samba-mirror/source4/lib/idtree.c

/* 
   Unix SMB/CIFS implementation.

   very efficient functions to manage mapping a id (such as a fnum) to
   a pointer. This is used for fnum and search id allocation.

   Copyright (C) Andrew Tridgell 2004

   This code is derived from lib/idr.c in the 2.6 Linux kernel, which was 
   written by Jim Houston jim.houston@ccur.com, and is
   Copyright (C) 2002 by Concurrent Computer Corporation
    
   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 of the License, 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.
*/

/*
  see the section marked "public interface" below for documentation
*/

#include "includes.h"

#define IDR_BITS 5
#define IDR_FULL 0xfffffffful
#define TOP_LEVEL_FULL (IDR_FULL >> 30)
#define IDR_SIZE (1 << IDR_BITS)
#define IDR_MASK ((1 << IDR_BITS)-1)
#define MAX_ID_SHIFT (sizeof(int)*8 - 1)
#define MAX_ID_BIT (1U << MAX_ID_SHIFT)
#define MAX_ID_MASK (MAX_ID_BIT - 1)
#define MAX_LEVEL (MAX_ID_SHIFT + IDR_BITS - 1) / IDR_BITS
#define IDR_FREE_MAX MAX_LEVEL + MAX_LEVEL

#define set_bit(bit, v) (v) |= (1<<(bit))
#define clear_bit(bit, v) (v) &= ~(1<<(bit))
				   
struct idr_layer {
	uint32_t		 bitmap;
	struct idr_layer	*ary[IDR_SIZE];
	int			 count;
};

struct idr {
	struct idr_layer *top;
	struct idr_layer *id_free;
	int		  layers;
	int		  id_free_cnt;
};

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

	if (!(p = idp->id_free))
		return NULL;
	idp->id_free = p->ary[0];
	idp->id_free_cnt--;
	p->ary[0] = NULL;
	return p;
}

static int find_next_bit(uint32_t bm, int maxid, int n)
{
	while (n<maxid && ((bm & (1<<n)) == 0)) n++;
	return n;
}

static void free_layer(struct idr *idp, struct idr_layer *p)
{
	p->ary[0] = idp->id_free;
	idp->id_free = p;
	idp->id_free_cnt++;
}

static int idr_pre_get(struct idr *idp)
{
	while (idp->id_free_cnt < IDR_FREE_MAX) {
		struct idr_layer *new = talloc_zero_p(idp, struct idr_layer);
		if(new == NULL)
			return (0);
		free_layer(idp, new);
	}
	return 1;
}

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;
	uint32_t 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 -1;
		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;

	idr_pre_get(idp);
	
	id = starting_id;
build_up:
	p = idp->top;
	layers = idp->layers;
	if (!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);
}

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 (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;
	}
}

static void *_idr_find(struct idr *idp, int id)
{
	int n;
	struct idr_layer *p;

	n = idp->layers * IDR_BITS;
	p = idp->top;
	/*
	 * This tests to see if bits outside the current tree are
	 * present.  If so, tain't one of ours!
	 */
	if ((id & ~(~0 << MAX_ID_SHIFT)) >> (n + IDR_BITS))
	     return NULL;

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

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

static void _idr_remove(struct idr *idp, int id)
{
	struct idr_layer *p;

	if (_idr_find(idp, id) == NULL) {
		DEBUG(0,("WARNING: attempt to remove non-existant id %d in idtree\n",
			 id));
		return;
	}

	/* 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);
		talloc_free(p);
		return;
	}
}

/************************************************************************
  this is the public interface
**************************************************************************/

/*
  initialise a idr tree. The context return value must be passed to
  all subsequent idr calls. To destroy the idr tree use talloc_free()
  on this context
 */
void *idr_init(TALLOC_CTX *mem_ctx)
{
	return talloc_zero_p(mem_ctx, struct idr);
}

/*
  allocate the next available id, and assign 'ptr' into its slot.
  you can retrieve later this pointer using idr_find()
*/
int idr_get_new(void *idp, void *ptr, int limit)
{
	int ret = idr_get_new_above_int((struct idr *)idp, ptr, 0);
	if (ret > limit) {
		idr_remove(idp, ret);
		return -1;
	}
	return ret;
}

/* 
   allocate a new id, giving the first available value greater than or
   equal to the given starting id
*/
int idr_get_new_above(void *idp, void *ptr, int starting_id, int limit)
{
	int ret = idr_get_new_above_int((struct idr *)idp, ptr, starting_id);
	if (ret > limit) {
		idr_remove(idp, ret);
		return -1;
	}
	return ret;
}

/*
  find a pointer value previously set with idr_get_new given an id
*/
void *idr_find(void *idp, int id)
{
	return _idr_find((struct idr *)idp, id);
}

/*
  remove an id from the idr tree
*/
void idr_remove(void *idp, int id)
{
	return _idr_remove((struct idr *)idp, id);
}