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[pohmelfs.git] / lib / idr.c

/*
 * 2002-10-18  written by Jim Houston jim.houston@ccur.com
 *      Copyright (C) 2002 by Concurrent Computer Corporation
 *      Distributed under the GNU GPL license version 2.
 *
 * Modified by George Anzinger to reuse immediately and to use
 * find bit instructions.  Also removed _irq on spinlocks.
 *
 * Modified by Nadia Derbey to make it RCU safe.
 *
 * Small id to pointer translation service.
 *
 * It uses a radix tree like structure as a sparse array indexed
 * by the id to obtain the pointer.  The bitmap makes allocating
 * a new id quick.
 *
 * You call it to allocate an id (an int) an associate with that id a
 * pointer or what ever, we treat it as a (void *).  You can pass this
 * id to a user for him to pass back at a later time.  You then pass
 * that id to this code and it returns your pointer.

 * You can release ids at any time. When all ids are released, most of
 * the memory is returned (we keep IDR_FREE_MAX) in a local pool so we
 * don't need to go to the memory "store" during an id allocate, just
 * so you don't need to be too concerned about locking and conflicts
 * with the slab allocator.
 */

#ifndef TEST                        // to test in user space...
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/module.h>
#endif
#include <linux/err.h>
#include <linux/string.h>
#include <linux/idr.h>

static struct kmem_cache *idr_layer_cache;

static struct idr_layer *get_from_free_list(struct idr *idp)
{
        struct idr_layer *p;
        unsigned long flags;

        spin_lock_irqsave(&idp->lock, flags);
        if ((p = idp->id_free)) {
                idp->id_free = p->ary[0];
                idp->id_free_cnt--;
                p->ary[0] = NULL;
        }
        spin_unlock_irqrestore(&idp->lock, flags);
        return(p);
}

static void idr_layer_rcu_free(struct rcu_head *head)
{
        struct idr_layer *layer;

        layer = container_of(head, struct idr_layer, rcu_head);
        kmem_cache_free(idr_layer_cache, layer);
}

static inline void free_layer(struct idr_layer *p)
{
        call_rcu(&p->rcu_head, idr_layer_rcu_free);
}

/* only called when idp->lock is held */
static void __move_to_free_list(struct idr *idp, struct idr_layer *p)
{
        p->ary[0] = idp->id_free;
        idp->id_free = p;
        idp->id_free_cnt++;
}

static void move_to_free_list(struct idr *idp, struct idr_layer *p)
{
        unsigned long flags;

        /*
         * Depends on the return element being zeroed.
         */
        spin_lock_irqsave(&idp->lock, flags);
        __move_to_free_list(idp, p);
        spin_unlock_irqrestore(&idp->lock, flags);
}

static void idr_mark_full(struct idr_layer **pa, int id)
{
        struct idr_layer *p = pa[0];
        int l = 0;

        __set_bit(id & IDR_MASK, &p->bitmap);
        /*
         * If this layer is full mark the bit in the layer above to
         * show that this part of the radix tree is full.  This may
         * complete the layer above and require walking up the radix
         * tree.
         */
        while (p->bitmap == IDR_FULL) {
                if (!(p = pa[++l]))
                        break;
                id = id >> IDR_BITS;
                __set_bit((id & IDR_MASK), &p->bitmap);
        }
}

/**
 * idr_pre_get - reserver resources for idr allocation
 * @idp:        idr handle
 * @gfp_mask:   memory allocation flags
 *
 * This function should be called prior to locking and calling the
 * idr_get_new* functions. It preallocates enough memory to satisfy
 * the worst possible allocation.
 *
 * If the system is REALLY out of memory this function returns 0,
 * otherwise 1.
 */
int idr_pre_get(struct idr *idp, gfp_t gfp_mask)
{
        while (idp->id_free_cnt < IDR_FREE_MAX) {
                struct idr_layer *new;
                new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
                if (new == NULL)
                        return (0);
                move_to_free_list(idp, new);
        }
        return 1;
}
EXPORT_SYMBOL(idr_pre_get);

static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa)
{
        int n, m, sh;
        struct idr_layer *p, *new;
        int l, id, oid;
        unsigned long bm;

        id = *starting_id;
 restart:
        p = idp->top;
        l = idp->layers;
        pa[l--] = NULL;
        while (1) {
                /*
                 * We run around this while until we reach the leaf node...
                 */
                n = (id >> (IDR_BITS*l)) & IDR_MASK;
                bm = ~p->bitmap;
                m = find_next_bit(&bm, IDR_SIZE, n);
                if (m == IDR_SIZE) {
                        /* no space available go back to previous layer. */
                        l++;
                        oid = id;
                        id = (id | ((1 << (IDR_BITS * l)) - 1)) + 1;

                        /* if already at the top layer, we need to grow */
                        if (!(p = pa[l])) {
                                *starting_id = id;
                                return IDR_NEED_TO_GROW;
                        }

                        /* If we need to go up one layer, continue the
                         * loop; otherwise, restart from the top.
                         */
                        sh = IDR_BITS * (l + 1);
                        if (oid >> sh == id >> sh)
                                continue;
                        else
                                goto restart;
                }
                if (m != n) {
                        sh = IDR_BITS*l;
                        id = ((id >> sh) ^ n ^ m) << sh;
                }
                if ((id >= MAX_ID_BIT) || (id < 0))
                        return IDR_NOMORE_SPACE;
                if (l == 0)
                        break;
                /*
                 * Create the layer below if it is missing.
                 */
                if (!p->ary[m]) {
                        new = get_from_free_list(idp);
                        if (!new)
                                return -1;
                        new->layer = l-1;
                        rcu_assign_pointer(p->ary[m], new);
                        p->count++;
                }
                pa[l--] = p;
                p = p->ary[m];
        }

        pa[l] = p;
        return id;
}

static int idr_get_empty_slot(struct idr *idp, int starting_id,
                              struct idr_layer **pa)
{
        struct idr_layer *p, *new;
        int layers, v, id;
        unsigned long flags;

        id = starting_id;
build_up:
        p = idp->top;
        layers = idp->layers;
        if (unlikely(!p)) {
                if (!(p = get_from_free_list(idp)))
                        return -1;
                p->layer = 0;
                layers = 1;
        }
        /*
         * Add a new layer to the top of the tree if the requested
         * id is larger than the currently allocated space.
         */
        while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {
                layers++;
                if (!p->count) {
                        /* special case: if the tree is currently empty,
                         * then we grow the tree by moving the top node
                         * upwards.
                         */
                        p->layer++;
                        continue;
                }
                if (!(new = get_from_free_list(idp))) {
                        /*
                         * The allocation failed.  If we built part of
                         * the structure tear it down.
                         */
                        spin_lock_irqsave(&idp->lock, flags);
                        for (new = p; p && p != idp->top; new = p) {
                                p = p->ary[0];
                                new->ary[0] = NULL;
                                new->bitmap = new->count = 0;
                                __move_to_free_list(idp, new);
                        }
                        spin_unlock_irqrestore(&idp->lock, flags);
                        return -1;
                }
                new->ary[0] = p;
                new->count = 1;
                new->layer = layers-1;
                if (p->bitmap == IDR_FULL)
                        __set_bit(0, &new->bitmap);
                p = new;
        }
        rcu_assign_pointer(idp->top, p);
        idp->layers = layers;
        v = sub_alloc(idp, &id, pa);
        if (v == IDR_NEED_TO_GROW)
                goto build_up;
        return(v);
}

static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
{
        struct idr_layer *pa[MAX_LEVEL];
        int id;

        id = idr_get_empty_slot(idp, starting_id, pa);
        if (id >= 0) {
                /*
                 * Successfully found an empty slot.  Install the user
                 * pointer and mark the slot full.
                 */
                rcu_assign_pointer(pa[0]->ary[id & IDR_MASK],
                                (struct idr_layer *)ptr);
                pa[0]->count++;
                idr_mark_full(pa, id);
        }

        return id;
}

/**
 * idr_get_new_above - allocate new idr entry above or equal to a start id
 * @idp: idr handle
 * @ptr: pointer you want associated with the ide
 * @start_id: id to start search at
 * @id: pointer to the allocated handle
 *
 * This is the allocate id function.  It should be called with any
 * required locks.
 *
 * If memory is required, it will return -EAGAIN, you should unlock
 * and go back to the idr_pre_get() call.  If the idr is full, it will
 * return -ENOSPC.
 *
 * @id returns a value in the range @starting_id ... 0x7fffffff
 */
int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
{
        int rv;

        rv = idr_get_new_above_int(idp, ptr, starting_id);
        /*
         * This is a cheap hack until the IDR code can be fixed to
         * return proper error values.
         */
        if (rv < 0)
                return _idr_rc_to_errno(rv);
        *id = rv;
        return 0;
}
EXPORT_SYMBOL(idr_get_new_above);

/**
 * idr_get_new - allocate new idr entry
 * @idp: idr handle
 * @ptr: pointer you want associated with the ide
 * @id: pointer to the allocated handle
 *
 * This is the allocate id function.  It should be called with any
 * required locks.
 *
 * If memory is required, it will return -EAGAIN, you should unlock
 * and go back to the idr_pre_get() call.  If the idr is full, it will
 * return -ENOSPC.
 *
 * @id returns a value in the range 0 ... 0x7fffffff
 */
int idr_get_new(struct idr *idp, void *ptr, int *id)
{
        int rv;

        rv = idr_get_new_above_int(idp, ptr, 0);
        /*
         * This is a cheap hack until the IDR code can be fixed to
         * return proper error values.
         */
        if (rv < 0)
                return _idr_rc_to_errno(rv);
        *id = rv;
        return 0;
}
EXPORT_SYMBOL(idr_get_new);

static void idr_remove_warning(int id)
{
        printk(KERN_WARNING
                "idr_remove called for id=%d which is not allocated.\n", id);
        dump_stack();
}

static void sub_remove(struct idr *idp, int shift, int id)
{
        struct idr_layer *p = idp->top;
        struct idr_layer **pa[MAX_LEVEL];
        struct idr_layer ***paa = &pa[0];
        struct idr_layer *to_free;
        int n;

        *paa = NULL;
        *++paa = &idp->top;

        while ((shift > 0) && p) {
                n = (id >> shift) & IDR_MASK;
                __clear_bit(n, &p->bitmap);
                *++paa = &p->ary[n];
                p = p->ary[n];
                shift -= IDR_BITS;
        }
        n = id & IDR_MASK;
        if (likely(p != NULL && test_bit(n, &p->bitmap))){
                __clear_bit(n, &p->bitmap);
                rcu_assign_pointer(p->ary[n], NULL);
                to_free = NULL;
                while(*paa && ! --((**paa)->count)){
                        if (to_free)
                                free_layer(to_free);
                        to_free = **paa;
                        **paa-- = NULL;
                }
                if (!*paa)
                        idp->layers = 0;
                if (to_free)
                        free_layer(to_free);
        } else
                idr_remove_warning(id);
}

/**
 * idr_remove - remove the given id and free it's slot
 * @idp: idr handle
 * @id: unique key
 */
void idr_remove(struct idr *idp, int id)
{
        struct idr_layer *p;
        struct idr_layer *to_free;

        /* Mask off upper bits we don't use for the search. */
        id &= MAX_ID_MASK;

        sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
        if (idp->top && idp->top->count == 1 && (idp->layers > 1) &&
            idp->top->ary[0]) {
                /*
                 * Single child at leftmost slot: we can shrink the tree.
                 * This level is not needed anymore since when layers are
                 * inserted, they are inserted at the top of the existing
                 * tree.
                 */
                to_free = idp->top;
                p = idp->top->ary[0];
                rcu_assign_pointer(idp->top, p);
                --idp->layers;
                to_free->bitmap = to_free->count = 0;
                free_layer(to_free);
        }
        while (idp->id_free_cnt >= IDR_FREE_MAX) {
                p = get_from_free_list(idp);
                /*
                 * Note: we don't call the rcu callback here, since the only
                 * layers that fall into the freelist are those that have been
                 * preallocated.
                 */
                kmem_cache_free(idr_layer_cache, p);
        }
        return;
}
EXPORT_SYMBOL(idr_remove);

/**
 * idr_remove_all - remove all ids from the given idr tree
 * @idp: idr handle
 *
 * idr_destroy() only frees up unused, cached idp_layers, but this
 * function will remove all id mappings and leave all idp_layers
 * unused.
 *
 * A typical clean-up sequence for objects stored in an idr tree, will
 * use idr_for_each() to free all objects, if necessay, then
 * idr_remove_all() to remove all ids, and idr_destroy() to free
 * up the cached idr_layers.
 */
void idr_remove_all(struct idr *idp)
{
        int n, id, max;
        struct idr_layer *p;
        struct idr_layer *pa[MAX_LEVEL];
        struct idr_layer **paa = &pa[0];

        n = idp->layers * IDR_BITS;
        p = idp->top;
        rcu_assign_pointer(idp->top, NULL);
        max = 1 << n;

        id = 0;
        while (id < max) {
                while (n > IDR_BITS && p) {
                        n -= IDR_BITS;
                        *paa++ = p;
                        p = p->ary[(id >> n) & IDR_MASK];
                }

                id += 1 << n;
                while (n < fls(id)) {
                        if (p)
                                free_layer(p);
                        n += IDR_BITS;
                        p = *--paa;
                }
        }
        idp->layers = 0;
}
EXPORT_SYMBOL(idr_remove_all);

/**
 * idr_destroy - release all cached layers within an idr tree
 * idp: idr handle
 */
void idr_destroy(struct idr *idp)
{
        while (idp->id_free_cnt) {
                struct idr_layer *p = get_from_free_list(idp);
                kmem_cache_free(idr_layer_cache, p);
        }
}
EXPORT_SYMBOL(idr_destroy);

/**
 * idr_find - return pointer for given id
 * @idp: idr handle
 * @id: lookup key
 *
 * Return the pointer given the id it has been registered with.  A %NULL
 * return indicates that @id is not valid or you passed %NULL in
 * idr_get_new().
 *
 * This function can be called under rcu_read_lock(), given that the leaf
 * pointers lifetimes are correctly managed.
 */
void *idr_find(struct idr *idp, int id)
{
        int n;
        struct idr_layer *p;

        p = rcu_dereference(idp->top);
        if (!p)
                return NULL;
        n = (p->layer+1) * IDR_BITS;

        /* Mask off upper bits we don't use for the search. */
        id &= MAX_ID_MASK;

        if (id >= (1 << n))
                return NULL;
        BUG_ON(n == 0);

        while (n > 0 && p) {
                n -= IDR_BITS;
                BUG_ON(n != p->layer*IDR_BITS);
                p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
        }
        return((void *)p);
}
EXPORT_SYMBOL(idr_find);

/**
 * idr_for_each - iterate through all stored pointers
 * @idp: idr handle
 * @fn: function to be called for each pointer
 * @data: data passed back to callback function
 *
 * Iterate over the pointers registered with the given idr.  The
 * callback function will be called for each pointer currently
 * registered, passing the id, the pointer and the data pointer passed
 * to this function.  It is not safe to modify the idr tree while in
 * the callback, so functions such as idr_get_new and idr_remove are
 * not allowed.
 *
 * We check the return of @fn each time. If it returns anything other
 * than 0, we break out and return that value.
 *
 * The caller must serialize idr_for_each() vs idr_get_new() and idr_remove().
 */
int idr_for_each(struct idr *idp,
                 int (*fn)(int id, void *p, void *data), void *data)
{
        int n, id, max, error = 0;
        struct idr_layer *p;
        struct idr_layer *pa[MAX_LEVEL];
        struct idr_layer **paa = &pa[0];

        n = idp->layers * IDR_BITS;
        p = rcu_dereference(idp->top);
        max = 1 << n;

        id = 0;
        while (id < max) {
                while (n > 0 && p) {
                        n -= IDR_BITS;
                        *paa++ = p;
                        p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
                }

                if (p) {
                        error = fn(id, (void *)p, data);
                        if (error)
                                break;
                }

                id += 1 << n;
                while (n < fls(id)) {
                        n += IDR_BITS;
                        p = *--paa;
                }
        }

        return error;
}
EXPORT_SYMBOL(idr_for_each);

/**
 * idr_get_next - lookup next object of id to given id.
 * @idp: idr handle
 * @id:  pointer to lookup key
 *
 * Returns pointer to registered object with id, which is next number to
 * given id.
 */

void *idr_get_next(struct idr *idp, int *nextidp)
{
        struct idr_layer *p, *pa[MAX_LEVEL];
        struct idr_layer **paa = &pa[0];
        int id = *nextidp;
        int n, max;

        /* find first ent */
        n = idp->layers * IDR_BITS;
        max = 1 << n;
        p = rcu_dereference(idp->top);
        if (!p)
                return NULL;

        while (id < max) {
                while (n > 0 && p) {
                        n -= IDR_BITS;
                        *paa++ = p;
                        p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]);
                }

                if (p) {
                        *nextidp = id;
                        return p;
                }

                id += 1 << n;
                while (n < fls(id)) {
                        n += IDR_BITS;
                        p = *--paa;
                }
        }
        return NULL;
}



/**
 * idr_replace - replace pointer for given id
 * @idp: idr handle
 * @ptr: pointer you want associated with the id
 * @id: lookup key
 *
 * Replace the pointer registered with an id and return the old value.
 * A -ENOENT return indicates that @id was not found.
 * A -EINVAL return indicates that @id was not within valid constraints.
 *
 * The caller must serialize with writers.
 */
void *idr_replace(struct idr *idp, void *ptr, int id)
{
        int n;
        struct idr_layer *p, *old_p;

        p = idp->top;
        if (!p)
                return ERR_PTR(-EINVAL);

        n = (p->layer+1) * IDR_BITS;

        id &= MAX_ID_MASK;

        if (id >= (1 << n))
                return ERR_PTR(-EINVAL);

        n -= IDR_BITS;
        while ((n > 0) && p) {
                p = p->ary[(id >> n) & IDR_MASK];
                n -= IDR_BITS;
        }

        n = id & IDR_MASK;
        if (unlikely(p == NULL || !test_bit(n, &p->bitmap)))
                return ERR_PTR(-ENOENT);

        old_p = p->ary[n];
        rcu_assign_pointer(p->ary[n], ptr);

        return old_p;
}
EXPORT_SYMBOL(idr_replace);

void __init idr_init_cache(void)
{
        idr_layer_cache = kmem_cache_create("idr_layer_cache",
                                sizeof(struct idr_layer), 0, SLAB_PANIC, NULL);
}

/**
 * idr_init - initialize idr handle
 * @idp:        idr handle
 *
 * This function is use to set up the handle (@idp) that you will pass
 * to the rest of the functions.
 */
void idr_init(struct idr *idp)
{
        memset(idp, 0, sizeof(struct idr));
        spin_lock_init(&idp->lock);
}
EXPORT_SYMBOL(idr_init);


/*
 * IDA - IDR based ID allocator
 *
 * this is id allocator without id -> pointer translation.  Memory
 * usage is much lower than full blown idr because each id only
 * occupies a bit.  ida uses a custom leaf node which contains
 * IDA_BITMAP_BITS slots.
 *
 * 2007-04-25  written by Tejun Heo <htejun@gmail.com>
 */

static void free_bitmap(struct ida *ida, struct ida_bitmap *bitmap)
{
        unsigned long flags;

        if (!ida->free_bitmap) {
                spin_lock_irqsave(&ida->idr.lock, flags);
                if (!ida->free_bitmap) {
                        ida->free_bitmap = bitmap;
                        bitmap = NULL;
                }
                spin_unlock_irqrestore(&ida->idr.lock, flags);
        }

        kfree(bitmap);
}

/**
 * ida_pre_get - reserve resources for ida allocation
 * @ida:        ida handle
 * @gfp_mask:   memory allocation flag
 *
 * This function should be called prior to locking and calling the
 * following function.  It preallocates enough memory to satisfy the
 * worst possible allocation.
 *
 * If the system is REALLY out of memory this function returns 0,
 * otherwise 1.
 */
int ida_pre_get(struct ida *ida, gfp_t gfp_mask)
{
        /* allocate idr_layers */
        if (!idr_pre_get(&ida->idr, gfp_mask))
                return 0;

        /* allocate free_bitmap */
        if (!ida->free_bitmap) {
                struct ida_bitmap *bitmap;

                bitmap = kmalloc(sizeof(struct ida_bitmap), gfp_mask);
                if (!bitmap)
                        return 0;

                free_bitmap(ida, bitmap);
        }

        return 1;
}
EXPORT_SYMBOL(ida_pre_get);

/**
 * ida_get_new_above - allocate new ID above or equal to a start id
 * @ida:        ida handle
 * @staring_id: id to start search at
 * @p_id:       pointer to the allocated handle
 *
 * Allocate new ID above or equal to @ida.  It should be called with
 * any required locks.
 *
 * If memory is required, it will return -EAGAIN, you should unlock
 * and go back to the ida_pre_get() call.  If the ida is full, it will
 * return -ENOSPC.
 *
 * @p_id returns a value in the range @starting_id ... 0x7fffffff.
 */
int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)
{
        struct idr_layer *pa[MAX_LEVEL];
        struct ida_bitmap *bitmap;
        unsigned long flags;
        int idr_id = starting_id / IDA_BITMAP_BITS;
        int offset = starting_id % IDA_BITMAP_BITS;
        int t, id;

 restart:
        /* get vacant slot */
        t = idr_get_empty_slot(&ida->idr, idr_id, pa);
        if (t < 0)
                return _idr_rc_to_errno(t);

        if (t * IDA_BITMAP_BITS >= MAX_ID_BIT)
                return -ENOSPC;

        if (t != idr_id)
                offset = 0;
        idr_id = t;

        /* if bitmap isn't there, create a new one */
        bitmap = (void *)pa[0]->ary[idr_id & IDR_MASK];
        if (!bitmap) {
                spin_lock_irqsave(&ida->idr.lock, flags);
                bitmap = ida->free_bitmap;
                ida->free_bitmap = NULL;
                spin_unlock_irqrestore(&ida->idr.lock, flags);

                if (!bitmap)
                        return -EAGAIN;

                memset(bitmap, 0, sizeof(struct ida_bitmap));
                rcu_assign_pointer(pa[0]->ary[idr_id & IDR_MASK],
                                (void *)bitmap);
                pa[0]->count++;
        }

        /* lookup for empty slot */
        t = find_next_zero_bit(bitmap->bitmap, IDA_BITMAP_BITS, offset);
        if (t == IDA_BITMAP_BITS) {
                /* no empty slot after offset, continue to the next chunk */
                idr_id++;
                offset = 0;
                goto restart;
        }

        id = idr_id * IDA_BITMAP_BITS + t;
        if (id >= MAX_ID_BIT)
                return -ENOSPC;

        __set_bit(t, bitmap->bitmap);
        if (++bitmap->nr_busy == IDA_BITMAP_BITS)
                idr_mark_full(pa, idr_id);

        *p_id = id;

        /* Each leaf node can handle nearly a thousand slots and the
         * whole idea of ida is to have small memory foot print.
         * Throw away extra resources one by one after each successful
         * allocation.
         */
        if (ida->idr.id_free_cnt || ida->free_bitmap) {
                struct idr_layer *p = get_from_free_list(&ida->idr);
                if (p)
                        kmem_cache_free(idr_layer_cache, p);
        }

        return 0;
}
EXPORT_SYMBOL(ida_get_new_above);

/**
 * ida_get_new - allocate new ID
 * @ida:        idr handle
 * @p_id:       pointer to the allocated handle
 *
 * Allocate new ID.  It should be called with any required locks.
 *
 * If memory is required, it will return -EAGAIN, you should unlock
 * and go back to the idr_pre_get() call.  If the idr is full, it will
 * return -ENOSPC.
 *
 * @id returns a value in the range 0 ... 0x7fffffff.
 */
int ida_get_new(struct ida *ida, int *p_id)
{
        return ida_get_new_above(ida, 0, p_id);
}
EXPORT_SYMBOL(ida_get_new);

/**
 * ida_remove - remove the given ID
 * @ida:        ida handle
 * @id:         ID to free
 */
void ida_remove(struct ida *ida, int id)
{
        struct idr_layer *p = ida->idr.top;
        int shift = (ida->idr.layers - 1) * IDR_BITS;
        int idr_id = id / IDA_BITMAP_BITS;
        int offset = id % IDA_BITMAP_BITS;
        int n;
        struct ida_bitmap *bitmap;

        /* clear full bits while looking up the leaf idr_layer */
        while ((shift > 0) && p) {
                n = (idr_id >> shift) & IDR_MASK;
                __clear_bit(n, &p->bitmap);
                p = p->ary[n];
                shift -= IDR_BITS;
        }

        if (p == NULL)
                goto err;

        n = idr_id & IDR_MASK;
        __clear_bit(n, &p->bitmap);

        bitmap = (void *)p->ary[n];
        if (!test_bit(offset, bitmap->bitmap))
                goto err;

        /* update bitmap and remove it if empty */
        __clear_bit(offset, bitmap->bitmap);
        if (--bitmap->nr_busy == 0) {
                __set_bit(n, &p->bitmap);       /* to please idr_remove() */
                idr_remove(&ida->idr, idr_id);
                free_bitmap(ida, bitmap);
        }

        return;

 err:
        printk(KERN_WARNING
               "ida_remove called for id=%d which is not allocated.\n", id);
}
EXPORT_SYMBOL(ida_remove);

/**
 * ida_destroy - release all cached layers within an ida tree
 * ida:         ida handle
 */
void ida_destroy(struct ida *ida)
{
        idr_destroy(&ida->idr);
        kfree(ida->free_bitmap);
}
EXPORT_SYMBOL(ida_destroy);

/**
 * ida_init - initialize ida handle
 * @ida:        ida handle
 *
 * This function is use to set up the handle (@ida) that you will pass
 * to the rest of the functions.
 */
void ida_init(struct ida *ida)
{
        memset(ida, 0, sizeof(struct ida));
        idr_init(&ida->idr);

}
EXPORT_SYMBOL(ida_init);