/*
   * 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.

   */
  
  #ifndef TEST                        // to test in user space...
  #include <linux/slab.h>
  #include <linux/init.h>

  #include <linux/export.h>

  #endif

  #include <linux/err.h>

  #include <linux/string.h>
  #include <linux/idr.h>

  #include <linux/spinlock.h>

  #include <linux/percpu.h>

  #define MAX_IDR_SHIFT		(sizeof(int) * 8 - 1)
  #define MAX_IDR_BIT		(1U << MAX_IDR_SHIFT)
  
  /* Leave the possibility of an incomplete final layer */
  #define MAX_IDR_LEVEL ((MAX_IDR_SHIFT + IDR_BITS - 1) / IDR_BITS)
  
  /* Number of id_layer structs to leave in free list */
  #define MAX_IDR_FREE (MAX_IDR_LEVEL * 2)

  static struct kmem_cache *idr_layer_cache;

  static DEFINE_PER_CPU(struct idr_layer *, idr_preload_head);
  static DEFINE_PER_CPU(int, idr_preload_cnt);

  static DEFINE_SPINLOCK(simple_ida_lock);

  /* the maximum ID which can be allocated given idr->layers */
  static int idr_max(int layers)
  {
  	int bits = min_t(int, layers * IDR_BITS, MAX_IDR_SHIFT);
  
  	return (1 << bits) - 1;
  }

  /*
   * Prefix mask for an idr_layer at @layer.  For layer 0, the prefix mask is
   * all bits except for the lower IDR_BITS.  For layer 1, 2 * IDR_BITS, and
   * so on.
   */
  static int idr_layer_prefix_mask(int layer)
  {
  	return ~idr_max(layer + 1);
  }

  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);
  }

  /**
   * idr_layer_alloc - allocate a new idr_layer
   * @gfp_mask: allocation mask
   * @layer_idr: optional idr to allocate from
   *
   * If @layer_idr is %NULL, directly allocate one using @gfp_mask or fetch
   * one from the per-cpu preload buffer.  If @layer_idr is not %NULL, fetch
   * an idr_layer from @idr->id_free.
   *
   * @layer_idr is to maintain backward compatibility with the old alloc
   * interface - idr_pre_get() and idr_get_new*() - and will be removed
   * together with per-pool preload buffer.
   */
  static struct idr_layer *idr_layer_alloc(gfp_t gfp_mask, struct idr *layer_idr)
  {
  	struct idr_layer *new;
  
  	/* this is the old path, bypass to get_from_free_list() */
  	if (layer_idr)
  		return get_from_free_list(layer_idr);

  	/*
  	 * Try to allocate directly from kmem_cache.  We want to try this
  	 * before preload buffer; otherwise, non-preloading idr_alloc()
  	 * users will end up taking advantage of preloading ones.  As the
  	 * following is allowed to fail for preloaded cases, suppress
  	 * warning this time.
  	 */
  	new = kmem_cache_zalloc(idr_layer_cache, gfp_mask | __GFP_NOWARN);

  	if (new)
  		return new;
  
  	/*
  	 * Try to fetch one from the per-cpu preload buffer if in process
  	 * context.  See idr_preload() for details.
  	 */

  	if (!in_interrupt()) {
  		preempt_disable();
  		new = __this_cpu_read(idr_preload_head);
  		if (new) {
  			__this_cpu_write(idr_preload_head, new->ary[0]);
  			__this_cpu_dec(idr_preload_cnt);
  			new->ary[0] = NULL;
  		}
  		preempt_enable();
  		if (new)
  			return new;

  	}

  
  	/*
  	 * Both failed.  Try kmem_cache again w/o adding __GFP_NOWARN so
  	 * that memory allocation failure warning is printed as intended.
  	 */
  	return kmem_cache_zalloc(idr_layer_cache, gfp_mask);

  }

  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 *idr, struct idr_layer *p)

  {

  	if (idr->hint == p)

  		RCU_INIT_POINTER(idr->hint, NULL);

  	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 (bitmap_full(p->bitmap, IDR_SIZE)) {

  		if (!(p = pa[++l]))
  			break;
  		id = id >> IDR_BITS;

  		__set_bit((id & IDR_MASK), p->bitmap);

  	}
  }

  static int __idr_pre_get(struct idr *idp, gfp_t gfp_mask)

  {

  	while (idp->id_free_cnt < MAX_IDR_FREE) {

  		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;
  }

  /**
   * sub_alloc - try to allocate an id without growing the tree depth
   * @idp: idr handle
   * @starting_id: id to start search at

   * @pa: idr_layer[MAX_IDR_LEVEL] used as backtrack buffer

   * @gfp_mask: allocation mask for idr_layer_alloc()
   * @layer_idr: optional idr passed to idr_layer_alloc()

   *
   * Allocate an id in range [@starting_id, INT_MAX] from @idp without
   * growing its depth.  Returns
   *
   *  the allocated id >= 0 if successful,
   *  -EAGAIN if the tree needs to grow for allocation to succeed,
   *  -ENOSPC if the id space is exhausted,
   *  -ENOMEM if more idr_layers need to be allocated.
   */

  static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa,
  		     gfp_t gfp_mask, struct idr *layer_idr)

  {
  	int n, m, sh;
  	struct idr_layer *p, *new;

  	int l, id, oid;

  
  	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;

  		m = find_next_zero_bit(p->bitmap, 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 (id > idr_max(idp->layers)) {

  				*starting_id = id;

  				return -EAGAIN;

  			}

  			p = pa[l];
  			BUG_ON(!p);

  
  			/* 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_IDR_BIT) || (id < 0))

  			return -ENOSPC;

  		if (l == 0)
  			break;
  		/*
  		 * Create the layer below if it is missing.
  		 */
  		if (!p->ary[m]) {

  			new = idr_layer_alloc(gfp_mask, layer_idr);

  			if (!new)

  				return -ENOMEM;

  			new->layer = l-1;

  			new->prefix = id & idr_layer_prefix_mask(new->layer);

  			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, gfp_t gfp_mask,
  			      struct idr *layer_idr)

  {
  	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 = idr_layer_alloc(gfp_mask, layer_idr)))

  			return -ENOMEM;

  		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 (id > idr_max(layers)) {

  		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++;

  			WARN_ON_ONCE(p->prefix);

  			continue;

  		}

  		if (!(new = idr_layer_alloc(gfp_mask, layer_idr))) {

  			/*
  			 * 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->count = 0;
  				bitmap_clear(new->bitmap, 0, IDR_SIZE);

  				__move_to_free_list(idp, new);

  			}

  			spin_unlock_irqrestore(&idp->lock, flags);

  			return -ENOMEM;

  		}
  		new->ary[0] = p;
  		new->count = 1;

  		new->layer = layers-1;

  		new->prefix = id & idr_layer_prefix_mask(new->layer);

  		if (bitmap_full(p->bitmap, IDR_SIZE))
  			__set_bit(0, new->bitmap);

  		p = new;
  	}

  	rcu_assign_pointer(idp->top, p);

  	idp->layers = layers;

  	v = sub_alloc(idp, &id, pa, gfp_mask, layer_idr);

  	if (v == -EAGAIN)

  		goto build_up;
  	return(v);
  }

  /*
   * @id and @pa are from a successful allocation from idr_get_empty_slot().
   * Install the user pointer @ptr and mark the slot full.
   */

  static void idr_fill_slot(struct idr *idr, void *ptr, int id,
  			  struct idr_layer **pa)

  {

  	/* update hint used for lookup, cleared from free_layer() */
  	rcu_assign_pointer(idr->hint, pa[0]);

  	rcu_assign_pointer(pa[0]->ary[id & IDR_MASK], (struct idr_layer *)ptr);
  	pa[0]->count++;
  	idr_mark_full(pa, id);

  }

  /**
   * idr_preload - preload for idr_alloc()
   * @gfp_mask: allocation mask to use for preloading
   *
   * Preload per-cpu layer buffer for idr_alloc().  Can only be used from
   * process context and each idr_preload() invocation should be matched with
   * idr_preload_end().  Note that preemption is disabled while preloaded.
   *
   * The first idr_alloc() in the preloaded section can be treated as if it
   * were invoked with @gfp_mask used for preloading.  This allows using more
   * permissive allocation masks for idrs protected by spinlocks.
   *
   * For example, if idr_alloc() below fails, the failure can be treated as
   * if idr_alloc() were called with GFP_KERNEL rather than GFP_NOWAIT.
   *
   *	idr_preload(GFP_KERNEL);
   *	spin_lock(lock);
   *
   *	id = idr_alloc(idr, ptr, start, end, GFP_NOWAIT);
   *
   *	spin_unlock(lock);
   *	idr_preload_end();
   *	if (id < 0)
   *		error;
   */
  void idr_preload(gfp_t gfp_mask)
  {
  	/*
  	 * Consuming preload buffer from non-process context breaks preload
  	 * allocation guarantee.  Disallow usage from those contexts.
  	 */
  	WARN_ON_ONCE(in_interrupt());

  	might_sleep_if(gfpflags_allow_blocking(gfp_mask));

  
  	preempt_disable();
  
  	/*
  	 * idr_alloc() is likely to succeed w/o full idr_layer buffer and
  	 * return value from idr_alloc() needs to be checked for failure
  	 * anyway.  Silently give up if allocation fails.  The caller can
  	 * treat failures from idr_alloc() as if idr_alloc() were called
  	 * with @gfp_mask which should be enough.
  	 */
  	while (__this_cpu_read(idr_preload_cnt) < MAX_IDR_FREE) {
  		struct idr_layer *new;
  
  		preempt_enable();
  		new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
  		preempt_disable();
  		if (!new)
  			break;
  
  		/* link the new one to per-cpu preload list */
  		new->ary[0] = __this_cpu_read(idr_preload_head);
  		__this_cpu_write(idr_preload_head, new);
  		__this_cpu_inc(idr_preload_cnt);
  	}
  }
  EXPORT_SYMBOL(idr_preload);
  
  /**
   * idr_alloc - allocate new idr entry
   * @idr: the (initialized) idr
   * @ptr: pointer to be associated with the new id
   * @start: the minimum id (inclusive)
   * @end: the maximum id (exclusive, <= 0 for max)
   * @gfp_mask: memory allocation flags
   *
   * Allocate an id in [start, end) and associate it with @ptr.  If no ID is
   * available in the specified range, returns -ENOSPC.  On memory allocation
   * failure, returns -ENOMEM.
   *
   * Note that @end is treated as max when <= 0.  This is to always allow
   * using @start + N as @end as long as N is inside integer range.
   *
   * The user is responsible for exclusively synchronizing all operations
   * which may modify @idr.  However, read-only accesses such as idr_find()
   * or iteration can be performed under RCU read lock provided the user
   * destroys @ptr in RCU-safe way after removal from idr.
   */
  int idr_alloc(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask)
  {
  	int max = end > 0 ? end - 1 : INT_MAX;	/* inclusive upper limit */

  	struct idr_layer *pa[MAX_IDR_LEVEL + 1];

  	int id;

  	might_sleep_if(gfpflags_allow_blocking(gfp_mask));

  
  	/* sanity checks */
  	if (WARN_ON_ONCE(start < 0))
  		return -EINVAL;
  	if (unlikely(max < start))
  		return -ENOSPC;
  
  	/* allocate id */
  	id = idr_get_empty_slot(idr, start, pa, gfp_mask, NULL);
  	if (unlikely(id < 0))
  		return id;
  	if (unlikely(id > max))
  		return -ENOSPC;

  	idr_fill_slot(idr, ptr, id, pa);

  	return id;
  }
  EXPORT_SYMBOL_GPL(idr_alloc);

  /**
   * idr_alloc_cyclic - allocate new idr entry in a cyclical fashion
   * @idr: the (initialized) idr
   * @ptr: pointer to be associated with the new id
   * @start: the minimum id (inclusive)
   * @end: the maximum id (exclusive, <= 0 for max)
   * @gfp_mask: memory allocation flags
   *
   * Essentially the same as idr_alloc, but prefers to allocate progressively
   * higher ids if it can. If the "cur" counter wraps, then it will start again
   * at the "start" end of the range and allocate one that has already been used.
   */
  int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end,
  			gfp_t gfp_mask)
  {
  	int id;
  
  	id = idr_alloc(idr, ptr, max(start, idr->cur), end, gfp_mask);
  	if (id == -ENOSPC)
  		id = idr_alloc(idr, ptr, start, end, gfp_mask);
  
  	if (likely(id >= 0))
  		idr->cur = id + 1;
  	return id;
  }
  EXPORT_SYMBOL(idr_alloc_cyclic);

  static void idr_remove_warning(int id)
  {

  	WARN(1, "idr_remove called for id=%d which is not allocated.
  ", id);

  }
  
  static void sub_remove(struct idr *idp, int shift, int id)
  {
  	struct idr_layer *p = idp->top;

  	struct idr_layer **pa[MAX_IDR_LEVEL + 1];

  	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_INIT_POINTER(p->ary[n], NULL);

  		to_free = NULL;

  		while(*paa && ! --((**paa)->count)){

  			if (to_free)

  				free_layer(idp, to_free);

  			to_free = **paa;

  			**paa-- = NULL;
  		}

  		if (!*paa)

  			idp->layers = 0;

  		if (to_free)

  			free_layer(idp, to_free);

  	} else

  		idr_remove_warning(id);

  }
  
  /**

   * idr_remove - remove the given id and free its slot

   * @idp: idr handle
   * @id: unique key

   */
  void idr_remove(struct idr *idp, int id)
  {
  	struct idr_layer *p;

  	struct idr_layer *to_free;

  	if (id < 0)

  		return;

  	if (id > idr_max(idp->layers)) {
  		idr_remove_warning(id);
  		return;
  	}

  	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->count = 0;
  		bitmap_clear(to_free->bitmap, 0, IDR_SIZE);

  		free_layer(idp, to_free);

  	}

  }
  EXPORT_SYMBOL(idr_remove);

  static void __idr_remove_all(struct idr *idp)

  {

  	int n, id, max;

  	int bt_mask;

  	struct idr_layer *p;

  	struct idr_layer *pa[MAX_IDR_LEVEL + 1];

  	struct idr_layer **paa = &pa[0];
  
  	n = idp->layers * IDR_BITS;

  	*paa = idp->top;

  	RCU_INIT_POINTER(idp->top, NULL);

  	max = idr_max(idp->layers);

  
  	id = 0;

  	while (id >= 0 && id <= max) {

  		p = *paa;

  		while (n > IDR_BITS && p) {
  			n -= IDR_BITS;

  			p = p->ary[(id >> n) & IDR_MASK];

  			*++paa = p;

  		}

  		bt_mask = id;

  		id += 1 << n;

  		/* Get the highest bit that the above add changed from 0->1. */
  		while (n < fls(id ^ bt_mask)) {

  			if (*paa)
  				free_layer(idp, *paa);

  			n += IDR_BITS;

  			--paa;

  		}
  	}

  	idp->layers = 0;
  }

  
  /**

   * idr_destroy - release all cached layers within an idr tree

   * @idp: idr handle

   *
   * Free all id mappings and all idp_layers.  After this function, @idp is
   * completely unused and can be freed / recycled.  The caller is
   * responsible for ensuring that no one else accesses @idp during or after
   * idr_destroy().
   *
   * A typical clean-up sequence for objects stored in an idr tree will use

   * idr_for_each() to free all objects, if necessary, then idr_destroy() to

   * free up the id mappings and cached idr_layers.

   */
  void idr_destroy(struct idr *idp)
  {

  	__idr_remove_all(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);

  void *idr_find_slowpath(struct idr *idp, int id)

  {
  	int n;
  	struct idr_layer *p;

  	if (id < 0)

  		return NULL;

  	p = rcu_dereference_raw(idp->top);

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

  	if (id > idr_max(p->layer + 1))

  		return NULL;

  	BUG_ON(n == 0);

  
  	while (n > 0 && p) {
  		n -= IDR_BITS;

  		BUG_ON(n != p->layer*IDR_BITS);

  		p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);

  	}
  	return((void *)p);
  }

  EXPORT_SYMBOL(idr_find_slowpath);

  /**

   * 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_IDR_LEVEL + 1];

  	struct idr_layer **paa = &pa[0];
  
  	n = idp->layers * IDR_BITS;

  	*paa = rcu_dereference_raw(idp->top);

  	max = idr_max(idp->layers);

  
  	id = 0;

  	while (id >= 0 && id <= max) {

  		p = *paa;

  		while (n > 0 && p) {
  			n -= IDR_BITS;

  			p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);

  			*++paa = p;

  		}
  
  		if (p) {
  			error = fn(id, (void *)p, data);
  			if (error)
  				break;
  		}
  
  		id += 1 << n;
  		while (n < fls(id)) {
  			n += IDR_BITS;

  			--paa;

  		}
  	}
  
  	return error;
  }
  EXPORT_SYMBOL(idr_for_each);
  
  /**

   * idr_get_next - lookup next object of id to given id.
   * @idp: idr handle

   * @nextidp:  pointer to lookup key

   *
   * Returns pointer to registered object with id, which is next number to

   * given id. After being looked up, *@nextidp will be updated for the next
   * iteration.

   *
   * This function can be called under rcu_read_lock(), given that the leaf
   * pointers lifetimes are correctly managed.

   */

  void *idr_get_next(struct idr *idp, int *nextidp)
  {

  	struct idr_layer *p, *pa[MAX_IDR_LEVEL + 1];

  	struct idr_layer **paa = &pa[0];
  	int id = *nextidp;
  	int n, max;
  
  	/* find first ent */

  	p = *paa = rcu_dereference_raw(idp->top);

  	if (!p)
  		return NULL;

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

  	max = idr_max(p->layer + 1);

  	while (id >= 0 && id <= max) {

  		p = *paa;

  		while (n > 0 && p) {
  			n -= IDR_BITS;

  			p = rcu_dereference_raw(p->ary[(id >> n) & IDR_MASK]);

  			*++paa = p;

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

  		/*
  		 * Proceed to the next layer at the current level.  Unlike
  		 * idr_for_each(), @id isn't guaranteed to be aligned to
  		 * layer boundary at this point and adding 1 << n may
  		 * incorrectly skip IDs.  Make sure we jump to the
  		 * beginning of the next layer using round_up().
  		 */
  		id = round_up(id + 1, 1 << n);

  		while (n < fls(id)) {
  			n += IDR_BITS;

  			--paa;

  		}
  	}
  	return NULL;
  }

  EXPORT_SYMBOL(idr_get_next);

  
  
  /**

   * 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;

  	if (id < 0)

  		return ERR_PTR(-EINVAL);

  	p = idp->top;

  	if (!p)

  		return ERR_PTR(-ENOENT);

  	if (id > idr_max(p->layer + 1))

  		return ERR_PTR(-ENOENT);

  	n = p->layer * 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);

  static int idr_has_entry(int id, void *p, void *data)
  {
  	return 1;
  }
  
  bool idr_is_empty(struct idr *idp)
  {
  	return !idr_for_each(idp, idr_has_entry, NULL);
  }
  EXPORT_SYMBOL(idr_is_empty);

  /**
   * DOC: IDA description

   * 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

   * @starting_id: id to start search at

   * @p_id:	pointer to the allocated handle
   *

   * Allocate new ID above or equal to @starting_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 ida_pre_get() call.  If the ida is full, it will

   * return %-ENOSPC.

   *

   * Note that callers must ensure that concurrent access to @ida is not possible.
   * See ida_simple_get() for a varaint which takes care of locking.
   *

   * @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_IDR_LEVEL + 1];

  	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, 0, &ida->idr);

  	if (t < 0)

  		return t == -ENOMEM ? -EAGAIN : t;

  	if (t * IDA_BITMAP_BITS >= MAX_IDR_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_IDR_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_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;

  	if (idr_id > idr_max(ida->idr.layers))
  		goto err;

  	/* 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 (!bitmap || !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:

  	WARN(1, "ida_remove called for id=%d which is not allocated.
  ", 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_simple_get - get a new id.
   * @ida: the (initialized) ida.
   * @start: the minimum id (inclusive, < 0x8000000)
   * @end: the maximum id (exclusive, < 0x8000000 or 0)
   * @gfp_mask: memory allocation flags
   *
   * Allocates an id in the range start <= id < end, or returns -ENOSPC.
   * On memory allocation failure, returns -ENOMEM.
   *

   * Compared to ida_get_new_above() this function does its own locking, and
   * should be used unless there are special requirements.
   *

   * Use ida_simple_remove() to get rid of an id.
   */
  int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
  		   gfp_t gfp_mask)
  {
  	int ret, id;
  	unsigned int max;

  	unsigned long flags;

  
  	BUG_ON((int)start < 0);
  	BUG_ON((int)end < 0);
  
  	if (end == 0)
  		max = 0x80000000;
  	else {
  		BUG_ON(end < start);
  		max = end - 1;
  	}
  
  again:
  	if (!ida_pre_get(ida, gfp_mask))
  		return -ENOMEM;

  	spin_lock_irqsave(&simple_ida_lock, flags);

  	ret = ida_get_new_above(ida, start, &id);
  	if (!ret) {
  		if (id > max) {
  			ida_remove(ida, id);
  			ret = -ENOSPC;
  		} else {
  			ret = id;
  		}
  	}

  	spin_unlock_irqrestore(&simple_ida_lock, flags);

  
  	if (unlikely(ret == -EAGAIN))
  		goto again;
  
  	return ret;
  }
  EXPORT_SYMBOL(ida_simple_get);
  
  /**
   * ida_simple_remove - remove an allocated id.
   * @ida: the (initialized) ida.
   * @id: the id returned by ida_simple_get.

   *
   * Use to release an id allocated with ida_simple_get().
   *
   * Compared to ida_remove() this function does its own locking, and should be
   * used unless there are special requirements.

   */
  void ida_simple_remove(struct ida *ida, unsigned int id)
  {

  	unsigned long flags;

  	BUG_ON((int)id < 0);

  	spin_lock_irqsave(&simple_ida_lock, flags);

  	ida_remove(ida, id);

  	spin_unlock_irqrestore(&simple_ida_lock, flags);

  }
  EXPORT_SYMBOL(ida_simple_remove);
  
  /**

   * 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);