--- /dev/null
+ ========================================
+ GENERIC ASSOCIATIVE ARRAY IMPLEMENTATION
+ ========================================
+
+Contents:
+
+ - Overview.
+
+ - The public API.
+ - Edit script.
+ - Operations table.
+ - Manipulation functions.
+ - Access functions.
+ - Index key form.
+
+ - Internal workings.
+ - Basic internal tree layout.
+ - Shortcuts.
+ - Splitting and collapsing nodes.
+ - Non-recursive iteration.
+ - Simultaneous alteration and iteration.
+
+
+========
+OVERVIEW
+========
+
+This associative array implementation is an object container with the following
+properties:
+
+ (1) Objects are opaque pointers. The implementation does not care where they
+ point (if anywhere) or what they point to (if anything).
+
+ [!] NOTE: Pointers to objects _must_ be zero in the least significant bit.
+
+ (2) Objects do not need to contain linkage blocks for use by the array. This
+ permits an object to be located in multiple arrays simultaneously.
+ Rather, the array is made up of metadata blocks that point to objects.
+
+ (3) Objects require index keys to locate them within the array.
+
+ (4) Index keys must be unique. Inserting an object with the same key as one
+ already in the array will replace the old object.
+
+ (5) Index keys can be of any length and can be of different lengths.
+
+ (6) Index keys should encode the length early on, before any variation due to
+ length is seen.
+
+ (7) Index keys can include a hash to scatter objects throughout the array.
+
+ (8) The array can iterated over. The objects will not necessarily come out in
+ key order.
+
+ (9) The array can be iterated over whilst it is being modified, provided the
+ RCU readlock is being held by the iterator. Note, however, under these
+ circumstances, some objects may be seen more than once. If this is a
+ problem, the iterator should lock against modification. Objects will not
+ be missed, however, unless deleted.
+
+(10) Objects in the array can be looked up by means of their index key.
+
+(11) Objects can be looked up whilst the array is being modified, provided the
+ RCU readlock is being held by the thread doing the look up.
+
+The implementation uses a tree of 16-pointer nodes internally that are indexed
+on each level by nibbles from the index key in the same manner as in a radix
+tree. To improve memory efficiency, shortcuts can be emplaced to skip over
+what would otherwise be a series of single-occupancy nodes. Further, nodes
+pack leaf object pointers into spare space in the node rather than making an
+extra branch until as such time an object needs to be added to a full node.
+
+
+==============
+THE PUBLIC API
+==============
+
+The public API can be found in <linux/assoc_array.h>. The associative array is
+rooted on the following structure:
+
+ struct assoc_array {
+ ...
+ };
+
+The code is selected by enabling CONFIG_ASSOCIATIVE_ARRAY.
+
+
+EDIT SCRIPT
+-----------
+
+The insertion and deletion functions produce an 'edit script' that can later be
+applied to effect the changes without risking ENOMEM. This retains the
+preallocated metadata blocks that will be installed in the internal tree and
+keeps track of the metadata blocks that will be removed from the tree when the
+script is applied.
+
+This is also used to keep track of dead blocks and dead objects after the
+script has been applied so that they can be freed later. The freeing is done
+after an RCU grace period has passed - thus allowing access functions to
+proceed under the RCU read lock.
+
+The script appears as outside of the API as a pointer of the type:
+
+ struct assoc_array_edit;
+
+There are two functions for dealing with the script:
+
+ (1) Apply an edit script.
+
+ void assoc_array_apply_edit(struct assoc_array_edit *edit);
+
+ This will perform the edit functions, interpolating various write barriers
+ to permit accesses under the RCU read lock to continue. The edit script
+ will then be passed to call_rcu() to free it and any dead stuff it points
+ to.
+
+ (2) Cancel an edit script.
+
+ void assoc_array_cancel_edit(struct assoc_array_edit *edit);
+
+ This frees the edit script and all preallocated memory immediately. If
+ this was for insertion, the new object is _not_ released by this function,
+ but must rather be released by the caller.
+
+These functions are guaranteed not to fail.
+
+
+OPERATIONS TABLE
+----------------
+
+Various functions take a table of operations:
+
+ struct assoc_array_ops {
+ ...
+ };
+
+This points to a number of methods, all of which need to be provided:
+
+ (1) Get a chunk of index key from caller data:
+
+ unsigned long (*get_key_chunk)(const void *index_key, int level);
+
+ This should return a chunk of caller-supplied index key starting at the
+ *bit* position given by the level argument. The level argument will be a
+ multiple of ASSOC_ARRAY_KEY_CHUNK_SIZE and the function should return
+ ASSOC_ARRAY_KEY_CHUNK_SIZE bits. No error is possible.
+
+
+ (2) Get a chunk of an object's index key.
+
+ unsigned long (*get_object_key_chunk)(const void *object, int level);
+
+ As the previous function, but gets its data from an object in the array
+ rather than from a caller-supplied index key.
+
+
+ (3) See if this is the object we're looking for.
+
+ bool (*compare_object)(const void *object, const void *index_key);
+
+ Compare the object against an index key and return true if it matches and
+ false if it doesn't.
+
+
+ (4) Diff the index keys of two objects.
+
+ int (*diff_objects)(const void *a, const void *b);
+
+ Return the bit position at which the index keys of two objects differ or
+ -1 if they are the same.
+
+
+ (5) Free an object.
+
+ void (*free_object)(void *object);
+
+ Free the specified object. Note that this may be called an RCU grace
+ period after assoc_array_apply_edit() was called, so synchronize_rcu() may
+ be necessary on module unloading.
+
+
+MANIPULATION FUNCTIONS
+----------------------
+
+There are a number of functions for manipulating an associative array:
+
+ (1) Initialise an associative array.
+
+ void assoc_array_init(struct assoc_array *array);
+
+ This initialises the base structure for an associative array. It can't
+ fail.
+
+
+ (2) Insert/replace an object in an associative array.
+
+ struct assoc_array_edit *
+ assoc_array_insert(struct assoc_array *array,
+ const struct assoc_array_ops *ops,
+ const void *index_key,
+ void *object);
+
+ This inserts the given object into the array. Note that the least
+ significant bit of the pointer must be zero as it's used to type-mark
+ pointers internally.
+
+ If an object already exists for that key then it will be replaced with the
+ new object and the old one will be freed automatically.
+
+ The index_key argument should hold index key information and is
+ passed to the methods in the ops table when they are called.
+
+ This function makes no alteration to the array itself, but rather returns
+ an edit script that must be applied. -ENOMEM is returned in the case of
+ an out-of-memory error.
+
+ The caller should lock exclusively against other modifiers of the array.
+
+
+ (3) Delete an object from an associative array.
+
+ struct assoc_array_edit *
+ assoc_array_delete(struct assoc_array *array,
+ const struct assoc_array_ops *ops,
+ const void *index_key);
+
+ This deletes an object that matches the specified data from the array.
+
+ The index_key argument should hold index key information and is
+ passed to the methods in the ops table when they are called.
+
+ This function makes no alteration to the array itself, but rather returns
+ an edit script that must be applied. -ENOMEM is returned in the case of
+ an out-of-memory error. NULL will be returned if the specified object is
+ not found within the array.
+
+ The caller should lock exclusively against other modifiers of the array.
+
+
+ (4) Delete all objects from an associative array.
+
+ struct assoc_array_edit *
+ assoc_array_clear(struct assoc_array *array,
+ const struct assoc_array_ops *ops);
+
+ This deletes all the objects from an associative array and leaves it
+ completely empty.
+
+ This function makes no alteration to the array itself, but rather returns
+ an edit script that must be applied. -ENOMEM is returned in the case of
+ an out-of-memory error.
+
+ The caller should lock exclusively against other modifiers of the array.
+
+
+ (5) Destroy an associative array, deleting all objects.
+
+ void assoc_array_destroy(struct assoc_array *array,
+ const struct assoc_array_ops *ops);
+
+ This destroys the contents of the associative array and leaves it
+ completely empty. It is not permitted for another thread to be traversing
+ the array under the RCU read lock at the same time as this function is
+ destroying it as no RCU deferral is performed on memory release -
+ something that would require memory to be allocated.
+
+ The caller should lock exclusively against other modifiers and accessors
+ of the array.
+
+
+ (6) Garbage collect an associative array.
+
+ int assoc_array_gc(struct assoc_array *array,
+ const struct assoc_array_ops *ops,
+ bool (*iterator)(void *object, void *iterator_data),
+ void *iterator_data);
+
+ This iterates over the objects in an associative array and passes each one
+ to iterator(). If iterator() returns true, the object is kept. If it
+ returns false, the object will be freed. If the iterator() function
+ returns true, it must perform any appropriate refcount incrementing on the
+ object before returning.
+
+ The internal tree will be packed down if possible as part of the iteration
+ to reduce the number of nodes in it.
+
+ The iterator_data is passed directly to iterator() and is otherwise
+ ignored by the function.
+
+ The function will return 0 if successful and -ENOMEM if there wasn't
+ enough memory.
+
+ It is possible for other threads to iterate over or search the array under
+ the RCU read lock whilst this function is in progress. The caller should
+ lock exclusively against other modifiers of the array.
+
+
+ACCESS FUNCTIONS
+----------------
+
+There are two functions for accessing an associative array:
+
+ (1) Iterate over all the objects in an associative array.
+
+ int assoc_array_iterate(const struct assoc_array *array,
+ int (*iterator)(const void *object,
+ void *iterator_data),
+ void *iterator_data);
+
+ This passes each object in the array to the iterator callback function.
+ iterator_data is private data for that function.
+
+ This may be used on an array at the same time as the array is being
+ modified, provided the RCU read lock is held. Under such circumstances,
+ it is possible for the iteration function to see some objects twice. If
+ this is a problem, then modification should be locked against. The
+ iteration algorithm should not, however, miss any objects.
+
+ 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.
+
+
+ (2) Find an object in an associative array.
+
+ void *assoc_array_find(const struct assoc_array *array,
+ const struct assoc_array_ops *ops,
+ const void *index_key);
+
+ This walks through the array's internal tree directly to the object
+ specified by the index key..
+
+ This may be used on an array at the same time as the array is being
+ modified, provided the RCU read lock is held.
+
+ The function will return the object if found (and set *_type to the object
+ type) or will return NULL if the object was not found.
+
+
+INDEX KEY FORM
+--------------
+
+The index key can be of any form, but since the algorithms aren't told how long
+the key is, it is strongly recommended that the index key includes its length
+very early on before any variation due to the length would have an effect on
+comparisons.
+
+This will cause leaves with different length keys to scatter away from each
+other - and those with the same length keys to cluster together.
+
+It is also recommended that the index key begin with a hash of the rest of the
+key to maximise scattering throughout keyspace.
+
+The better the scattering, the wider and lower the internal tree will be.
+
+Poor scattering isn't too much of a problem as there are shortcuts and nodes
+can contain mixtures of leaves and metadata pointers.
+
+The index key is read in chunks of machine word. Each chunk is subdivided into
+one nibble (4 bits) per level, so on a 32-bit CPU this is good for 8 levels and
+on a 64-bit CPU, 16 levels. Unless the scattering is really poor, it is
+unlikely that more than one word of any particular index key will have to be
+used.
+
+
+=================
+INTERNAL WORKINGS
+=================
+
+The associative array data structure has an internal tree. This tree is
+constructed of two types of metadata blocks: nodes and shortcuts.
+
+A node is an array of slots. Each slot can contain one of four things:
+
+ (*) A NULL pointer, indicating that the slot is empty.
+
+ (*) A pointer to an object (a leaf).
+
+ (*) A pointer to a node at the next level.
+
+ (*) A pointer to a shortcut.
+
+
+BASIC INTERNAL TREE LAYOUT
+--------------------------
+
+Ignoring shortcuts for the moment, the nodes form a multilevel tree. The index
+key space is strictly subdivided by the nodes in the tree and nodes occur on
+fixed levels. For example:
+
+ Level: 0 1 2 3
+ =============== =============== =============== ===============
+ NODE D
+ NODE B NODE C +------>+---+
+ +------>+---+ +------>+---+ | | 0 |
+ NODE A | | 0 | | | 0 | | +---+
+ +---+ | +---+ | +---+ | : :
+ | 0 | | : : | : : | +---+
+ +---+ | +---+ | +---+ | | f |
+ | 1 |---+ | 3 |---+ | 7 |---+ +---+
+ +---+ +---+ +---+
+ : : : : | 8 |---+
+ +---+ +---+ +---+ | NODE E
+ | e |---+ | f | : : +------>+---+
+ +---+ | +---+ +---+ | 0 |
+ | f | | | f | +---+
+ +---+ | +---+ : :
+ | NODE F +---+
+ +------>+---+ | f |
+ | 0 | NODE G +---+
+ +---+ +------>+---+
+ : : | | 0 |
+ +---+ | +---+
+ | 6 |---+ : :
+ +---+ +---+
+ : : | f |
+ +---+ +---+
+ | f |
+ +---+
+
+In the above example, there are 7 nodes (A-G), each with 16 slots (0-f).
+Assuming no other meta data nodes in the tree, the key space is divided thusly:
+
+ KEY PREFIX NODE
+ ========== ====
+ 137* D
+ 138* E
+ 13[0-69-f]* C
+ 1[0-24-f]* B
+ e6* G
+ e[0-57-f]* F
+ [02-df]* A
+
+So, for instance, keys with the following example index keys will be found in
+the appropriate nodes:
+
+ INDEX KEY PREFIX NODE
+ =============== ======= ====
+ 13694892892489 13 C
+ 13795289025897 137 D
+ 13889dde88793 138 E
+ 138bbb89003093 138 E
+ 1394879524789 12 C
+ 1458952489 1 B
+ 9431809de993ba - A
+ b4542910809cd - A
+ e5284310def98 e F
+ e68428974237 e6 G
+ e7fffcbd443 e F
+ f3842239082 - A
+
+To save memory, if a node can hold all the leaves in its portion of keyspace,
+then the node will have all those leaves in it and will not have any metadata
+pointers - even if some of those leaves would like to be in the same slot.
+
+A node can contain a heterogeneous mix of leaves and metadata pointers.
+Metadata pointers must be in the slots that match their subdivisions of key
+space. The leaves can be in any slot not occupied by a metadata pointer. It
+is guaranteed that none of the leaves in a node will match a slot occupied by a
+metadata pointer. If the metadata pointer is there, any leaf whose key matches
+the metadata key prefix must be in the subtree that the metadata pointer points
+to.
+
+In the above example list of index keys, node A will contain:
+
+ SLOT CONTENT INDEX KEY (PREFIX)
+ ==== =============== ==================
+ 1 PTR TO NODE B 1*
+ any LEAF 9431809de993ba
+ any LEAF b4542910809cd
+ e PTR TO NODE F e*
+ any LEAF f3842239082
+
+and node B:
+
+ 3 PTR TO NODE C 13*
+ any LEAF 1458952489
+
+
+SHORTCUTS
+---------
+
+Shortcuts are metadata records that jump over a piece of keyspace. A shortcut
+is a replacement for a series of single-occupancy nodes ascending through the
+levels. Shortcuts exist to save memory and to speed up traversal.
+
+It is possible for the root of the tree to be a shortcut - say, for example,
+the tree contains at least 17 nodes all with key prefix '1111'. The insertion
+algorithm will insert a shortcut to skip over the '1111' keyspace in a single
+bound and get to the fourth level where these actually become different.
+
+
+SPLITTING AND COLLAPSING NODES
+------------------------------
+
+Each node has a maximum capacity of 16 leaves and metadata pointers. If the
+insertion algorithm finds that it is trying to insert a 17th object into a
+node, that node will be split such that at least two leaves that have a common
+key segment at that level end up in a separate node rooted on that slot for
+that common key segment.
+
+If the leaves in a full node and the leaf that is being inserted are
+sufficiently similar, then a shortcut will be inserted into the tree.
+
+When the number of objects in the subtree rooted at a node falls to 16 or
+fewer, then the subtree will be collapsed down to a single node - and this will
+ripple towards the root if possible.
+
+
+NON-RECURSIVE ITERATION
+-----------------------
+
+Each node and shortcut contains a back pointer to its parent and the number of
+slot in that parent that points to it. None-recursive iteration uses these to
+proceed rootwards through the tree, going to the parent node, slot N + 1 to
+make sure progress is made without the need for a stack.
+
+The backpointers, however, make simultaneous alteration and iteration tricky.
+
+
+SIMULTANEOUS ALTERATION AND ITERATION
+-------------------------------------
+
+There are a number of cases to consider:
+
+ (1) Simple insert/replace. This involves simply replacing a NULL or old
+ matching leaf pointer with the pointer to the new leaf after a barrier.
+ The metadata blocks don't change otherwise. An old leaf won't be freed
+ until after the RCU grace period.
+
+ (2) Simple delete. This involves just clearing an old matching leaf. The
+ metadata blocks don't change otherwise. The old leaf won't be freed until
+ after the RCU grace period.
+
+ (3) Insertion replacing part of a subtree that we haven't yet entered. This
+ may involve replacement of part of that subtree - but that won't affect
+ the iteration as we won't have reached the pointer to it yet and the
+ ancestry blocks are not replaced (the layout of those does not change).
+
+ (4) Insertion replacing nodes that we're actively processing. This isn't a
+ problem as we've passed the anchoring pointer and won't switch onto the
+ new layout until we follow the back pointers - at which point we've
+ already examined the leaves in the replaced node (we iterate over all the
+ leaves in a node before following any of its metadata pointers).
+
+ We might, however, re-see some leaves that have been split out into a new
+ branch that's in a slot further along than we were at.
+
+ (5) Insertion replacing nodes that we're processing a dependent branch of.
+ This won't affect us until we follow the back pointers. Similar to (4).
+
+ (6) Deletion collapsing a branch under us. This doesn't affect us because the
+ back pointers will get us back to the parent of the new node before we
+ could see the new node. The entire collapsed subtree is thrown away
+ unchanged - and will still be rooted on the same slot, so we shouldn't
+ process it a second time as we'll go back to slot + 1.
+
+Note:
+
+ (*) Under some circumstances, we need to simultaneously change the parent
+ pointer and the parent slot pointer on a node (say, for example, we
+ inserted another node before it and moved it up a level). We cannot do
+ this without locking against a read - so we have to replace that node too.
+
+ However, when we're changing a shortcut into a node this isn't a problem
+ as shortcuts only have one slot and so the parent slot number isn't used
+ when traversing backwards over one. This means that it's okay to change
+ the slot number first - provided suitable barriers are used to make sure
+ the parent slot number is read after the back pointer.
+
+Obsolete blocks and leaves are freed up after an RCU grace period has passed,
+so as long as anyone doing walking or iteration holds the RCU read lock, the
+old superstructure should not go away on them.
--- /dev/null
+/* Generic associative array implementation.
+ *
+ * See Documentation/assoc_array.txt for information.
+ *
+ * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+//#define DEBUG
+#include <linux/slab.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);
+ smp_read_barrier_depends();
+ cursor = ACCESS_ONCE(shortcut->next_node);
+ }
+
+ node = assoc_array_ptr_to_node(cursor);
+ smp_read_barrier_depends();
+ 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 = ACCESS_ONCE(node->slots[slot]);
+ has_meta |= (unsigned long)ptr;
+ 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.
+ */
+ smp_read_barrier_depends();
+
+ /* 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);
+ smp_read_barrier_depends();
+
+ for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
+ ptr = ACCESS_ONCE(node->slots[slot]);
+ 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 = ACCESS_ONCE(node->back_pointer);
+ slot = node->parent_slot;
+ if (parent == stop)
+ return 0;
+
+ if (assoc_array_ptr_is_shortcut(parent)) {
+ shortcut = assoc_array_ptr_to_shortcut(parent);
+ smp_read_barrier_depends();
+ cursor = parent;
+ parent = ACCESS_ONCE(shortcut->back_pointer);
+ 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 = ACCESS_ONCE(array->root);
+
+ 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,
+} status;
+
+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 = ACCESS_ONCE(array->root);
+ 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);
+ smp_read_barrier_depends();
+
+ slot = segments >> (level & ASSOC_ARRAY_KEY_CHUNK_MASK);
+ slot &= ASSOC_ARRAY_FAN_MASK;
+ ptr = ACCESS_ONCE(node->slots[slot]);
+
+ 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);
+ smp_read_barrier_depends();
+ 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 = ACCESS_ONCE(shortcut->next_node);
+ 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;
+ smp_read_barrier_depends();
+
+ /* 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 = ACCESS_ONCE(node->slots[slot]);
+ 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);
+ smp_read_barrier_depends();
+ 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 (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 we can just insert a new node ahead of the old
+ * one.
+ */
+ goto present_leaves_cluster_but_not_new_leaf;
+ }
+
+split_node:
+ pr_devel("split node\n");
+
+ /* We need to split the current node; we know that the node doesn't
+ * simply contain a full set of leaves that cluster together (it
+ * contains meta pointers and/or non-clustering leaves).
+ *
+ * We need to expel at least two leaves out of a set consisting of the
+ * leaves in the node and the new leaf.
+ *
+ * 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;
+
+present_leaves_cluster_but_not_new_leaf:
+ /* 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 to hold the new
+ * leaf and a pointer to a new node holding all the old leaves.
+ */
+ pr_devel("present leaves cluster but not new leaf\n");
+
+ 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;
+ new_n1->back_pointer = assoc_array_node_to_ptr(new_n0);
+ new_n1->parent_slot = edit->segment_cache[0];
+ new_n1->nr_leaves_on_branch = node->nr_leaves_on_branch;
+ edit->adjust_count_on = new_n0;
+
+ for (i = 0; i < ASSOC_ARRAY_FAN_OUT; i++)
+ new_n1->slots[i] = node->slots[i];
+
+ new_n0->slots[edit->segment_cache[0]] = assoc_array_node_to_ptr(new_n0);
+ edit->leaf_p = &new_n0->slots[edit->segment_cache[ASSOC_ARRAY_FAN_OUT]];
+
+ edit->set[0].ptr = &assoc_array_ptr_to_node(node->back_pointer)->slots[node->parent_slot];
+ edit->set[0].to = assoc_array_node_to_ptr(new_n0);
+ edit->excised_meta[0] = assoc_array_node_to_ptr(node);
+ pr_devel("<--%s() = ok [insert node before]\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(edit->leaf),
+ assoc_array_ptr_to_leaf(node->slots[i]));
+ 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);
+
+ 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;
+ }
+ 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;
+ 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;
+ }
+
+ 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 */
+ 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);
+ }
+ }
+
+ 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;
+ } else {
+ slot = node->parent_slot;
+ cursor = ptr;
+ }
+ BUG_ON(!ptr);
+ node = assoc_array_ptr_to_node(cursor);
+ slot++;
+ goto continue_node;
+
+gc_complete:
+ edit->set[0].to = new_root;
+ assoc_array_apply_edit(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;
+}
projects / GitHub / LineageOS / android_kernel_motorola_exynos9610.git / commitdiff