btree.c

linux 内核源代码

/**
 * 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