- 根目录:
- fs
- befs
- btree.c
/*
* 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 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);
/**
* 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 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
* 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)
{
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