lib/radix-tree.c

/*
 * Copyright (C) 2001 Momchil Velikov
 * Portions Copyright (C) 2001 Christoph Hellwig
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2, or (at
 * your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/errno.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/radix-tree.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/gfp.h>
#include <linux/string.h>

/*
 * Radix tree node definition.
 */
#define RADIX_TREE_MAP_SHIFT  6
#define RADIX_TREE_MAP_SIZE  (1UL << RADIX_TREE_MAP_SHIFT)
#define RADIX_TREE_MAP_MASK  (RADIX_TREE_MAP_SIZE-1)

struct radix_tree_node {
	unsigned int	count;
	void		*slots[RADIX_TREE_MAP_SIZE];
};

struct radix_tree_path {
	struct radix_tree_node *node, **slot;
};

#define RADIX_TREE_INDEX_BITS  (8 /* CHAR_BIT */ * sizeof(unsigned long))
#define RADIX_TREE_MAX_PATH (RADIX_TREE_INDEX_BITS/RADIX_TREE_MAP_SHIFT + 2)

static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH];

/*
 * Radix tree node cache.
 */
static kmem_cache_t *radix_tree_node_cachep;

/*
 * Per-cpu pool of preloaded nodes
 */
struct radix_tree_preload {
	int nr;
	struct radix_tree_node *nodes[RADIX_TREE_MAX_PATH];
};
DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };

/*
 * This assumes that the caller has performed appropriate preallocation, and
 * that the caller has pinned this thread of control to the current CPU.
 */
static struct radix_tree_node *
radix_tree_node_alloc(struct radix_tree_root *root)
{
	struct radix_tree_node *ret;

	ret = kmem_cache_alloc(radix_tree_node_cachep, root->gfp_mask);
	if (ret == NULL && !(root->gfp_mask & __GFP_WAIT)) {
		struct radix_tree_preload *rtp;

		rtp = &__get_cpu_var(radix_tree_preloads);
		if (rtp->nr) {
			ret = rtp->nodes[rtp->nr - 1];
			rtp->nodes[rtp->nr - 1] = NULL;
			rtp->nr--;
		}
	}
	return ret;
}

static inline void
radix_tree_node_free(struct radix_tree_node *node)
{
	kmem_cache_free(radix_tree_node_cachep, node);
}

/*
 * Load up this CPU's radix_tree_node buffer with sufficient objects to
 * ensure that the addition of a single element in the tree cannot fail.  On
 * success, return zero, with preemption disabled.  On error, return -ENOMEM
 * with preemption not disabled.
 */
int radix_tree_preload(int gfp_mask)
{
	struct radix_tree_preload *rtp;
	struct radix_tree_node *node;
	int ret = -ENOMEM;

	preempt_disable();
	rtp = &__get_cpu_var(radix_tree_preloads);
	while (rtp->nr < ARRAY_SIZE(rtp->nodes)) {
		preempt_enable();
		node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
		if (node == NULL)
			goto out;
		preempt_disable();
		rtp = &__get_cpu_var(radix_tree_preloads);
		if (rtp->nr < ARRAY_SIZE(rtp->nodes))
			rtp->nodes[rtp->nr++] = node;
		else
			kmem_cache_free(radix_tree_node_cachep, node);
	}
	ret = 0;
out:
	return ret;
}

/*
 *	Return the maximum key which can be store into a
 *	radix tree with height HEIGHT.
 */
static inline unsigned long radix_tree_maxindex(unsigned int height)
{
	return height_to_maxindex[height];
}

/*
 *	Extend a radix tree so it can store key @index.
 */
static int radix_tree_extend(struct radix_tree_root *root, unsigned long index)
{
	struct radix_tree_node *node;
	unsigned int height;

	/* Figure out what the height should be.  */
	height = root->height + 1;
	while (index > radix_tree_maxindex(height))
		height++;

	if (root->rnode) {
		do {
			if (!(node = radix_tree_node_alloc(root)))
				return -ENOMEM;

			/* Increase the height.  */
			node->slots[0] = root->rnode;
			node->count = 1;
			root->rnode = node;
			root->height++;
		} while (height > root->height);
	} else 
		root->height = height;

	return 0;
}

/**
 *	radix_tree_insert    -    insert into a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *	@item:		item to insert
 *
 *	Insert an item into the radix tree at position @index.
 */
int radix_tree_insert(struct radix_tree_root *root, unsigned long index, void *item)
{
	struct radix_tree_node *node = NULL, *tmp, **slot;
	unsigned int height, shift;
	int error;

	/* Make sure the tree is high enough.  */
	if (index > radix_tree_maxindex(root->height)) {
		error = radix_tree_extend(root, index);
		if (error)
			return error;
	}
    
	slot = &root->rnode;
	height = root->height;
	shift = (height-1) * RADIX_TREE_MAP_SHIFT;

	while (height > 0) {
		if (*slot == NULL) {
			/* Have to add a child node.  */
			if (!(tmp = radix_tree_node_alloc(root)))
				return -ENOMEM;
			*slot = tmp;
			if (node)
				node->count++;
		}

		/* Go a level down.  */
		node = *slot;
		slot = (struct radix_tree_node **)
			(node->slots + ((index >> shift) & RADIX_TREE_MAP_MASK));
		shift -= RADIX_TREE_MAP_SHIFT;
		height--;
	}

	if (*slot != NULL)
		return -EEXIST;
	if (node)
		node->count++;

	*slot = item;
	return 0;
}
EXPORT_SYMBOL(radix_tree_insert);

/**
 *	radix_tree_lookup    -    perform lookup operation on a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *
 *	Lookup them item at the position @index in the radix tree @root.
 */
void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
{
	unsigned int height, shift;
	struct radix_tree_node **slot;

	height = root->height;
	if (index > radix_tree_maxindex(height))
		return NULL;

	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
	slot = &root->rnode;

	while (height > 0) {
		if (*slot == NULL)
			return NULL;

		slot = (struct radix_tree_node **)
			((*slot)->slots + ((index >> shift) & RADIX_TREE_MAP_MASK));
		shift -= RADIX_TREE_MAP_SHIFT;
		height--;
	}

	return (void *) *slot;
}
EXPORT_SYMBOL(radix_tree_lookup);

static /* inline */ unsigned int
__lookup(struct radix_tree_root *root, void **results, unsigned long index,
	unsigned int max_items, unsigned long *next_index)
{
	unsigned int nr_found = 0;
	unsigned int shift;
	unsigned int height = root->height;
	struct radix_tree_node *slot;

	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
	slot = root->rnode;

	while (height > 0) {
		unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK;

		for ( ; i < RADIX_TREE_MAP_SIZE; i++) {
			if (slot->slots[i] != NULL)
				break;
			index &= ~((1 << shift) - 1);
			index += 1 << shift;
			if (index == 0)
				goto out;	/* 32-bit wraparound */
		}
		if (i == RADIX_TREE_MAP_SIZE)
			goto out;
		height--;
		if (height == 0) {	/* Bottom level: grab some items */
			unsigned long j = index & RADIX_TREE_MAP_MASK;

			for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
				index++;
				if (slot->slots[j]) {
					results[nr_found++] = slot->slots[j];
					if (nr_found == max_items)
						goto out;
				}
			}
		}
		shift -= RADIX_TREE_MAP_SHIFT;
		slot = slot->slots[i];
	}
out:
	*next_index = index;
	return nr_found;
}

/**
 *	radix_tree_gang_lookup - perform multiple lookup on a radix tree
 *	@root:		radix tree root
 *	@results:	where the results of the lookup are placed
 *	@first_index:	start the lookup from this key
 *	@max_items:	place up to this many items at *results
 *
 *	Performs an index-ascending scan of the tree for present items.  Places
 *	them at *@results and returns the number of items which were placed at
 *	*@results.
 *
 *	The implementation is naive.
 */
unsigned int
radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
			unsigned long first_index, unsigned int max_items)
{
	const unsigned long max_index = radix_tree_maxindex(root->height);
	unsigned long cur_index = first_index;
	unsigned int ret = 0;

	if (root->rnode == NULL)
		goto out;
	if (max_index == 0) {			/* Bah.  Special case */
		if (first_index == 0) {
			if (max_items > 0) {
				*results = root->rnode;
				ret = 1;
			}
		}
		goto out;
	}
	while (ret < max_items) {
		unsigned int nr_found;
		unsigned long next_index;	/* Index of next search */

		if (cur_index > max_index)
			break;
		nr_found = __lookup(root, results + ret, cur_index,
					max_items - ret, &next_index);
		ret += nr_found;
		if (next_index == 0)
			break;
		cur_index = next_index;
	}
out:
	return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup);

/**
 *	radix_tree_delete    -    delete an item from a radix tree
 *	@root:		radix tree root
 *	@index:		index key
 *
 *	Remove the item at @index from the radix tree rooted at @root.
 *
 *	Returns the address of the deleted item, or NULL if it was not present.
 */
void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
{
	struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
	unsigned int height, shift;
	void *ret = NULL;

	height = root->height;
	if (index > radix_tree_maxindex(height))
		goto out;

	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
	pathp->node = NULL;
	pathp->slot = &root->rnode;

	while (height > 0) {
		if (*pathp->slot == NULL)
			goto out;

		pathp[1].node = *pathp[0].slot;
		pathp[1].slot = (struct radix_tree_node **)
		    (pathp[1].node->slots + ((index >> shift) & RADIX_TREE_MAP_MASK));
		pathp++;
		shift -= RADIX_TREE_MAP_SHIFT;
		height--;
	}

	ret = *pathp[0].slot;
	if (ret == NULL)
		goto out;

	*pathp[0].slot = NULL;
	while (pathp[0].node && --pathp[0].node->count == 0) {
		pathp--;
		*pathp[0].slot = NULL;
		radix_tree_node_free(pathp[1].node);
	}

	if (root->rnode == NULL)
		root->height = 0;  /* Empty tree, we can reset the height */
out:
	return ret;
}
EXPORT_SYMBOL(radix_tree_delete);

static void
radix_tree_node_ctor(void *node, kmem_cache_t *cachep, unsigned long flags)
{
	memset(node, 0, sizeof(struct radix_tree_node));
}

static __init unsigned long __maxindex(unsigned int height)
{
	unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
	unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;

	if (tmp >= RADIX_TREE_INDEX_BITS)
		index = ~0UL;
	return index;
}

static __init void radix_tree_init_maxindex(void)
{
	unsigned int i;

	for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
		height_to_maxindex[i] = __maxindex(i);
}

void __init radix_tree_init(void)
{
	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
			sizeof(struct radix_tree_node), 0,
			0, radix_tree_node_ctor, NULL);
	if (!radix_tree_node_cachep)
		panic ("Failed to create radix_tree_node cache\n");
	radix_tree_init_maxindex();
}