root/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/notifier.h>
#include <linux/cpu.h>
#include <linux/gfp.h>
#include <linux/string.h>
#include <linux/bitops.h>


#ifdef __KERNEL__
#define RADIX_TREE_MAP_SHIFT    6
#else
#define RADIX_TREE_MAP_SHIFT    3       /* For more stressful testing */
#endif
#define RADIX_TREE_TAGS         2

#define RADIX_TREE_MAP_SIZE     (1UL << RADIX_TREE_MAP_SHIFT)
#define RADIX_TREE_MAP_MASK     (RADIX_TREE_MAP_SIZE-1)

#define RADIX_TREE_TAG_LONGS    \
        ((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)

struct radix_tree_node {
        unsigned int    count;
        void            *slots[RADIX_TREE_MAP_SIZE];
        unsigned long   tags[RADIX_TREE_TAGS][RADIX_TREE_TAG_LONGS];
};

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

#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;
}

static inline void tag_set(struct radix_tree_node *node, int tag, int offset)
{
        if (!test_bit(offset, &node->tags[tag][0]))
                __set_bit(offset, &node->tags[tag][0]);
}

static inline void tag_clear(struct radix_tree_node *node, int tag, int offset)
{
        __clear_bit(offset, &node->tags[tag][0]);
}

static inline int tag_get(struct radix_tree_node *node, int tag, int offset)
{
        return test_bit(offset, &node->tags[tag][0]);
}

/*
 *      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;
        char tags[RADIX_TREE_TAGS];
        int tag;

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

        if (root->rnode == NULL) {
                root->height = height;
                goto out;
        }

        /*
         * Prepare the tag status of the top-level node for propagation
         * into the newly-pushed top-level node(s)
         */
        for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
                int idx;

                tags[tag] = 0;
                for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
                        if (root->rnode->tags[tag][idx]) {
                                tags[tag] = 1;
                                break;
                        }
                }
        }

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

                /* Increase the height.  */
                node->slots[0] = root->rnode;

                /* Propagate the aggregated tag info into the new root */
                for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
                        if (tags[tag])
                                tag_set(node, tag, 0);
                }

                node->count = 1;
                root->rnode = node;
                root->height++;
        } while (height > root->height);
out:
        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 offset;
        int error;

        /* Make sure the tree is high enough.  */
        if ((!index && !root->rnode) ||
                        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;

        offset = 0;                     /* uninitialised var warning */
        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 */
                offset = (index >> shift) & RADIX_TREE_MAP_MASK;
                node = *slot;
                slot = (struct radix_tree_node **)(node->slots + offset);
                shift -= RADIX_TREE_MAP_SHIFT;
                height--;
        }

        if (*slot != NULL)
                return -EEXIST;
        if (node) {
                node->count++;
                BUG_ON(tag_get(node, 0, offset));
                BUG_ON(tag_get(node, 1, offset));
        }

        *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 the 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 *slot;
}
EXPORT_SYMBOL(radix_tree_lookup);

/**
 *      radix_tree_tag_set - set a tag on a radix tree node
 *      @root:          radix tree root
 *      @index:         index key
 *      @tag:           tag index
 *
 *      Set the search tag corresponging to @index in the radix tree.  From
 *      the root all the way down to the leaf node.
 *
 *      Returns the address of the tagged item.   Setting a tag on a not-present
 *      item is a bug.
 */
void *radix_tree_tag_set(struct radix_tree_root *root,
                        unsigned long index, int tag)
{
        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) {
                int offset;

                offset = (index >> shift) & RADIX_TREE_MAP_MASK;
                tag_set(*slot, tag, offset);
                slot = (struct radix_tree_node **)((*slot)->slots + offset);
                BUG_ON(*slot == NULL);
                shift -= RADIX_TREE_MAP_SHIFT;
                height--;
        }

        return *slot;
}
EXPORT_SYMBOL(radix_tree_tag_set);

/**
 *      radix_tree_tag_clear - clear a tag on a radix tree node
 *      @root:          radix tree root
 *      @index:         index key
 *      @tag:           tag index
 *
 *      Clear the search tag corresponging to @index in the radix tree.  If
 *      this causes the leaf node to have no tags set then clear the tag in the
 *      next-to-leaf node, etc.
 *
 *      Returns the address of the tagged item on success, else NULL.  ie:
 *      has the same return value and semantics as radix_tree_lookup().
 */
void *radix_tree_tag_clear(struct radix_tree_root *root,
                        unsigned long index, int tag)
{
        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) {
                int offset;

                if (*pathp->slot == NULL)
                        goto out;

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

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

        do {
                int idx;

                tag_clear(pathp[0].node, tag, pathp[0].offset);
                for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
                        if (pathp[0].node->tags[tag][idx])
                                goto out;
                }
                pathp--;
        } while (pathp[0].node);
out:
        return ret;
}
EXPORT_SYMBOL(radix_tree_tag_clear);

#ifndef __KERNEL__      /* Only the test harness uses this at present */
/**
 *      radix_tree_tag_get - get a tag on a radix tree node
 *      @root:          radix tree root
 *      @index:         index key
 *      @tag:           tag index
 *
 *      Return the search tag corresponging to @index in the radix tree.
 *
 *      Returns zero if the tag is unset, or if there is no corresponding item
 *      in the tree.
 */
int radix_tree_tag_get(struct radix_tree_root *root,
                        unsigned long index, int tag)
{
        unsigned int height, shift;
        struct radix_tree_node **slot;
        int saw_unset_tag = 0;

        height = root->height;
        if (index > radix_tree_maxindex(height))
                return 0;

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

        for ( ; ; ) {
                int offset;

                if (*slot == NULL)
                        return 0;

                offset = (index >> shift) & RADIX_TREE_MAP_MASK;

                /*
                 * This is just a debug check.  Later, we can bale as soon as
                 * we see an unset tag.
                 */
                if (!tag_get(*slot, tag, offset))
                        saw_unset_tag = 1;
                if (height == 1) {
                        int ret = tag_get(*slot, tag, offset);

                        BUG_ON(ret && saw_unset_tag);
                        return ret;
                }
                slot = (struct radix_tree_node **)((*slot)->slots + offset);
                shift -= RADIX_TREE_MAP_SHIFT;
                height--;
        }
}
EXPORT_SYMBOL(radix_tree_tag_get);
#endif

static 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;

        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;
        }
        return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup);

/*
 * FIXME: the two tag_get()s here should use find_next_bit() instead of
 * open-coding the search.
 */
static unsigned int
__lookup_tag(struct radix_tree_root *root, void **results, unsigned long index,
        unsigned int max_items, unsigned long *next_index, int tag)
{
        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 (tag_get(slot, tag, i)) {
                                BUG_ON(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 (tag_get(slot, tag, j)) {
                                        BUG_ON(slot->slots[j] == NULL);
                                        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_tag - perform multiple lookup on a radix tree
 *                                   based on a tag
 *      @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
 *      @tag:           the tag index
 *
 *      Performs an index-ascending scan of the tree for present items which
 *      have the tag indexed by @tag set.  Places the items at *@results and
 *      returns the number of items which were placed at *@results.
 */
unsigned int
radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
                unsigned long first_index, unsigned int max_items, int tag)
{
        const unsigned long max_index = radix_tree_maxindex(root->height);
        unsigned long cur_index = first_index;
        unsigned int ret = 0;

        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_tag(root, results + ret, cur_index,
                                        max_items - ret, &next_index, tag);
                ret += nr_found;
                if (next_index == 0)
                        break;
                cur_index = next_index;
        }
        return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup_tag);

/**
 *      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;
        struct radix_tree_path *orig_pathp;
        unsigned int height, shift;
        void *ret = NULL;
        char tags[RADIX_TREE_TAGS];
        int nr_cleared_tags;

        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) {
                int offset;

                if (*pathp->slot == NULL)
                        goto out;

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

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

        orig_pathp = pathp;

        /*
         * Clear all tags associated with the just-deleted item
         */
        memset(tags, 0, sizeof(tags));
        do {
                int tag;

                nr_cleared_tags = RADIX_TREE_TAGS;
                for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
                        int idx;

                        if (!tags[tag])
                                tag_clear(pathp[0].node, tag, pathp[0].offset);

                        for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
                                if (pathp[0].node->tags[tag][idx]) {
                                        tags[tag] = 1;
                                        nr_cleared_tags--;
                                        break;
                                }
                        }
                }
                pathp--;
        } while (pathp[0].node && nr_cleared_tags);

        pathp = orig_pathp;
        *pathp[0].slot = NULL;
        while (pathp[0].node && --pathp[0].node->count == 0) {
                pathp--;
                BUG_ON(*pathp[0].slot == NULL);
                *pathp[0].slot = NULL;
                radix_tree_node_free(pathp[1].node);
        }
        if (root->rnode == NULL)
                root->height = 0;
out:
        return ret;
}
EXPORT_SYMBOL(radix_tree_delete);

/**
 *      radix_tree_tagged - test whether any items in the tree are tagged
 *      @root:          radix tree root
 *      @tag:           tag to test
 */
int radix_tree_tagged(struct radix_tree_root *root, int tag)
{
        int idx;

        if (!root->rnode)
                return 0;
        for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
                if (root->rnode->tags[tag][idx])
                        return 1;
        }
        return 0;
}
EXPORT_SYMBOL(radix_tree_tagged);

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);
}

#ifdef CONFIG_HOTPLUG_CPU
static int radix_tree_callback(struct notifier_block *nfb,
                            unsigned long action,
                            void *hcpu)
{
       int cpu = (long)hcpu;
       struct radix_tree_preload *rtp;

       /* Free per-cpu pool of perloaded nodes */
       if (action == CPU_DEAD) {
               rtp = &per_cpu(radix_tree_preloads, cpu);
               while (rtp->nr) {
                       kmem_cache_free(radix_tree_node_cachep,
                                       rtp->nodes[rtp->nr-1]);
                       rtp->nodes[rtp->nr-1] = NULL;
                       rtp->nr--;
               }
       }
       return NOTIFY_OK;
}
#endif /* CONFIG_HOTPLUG_CPU */

void __init radix_tree_init(void)
{
        radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
                        sizeof(struct radix_tree_node), 0,
                        SLAB_PANIC, radix_tree_node_ctor, NULL);
        radix_tree_init_maxindex();
        hotcpu_notifier(radix_tree_callback, 0);
}