_pointer; + new_n0->parent_slot = shortcut->parent_slot; + } + + side = assoc_array_ptr_to_node(shortcut->next_node); + new_n0->nr_leaves_on_branch = side->nr_leaves_on_branch; + + /* We need to know which slot in the new node is going to take a + * metadata pointer. + */ + sc_slot = sc_segments >> (diff & ASSOC_ARRAY_KEY_CHUNK_MASK); + sc_slot &= ASSOC_ARRAY_FAN_MASK; + + pr_devel("new slot %lx >> %d -> %d\n", + sc_segments, diff & ASSOC_ARRAY_KEY_CHUNK_MASK, sc_slot); + + /* Determine whether we need to follow the new node with a replacement + * for the current shortcut. We could in theory reuse the current + * shortcut if its parent slot number doesn't change - but that's a + * 1-in-16 chance so not worth expending the code upon. + */ + level = diff + ASSOC_ARRAY_LEVEL_STEP; + if (level < shortcut->skip_to_level) { + pr_devel("post-shortcut %d...%d\n", level, shortcut->skip_to_level); + keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE); + keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT; + + new_s1 = kzalloc(sizeof(struct assoc_array_shortcut) + + keylen * sizeof(unsigned long), GFP_KERNEL); + if (!new_s1) + return false; + edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s1); + + new_s1->back_pointer = assoc_array_node_to_ptr(new_n0); + new_s1->parent_slot = sc_slot; + new_s1->next_node = shortcut->next_node; + new_s1->skip_to_level = shortcut->skip_to_level; + + new_n0->slots[sc_slot] = assoc_array_shortcut_to_ptr(new_s1); + + memcpy(new_s1->index_key, shortcut->index_key, + keylen * sizeof(unsigned long)); + + edit->set[1].ptr = &side->back_pointer; + edit->set[1].to = assoc_array_shortcut_to_ptr(new_s1); + } else { + pr_devel("no post-shortcut\n"); + + /* We don't have to replace the pointed-to node as long as we + * use memory barriers to make sure the parent slot number is + * changed before the back pointer (the parent slot number is + * irrelevant to the old parent shortcut). + */ + new_n0->slots[sc_slot] = shortcut->next_node; + edit->set_parent_slot[0].p = &side->parent_slot; + edit->set_parent_slot[0].to = sc_slot; + edit->set[1].ptr = &side->back_pointer; + edit->set[1].to = assoc_array_node_to_ptr(new_n0); + } + + /* Install the new leaf in a spare slot in the new node. */ + if (sc_slot == 0) + edit->leaf_p = &new_n0->slots[1]; + else + edit->leaf_p = &new_n0->slots[0]; + + pr_devel("<--%s() = ok [split shortcut]\n", __func__); + return edit; +} + +/** + * assoc_array_insert - Script insertion of an object into an associative array + * @array: The array to insert into. + * @ops: The operations to use. + * @index_key: The key to insert at. + * @object: The object to insert. + * + * Precalculate and preallocate a script for the insertion or replacement of an + * object in an associative array. This results in an edit script that can + * either be applied or cancelled. + * + * The function returns a pointer to an edit script or -ENOMEM. + * + * The caller should lock against other modifications and must continue to hold + * the lock until assoc_array_apply_edit() has been called. + * + * Accesses to the tree may take place concurrently with this function, + * provided they hold the RCU read lock. + */ +struct assoc_array_edit *assoc_array_insert(struct assoc_array *array, + const struct assoc_array_ops *ops, + const void *index_key, + void *object) +{ + struct assoc_array_walk_result result; + struct assoc_array_edit *edit; + + pr_devel("-->%s()\n", __func__); + + /* The leaf pointer we're given must not have the bottom bit set as we + * use those for type-marking the pointer. NULL pointers are also not + * allowed as they indicate an empty slot but we have to allow them + * here as they can be updated later. + */ + BUG_ON(assoc_array_ptr_is_meta(object)); + + edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL); + if (!edit) + return ERR_PTR(-ENOMEM); + edit->array = array; + edit->ops = ops; + edit->leaf = assoc_array_leaf_to_ptr(object); + edit->adjust_count_by = 1; + + switch (assoc_array_walk(array, ops, index_key, &result)) { + case assoc_array_walk_tree_empty: + /* Allocate a root node if there isn't one yet */ + if (!assoc_array_insert_in_empty_tree(edit)) + goto enomem; + return edit; + + case assoc_array_walk_found_terminal_node: + /* We found a node that doesn't have a node/shortcut pointer in + * the slot corresponding to the index key that we have to + * follow. + */ + if (!assoc_array_insert_into_terminal_node(edit, ops, index_key, + &result)) + goto enomem; + return edit; + + case assoc_array_walk_found_wrong_shortcut: + /* We found a shortcut that didn't match our key in a slot we + * needed to follow. + */ + if (!assoc_array_insert_mid_shortcut(edit, ops, &result)) + goto enomem; + return edit; + } + +enomem: + /* Clean up after an out of memory error */ + pr_devel("enomem\n"); + assoc_array_cancel_edit(edit); + return ERR_PTR(-ENOMEM); +} + +/** + * assoc_array_insert_set_object - Set the new object pointer in an edit script + * @edit: The edit script to modify. + * @object: The object pointer to set. + * + * Change the object to be inserted in an edit script. The object pointed to + * by the old object is not freed. This must be done prior to applying the + * script. + */ +void assoc_array_insert_set_object(struct assoc_array_edit *edit, void *object) +{ + BUG_ON(!object); + edit->leaf = assoc_array_leaf_to_ptr(object); +} + +struct assoc_array_delete_collapse_context { + struct assoc_array_node *node; + const void *skip_leaf; + int slot; +}; + +/* + * Subtree collapse to node iterator. + */ +static int assoc_array_delete_collapse_iterator(const void *leaf, + void *iterator_data) +{ + struct assoc_array_delete_collapse_context *collapse = iterator_data; + + if (leaf == collapse->skip_leaf) + return 0; + + BUG_ON(collapse->slot >= ASSOC_ARRAY_FAN_OUT); + + collapse->node->slots[collapse->slot++] = assoc_array_leaf_to_ptr(leaf); + return 0; +} + +/** + * assoc_array_delete - Script deletion of an object from an associative array + * @array: The array to search. + * @ops: The operations to use. + * @index_key: The key to the object. + * + * Precalculate and preallocate a script for the deletion of an object from an + * associative array. This results in an edit script that can either be + * applied or cancelled. + * + * The function returns a pointer to an edit script if the object was found, + * NULL if the object was not found or -ENOMEM. + * + * The caller should lock against other modifications and must continue to hold + * the lock until assoc_array_apply_edit() has been called. + * + * Accesses to the tree may take place concurrently with this function, + * provided they hold the RCU read lock. + */ +struct assoc_array_edit *assoc_array_delete(struct assoc_array *array, + const struct assoc_array_ops *ops, + const void *index_key) +{ + struct assoc_array_delete_collapse_context collapse; + struct assoc_array_walk_result result; + struct assoc_array_node *node, *new_n0; + struct assoc_array_edit *edit; + struct assoc_array_ptr *ptr; + bool has_meta; + int slot, i; + + pr_devel("-->%s()\n", __func__); + + edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL); + if (!edit) + return ERR_PTR(-ENOMEM); + edit->array = array; + edit->ops = ops; + edit->adjust_count_by = -1; + + switch (assoc_array_walk(array, ops, index_key, &result)) { + case assoc_array_walk_found_terminal_node: + /* We found a node that should contain the leaf we've been + * asked to remove - *if* it's in the tree. + */ + pr_devel("terminal_node\n"); + node = result.terminal_node.node; + + for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) { + ptr = node->slots[slot]; + if (ptr && + assoc_array_ptr_is_leaf(ptr) && + ops->compare_object(assoc_array_ptr_to_leaf(ptr), + index_key)) + goto found_leaf; + } + /* fall through */ + case assoc_array_walk_tree_empty: + case assoc_array_walk_found_wrong_shortcut: + default: + assoc_array_cancel_edit(edit); + pr_devel("not found\n"); + return NULL; + } + +found_leaf: + BUG_ON(array->nr_leaves_on_tree <= 0); + + /* In the simplest form of deletion we just clear the slot and release + * the leaf after a suitable interval. + */ + edit->dead_leaf = node->slots[slot]; + edit->set[0].ptr = &node->slots[slot]; + edit->set[0].to = NULL; + edit->adjust_count_on = node; + + /* If that concludes erasure of the last leaf, then delete the entire + * internal array. + */ + if (array->nr_leaves_on_tree == 1) { + edit->set[1].ptr = &array->root; + edit->set[1].to = NULL; + edit->adjust_count_on = NULL; + edit->excised_subtree = array->root; + pr_devel("all gone\n"); + return edit; + } + + /* However, we'd also like to clear up some metadata blocks if we + * possibly can. + * + * We go for a simple algorithm of: if this node has FAN_OUT or fewer + * leaves in it, then attempt to collapse it - and attempt to + * recursively collapse up the tree. + * + * We could also try and collapse in partially filled subtrees to take + * up space in this node. + */ + if (node->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) { + struct assoc_array_node *parent, *grandparent; + struct assoc_array_ptr *ptr; + + /* First of all, we need to know if this node has metadata so + * that we don't try collapsing if all the leaves are already + * here. + */ + has_meta = false; + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) { + ptr = node->slots[i]; + if (assoc_array_ptr_is_meta(ptr)) { + has_meta = true; + break; + } + } + + pr_devel("leaves: %ld [m=%d]\n", + node->nr_leaves_on_branch - 1, has_meta); + + /* Look further up the tree to see if we can collapse this node + * into a more proximal node too. + */ + parent = node; + collapse_up: + pr_devel("collapse subtree: %ld\n", parent->nr_leaves_on_branch); + + ptr = parent->back_pointer; + if (!ptr) + goto do_collapse; + if (assoc_array_ptr_is_shortcut(ptr)) { + struct assoc_array_shortcut *s = assoc_array_ptr_to_shortcut(ptr); + ptr = s->back_pointer; + if (!ptr) + goto do_collapse; + } + + grandparent = assoc_array_ptr_to_node(ptr); + if (grandparent->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT + 1) { + parent = grandparent; + goto collapse_up; + } + + do_collapse: + /* There's no point collapsing if the original node has no meta + * pointers to discard and if we didn't merge into one of that + * node's ancestry. + */ + if (has_meta || parent != node) { + node = parent; + + /* Create a new node to collapse into */ + new_n0 = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL); + if (!new_n0) + goto enomem; + edit->new_meta[0] = assoc_array_node_to_ptr(new_n0); + + new_n0->back_pointer = node->back_pointer; + new_n0->parent_slot = node->parent_slot; + new_n0->nr_leaves_on_branch = node->nr_leaves_on_branch; + edit->adjust_count_on = new_n0; + + collapse.node = new_n0; + collapse.skip_leaf = assoc_array_ptr_to_leaf(edit->dead_leaf); + collapse.slot = 0; + assoc_array_subtree_iterate(assoc_array_node_to_ptr(node), + node->back_pointer, + assoc_array_delete_collapse_iterator, + &collapse); + pr_devel("collapsed %d,%lu\n", collapse.slot, new_n0->nr_leaves_on_branch); + BUG_ON(collapse.slot != new_n0->nr_leaves_on_branch - 1); + + if (!node->back_pointer) { + edit->set[1].ptr = &array->root; + } else if (assoc_array_ptr_is_leaf(node->back_pointer)) { + BUG(); + } else if (assoc_array_ptr_is_node(node->back_pointer)) { + struct assoc_array_node *p = + assoc_array_ptr_to_node(node->back_pointer); + edit->set[1].ptr = &p->slots[node->parent_slot]; + } else if (assoc_array_ptr_is_shortcut(node->back_pointer)) { + struct assoc_array_shortcut *s = + assoc_array_ptr_to_shortcut(node->back_pointer); + edit->set[1].ptr = &s->next_node; + } + edit->set[1].to = assoc_array_node_to_ptr(new_n0); + edit->excised_subtree = assoc_array_node_to_ptr(node); + } + } + + return edit; + +enomem: + /* Clean up after an out of memory error */ + pr_devel("enomem\n"); + assoc_array_cancel_edit(edit); + return ERR_PTR(-ENOMEM); +} + +/** + * assoc_array_clear - Script deletion of all objects from an associative array + * @array: The array to clear. + * @ops: The operations to use. + * + * Precalculate and preallocate a script for the deletion of all the objects + * from an associative array. This results in an edit script that can either + * be applied or cancelled. + * + * The function returns a pointer to an edit script if there are objects to be + * deleted, NULL if there are no objects in the array or -ENOMEM. + * + * The caller should lock against other modifications and must continue to hold + * the lock until assoc_array_apply_edit() has been called. + * + * Accesses to the tree may take place concurrently with this function, + * provided they hold the RCU read lock. + */ +struct assoc_array_edit *assoc_array_clear(struct assoc_array *array, + const struct assoc_array_ops *ops) +{ + struct assoc_array_edit *edit; + + pr_devel("-->%s()\n", __func__); + + if (!array->root) + return NULL; + + edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL); + if (!edit) + return ERR_PTR(-ENOMEM); + edit->array = array; + edit->ops = ops; + edit->set[1].ptr = &array->root; + edit->set[1].to = NULL; + edit->excised_subtree = array->root; + edit->ops_for_excised_subtree = ops; + pr_devel("all gone\n"); + return edit; +} + +/* + * Handle the deferred destruction after an applied edit. + */ +static void assoc_array_rcu_cleanup(struct rcu_head *head) +{ + struct assoc_array_edit *edit = + container_of(head, struct assoc_array_edit, rcu); + int i; + + pr_devel("-->%s()\n", __func__); + + if (edit->dead_leaf) + edit->ops->free_object(assoc_array_ptr_to_leaf(edit->dead_leaf)); + for (i = 0; i < ARRAY_SIZE(edit->excised_meta); i++) + if (edit->excised_meta[i]) + kfree(assoc_array_ptr_to_node(edit->excised_meta[i])); + + if (edit->excised_subtree) { + BUG_ON(assoc_array_ptr_is_leaf(edit->excised_subtree)); + if (assoc_array_ptr_is_node(edit->excised_subtree)) { + struct assoc_array_node *n = + assoc_array_ptr_to_node(edit->excised_subtree); + n->back_pointer = NULL; + } else { + struct assoc_array_shortcut *s = + assoc_array_ptr_to_shortcut(edit->excised_subtree); + s->back_pointer = NULL; + } + assoc_array_destroy_subtree(edit->excised_subtree, + edit->ops_for_excised_subtree); + } + + kfree(edit); +} + +/** + * assoc_array_apply_edit - Apply an edit script to an associative array + * @edit: The script to apply. + * + * Apply an edit script to an associative array to effect an insertion, + * deletion or clearance. As the edit script includes preallocated memory, + * this is guaranteed not to fail. + * + * The edit script, dead objects and dead metadata will be scheduled for + * destruction after an RCU grace period to permit those doing read-only + * accesses on the array to continue to do so under the RCU read lock whilst + * the edit is taking place. + */ +void assoc_array_apply_edit(struct assoc_array_edit *edit) +{ + struct assoc_array_shortcut *shortcut; + struct assoc_array_node *node; + struct assoc_array_ptr *ptr; + int i; + + pr_devel("-->%s()\n", __func__); + + smp_wmb(); + if (edit->leaf_p) + *edit->leaf_p = edit->leaf; + + smp_wmb(); + for (i = 0; i < ARRAY_SIZE(edit->set_parent_slot); i++) + if (edit->set_parent_slot[i].p) + *edit->set_parent_slot[i].p = edit->set_parent_slot[i].to; + + smp_wmb(); + for (i = 0; i < ARRAY_SIZE(edit->set_backpointers); i++) + if (edit->set_backpointers[i]) + *edit->set_backpointers[i] = edit->set_backpointers_to; + + smp_wmb(); + for (i = 0; i < ARRAY_SIZE(edit->set); i++) + if (edit->set[i].ptr) + *edit->set[i].ptr = edit->set[i].to; + + if (edit->array->root == NULL) { + edit->array->nr_leaves_on_tree = 0; + } else if (edit->adjust_count_on) { + node = edit->adjust_count_on; + for (;;) { + node->nr_leaves_on_branch += edit->adjust_count_by; + + ptr = node->back_pointer; + if (!ptr) + break; + if (assoc_array_ptr_is_shortcut(ptr)) { + shortcut = assoc_array_ptr_to_shortcut(ptr); + ptr = shortcut->back_pointer; + if (!ptr) + break; + } + BUG_ON(!assoc_array_ptr_is_node(ptr)); + node = assoc_array_ptr_to_node(ptr); + } + + edit->array->nr_leaves_on_tree += edit->adjust_count_by; + } + + call_rcu(&edit->rcu, assoc_array_rcu_cleanup); +} + +/** + * assoc_array_cancel_edit - Discard an edit script. + * @edit: The script to discard. + * + * Free an edit script and all the preallocated data it holds without making + * any changes to the associative array it was intended for. + * + * NOTE! In the case of an insertion script, this does _not_ release the leaf + * that was to be inserted. That is left to the caller. + */ +void assoc_array_cancel_edit(struct assoc_array_edit *edit) +{ + struct assoc_array_ptr *ptr; + int i; + + pr_devel("-->%s()\n", __func__); + + /* Clean up after an out of memory error */ + for (i = 0; i < ARRAY_SIZE(edit->new_meta); i++) { + ptr = edit->new_meta[i]; + if (ptr) { + if (assoc_array_ptr_is_node(ptr)) + kfree(assoc_array_ptr_to_node(ptr)); + else + kfree(assoc_array_ptr_to_shortcut(ptr)); + } + } + kfree(edit); +} + +/** + * assoc_array_gc - Garbage collect an associative array. + * @array: The array to clean. + * @ops: The operations to use. + * @iterator: A callback function to pass judgement on each object. + * @iterator_data: Private data for the callback function. + * + * Collect garbage from an associative array and pack down the internal tree to + * save memory. + * + * The iterator function is asked to pass judgement upon each object in the + * array. If it returns false, the object is discard and if it returns true, + * the object is kept. If it returns true, it must increment the object's + * usage count (or whatever it needs to do to retain it) before returning. + * + * This function returns 0 if successful or -ENOMEM if out of memory. In the + * latter case, the array is not changed. + * + * The caller should lock against other modifications and must continue to hold + * the lock until assoc_array_apply_edit() has been called. + * + * Accesses to the tree may take place concurrently with this function, + * provided they hold the RCU read lock. + */ +int assoc_array_gc(struct assoc_array *array, + const struct assoc_array_ops *ops, + bool (*iterator)(void *object, void *iterator_data), + void *iterator_data) +{ + struct assoc_array_shortcut *shortcut, *new_s; + struct assoc_array_node *node, *new_n; + struct assoc_array_edit *edit; + struct assoc_array_ptr *cursor, *ptr; + struct assoc_array_ptr *new_root, *new_parent, **new_ptr_pp; + unsigned long nr_leaves_on_tree; + bool retained; + int keylen, slot, nr_free, next_slot, i; + + pr_devel("-->%s()\n", __func__); + + if (!array->root) + return 0; + + edit = kzalloc(sizeof(struct assoc_array_edit), GFP_KERNEL); + if (!edit) + return -ENOMEM; + edit->array = array; + edit->ops = ops; + edit->ops_for_excised_subtree = ops; + edit->set[0].ptr = &array->root; + edit->excised_subtree = array->root; + + new_root = new_parent = NULL; + new_ptr_pp = &new_root; + cursor = array->root; + +descend: + /* If this point is a shortcut, then we need to duplicate it and + * advance the target cursor. + */ + if (assoc_array_ptr_is_shortcut(cursor)) { + shortcut = assoc_array_ptr_to_shortcut(cursor); + keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE); + keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT; + new_s = kmalloc(sizeof(struct assoc_array_shortcut) + + keylen * sizeof(unsigned long), GFP_KERNEL); + if (!new_s) + goto enomem; + pr_devel("dup shortcut %p -> %p\n", shortcut, new_s); + memcpy(new_s, shortcut, (sizeof(struct assoc_array_shortcut) + + keylen * sizeof(unsigned long))); + new_s->back_pointer = new_parent; + new_s->parent_slot = shortcut->parent_slot; + *new_ptr_pp = new_parent = assoc_array_shortcut_to_ptr(new_s); + new_ptr_pp = &new_s->next_node; + cursor = shortcut->next_node; + } + + /* Duplicate the node at this position */ + node = assoc_array_ptr_to_node(cursor); + new_n = kzalloc(sizeof(struct assoc_array_node), GFP_KERNEL); + if (!new_n) + goto enomem; + pr_devel("dup node %p -> %p\n", node, new_n); + new_n->back_pointer = new_parent; + new_n->parent_slot = node->parent_slot; + *new_ptr_pp = new_parent = assoc_array_node_to_ptr(new_n); + new_ptr_pp = NULL; + slot = 0; + +continue_node: + /* Filter across any leaves and gc any subtrees */ + for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) { + ptr = node->slots[slot]; + if (!ptr) + continue; + + if (assoc_array_ptr_is_leaf(ptr)) { + if (iterator(assoc_array_ptr_to_leaf(ptr), + iterator_data)) + /* The iterator will have done any reference + * counting on the object for us. + */ + new_n->slots[slot] = ptr; + continue; + } + + new_ptr_pp = &new_n->slots[slot]; + cursor = ptr; + goto descend; + } + +retry_compress: + pr_devel("-- compress node %p --\n", new_n); + + /* Count up the number of empty slots in this node and work out the + * subtree leaf count. + */ + new_n->nr_leaves_on_branch = 0; + nr_free = 0; + for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) { + ptr = new_n->slots[slot]; + if (!ptr) + nr_free++; + else if (assoc_array_ptr_is_leaf(ptr)) + new_n->nr_leaves_on_branch++; + } + pr_devel("free=%d, leaves=%lu\n", nr_free, new_n->nr_leaves_on_branch); + + /* See what we can fold in */ + retained = false; + next_slot = 0; + for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) { + struct assoc_array_shortcut *s; + struct assoc_array_node *child; + + ptr = new_n->slots[slot]; + if (!ptr || assoc_array_ptr_is_leaf(ptr)) + continue; + + s = NULL; + if (assoc_array_ptr_is_shortcut(ptr)) { + s = assoc_array_ptr_to_shortcut(ptr); + ptr = s->next_node; + } + + child = assoc_array_ptr_to_node(ptr); + new_n->nr_leaves_on_branch += child->nr_leaves_on_branch; + + if (child->nr_leaves_on_branch <= nr_free + 1) { + /* Fold the child node into this one */ + pr_devel("[%d] fold node %lu/%d [nx %d]\n", + slot, child->nr_leaves_on_branch, nr_free + 1, + next_slot); + + /* We would already have reaped an intervening shortcut + * on the way back up the tree. + */ + BUG_ON(s); + + new_n->slots[slot] = NULL; + nr_free++; + if (slot < next_slot) + next_slot = slot; + for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++) { + struct assoc_array_ptr *p = child->slots[i]; + if (!p) + continue; + BUG_ON(assoc_array_ptr_is_meta(p)); + while (new_n->slots[next_slot]) + next_slot++; + BUG_ON(next_slot >= ASSOC_ARRAY_FAN_OUT); + new_n->slots[next_slot++] = p; + nr_free--; + } + kfree(child); + } else { + pr_devel("[%d] retain node %lu/%d [nx %d]\n", + slot, child->nr_leaves_on_branch, nr_free + 1, + next_slot); + retained = true; + } + } + + if (retained && new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) { + pr_devel("internal nodes remain despite enough space, retrying\n"); + goto retry_compress; + } + pr_devel("after: %lu\n", new_n->nr_leaves_on_branch); + + nr_leaves_on_tree = new_n->nr_leaves_on_branch; + + /* Excise this node if it is singly occupied by a shortcut */ + if (nr_free == ASSOC_ARRAY_FAN_OUT - 1) { + for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) + if ((ptr = new_n->slots[slot])) + break; + + if (assoc_array_ptr_is_meta(ptr) && + assoc_array_ptr_is_shortcut(ptr)) { + pr_devel("excise node %p with 1 shortcut\n", new_n); + new_s = assoc_array_ptr_to_shortcut(ptr); + new_parent = new_n->back_pointer; + slot = new_n->parent_slot; + kfree(new_n); + if (!new_parent) { + new_s->back_pointer = NULL; + new_s->parent_slot = 0; + new_root = ptr; + goto gc_complete; + } + + if (assoc_array_ptr_is_shortcut(new_parent)) { + /* We can discard any preceding shortcut also */ + struct assoc_array_shortcut *s = + assoc_array_ptr_to_shortcut(new_parent); + + pr_devel("excise preceding shortcut\n"); + + new_parent = new_s->back_pointer = s->back_pointer; + slot = new_s->parent_slot = s->parent_slot; + kfree(s); + if (!new_parent) { + new_s->back_pointer = NULL; + new_s->parent_slot = 0; + new_root = ptr; + goto gc_complete; + } + } + + new_s->back_pointer = new_parent; + new_s->parent_slot = slot; + new_n = assoc_array_ptr_to_node(new_parent); + new_n->slots[slot] = ptr; + goto ascend_old_tree; + } + } + + /* Excise any shortcuts we might encounter that point to nodes that + * only contain leaves. + */ + ptr = new_n->back_pointer; + if (!ptr) + goto gc_complete; + + if (assoc_array_ptr_is_shortcut(ptr)) { + new_s = assoc_array_ptr_to_shortcut(ptr); + new_parent = new_s->back_pointer; + slot = new_s->parent_slot; + + if (new_n->nr_leaves_on_branch <= ASSOC_ARRAY_FAN_OUT) { + struct assoc_array_node *n; + + pr_devel("excise shortcut\n"); + new_n->back_pointer = new_parent; + new_n->parent_slot = slot; + kfree(new_s); + if (!new_parent) { + new_root = assoc_array_node_to_ptr(new_n); + goto gc_complete; + } + + n = assoc_array_ptr_to_node(new_parent); + n->slots[slot] = assoc_array_node_to_ptr(new_n); + } + } else { + new_parent = ptr; + } + new_n = assoc_array_ptr_to_node(new_parent); + +ascend_old_tree: + ptr = node->back_pointer; + if (assoc_array_ptr_is_shortcut(ptr)) { + shortcut = assoc_array_ptr_to_shortcut(ptr); + slot = shortcut->parent_slot; + cursor = shortcut->back_pointer; + if (!cursor) + goto gc_complete; + } else { + slot = node->parent_slot; + cursor = ptr; + } + BUG_ON(!cursor); + node = assoc_array_ptr_to_node(cursor); + slot++; + goto continue_node; + +gc_complete: + edit->set[0].to = new_root; + assoc_array_apply_edit(edit); + array->nr_leaves_on_tree = nr_leaves_on_tree; + return 0; + +enomem: + pr_devel("enomem\n"); + assoc_array_destroy_subtree(new_root, edit->ops); + kfree(edit); + return -ENOMEM; +} |