lib/util/idtree.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    very efficient functions to manage mapping a id (such as a fnum) to
   5    a pointer. This is used for fnum and search id allocation.
   6
   7    Copyright (C) Andrew Tridgell 2004
   8
   9    This code is derived from lib/idr.c in the 2.6 Linux kernel, which was
  10    written by Jim Houston jim.houston@ccur.com, and is
  11    Copyright (C) 2002 by Concurrent Computer Corporation
  12
  13    This program is free software; you can redistribute it and/or modify
  14    it under the terms of the GNU General Public License as published by
  15    the Free Software Foundation; either version 2 of the License, or
  16    (at your option) any later version.
  17
  18    This program is distributed in the hope that it will be useful,
  19    but WITHOUT ANY WARRANTY; without even the implied warranty of
  20    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  21    GNU General Public License for more details.
  22
  23    You should have received a copy of the GNU General Public License
  24    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  25 */
  26
  27 /*
  28   see the section marked "public interface" below for documentation
  29 */
  30
  31 /**
  32  * @file
  33  */
  34
  35 #include <talloc.h>
  36 #include "replace.h"
  37 #include "debug.h"
  38 #include "idtree.h"
  39
  40 #define IDR_BITS 5
  41 #define IDR_FULL 0xfffffffful
  42 #if 0 /* unused */
  43 #define TOP_LEVEL_FULL (IDR_FULL >> 30)
  44 #endif
  45 #define IDR_SIZE (1 << IDR_BITS)
  46 #define IDR_MASK ((1 << IDR_BITS)-1)
  47 #define MAX_ID_SHIFT (sizeof(int)*8 - 1)
  48 #define MAX_ID_BIT (1U << MAX_ID_SHIFT)
  49 #define MAX_ID_MASK (MAX_ID_BIT - 1)
  50 #define MAX_LEVEL (MAX_ID_SHIFT + IDR_BITS - 1) / IDR_BITS
  51 #define IDR_FREE_MAX MAX_LEVEL + MAX_LEVEL
  52
  53 #define set_bit(bit, v) (v) |= (1<<(bit))
  54 #define clear_bit(bit, v) (v) &= ~(1<<(bit))
  55 #define test_bit(bit, v) ((v) & (1<<(bit)))
  56
  57 struct idr_layer {
  58         uint32_t                 bitmap;
  59         struct idr_layer        *ary[IDR_SIZE];
  60         int                      count;
  61 };
  62
  63 struct idr_context {
  64         struct idr_layer *top;
  65         struct idr_layer *id_free;
  66         int               layers;
  67         int               id_free_cnt;
  68 };
  69
  70 static struct idr_layer *alloc_layer(struct idr_context *idp)
  71 {
  72         struct idr_layer *p;
  73
  74         if (!(p = idp->id_free))
  75                 return NULL;
  76         idp->id_free = p->ary[0];
  77         idp->id_free_cnt--;
  78         p->ary[0] = NULL;
  79         return p;
  80 }
  81
  82 static int find_next_bit(uint32_t bm, int maxid, int n)
  83 {
  84         while (n<maxid && !test_bit(n, bm)) n++;
  85         return n;
  86 }
  87
  88 static void free_layer(struct idr_context *idp, struct idr_layer *p)
  89 {
  90         p->ary[0] = idp->id_free;
  91         idp->id_free = p;
  92         idp->id_free_cnt++;
  93 }
  94
  95 static int idr_pre_get(struct idr_context *idp)
  96 {
  97         while (idp->id_free_cnt < IDR_FREE_MAX) {
  98                 struct idr_layer *pn = talloc_zero(idp, struct idr_layer);
  99                 if(pn == NULL)
 100                         return (0);
 101                 free_layer(idp, pn);
 102         }
 103         return 1;
 104 }
 105
 106 static int sub_alloc(struct idr_context *idp, void *ptr, int *starting_id)
 107 {
 108         int n, m, sh;
 109         struct idr_layer *p, *pn;
 110         struct idr_layer *pa[MAX_LEVEL+1];
 111         unsigned int l, id, oid;
 112         uint32_t bm;
 113
 114         memset(pa, 0, sizeof(pa));
 115
 116         id = *starting_id;
 117 restart:
 118         p = idp->top;
 119         l = idp->layers;
 120         pa[l--] = NULL;
 121         while (1) {
 122                 /*
 123                  * We run around this while until we reach the leaf node...
 124                  */
 125                 n = (id >> (IDR_BITS*l)) & IDR_MASK;
 126                 bm = ~p->bitmap;
 127                 m = find_next_bit(bm, IDR_SIZE, n);
 128                 if (m == IDR_SIZE) {
 129                         /* no space available go back to previous layer. */
 130                         l++;
 131                         oid = id;
 132                         id = (id | ((1 << (IDR_BITS*l))-1)) + 1;
 133
 134                         /* if already at the top layer, we need to grow */
 135                         if (!(p = pa[l])) {
 136                                 *starting_id = id;
 137                                 return -2;
 138                         }
 139
 140                         /* If we need to go up one layer, continue the
 141                          * loop; otherwise, restart from the top.
 142                          */
 143                         sh = IDR_BITS * (l + 1);
 144                         if (oid >> sh == id >> sh)
 145                                 continue;
 146                         else
 147                                 goto restart;
 148                 }
 149                 if (m != n) {
 150                         sh = IDR_BITS*l;
 151                         id = ((id >> sh) ^ n ^ m) << sh;
 152                 }
 153                 if ((id >= MAX_ID_BIT) || (id < 0))
 154                         return -1;
 155                 if (l == 0)
 156                         break;
 157                 /*
 158                  * Create the layer below if it is missing.
 159                  */
 160                 if (!p->ary[m]) {
 161                         if (!(pn = alloc_layer(idp)))
 162                                 return -1;
 163                         p->ary[m] = pn;
 164                         p->count++;
 165                 }
 166                 pa[l--] = p;
 167                 p = p->ary[m];
 168         }
 169         /*
 170          * We have reached the leaf node, plant the
 171          * users pointer and return the raw id.
 172          */
 173         p->ary[m] = (struct idr_layer *)ptr;
 174         set_bit(m, p->bitmap);
 175         p->count++;
 176         /*
 177          * If this layer is full mark the bit in the layer above
 178          * to show that this part of the radix tree is full.
 179          * This may complete the layer above and require walking
 180          * up the radix tree.
 181          */
 182         n = id;
 183         while (p->bitmap == IDR_FULL) {
 184                 if (!(p = pa[++l]))
 185                         break;
 186                 n = n >> IDR_BITS;
 187                 set_bit((n & IDR_MASK), p->bitmap);
 188         }
 189         return(id);
 190 }
 191
 192 static int idr_get_new_above_int(struct idr_context *idp, void *ptr, int starting_id)
 193 {
 194         struct idr_layer *p, *pn;
 195         int layers, v, id;
 196
 197         idr_pre_get(idp);
 198
 199         id = starting_id;
 200 build_up:
 201         p = idp->top;
 202         layers = idp->layers;
 203         if (!p) {
 204                 if (!(p = alloc_layer(idp)))
 205                         return -1;
 206                 layers = 1;
 207         }
 208         /*
 209          * Add a new layer to the top of the tree if the requested
 210          * id is larger than the currently allocated space.
 211          */
 212         while ((layers < MAX_LEVEL) && (id >= (1 << (layers*IDR_BITS)))) {
 213                 layers++;
 214                 if (!p->count)
 215                         continue;
 216                 if (!(pn = alloc_layer(idp))) {
 217                         /*
 218                          * The allocation failed.  If we built part of
 219                          * the structure tear it down.
 220                          */
 221                         for (pn = p; p && p != idp->top; pn = p) {
 222                                 p = p->ary[0];
 223                                 pn->ary[0] = NULL;
 224                                 pn->bitmap = pn->count = 0;
 225                                 free_layer(idp, pn);
 226                         }
 227                         return -1;
 228                 }
 229                 pn->ary[0] = p;
 230                 pn->count = 1;
 231                 if (p->bitmap == IDR_FULL)
 232                         set_bit(0, pn->bitmap);
 233                 p = pn;
 234         }
 235         idp->top = p;
 236         idp->layers = layers;
 237         v = sub_alloc(idp, ptr, &id);
 238         if (v == -2)
 239                 goto build_up;
 240         return(v);
 241 }
 242
 243 static int sub_remove(struct idr_context *idp, int shift, int id)
 244 {
 245         struct idr_layer *p = idp->top;
 246         struct idr_layer **pa[1+MAX_LEVEL];
 247         struct idr_layer ***paa = &pa[0];
 248         int n;
 249
 250         *paa = NULL;
 251         *++paa = &idp->top;
 252
 253         while ((shift > 0) && p) {
 254                 n = (id >> shift) & IDR_MASK;
 255                 clear_bit(n, p->bitmap);
 256                 *++paa = &p->ary[n];
 257                 p = p->ary[n];
 258                 shift -= IDR_BITS;
 259         }
 260         n = id & IDR_MASK;
 261         if (p != NULL && test_bit(n, p->bitmap)) {
 262                 clear_bit(n, p->bitmap);
 263                 p->ary[n] = NULL;
 264                 while(*paa && ! --((**paa)->count)){
 265                         free_layer(idp, **paa);
 266                         **paa-- = NULL;
 267                 }
 268                 if ( ! *paa )
 269                         idp->layers = 0;
 270                 return 0;
 271         }
 272         return -1;
 273 }
 274
 275 static void *_idr_find(struct idr_context *idp, int id)
 276 {
 277         int n;
 278         struct idr_layer *p;
 279
 280         n = idp->layers * IDR_BITS;
 281         p = idp->top;
 282         /*
 283          * This tests to see if bits outside the current tree are
 284          * present.  If so, tain't one of ours!
 285          */
 286         if (n + IDR_BITS < 31 &&
 287             ((id & ~(~0 << MAX_ID_SHIFT)) >> (n + IDR_BITS))) {
 288                 return NULL;
 289         }
 290
 291         /* Mask off upper bits we don't use for the search. */
 292         id &= MAX_ID_MASK;
 293
 294         while (n >= IDR_BITS && p) {
 295                 n -= IDR_BITS;
 296                 p = p->ary[(id >> n) & IDR_MASK];
 297         }
 298         return((void *)p);
 299 }
 300
 301 static int _idr_remove(struct idr_context *idp, int id)
 302 {
 303         struct idr_layer *p;
 304
 305         /* Mask off upper bits we don't use for the search. */
 306         id &= MAX_ID_MASK;
 307
 308         if (sub_remove(idp, (idp->layers - 1) * IDR_BITS, id) == -1) {
 309                 return -1;
 310         }
 311
 312         if ( idp->top && idp->top->count == 1 &&
 313              (idp->layers > 1) &&
 314              idp->top->ary[0]) {
 315                 /* We can drop a layer */
 316                 p = idp->top->ary[0];
 317                 idp->top->bitmap = idp->top->count = 0;
 318                 free_layer(idp, idp->top);
 319                 idp->top = p;
 320                 --idp->layers;
 321         }
 322         while (idp->id_free_cnt >= IDR_FREE_MAX) {
 323                 p = alloc_layer(idp);
 324                 talloc_free(p);
 325         }
 326         return 0;
 327 }
 328
 329 /************************************************************************
 330   this is the public interface
 331 **************************************************************************/
 332
 333 /**
 334   initialise a idr tree. The context return value must be passed to
 335   all subsequent idr calls. To destroy the idr tree use talloc_free()
 336   on this context
 337  */
 338 _PUBLIC_ struct idr_context *idr_init(TALLOC_CTX *mem_ctx)
 339 {
 340         return talloc_zero(mem_ctx, struct idr_context);
 341 }
 342
 343 /**
 344   allocate the next available id, and assign 'ptr' into its slot.
 345   you can retrieve later this pointer using idr_find()
 346 */
 347 _PUBLIC_ int idr_get_new(struct idr_context *idp, void *ptr, int limit)
 348 {
 349         int ret = idr_get_new_above_int(idp, ptr, 0);
 350         if (ret > limit) {
 351                 idr_remove(idp, ret);
 352                 return -1;
 353         }
 354         return ret;
 355 }
 356
 357 /**
 358    allocate a new id, giving the first available value greater than or
 359    equal to the given starting id
 360 */
 361 _PUBLIC_ int idr_get_new_above(struct idr_context *idp, void *ptr, int starting_id, int limit)
 362 {
 363         int ret = idr_get_new_above_int(idp, ptr, starting_id);
 364         if (ret > limit) {
 365                 idr_remove(idp, ret);
 366                 return -1;
 367         }
 368         return ret;
 369 }
 370
 371 /**
 372   find a pointer value previously set with idr_get_new given an id
 373 */
 374 _PUBLIC_ void *idr_find(struct idr_context *idp, int id)
 375 {
 376         return _idr_find(idp, id);
 377 }
 378
 379 /**
 380   remove an id from the idr tree
 381 */
 382 _PUBLIC_ int idr_remove(struct idr_context *idp, int id)
 383 {
 384         int ret;
 385         ret = _idr_remove((struct idr_context *)idp, id);
 386         if (ret != 0) {
 387                 DEBUG(0,("WARNING: attempt to remove unset id %d in idtree\n", id));
 388         }
 389         return ret;
 390 }