btree.c

linux 内核源代码

/*
 * linux/fs/befs/btree.c
 *
 * Copyright (C) 2001-2002 Will Dyson <[e-mail]>
 *
 * 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;
}