btree.c

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/*
 * 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
 */
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);

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;
}

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;
}

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;
}

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;
}

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;
}

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;
}

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;
}

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);
}

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);
}

static char *
befs_bt_keydata(befs_btree_node * node)
{
    return (char *) ((void *) node->od_node + sizeof (befs_btree_nodehead));
}

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;
}

static int
befs_compare_strings(const void *key1, int keylen1,
             const void *key2, int keylen2)
{
    int len = min_t(int, keylen1, keylen2);
    int result = strncmp(key1, key2, len);
    if (result == 0)
        result = keylen1 - keylen2;
    return result;
}

/* 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