/*
 * 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.
 *
 * 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 kmem_cache_t *idr_layer_cache;

static struct idr_layer *alloc_layer(struct idr *idp)
{
        struct idr_layer *p;

        spin_lock(&idp->lock);
        if (!(p = idp->id_free)) {
                spin_unlock(&idp->lock);
                return NULL;
        }
        idp->id_free = p->ary[0];
        idp->id_free_cnt--;
        p->ary[0] = NULL;
        spin_unlock(&idp->lock);
        return(p);
}

static void free_layer(struct idr *idp, struct idr_layer *p)
{
        /*
         * Depends on the return element being zeroed.
         */
        spin_lock(&idp->lock);
        p->ary[0] = idp->id_free;
        idp->id_free = p;
        idp->id_free_cnt++;
        spin_unlock(&idp->lock);
}

/**
 * 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
 * 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 idr_pre_get(struct idr *idp, unsigned gfp_mask)
{
        while (idp->id_free_cnt < IDR_FREE_MAX) {
                struct idr_layer *new;
                new = kmem_cache_alloc(idr_layer_cache, gfp_mask);
                if(new == NULL)
                        return (0);
                free_layer(idp, new);
        }
        return 1;
}
EXPORT_SYMBOL(idr_pre_get);

static int sub_alloc(struct idr *idp, void *ptr, int *starting_id)
{
        int n, m, sh;
        struct idr_layer *p, *new;
        struct idr_layer *pa[MAX_LEVEL];
        int l, id;
        long bm;

        id = *starting_id;
        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++;
                        id = (id | ((1 << (IDR_BITS*l))-1)) + 1;
                        if (!(p = pa[l])) {
                                *starting_id = id;
                                return -2;
                        }
                        continue;
                }
                if (m != n) {
                        sh = IDR_BITS*l;
                        id = ((id >> sh) ^ n ^ m) << sh;
                }
                if ((id >= MAX_ID_BIT) || (id < 0))
                        return -3;
                if (l == 0)
                        break;
                /*
                 * Create the layer below if it is missing.
                 */
                if (!p->ary[m]) {
                        if (!(new = alloc_layer(idp)))
                                return -1;
                        p->ary[m] = new;
                        p->count++;
                }
                pa[l--] = p;
                p = p->ary[m];
        }
        /*
         * We have reached the leaf node, plant the
         * users pointer and return the raw id.
         */
        p->ary[m] = (struct idr_layer *)ptr;
        __set_bit(m, &p->bitmap);
        p->count++;
        /*
         * 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.
         */
        n = id;
        while (p->bitmap == IDR_FULL) {
                if (!(p = pa[++l]))
                        break;
                n = n >> IDR_BITS;
                __set_bit((n & IDR_MASK), &p->bitmap);
        }
        return(id);
}

static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
{
        struct idr_layer *p, *new;
        int layers, v, id;
        
        id = starting_id;
build_up:
        p = idp->top;
        layers = idp->layers;
        if (unlikely(!p)) {
                if (!(p = alloc_layer(idp)))
                        return -1;
                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) && (id >= (1 << (layers*IDR_BITS)))) {
                layers++;
                if (!p->count)
                        continue;
                if (!(new = alloc_layer(idp))) {
                        /*
                         * The allocation failed.  If we built part of
                         * the structure tear it down.
                         */
                        for (new = p; p && p != idp->top; new = p) {
                                p = p->ary[0];
                                new->ary[0] = NULL;
                                new->bitmap = new->count = 0;
                                free_layer(idp, new);
                        }
                        return -1;
                }
                new->ary[0] = p;
                new->count = 1;
                if (p->bitmap == IDR_FULL)
                        __set_bit(0, &new->bitmap);
                p = new;
        }
        idp->top = p;
        idp->layers = layers;
        v = sub_alloc(idp, ptr, &id);
        if (v == -2)
                goto build_up;
        return(v);
}

/**
 * idr_get_new_above - allocate new idr entry above 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 0 ... 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) {
                if (rv == -1)
                        return -EAGAIN;
                else /* Will be -3 */
                        return -ENOSPC;
        }
        *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) {
                if (rv == -1)
                        return -EAGAIN;
                else /* Will be -3 */
                        return -ENOSPC;
        }
        *id = rv;
        return 0;
}
EXPORT_SYMBOL(idr_get_new);

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];

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

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

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

        /* 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]){  // We can drop a layer

                p = idp->top->ary[0];
                idp->top->bitmap = idp->top->count = 0;
                free_layer(idp, idp->top);
                idp->top = p;
                --idp->layers;
        }
        while (idp->id_free_cnt >= IDR_FREE_MAX) {
                
                p = alloc_layer(idp);
                kmem_cache_free(idr_layer_cache, p);
                return;
        }
}
EXPORT_SYMBOL(idr_remove);

/**
 * 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().
 *
 * The caller must serialize idr_find() vs idr_get_new() and idr_remove().
 */
void *idr_find(struct idr *idp, int id)
{
        int n;
        struct idr_layer *p;

        n = idp->layers * IDR_BITS;
        p = idp->top;

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

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

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

/**
 * idr_replace - replace pointer for given id
 * @idp: idr handle
 * @ptr: pointer you want associated with the ide
 * @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 vs idr_find(), idr_get_new(), and idr_remove().
 */
void *idr_replace(struct idr *idp, void *ptr, int id)
{
        int n;
        struct idr_layer *p, *old_p;

        n = idp->layers * IDR_BITS;
        p = idp->top;

        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];
        p->ary[n] = ptr;

        return (void *)old_p;
}
EXPORT_SYMBOL(idr_replace);

static void idr_cache_ctor(void * idr_layer, 
                           kmem_cache_t *idr_layer_cache, unsigned long flags)
{
        memset(idr_layer, 0, sizeof(struct idr_layer));
}

static  int init_id_cache(void)
{
        if (!idr_layer_cache)
                idr_layer_cache = kmem_cache_create("idr_layer_cache", 
                        sizeof(struct idr_layer), 0, 0, idr_cache_ctor, NULL);
        return 0;
}

/**
 * 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)
{
        init_id_cache();
        memset(idp, 0, sizeof(struct idr));
        spin_lock_init(&idp->lock);
}
EXPORT_SYMBOL(idr_init);