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                 idp->id_free = p->ary[0];
  44                 idp->id_free_cnt--;
  45                 p->ary[0] = NULL;
  46         }
  47         spin_unlock(&idp->lock);
  48         return(p);
  49 }
  50
  51 static void free_layer(struct idr *idp, struct idr_layer *p)
  52 {
  53         /*
  54          * Depends on the return element being zeroed.
  55          */
  56         spin_lock(&idp->lock);
  57         p->ary[0] = idp->id_free;
  58         idp->id_free = p;
  59         idp->id_free_cnt++;
  60         spin_unlock(&idp->lock);
  61 }
  62
  63 /**
  64  * idr_pre_get - reserver resources for idr allocation
  65  * @idp:        idr handle
  66  * @gfp_mask:   memory allocation flags
  67  *
  68  * This function should be called prior to locking and calling the
  69  * following function.  It preallocates enough memory to satisfy
  70  * the worst possible allocation.
  71  *
  72  * If the system is REALLY out of memory this function returns 0,
  73  * otherwise 1.
  74  */
  75 int idr_pre_get(struct idr *idp, unsigned gfp_mask)
  76 {
  77         while (idp->id_free_cnt < IDR_FREE_MAX) {
  78                 struct idr_layer *new;
  79                 new = kmem_cache_alloc(idr_layer_cache, gfp_mask);
  80                 if(new == NULL)
  81                         return (0);
  82                 free_layer(idp, new);
  83         }
  84         return 1;
  85 }
  86 EXPORT_SYMBOL(idr_pre_get);
  87
  88 static int sub_alloc(struct idr *idp, void *ptr, int *starting_id)
  89 {
  90         int n, m, sh;
  91         struct idr_layer *p, *new;
  92         struct idr_layer *pa[MAX_LEVEL];
  93         int l, id;
  94         long bm;
  95
  96         id = *starting_id;
  97         p = idp->top;
  98         l = idp->layers;
  99         pa[l--] = NULL;
 100         while (1) {
 101                 /*
 102                  * We run around this while until we reach the leaf node...
 103                  */
 104                 n = (id >> (IDR_BITS*l)) & IDR_MASK;
 105                 bm = ~p->bitmap;
 106                 m = find_next_bit(&bm, IDR_SIZE, n);
 107                 if (m == IDR_SIZE) {
 108                         /* no space available go back to previous layer. */
 109                         l++;
 110                         id = (id | ((1 << (IDR_BITS*l))-1)) + 1;
 111                         if (!(p = pa[l])) {
 112                                 *starting_id = id;
 113                                 return -2;
 114                         }
 115                         continue;
 116                 }
 117                 if (m != n) {
 118                         sh = IDR_BITS*l;
 119                         id = ((id >> sh) ^ n ^ m) << sh;
 120                 }
 121                 if ((id >= MAX_ID_BIT) || (id < 0))
 122                         return -3;
 123                 if (l == 0)
 124                         break;
 125                 /*
 126                  * Create the layer below if it is missing.
 127                  */
 128                 if (!p->ary[m]) {
 129                         if (!(new = alloc_layer(idp)))
 130                                 return -1;
 131                         p->ary[m] = new;
 132                         p->count++;
 133                 }
 134                 pa[l--] = p;
 135                 p = p->ary[m];
 136         }
 137         /*
 138          * We have reached the leaf node, plant the
 139          * users pointer and return the raw id.
 140          */
 141         p->ary[m] = (struct idr_layer *)ptr;
 142         __set_bit(m, &p->bitmap);
 143         p->count++;
 144         /*
 145          * If this layer is full mark the bit in the layer above
 146          * to show that this part of the radix tree is full.
 147          * This may complete the layer above and require walking
 148          * up the radix tree.
 149          */
 150         n = id;
 151         while (p->bitmap == IDR_FULL) {
 152                 if (!(p = pa[++l]))
 153                         break;
 154                 n = n >> IDR_BITS;
 155                 __set_bit((n & IDR_MASK), &p->bitmap);
 156         }
 157         return(id);
 158 }
 159
 160 static int idr_get_new_above_int(struct idr *idp, void *ptr, int starting_id)
 161 {
 162         struct idr_layer *p, *new;
 163         int layers, v, id;
 164
 165         id = starting_id;
 166 build_up:
 167         p = idp->top;
 168         layers = idp->layers;
 169         if (unlikely(!p)) {
 170                 if (!(p = alloc_layer(idp)))
 171                         return -1;
 172                 layers = 1;
 173         }
 174         /*
 175          * Add a new layer to the top of the tree if the requested
 176          * id is larger than the currently allocated space.
 177          */
 178         while ((layers < (MAX_LEVEL - 1)) && (id >= (1 << (layers*IDR_BITS)))) {
 179                 layers++;
 180                 if (!p->count)
 181                         continue;
 182                 if (!(new = alloc_layer(idp))) {
 183                         /*
 184                          * The allocation failed.  If we built part of
 185                          * the structure tear it down.
 186                          */
 187                         for (new = p; p && p != idp->top; new = p) {
 188                                 p = p->ary[0];
 189                                 new->ary[0] = NULL;
 190                                 new->bitmap = new->count = 0;
 191                                 free_layer(idp, new);
 192                         }
 193                         return -1;
 194                 }
 195                 new->ary[0] = p;
 196                 new->count = 1;
 197                 if (p->bitmap == IDR_FULL)
 198                         __set_bit(0, &new->bitmap);
 199                 p = new;
 200         }
 201         idp->top = p;
 202         idp->layers = layers;
 203         v = sub_alloc(idp, ptr, &id);
 204         if (v == -2)
 205                 goto build_up;
 206         return(v);
 207 }
 208
 209 /**
 210  * idr_get_new_above - allocate new idr entry above a start id
 211  * @idp: idr handle
 212  * @ptr: pointer you want associated with the ide
 213  * @start_id: id to start search at
 214  * @id: pointer to the allocated handle
 215  *
 216  * This is the allocate id function.  It should be called with any
 217  * required locks.
 218  *
 219  * If memory is required, it will return -EAGAIN, you should unlock
 220  * and go back to the idr_pre_get() call.  If the idr is full, it will
 221  * return -ENOSPC.
 222  *
 223  * @id returns a value in the range 0 ... 0x7fffffff
 224  */
 225 int idr_get_new_above(struct idr *idp, void *ptr, int starting_id, int *id)
 226 {
 227         int rv;
 228         rv = idr_get_new_above_int(idp, ptr, starting_id);
 229         /*
 230          * This is a cheap hack until the IDR code can be fixed to
 231          * return proper error values.
 232          */
 233         if (rv < 0) {
 234                 if (rv == -1)
 235                         return -EAGAIN;
 236                 else /* Will be -3 */
 237                         return -ENOSPC;
 238         }
 239         *id = rv;
 240         return 0;
 241 }
 242 EXPORT_SYMBOL(idr_get_new_above);
 243
 244 /**
 245  * idr_get_new - allocate new idr entry
 246  * @idp: idr handle
 247  * @ptr: pointer you want associated with the ide
 248  * @id: pointer to the allocated handle
 249  *
 250  * This is the allocate id function.  It should be called with any
 251  * required locks.
 252  *
 253  * If memory is required, it will return -EAGAIN, you should unlock
 254  * and go back to the idr_pre_get() call.  If the idr is full, it will
 255  * return -ENOSPC.
 256  *
 257  * @id returns a value in the range 0 ... 0x7fffffff
 258  */
 259 int idr_get_new(struct idr *idp, void *ptr, int *id)
 260 {
 261         int rv;
 262         rv = idr_get_new_above_int(idp, ptr, 0);
 263         /*
 264          * This is a cheap hack until the IDR code can be fixed to
 265          * return proper error values.
 266          */
 267         if (rv < 0) {
 268                 if (rv == -1)
 269                         return -EAGAIN;
 270                 else /* Will be -3 */
 271                         return -ENOSPC;
 272         }
 273         *id = rv;
 274         return 0;
 275 }
 276 EXPORT_SYMBOL(idr_get_new);
 277
 278 static void idr_remove_warning(int id)
 279 {
 280         printk("idr_remove called for id=%d which is not allocated.\n", id);
 281         dump_stack();
 282 }
 283
 284 static void sub_remove(struct idr *idp, int shift, int id)
 285 {
 286         struct idr_layer *p = idp->top;
 287         struct idr_layer **pa[MAX_LEVEL];
 288         struct idr_layer ***paa = &pa[0];
 289         int n;
 290
 291         *paa = NULL;
 292         *++paa = &idp->top;
 293
 294         while ((shift > 0) && p) {
 295                 n = (id >> shift) & IDR_MASK;
 296                 __clear_bit(n, &p->bitmap);
 297                 *++paa = &p->ary[n];
 298                 p = p->ary[n];
 299                 shift -= IDR_BITS;
 300         }
 301         n = id & IDR_MASK;
 302         if (likely(p != NULL && test_bit(n, &p->bitmap))){
 303                 __clear_bit(n, &p->bitmap);
 304                 p->ary[n] = NULL;
 305                 while(*paa && ! --((**paa)->count)){
 306                         free_layer(idp, **paa);
 307                         **paa-- = NULL;
 308                 }
 309                 if ( ! *paa )
 310                         idp->layers = 0;
 311         } else {
 312                 idr_remove_warning(id);
 313         }
 314 }
 315
 316 /**
 317  * idr_remove - remove the given id and free it's slot
 318  * idp: idr handle
 319  * id: uniqueue key
 320  */
 321 void idr_remove(struct idr *idp, int id)
 322 {
 323         struct idr_layer *p;
 324
 325         /* Mask off upper bits we don't use for the search. */
 326         id &= MAX_ID_MASK;
 327
 328         sub_remove(idp, (idp->layers - 1) * IDR_BITS, id);
 329         if ( idp->top && idp->top->count == 1 &&
 330              (idp->layers > 1) &&
 331              idp->top->ary[0]){  // We can drop a layer
 332
 333                 p = idp->top->ary[0];
 334                 idp->top->bitmap = idp->top->count = 0;
 335                 free_layer(idp, idp->top);
 336                 idp->top = p;
 337                 --idp->layers;
 338         }
 339         while (idp->id_free_cnt >= IDR_FREE_MAX) {
 340
 341                 p = alloc_layer(idp);
 342                 kmem_cache_free(idr_layer_cache, p);
 343                 return;
 344         }
 345 }
 346 EXPORT_SYMBOL(idr_remove);
 347
 348 /**
 349  * idr_find - return pointer for given id
 350  * @idp: idr handle
 351  * @id: lookup key
 352  *
 353  * Return the pointer given the id it has been registered with.  A %NULL
 354  * return indicates that @id is not valid or you passed %NULL in
 355  * idr_get_new().
 356  *
 357  * The caller must serialize idr_find() vs idr_get_new() and idr_remove().
 358  */
 359 void *idr_find(struct idr *idp, int id)
 360 {
 361         int n;
 362         struct idr_layer *p;
 363
 364         n = idp->layers * IDR_BITS;
 365         p = idp->top;
 366
 367         /* Mask off upper bits we don't use for the search. */
 368         id &= MAX_ID_MASK;
 369
 370         if (id >= (1 << n))
 371                 return NULL;
 372
 373         while (n > 0 && p) {
 374                 n -= IDR_BITS;
 375                 p = p->ary[(id >> n) & IDR_MASK];
 376         }
 377         return((void *)p);
 378 }
 379 EXPORT_SYMBOL(idr_find);
 380
 381 static void idr_cache_ctor(void * idr_layer,
 382                            kmem_cache_t *idr_layer_cache, unsigned long flags)
 383 {
 384         memset(idr_layer, 0, sizeof(struct idr_layer));
 385 }
 386
 387 static  int init_id_cache(void)
 388 {
 389         if (!idr_layer_cache)
 390                 idr_layer_cache = kmem_cache_create("idr_layer_cache",
 391                         sizeof(struct idr_layer), 0, 0, idr_cache_ctor, NULL);
 392         return 0;
 393 }
 394
 395 /**
 396  * idr_init - initialize idr handle
 397  * @idp:        idr handle
 398  *
 399  * This function is use to set up the handle (@idp) that you will pass
 400  * to the rest of the functions.
 401  */
 402 void idr_init(struct idr *idp)
 403 {
 404         init_id_cache();
 405         memset(idp, 0, sizeof(struct idr));
 406         spin_lock_init(&idp->lock);
 407 }
 408 EXPORT_SYMBOL(idr_init);