lib/idr.c

   1 /*
   2  * 2002-10-18  written by Jim Houston jim.houston@ccur.com
   3  *      Copyright (C) 2002 by Concurrent Computer Corporation
   4  *      Distributed under the GNU GPL license version 2.
   5  *
   6  * Modified by George Anzinger to reuse immediately and to use
   7  * find bit instructions.  Also removed _irq on spinlocks.
   8  *
   9  * Small id to pointer translation service.
  10  *
  11  * It uses a radix tree like structure as a sparse array indexed
  12  * by the id to obtain the pointer.  The bitmap makes allocating
  13  * a new id quick.
  14  *
  15  * You call it to allocate an id (an int) an associate with that id a
  16  * pointer or what ever, we treat it as a (void *).  You can pass this
  17  * id to a user for him to pass back at a later time.  You then pass
  18  * that id to this code and it returns your pointer.
  19
  20  * You can release ids at any time. When all ids are released, most of
  21  * the memory is returned (we keep IDR_FREE_MAX) in a local pool so we
  22  * don't need to go to the memory "store" during an id allocate, just
  23  * so you don't need to be too concerned about locking and conflicts
  24  * with the slab allocator.
  25  */
  26
  27 #ifndef TEST                        // to test in user space...
  28 #include <linux/slab.h>
  29 #include <linux/init.h>
  30 #include <linux/module.h>
  31 #endif
  32 #include <linux/string.h>
  33 #include <linux/idr.h>
  34
  35 static kmem_cache_t *idr_layer_cache;
  36
  37 static struct idr_layer *alloc_layer(struct idr *idp)
  38 {
  39         struct idr_layer *p;
  40
  41         spin_lock(&idp->lock);
  42         if (!(p = idp->id_free)) {
  43                 spin_unlock(&idp->lock);
  44                 return NULL;
  45         }
  46         idp->id_free = p->ary[0];
  47         idp->id_free_cnt--;
  48         p->ary[0] = NULL;
  49         spin_unlock(&idp->lock);
  50         return(p);
  51 }
  52
  53 static void free_layer(struct idr *idp, struct idr_layer *p)
  54 {
  55         /*
  56          * Depends on the return element being zeroed.
  57          */
  58         spin_lock(&idp->lock);
  59         p->ary[0] = idp->id_free;
  60         idp->id_free = p;
  61         idp->id_free_cnt++;
  62         spin_unlock(&idp->lock);
  63 }
  64
  65 /**
  66  * idr_pre_get - reserver resources for idr allocation
  67  * @idp:        idr handle
  68  * @gfp_mask:   memory allocation flags
  69  *
  70  * This function should be called prior to locking and calling the
  71  * following function.  It preallocates enough memory to satisfy
  72  * the worst possible allocation.
  73  *
  74  * If the system is REALLY out of memory this function returns 0,
  75  * otherwise 1.
  76  */
  77 int idr_pre_get(struct idr *idp, unsigned gfp_mask)
  78 {
  79         while (idp->id_free_cnt < IDR_FREE_MAX) {
  80                 struct idr_layer *new;
  81                 new = kmem_cache_alloc(idr_layer_cache, gfp_mask);
  82                 if(new == NULL)
  83                         return (0);
  84                 free_layer(idp, new);
  85         }
  86         return 1;
  87 }
  88 EXPORT_SYMBOL(idr_pre_get);
  89
  90 static int sub_alloc(struct idr *idp, void *ptr, int *starting_id)
  91 {
  92         int n, m, sh;
  93         struct idr_layer *p, *new;
  94         struct idr_layer *pa[MAX_LEVEL];
  95         int l, id;
  96         long bm;
  97
  98         id = *starting_id;
  99         p = idp->top;
 100         l = idp->layers;
 101         pa[l--] = NULL;
 102         while (1) {
 103                 /*
 104                  * We run around this while until we reach the leaf node...
 105                  */
 106                 n = (id >> (IDR_BITS*l)) & IDR_MASK;
 107                 bm = ~p->bitmap;
 108                 m = find_next_bit(&bm, IDR_SIZE, n);
 109                 if (m == IDR_SIZE) {
 110                         /* no space available go back to previous layer. */
 111                         l++;
 112                         id = (id | ((1 << (IDR_BITS*l))-1)) + 1;
 113                         if (!(p = pa[l])) {
 114                                 *starting_id = id;
 115                                 return -2;
 116                         }
 117                         continue;
 118                 }
 119                 if (m != n) {
 120                         sh = IDR_BITS*l;
 121                         id = ((id >> sh) ^ n ^ m) << sh;
 122                 }
 123                 if ((id >= MAX_ID_BIT) || (id < 0))
 124                         return -3;
 125                 if (l == 0)
 126                         break;
 127                 /*
 128                  * Create the layer below if it is missing.
 129                  */
 130                 if (!p->ary[m]) {
 131                         if (!(new = alloc_layer(idp)))
 132                                 return -1;
 133                         p->ary[m] = new;
 134                         p->count++;
 135                 }
 136                 pa[l--] = p;
 137                 p = p->ary[m];
 138         }
 139         /*
 140          * We have reached the leaf node, plant the
 141          * users pointer and return the raw id.
 142          */
 143         p->ary[m] = (struct idr_layer *)ptr;
 144         __set_bit(m, &p->bitmap);
 145         p->count++;
 146         /*
 147          * If this layer is full mark the bit in the layer above
 148          * to show that this part of the radix tree is full.
 149          * This may complete the layer above and require walking
 150          * up the radix tree.
 151          */
 152         n = id;
 153         while (p->bitmap == IDR_FULL) {
 154                 if (!(p = pa[++l]))
 155                         break;
 156                 n = n >> IDR_BITS;
 157                 __set_bit((n & IDR_MASK), &p->bitmap);
 158         }
 159         return(id);
 160 }
 161
 162 static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
 163 {
 164         struct idr_layer *p, *new;
 165         int layers, v, id;
 166
 167         id = starting_id;
 168 build_up:
 169         p = idp->top;
 170         layers = idp->layers;
 171         if (unlikely(!p)) {
 172                 if (!(p = alloc_layer(idp)))
 173                         return -1;
 174                 layers = 1;
 175         }
 176         /*
 177          * Add a new layer to the top of the tree if the requested
 178          * id is larger than the currently allocated space.
 179          */
 180         while ((layers < MAX_LEVEL) && (id >= (1 << (layers*IDR_BITS)))) {
 181                 layers++;
 182                 if (!p->count)
 183                         continue;
 184                 if (!(new = alloc_layer(idp))) {
 185                         /*
 186                          * The allocation failed.  If we built part of
 187                          * the structure tear it down.
 188                          */
 189                         for (new = p; p && p != idp->top; new = p) {
 190                                 p = p->ary[0];
 191                                 new->ary[0] = NULL;
 192                                 new->bitmap = new->count = 0;
 193                                 free_layer(idp, new);
 194                         }
 195                         return -1;
 196                 }
 197                 new->ary[0] = p;
 198                 new->count = 1;
 199                 if (p->bitmap == IDR_FULL)
 200                         __set_bit(0, &new->bitmap);
 201                 p = new;
 202         }
 203         idp->top = p;
 204         idp->layers = layers;
 205         v = sub_alloc(idp, ptr, &id);
 206         if (v == -2)
 207                 goto build_up;
 208         return(v);
 209 }
 210
 211 /**
 212  * idr_get_new_above - allocate new idr entry above a start id
 213  * @idp: idr handle
 214  * @ptr: pointer you want associated with the ide
 215  * @start_id: id to start search at
 216  * @id: pointer to the allocated handle
 217  *
 218  * This is the allocate id function.  It should be called with any
 219  * required locks.
 220  *
 221  * If memory is required, it will return -EAGAIN, you should unlock
 222  * and go back to the idr_pre_get() call.  If the idr is full, it will
 223  * return -ENOSPC.
 224  *
 225  * @id returns a value in the range 0 ... 0x7fffffff
 226  */
 227 int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
 228 {
 229         int rv;
 230         rv = idr_get_new_above_int(idp, ptr, starting_id);
 231         /*
 232          * This is a cheap hack until the IDR code can be fixed to
 233          * return proper error values.
 234          */
 235         if (rv < 0) {
 236                 if (rv == -1)
 237                         return -EAGAIN;
 238                 else /* Will be -3 */
 239                         return -ENOSPC;
 240         }
 241         *id = rv;
 242         return 0;
 243 }
 244 EXPORT_SYMBOL(idr_get_new_above);
 245
 246 /**
 247  * idr_get_new - allocate new idr entry
 248  * @idp: idr handle
 249  * @ptr: pointer you want associated with the ide
 250  * @id: pointer to the allocated handle
 251  *
 252  * This is the allocate id function.  It should be called with any
 253  * required locks.
 254  *
 255  * If memory is required, it will return -EAGAIN, you should unlock
 256  * and go back to the idr_pre_get() call.  If the idr is full, it will
 257  * return -ENOSPC.
 258  *
 259  * @id returns a value in the range 0 ... 0x7fffffff
 260  */
 261 int idr_get_new(struct idr *idp, void *ptr, int *id)
 262 {
 263         int rv;
 264         rv = idr_get_new_above_int(idp, ptr, 0);
 265         /*
 266          * This is a cheap hack until the IDR code can be fixed to
 267          * return proper error values.
 268          */
 269         if (rv < 0) {
 270                 if (rv == -1)
 271                         return -EAGAIN;
 272                 else /* Will be -3 */
 273                         return -ENOSPC;
 274         }
 275         *id = rv;
 276         return 0;
 277 }
 278 EXPORT_SYMBOL(idr_get_new);
 279
 280 static void sub_remove(struct idr *idp, int shift, int id)
 281 {
 282         struct idr_layer *p = idp->top;
 283         struct idr_layer **pa[MAX_LEVEL];
 284         struct idr_layer ***paa = &pa[0];
 285
 286         *paa = NULL;
 287         *++paa = &idp->top;
 288
 289         while ((shift > 0) && p) {
 290                 int n = (id >> shift) & IDR_MASK;
 291                 __clear_bit(n, &p->bitmap);
 292                 *++paa = &p->ary[n];
 293                 p = p->ary[n];
 294                 shift -= IDR_BITS;
 295         }
 296         if (likely(p != NULL)){
 297                 int n = id & IDR_MASK;
 298                 __clear_bit(n, &p->bitmap);
 299                 p->ary[n] = NULL;
 300                 while(*paa && ! --((**paa)->count)){
 301                         free_layer(idp, **paa);
 302                         **paa-- = NULL;
 303                 }
 304                 if ( ! *paa )
 305                         idp->layers = 0;
 306         }
 307 }
 308
 309 /**
 310  * idr_remove - remove the given id and free it's slot
 311  * idp: idr handle
 312  * id: uniqueue key
 313  */
 314 void idr_remove(struct idr *idp, int id)
 315 {
 316         struct idr_layer *p;
 317
 318         /* Mask off upper bits we don't use for the search. */
 319         id &= MAX_ID_MASK;
 320
 321         sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
 322         if ( idp->top && idp->top->count == 1 &&
 323              (idp->layers > 1) &&
 324              idp->top->ary[0]){  // We can drop a layer
 325
 326                 p = idp->top->ary[0];
 327                 idp->top->bitmap = idp->top->count = 0;
 328                 free_layer(idp, idp->top);
 329                 idp->top = p;
 330                 --idp->layers;
 331         }
 332         while (idp->id_free_cnt >= IDR_FREE_MAX) {
 333
 334                 p = alloc_layer(idp);
 335                 kmem_cache_free(idr_layer_cache, p);
 336                 return;
 337         }
 338 }
 339 EXPORT_SYMBOL(idr_remove);
 340
 341 /**
 342  * idr_find - return pointer for given id
 343  * @idp: idr handle
 344  * @id: lookup key
 345  *
 346  * Return the pointer given the id it has been registered with.  A %NULL
 347  * return indicates that @id is not valid or you passed %NULL in
 348  * idr_get_new().
 349  *
 350  * The caller must serialize idr_find() vs idr_get_new() and idr_remove().
 351  */
 352 void *idr_find(struct idr *idp, int id)
 353 {
 354         int n;
 355         struct idr_layer *p;
 356
 357         n = idp->layers * IDR_BITS;
 358         p = idp->top;
 359
 360         /* Mask off upper bits we don't use for the search. */
 361         id &= MAX_ID_MASK;
 362
 363         if (id >= (1 << n))
 364                 return NULL;
 365
 366         while (n > 0 && p) {
 367                 n -= IDR_BITS;
 368                 p = p->ary[(id >> n) & IDR_MASK];
 369         }
 370         return((void *)p);
 371 }
 372 EXPORT_SYMBOL(idr_find);
 373
 374 static void idr_cache_ctor(void * idr_layer,
 375                            kmem_cache_t *idr_layer_cache, unsigned long flags)
 376 {
 377         memset(idr_layer, 0, sizeof(struct idr_layer));
 378 }
 379
 380 static  int init_id_cache(void)
 381 {
 382         if (!idr_layer_cache)
 383                 idr_layer_cache = kmem_cache_create("idr_layer_cache",
 384                         sizeof(struct idr_layer), 0, 0, idr_cache_ctor, NULL);
 385         return 0;
 386 }
 387
 388 /**
 389  * idr_init - initialize idr handle
 390  * @idp:        idr handle
 391  *
 392  * This function is use to set up the handle (@idp) that you will pass
 393  * to the rest of the functions.
 394  */
 395 void idr_init(struct idr *idp)
 396 {
 397         init_id_cache();
 398         memset(idp, 0, sizeof(struct idr));
 399         spin_lock_init(&idp->lock);
 400 }
 401 EXPORT_SYMBOL(idr_init);