/* * CDDL HEADER START * * This file and its contents are supplied under the terms of the * Common Development and Distribution License ("CDDL"), version 1.0. * You may only use this file in accordance with the terms of version * 1.0 of the CDDL. * * A full copy of the text of the CDDL should have accompanied this * source. A copy of the CDDL is also available via the Internet at * http://www.illumos.org/license/CDDL. * * CDDL HEADER END */ /* * Copyright (c) 2019 by Delphix. All rights reserved. */ #ifndef _BTREE_H #define _BTREE_H #ifdef __cplusplus extern "C" { #endif #include <sys/zfs_context.h> /* * This file defines the interface for a B-Tree implementation for ZFS. The * tree can be used to store arbitrary sortable data types with low overhead * and good operation performance. In addition the tree intelligently * optimizes bulk in-order insertions to improve memory use and performance. * * Note that for all B-Tree functions, the values returned are pointers to the * internal copies of the data in the tree. The internal data can only be * safely mutated if the changes cannot change the ordering of the element * with respect to any other elements in the tree. * * The major drawback of the B-Tree is that any returned elements or indexes * are only valid until a side-effectful operation occurs, since these can * result in reallocation or relocation of data. Side effectful operations are * defined as insertion, removal, and zfs_btree_destroy_nodes. * * The B-Tree has two types of nodes: core nodes, and leaf nodes. Core * nodes have an array of children pointing to other nodes, and an array of * elements that act as separators between the elements of the subtrees rooted * at its children. Leaf nodes only contain data elements, and form the bottom * layer of the tree. Unlike B+ Trees, in this B-Tree implementation the * elements in the core nodes are not copies of or references to leaf node * elements. Each element occcurs only once in the tree, no matter what kind * of node it is in. * * The tree's height is the same throughout, unlike many other forms of search * tree. Each node (except for the root) must be between half minus one and * completely full of elements (and children) at all times. Any operation that * would put the node outside of that range results in a rebalancing operation * (taking, merging, or splitting). * * This tree was implemented using descriptions from Wikipedia's articles on * B-Trees and B+ Trees. */ /* * Decreasing these values results in smaller memmove operations, but more of * them, and increased memory overhead. Increasing these values results in * higher variance in operation time, and reduces memory overhead. */ #define BTREE_CORE_ELEMS 128 #define BTREE_LEAF_SIZE 4096 typedef struct zfs_btree_hdr { struct zfs_btree_core *bth_parent; /* * Set to -1 to indicate core nodes. Other values represent first * valid element offset for leaf nodes. */ uint32_t bth_first; /* * For both leaf and core nodes, represents the number of elements in * the node. For core nodes, they will have bth_count + 1 children. */ uint32_t bth_count; } zfs_btree_hdr_t; typedef struct zfs_btree_core { zfs_btree_hdr_t btc_hdr; zfs_btree_hdr_t *btc_children[BTREE_CORE_ELEMS + 1]; uint8_t btc_elems[]; } zfs_btree_core_t; typedef struct zfs_btree_leaf { zfs_btree_hdr_t btl_hdr; uint8_t btl_elems[]; } zfs_btree_leaf_t; #define BTREE_LEAF_ESIZE (BTREE_LEAF_SIZE - \ offsetof(zfs_btree_leaf_t, btl_elems)) typedef struct zfs_btree_index { zfs_btree_hdr_t *bti_node; uint32_t bti_offset; /* * True if the location is before the list offset, false if it's at * the listed offset. */ boolean_t bti_before; } zfs_btree_index_t; typedef struct btree { zfs_btree_hdr_t *bt_root; int64_t bt_height; size_t bt_elem_size; uint32_t bt_leaf_cap; uint64_t bt_num_elems; uint64_t bt_num_nodes; zfs_btree_leaf_t *bt_bulk; // non-null if bulk loading int (*bt_compar) (const void *, const void *); } zfs_btree_t; /* * Allocate and deallocate caches for btree nodes. */ void zfs_btree_init(void); void zfs_btree_fini(void); /* * Initialize an B-Tree. Arguments are: * * tree - the tree to be initialized * compar - function to compare two nodes, it must return exactly: -1, 0, or +1 * -1 for <, 0 for ==, and +1 for > * size - the value of sizeof(struct my_type) */ void zfs_btree_create(zfs_btree_t *, int (*) (const void *, const void *), size_t); /* * Find a node with a matching value in the tree. Returns the matching node * found. If not found, it returns NULL and then if "where" is not NULL it sets * "where" for use with zfs_btree_add_idx() or zfs_btree_nearest(). * * node - node that has the value being looked for * where - position for use with zfs_btree_nearest() or zfs_btree_add_idx(), * may be NULL */ void *zfs_btree_find(zfs_btree_t *, const void *, zfs_btree_index_t *); /* * Insert a node into the tree. * * node - the node to insert * where - position as returned from zfs_btree_find() */ void zfs_btree_add_idx(zfs_btree_t *, const void *, const zfs_btree_index_t *); /* * Return the first or last valued node in the tree. Will return NULL if the * tree is empty. The index can be NULL if the location of the first or last * element isn't required. */ void *zfs_btree_first(zfs_btree_t *, zfs_btree_index_t *); void *zfs_btree_last(zfs_btree_t *, zfs_btree_index_t *); /* * Return the next or previous valued node in the tree. The second index can * safely be NULL, if the location of the next or previous value isn't * required. */ void *zfs_btree_next(zfs_btree_t *, const zfs_btree_index_t *, zfs_btree_index_t *); void *zfs_btree_prev(zfs_btree_t *, const zfs_btree_index_t *, zfs_btree_index_t *); /* * Get a value from a tree and an index. */ void *zfs_btree_get(zfs_btree_t *, zfs_btree_index_t *); /* * Add a single value to the tree. The value must not compare equal to any * other node already in the tree. Note that the value will be copied out, not * inserted directly. It is safe to free or destroy the value once this * function returns. */ void zfs_btree_add(zfs_btree_t *, const void *); /* * Remove a single value from the tree. The value must be in the tree. The * pointer passed in may be a pointer into a tree-controlled buffer, but it * need not be. */ void zfs_btree_remove(zfs_btree_t *, const void *); /* * Remove the value at the given location from the tree. */ void zfs_btree_remove_idx(zfs_btree_t *, zfs_btree_index_t *); /* * Return the number of nodes in the tree */ ulong_t zfs_btree_numnodes(zfs_btree_t *); /* * Used to destroy any remaining nodes in a tree. The cookie argument should * be initialized to NULL before the first call. Returns a node that has been * removed from the tree and may be free()'d. Returns NULL when the tree is * empty. * * Once you call zfs_btree_destroy_nodes(), you can only continuing calling it * and finally zfs_btree_destroy(). No other B-Tree routines will be valid. * * cookie - an index used to save state between calls to * zfs_btree_destroy_nodes() * * EXAMPLE: * zfs_btree_t *tree; * struct my_data *node; * zfs_btree_index_t *cookie; * * cookie = NULL; * while ((node = zfs_btree_destroy_nodes(tree, &cookie)) != NULL) * data_destroy(node); * zfs_btree_destroy(tree); */ void *zfs_btree_destroy_nodes(zfs_btree_t *, zfs_btree_index_t **); /* * Destroys all nodes in the tree quickly. This doesn't give the caller an * opportunity to iterate over each node and do its own cleanup; for that, use * zfs_btree_destroy_nodes(). */ void zfs_btree_clear(zfs_btree_t *); /* * Final destroy of an B-Tree. Arguments are: * * tree - the empty tree to destroy */ void zfs_btree_destroy(zfs_btree_t *tree); /* Runs a variety of self-checks on the btree to verify integrity. */ void zfs_btree_verify(zfs_btree_t *tree); #ifdef __cplusplus } #endif #endif /* _BTREE_H */
