freebsd-nq/include/sys/btree.h
Paul Dagnelie 516a83f886 Function name and comment updates
Rename certain functions for more consistency when they share common 
features. Make comments clearer about what arguments should be passed 
to the insert and add functions.

Reviewed by: Sara Hartse <sara.hartse@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes #9441
2019-10-11 10:13:21 -07:00

244 lines
7.7 KiB
C

/*
* 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
extern kmem_cache_t *zfs_btree_leaf_cache;
typedef struct zfs_btree_hdr {
struct zfs_btree_core *bth_parent;
boolean_t bth_core;
/*
* 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;
typedef struct zfs_btree_index {
zfs_btree_hdr_t *bti_node;
uint64_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;
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 */