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/*

 * linux/fs/befs/btree.c

 *

 * Copyright (C) 2001-2002 Will Dyson <will_dyson@pobox.com>

 *

 * Licensed under the GNU GPL. See the file COPYING for details.

 *

 * 2002-02-05: Sergey S. Kostyliov added binary search withing

 *              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

 */

typedef struct {

        befs_host_btree_nodehead head;  /* head of node converted to cpu byteorder */

        struct buffer_head *bh;

        befs_btree_nodehead *od_node;   /* on disk node */

} befs_btree_node;

/* local constants */

static const befs_off_t befs_bt_inval = 0xffffffffffffffffULL;

/* local functions */

static int befs_btree_seekleaf(struct super_block *sb, befs_data_stream * ds,

                               befs_btree_super * bt_super,

                               befs_btree_node * this_node,

                               befs_off_t * node_off);

static int befs_bt_read_super(struct super_block *sb, befs_data_stream * ds,

                              befs_btree_super * sup);

static int befs_bt_read_node(struct super_block *sb, befs_data_stream * ds,

                             befs_btree_node * node, befs_off_t node_off);

static int befs_leafnode(befs_btree_node * node);

static fs16 *befs_bt_keylen_index(befs_btree_node * node);

static fs64 *befs_bt_valarray(befs_btree_node * node);

static char *befs_bt_keydata(befs_btree_node * node);

static int befs_find_key(struct super_block *sb, befs_btree_node * node,

                         const char *findkey, befs_off_t * value);

static char *befs_bt_get_key(struct super_block *sb, 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.

 *

 * On success, returns BEFS_OK and *@sup contains the btree superblock,

 * in cpu byte order.

 *

 * On failure, BEFS_ERR is returned.

 */

static int

befs_bt_read_super(struct super_block *sb, befs_data_stream * ds,

                   befs_btree_super * sup)

{

        struct buffer_head *bh = NULL;

        befs_disk_btree_super *od_sup = NULL;

        befs_debug(sb, "---> befs_btree_read_super()");

        bh = befs_read_datastream(sb, ds, 0, NULL);

        if (!bh) {

                befs_error(sb, "Couldn't read index header.");

                goto error;

        }

        od_sup = (befs_disk_btree_super *) bh->b_data;

        befs_dump_index_entry(sb, od_sup);

        sup->magic = fs32_to_cpu(sb, od_sup->magic);

        sup->node_size = fs32_to_cpu(sb, od_sup->node_size);

        sup->max_depth = fs32_to_cpu(sb, od_sup->max_depth);

        sup->data_type = fs32_to_cpu(sb, od_sup->data_type);

        sup->root_node_ptr = fs64_to_cpu(sb, od_sup->root_node_ptr);

        sup->free_node_ptr = fs64_to_cpu(sb, od_sup->free_node_ptr);

        sup->max_size = fs64_to_cpu(sb, od_sup->max_size);

        brelse(bh);

        if (sup->magic != BEFS_BTREE_MAGIC) {

                befs_error(sb, "Index header has bad magic.");

                goto error;

        }

        befs_debug(sb, "<--- befs_btree_read_super()");

        return BEFS_OK;

      error:

        befs_debug(sb, "<--- befs_btree_read_super() ERROR");

        return BEFS_ERR;

}

/**

 * 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 called 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, befs_data_stream * ds,

                  befs_btree_node * node, befs_off_t node_off)

{

        uint off = 0;

        befs_debug(sb, "---> befs_bt_read_node()");

        if (node->bh)

                brelse(node->bh);

        node->bh = befs_read_datastream(sb, ds, node_off, &off);

        if (!node->bh) {

                befs_error(sb, "befs_bt_read_node() failed to read "

                           "node at %Lu", node_off);

                befs_debug(sb, "<--- befs_bt_read_node() ERROR");

                return BEFS_ERR;

        }

        node->od_node =

            (befs_btree_nodehead *) ((void *) node->bh->b_data + off);

        befs_dump_index_node(sb, node->od_node);

        node->head.left = fs64_to_cpu(sb, node->od_node->left);

        node->head.right = fs64_to_cpu(sb, node->od_node->right);

        node->head.overflow = fs64_to_cpu(sb, node->od_node->overflow);

        node->head.all_key_count =

            fs16_to_cpu(sb, node->od_node->all_key_count);

        node->head.all_key_length =

            fs16_to_cpu(sb, node->od_node->all_key_length);

        befs_debug(sb, "<--- befs_btree_read_node()");

        return BEFS_OK;

}

/**

 * 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 sucess, 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

 *   actuall value stored with the key.

 */

int

befs_btree_find(struct super_block *sb, befs_data_stream * ds,

                const char *key, befs_off_t * value)

{

        befs_btree_node *this_node = NULL;

        befs_btree_super bt_super;

        befs_off_t node_off;

        int res;

        befs_debug(sb, "---> befs_btree_find() Key: %s", key);

        if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {

                befs_error(sb,

                           "befs_btree_find() failed to read index superblock");

                goto error;

        }

        this_node = kmalloc(sizeof (befs_btree_node),

                                                GFP_NOFS);

        if (!this_node) {

                befs_error(sb, "befs_btree_find() failed to allocate %u "

                           "bytes of memory", sizeof (befs_btree_node));

                goto error;

        }

        this_node->bh = NULL;

        /* read in root node */

        node_off = bt_super.root_node_ptr;

        if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {

                befs_error(sb, "befs_btree_find() failed to read "

                           "node at %Lu", node_off);

                goto error_alloc;

        }

        while (!befs_leafnode(this_node)) {

                res = befs_find_key(sb, this_node, key, &node_off);

                if (res == BEFS_BT_NOT_FOUND)

                        node_off = this_node->head.overflow;

                /* if no match, go to overflow node */

                if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {

                        befs_error(sb, "befs_btree_find() failed to read "

                                   "node at %Lu", node_off);

                        goto error_alloc;

                }

        }

        /* at the correct leaf node now */

        res = befs_find_key(sb, this_node, key, value);

        brelse(this_node->bh);

        kfree(this_node);

        if (res != BEFS_BT_MATCH) {

                befs_debug(sb, "<--- befs_btree_find() Key %s not found", key);

                *value = 0;

                return BEFS_BT_NOT_FOUND;

        }

        befs_debug(sb, "<--- befs_btree_find() Found key %s, value %Lu",

                   key, *value);

        return BEFS_OK;

      error_alloc:

        kfree(this_node);

      error:

        *value = 0;

        befs_debug(sb, "<--- befs_btree_find() ERROR");

        return BEFS_ERR;

}

/**

 * befs_find_key - Search for a key within a node

 * @sb: Filesystem superblock

 * @node: Node to find the key within

 * @key: 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 no exact match, finds first key in node that is greater

 * (alphabetically) than the search key and returns BEFS_BT_PARMATCH

 * (for partial match, I guess). Can you think of something better to

 * call it?

 *

 * If no key was a match or greater than the search key, return

 * BEFS_BT_NOT_FOUND.

 *

 * Use binary search instead of a linear.

 */

static int

befs_find_key(struct super_block *sb, befs_btree_node * node,

              const char *findkey, befs_off_t * value)

{

        int first, last, mid;

        int eq;

        u16 keylen;

        int findkey_len;

        char *thiskey;

        fs64 *valarray;

        befs_debug(sb, "---> befs_find_key() %s", findkey);

        *value = 0;

        findkey_len = strlen(findkey);

        /* if node can not contain key, just skeep this node */

        last = node->head.all_key_count - 1;

        thiskey = befs_bt_get_key(sb, node, last, &keylen);

        eq = befs_compare_strings(thiskey, keylen, findkey, findkey_len);

        if (eq < 0) {

                befs_debug(sb, "<--- befs_find_key() %s not found", findkey);

                return BEFS_BT_NOT_FOUND;

        }

        valarray = befs_bt_valarray(node);

        /* simple binary search */

        first = 0;

        mid = 0;

        while (last >= first) {

                mid = (last + first) / 2;

                befs_debug(sb, "first: %d, last: %d, mid: %d", first, last,

                           mid);

                thiskey = befs_bt_get_key(sb, node, mid, &keylen);

                eq = befs_compare_strings(thiskey, keylen, findkey,

                                          findkey_len);

                if (eq == 0) {

                        befs_debug(sb, "<--- befs_find_key() found %s at %d",

                                   thiskey, mid);

                        *value = fs64_to_cpu(sb, valarray[mid]);

                        return BEFS_BT_MATCH;

                }

                if (eq > 0)

                        last = mid - 1;

                else

                        first = mid + 1;

        }

        if (eq < 0)

                *value = fs64_to_cpu(sb, valarray[mid + 1]);

        else

                *value = fs64_to_cpu(sb, valarray[mid]);

        befs_debug(sb, "<--- befs_find_key() found %s at %d", thiskey, mid);

        return BEFS_BT_PARMATCH;

}

/**

 * 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

 *

 * Heres 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 charecters 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, befs_data_stream * ds,

                loff_t key_no, size_t bufsize, char *keybuf, size_t * keysize,

                befs_off_t * value)

{

        befs_btree_node *this_node;

        befs_btree_super bt_super;

        befs_off_t node_off = 0;

        int cur_key;

        fs64 *valarray;

        char *keystart;

        u16 keylen;

        int res;

        uint key_sum = 0;

        befs_debug(sb, "---> befs_btree_read()");

        if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {

                befs_error(sb,

                           "befs_btree_read() failed to read index superblock");

                goto error;

        }

        if ((this_node = (befs_btree_node *)

             kmalloc(sizeof (befs_btree_node), GFP_NOFS)) == NULL) {

                befs_error(sb, "befs_btree_read() failed to allocate %u "

                           "bytes of memory", sizeof (befs_btree_node));

                goto error;

        }

        node_off = bt_super.root_node_ptr;

        this_node->bh = NULL;

        /* seeks down to first leafnode, reads it into this_node */

        res = befs_btree_seekleaf(sb, ds, &bt_super, this_node, &node_off);

        if (res == BEFS_BT_EMPTY) {

                brelse(this_node->bh);

                kfree(this_node);

                *value = 0;

                *keysize = 0;

                befs_debug(sb, "<--- befs_btree_read() Tree is EMPTY");

                return BEFS_BT_EMPTY;

        } else if (res == BEFS_ERR) {

                goto error_alloc;

        }

        /* find the leaf node containing the key_no key */

        while (key_sum + this_node->head.all_key_count <= key_no) {

                /* no more nodes to look in: key_no is too large */

                if (this_node->head.right == befs_bt_inval) {

                        *keysize = 0;

                        *value = 0;

                        befs_debug(sb,

                                   "<--- befs_btree_read() END of keys at %Lu",

                                   key_sum + this_node->head.all_key_count);

                        brelse(this_node->bh);

                        kfree(this_node);

                        return BEFS_BT_END;

                }

                key_sum += this_node->head.all_key_count;

                node_off = this_node->head.right;

                if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {

                        befs_error(sb, "befs_btree_read() failed to read "

                                   "node at %Lu", node_off);

                        goto error_alloc;

                }

        }

        /* how many keys into this_node is key_no */

        cur_key = key_no - key_sum;

        /* get pointers to datastructures within the node body */

        valarray = befs_bt_valarray(this_node);

        keystart = befs_bt_get_key(sb, this_node, cur_key, &keylen);

        befs_debug(sb, "Read [%Lu,%d]: keysize %d", node_off, cur_key, keylen);

        if (bufsize < keylen + 1) {

                befs_error(sb, "befs_btree_read() keybuf too small (%u) "

                           "for key of size %d", bufsize, keylen);

                brelse(this_node->bh);

                goto error_alloc;

        };

        strncpy(keybuf, keystart, keylen);

        *value = fs64_to_cpu(sb, valarray[cur_key]);

        *keysize = keylen;

        keybuf[keylen] = '\0';

        befs_debug(sb, "Read [%Lu,%d]: Key \"%.*s\", Value %Lu", node_off,

                   cur_key, keylen, keybuf, *value);

        brelse(this_node->bh);

        kfree(this_node);

        befs_debug(sb, "<--- befs_btree_read()");

        return BEFS_OK;

      error_alloc:

        kfree(this_node);

      error:

        *keysize = 0;

        *value = 0;

        befs_debug(sb, "<--- befs_btree_read() ERROR");

        return BEFS_ERR;

}

/**

 * 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, befs_data_stream * ds,

                    befs_btree_super * bt_super, befs_btree_node * this_node,

                    befs_off_t * node_off)

{

        befs_debug(sb, "---> befs_btree_seekleaf()");

        if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {

                befs_error(sb, "befs_btree_seekleaf() failed to read "

                           "node at %Lu", *node_off);

                goto error;

        }

        befs_debug(sb, "Seekleaf to root node %Lu", *node_off);

        if (this_node->head.all_key_count == 0 && befs_leafnode(this_node)) {

                befs_debug(sb, "<--- befs_btree_seekleaf() Tree is EMPTY");

                return BEFS_BT_EMPTY;

        }

        while (!befs_leafnode(this_node)) {

                if (this_node->head.all_key_count == 0) {

                        befs_debug(sb, "befs_btree_seekleaf() encountered "

                                   "an empty interior node: %Lu. Using Overflow "

                                   "node: %Lu", *node_off,

                                   this_node->head.overflow);

                        *node_off = this_node->head.overflow;

                } else {

                        fs64 *valarray = befs_bt_valarray(this_node);

                        *node_off = fs64_to_cpu(sb, valarray[0]);

                }

                if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {

                        befs_error(sb, "befs_btree_seekleaf() failed to read "

                                   "node at %Lu", *node_off);

                        goto error;

                }

                befs_debug(sb, "Seekleaf to child node %Lu", *node_off);

        }

        befs_debug(sb, "Node %Lu is a leaf node", *node_off);

        return BEFS_OK;

      error:

        befs_debug(sb, "<--- befs_btree_seekleaf() ERROR");

        return BEFS_ERR;

}

/**

 * 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(befs_btree_node * node)

{

        /* all interior nodes (and only interior nodes) have an overflow node */

        if (node->head.overflow == befs_bt_inval)

                return 1;

        else

                return 0;

}

/**

 * 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(befs_btree_node * node)

{

        const int keylen_align = 8;

        unsigned long int off =

            (sizeof (befs_btree_nodehead) + node->head.all_key_length);

        ulong tmp = off % keylen_align;

        if (tmp)

                off += keylen_align - tmp;

        return (fs16 *) ((void *) node->od_node + off);

}

/**

 * 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(befs_btree_node * node)

{

        void *keylen_index_start = (void *) befs_bt_keylen_index(node);

        size_t keylen_index_size = node->head.all_key_count * sizeof (fs16);

        return (fs64 *) (keylen_index_start + keylen_index_size);

}

/**

 * 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(befs_btree_node * node)

{

        return (char *) ((void *) node->od_node + sizeof (befs_btree_nodehead));

}

/**

 * 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, befs_btree_node * node,

                int index, u16 * keylen)

{

        int prev_key_end;

        char *keystart;

        fs16 *keylen_index;

        if (index < 0 || index > node->head.all_key_count) {

                *keylen = 0;

                return NULL;

        }

        keystart = befs_bt_keydata(node);

        keylen_index = befs_bt_keylen_index(node);

        if (index == 0)

                prev_key_end = 0;

        else

                prev_key_end = fs16_to_cpu(sb, keylen_index[index - 1]);

        *keylen = fs16_to_cpu(sb, keylen_index[index]) - prev_key_end;

        return keystart + prev_key_end;

}

/**

 * 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

 * @kelen2: 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)

{