/* * linux/fs/befs/btree.c * * Copyright (C) 2001-2002 Will Dyson <[email protected]> * * Licensed under the GNU GPL. See the file COPYING for details. * * 2002-02-05: Sergey S. Kostyliov added binary search within * btree nodes. * * Many thanks to: * * Dominic Giampaolo, author of "Practical File System * Design with the Be File System", for such a helpful book. * * Marcus J. Ranum, author of the b+tree package in * comp.sources.misc volume 10. This code is not copied from that * work, but it is partially based on it. * * Makoto Kato, author of the original BeFS for linux filesystem * driver. */ #include <linux/kernel.h> #include <linux/string.h> #include <linux/slab.h> #include <linux/mm.h> #include <linux/buffer_head.h> #include "befs.h" #include "btree.h" #include "datastream.h" /* * The btree functions in this file are built on top of the * datastream.c interface, which is in turn built on top of the * io.c interface. */ /* Befs B+tree structure: * * The first thing in the tree is the tree superblock. It tells you * all kinds of useful things about the tree, like where the rootnode * is located, and the size of the nodes (always 1024 with current version * of BeOS). * * The rest of the tree consists of a series of nodes. Nodes contain a header * (struct befs_btree_nodehead), the packed key data, an array of shorts * containing the ending offsets for each of the keys, and an array of * befs_off_t values. In interior nodes, the keys are the ending keys for * the childnode they point to, and the values are offsets into the * datastream containing the tree. */ /* Note: * * The book states 2 confusing things about befs b+trees. First, * it states that the overflow field of node headers is used by internal nodes * to point to another node that "effectively continues this one". Here is what * I believe that means. Each key in internal nodes points to another node that * contains key values less than itself. Inspection reveals that the last key * in the internal node is not the last key in the index. Keys that are * greater than the last key in the internal node go into the overflow node. * I imagine there is a performance reason for this. * * Second, it states that the header of a btree node is sufficient to * distinguish internal nodes from leaf nodes. Without saying exactly how. * After figuring out the first, it becomes obvious that internal nodes have * overflow nodes and leafnodes do not. */ /* * Currently, this code is only good for directory B+trees. * In order to be used for other BFS indexes, it needs to be extended to handle * duplicate keys and non-string keytypes (int32, int64, float, double). */ /* * In memory structure of each btree node */ struct befs_btree_node { … }; /* local constants */ static const befs_off_t BEFS_BT_INVAL = …; /* local functions */ static int befs_btree_seekleaf(struct super_block *sb, const befs_data_stream *ds, befs_btree_super * bt_super, struct befs_btree_node *this_node, befs_off_t * node_off); static int befs_bt_read_super(struct super_block *sb, const befs_data_stream *ds, befs_btree_super * sup); static int befs_bt_read_node(struct super_block *sb, const befs_data_stream *ds, struct befs_btree_node *node, befs_off_t node_off); static int befs_leafnode(struct befs_btree_node *node); static fs16 *befs_bt_keylen_index(struct befs_btree_node *node); static fs64 *befs_bt_valarray(struct befs_btree_node *node); static char *befs_bt_keydata(struct befs_btree_node *node); static int befs_find_key(struct super_block *sb, struct befs_btree_node *node, const char *findkey, befs_off_t * value); static char *befs_bt_get_key(struct super_block *sb, struct befs_btree_node *node, int index, u16 * keylen); static int befs_compare_strings(const void *key1, int keylen1, const void *key2, int keylen2); /** * befs_bt_read_super() - read in btree superblock convert to cpu byteorder * @sb: Filesystem superblock * @ds: Datastream to read from * @sup: Buffer in which to place the btree superblock * * Calls befs_read_datastream to read in the btree superblock and * makes sure it is in cpu byteorder, byteswapping if necessary. * Return: BEFS_OK on success and if *@sup contains the btree superblock in cpu * byte order. Otherwise return BEFS_ERR on error. */ static int befs_bt_read_super(struct super_block *sb, const befs_data_stream *ds, befs_btree_super * sup) { … } /** * befs_bt_read_node - read in btree node and convert to cpu byteorder * @sb: Filesystem superblock * @ds: Datastream to read from * @node: Buffer in which to place the btree node * @node_off: Starting offset (in bytes) of the node in @ds * * Calls befs_read_datastream to read in the indicated btree node and * makes sure its header fields are in cpu byteorder, byteswapping if * necessary. * Note: node->bh must be NULL when this function is called the first time. * Don't forget brelse(node->bh) after last call. * * On success, returns BEFS_OK and *@node contains the btree node that * starts at @node_off, with the node->head fields in cpu byte order. * * On failure, BEFS_ERR is returned. */ static int befs_bt_read_node(struct super_block *sb, const befs_data_stream *ds, struct befs_btree_node *node, befs_off_t node_off) { … } /** * befs_btree_find - Find a key in a befs B+tree * @sb: Filesystem superblock * @ds: Datastream containing btree * @key: Key string to lookup in btree * @value: Value stored with @key * * On success, returns BEFS_OK and sets *@value to the value stored * with @key (usually the disk block number of an inode). * * On failure, returns BEFS_ERR or BEFS_BT_NOT_FOUND. * * Algorithm: * Read the superblock and rootnode of the b+tree. * Drill down through the interior nodes using befs_find_key(). * Once at the correct leaf node, use befs_find_key() again to get the * actual value stored with the key. */ int befs_btree_find(struct super_block *sb, const befs_data_stream *ds, const char *key, befs_off_t * value) { … } /** * befs_find_key - Search for a key within a node * @sb: Filesystem superblock * @node: Node to find the key within * @findkey: Keystring to search for * @value: If key is found, the value stored with the key is put here * * Finds exact match if one exists, and returns BEFS_BT_MATCH. * If there is no match and node's value array is too small for key, return * BEFS_BT_OVERFLOW. * If no match and node should countain this key, return BEFS_BT_NOT_FOUND. * * Uses binary search instead of a linear. */ static int befs_find_key(struct super_block *sb, struct befs_btree_node *node, const char *findkey, befs_off_t * value) { … } /** * befs_btree_read - Traverse leafnodes of a btree * @sb: Filesystem superblock * @ds: Datastream containing btree * @key_no: Key number (alphabetical order) of key to read * @bufsize: Size of the buffer to return key in * @keybuf: Pointer to a buffer to put the key in * @keysize: Length of the returned key * @value: Value stored with the returned key * * Here's how it works: Key_no is the index of the key/value pair to * return in keybuf/value. * Bufsize is the size of keybuf (BEFS_NAME_LEN+1 is a good size). Keysize is * the number of characters in the key (just a convenience). * * Algorithm: * Get the first leafnode of the tree. See if the requested key is in that * node. If not, follow the node->right link to the next leafnode. Repeat * until the (key_no)th key is found or the tree is out of keys. */ int befs_btree_read(struct super_block *sb, const befs_data_stream *ds, loff_t key_no, size_t bufsize, char *keybuf, size_t * keysize, befs_off_t * value) { … } /** * befs_btree_seekleaf - Find the first leafnode in the btree * @sb: Filesystem superblock * @ds: Datastream containing btree * @bt_super: Pointer to the superblock of the btree * @this_node: Buffer to return the leafnode in * @node_off: Pointer to offset of current node within datastream. Modified * by the function. * * Helper function for btree traverse. Moves the current position to the * start of the first leaf node. * * Also checks for an empty tree. If there are no keys, returns BEFS_BT_EMPTY. */ static int befs_btree_seekleaf(struct super_block *sb, const befs_data_stream *ds, befs_btree_super *bt_super, struct befs_btree_node *this_node, befs_off_t * node_off) { … } /** * befs_leafnode - Determine if the btree node is a leaf node or an * interior node * @node: Pointer to node structure to test * * Return 1 if leaf, 0 if interior */ static int befs_leafnode(struct befs_btree_node *node) { … } /** * befs_bt_keylen_index - Finds start of keylen index in a node * @node: Pointer to the node structure to find the keylen index within * * Returns a pointer to the start of the key length index array * of the B+tree node *@node * * "The length of all the keys in the node is added to the size of the * header and then rounded up to a multiple of four to get the beginning * of the key length index" (p.88, practical filesystem design). * * Except that rounding up to 8 works, and rounding up to 4 doesn't. */ static fs16 * befs_bt_keylen_index(struct befs_btree_node *node) { … } /** * befs_bt_valarray - Finds the start of value array in a node * @node: Pointer to the node structure to find the value array within * * Returns a pointer to the start of the value array * of the node pointed to by the node header */ static fs64 * befs_bt_valarray(struct befs_btree_node *node) { … } /** * befs_bt_keydata - Finds start of keydata array in a node * @node: Pointer to the node structure to find the keydata array within * * Returns a pointer to the start of the keydata array * of the node pointed to by the node header */ static char * befs_bt_keydata(struct befs_btree_node *node) { … } /** * befs_bt_get_key - returns a pointer to the start of a key * @sb: filesystem superblock * @node: node in which to look for the key * @index: the index of the key to get * @keylen: modified to be the length of the key at @index * * Returns a valid pointer into @node on success. * Returns NULL on failure (bad input) and sets *@keylen = 0 */ static char * befs_bt_get_key(struct super_block *sb, struct befs_btree_node *node, int index, u16 * keylen) { … } /** * befs_compare_strings - compare two strings * @key1: pointer to the first key to be compared * @keylen1: length in bytes of key1 * @key2: pointer to the second key to be compared * @keylen2: length in bytes of key2 * * Returns 0 if @key1 and @key2 are equal. * Returns >0 if @key1 is greater. * Returns <0 if @key2 is greater. */ static int befs_compare_strings(const void *key1, int keylen1, const void *key2, int keylen2) { … } /* These will be used for non-string keyed btrees */ #if 0 static int btree_compare_int32(cont void *key1, int keylen1, const void *key2, int keylen2) { return *(int32_t *) key1 - *(int32_t *) key2; } static int btree_compare_uint32(cont void *key1, int keylen1, const void *key2, int keylen2) { if (*(u_int32_t *) key1 == *(u_int32_t *) key2) return 0; else if (*(u_int32_t *) key1 > *(u_int32_t *) key2) return 1; return -1; } static int btree_compare_int64(cont void *key1, int keylen1, const void *key2, int keylen2) { if (*(int64_t *) key1 == *(int64_t *) key2) return 0; else if (*(int64_t *) key1 > *(int64_t *) key2) return 1; return -1; } static int btree_compare_uint64(cont void *key1, int keylen1, const void *key2, int keylen2) { if (*(u_int64_t *) key1 == *(u_int64_t *) key2) return 0; else if (*(u_int64_t *) key1 > *(u_int64_t *) key2) return 1; return -1; } static int btree_compare_float(cont void *key1, int keylen1, const void *key2, int keylen2) { float result = *(float *) key1 - *(float *) key2; if (result == 0.0f) return 0; return (result < 0.0f) ? -1 : 1; } static int btree_compare_double(cont void *key1, int keylen1, const void *key2, int keylen2) { double result = *(double *) key1 - *(double *) key2; if (result == 0.0) return 0; return (result < 0.0) ? -1 : 1; } #endif //0
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