Loading...
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 | /*
* linux/kernel/id.c
*
* 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.
*
* 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.
* Modified by George Anzinger to reuse immediately and to use
* find bit instructions. Also removed _irq on spinlocks.
* So here is what this bit of code does:
* 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.
* You can release ids at any time. When all ids are released, most of
* the memory is returned (we keep IDR_FREE_MAX) in a local pool so we
* don't need to go to the memory "store" during an id allocate, just
* so you don't need to be too concerned about locking and conflicts
* with the slab allocator.
* A word on reuse. We reuse empty id slots as soon as we can, always
* using the lowest one available. But we also merge a counter in the
* high bits of the id. The counter is RESERVED_ID_BITS (8 at this time)
* long. This means that if you allocate and release the same id in a
* loop we will reuse an id after about 256 times around the loop. The
* word about is used here as we will NOT return a valid id of -1 so if
* you loop on the largest possible id (and that is 24 bits, wow!) we
* will kick the counter to avoid -1. (Paranoid? You bet!)
*
* What you need to do is, since we don't keep the counter as part of
* id / ptr pair, to keep a copy of it in the pointed to structure
* (or else where) so that when you ask for a ptr you can varify that
* the returned ptr is correct by comparing the id it contains with the one
* you asked for. In other words, we only did half the reuse protection.
* Since the code depends on your code doing this check, we ignore high
* order bits in the id, not just the count, but bits that would, if used,
* index outside of the allocated ids. In other words, if the largest id
* currently allocated is 32 a look up will only look at the low 5 bits of
* the id. Since you will want to keep this id in the structure anyway
* (if for no other reason than to be able to eliminate the id when the
* structure is found in some other way) this seems reasonable. If you
* really think otherwise, the code to check these bits here, it is just
* disabled with a #if 0.
* So here are the complete details:
* include <linux/idr.h>
* void idr_init(struct idr *idp)
* This function is use to set up the handle (idp) that you will pass
* to the rest of the functions. The structure is defined in the
* header.
* int idr_pre_get(struct idr *idp)
* This function should be called prior to locking and calling the
* following function. It pre allocates enough memory to satisfy the
* worst possible allocation. It can sleep, so must not be called
* with any spinlocks held. If the system is REALLY out of memory
* this function returns 0, other wise 1.
* int idr_get_new(struct idr *idp, void *ptr);
* This is the allocate id function. It should be called with any
* required locks. In fact, in the SMP case, you MUST lock prior to
* calling this function to avoid possible out of memory problems. If
* memory is required, it will return a -1, in which case you should
* unlock and go back to the idr_pre_get() call. ptr is the pointer
* you want associated with the id. In other words:
* void *idr_find(struct idr *idp, int id);
* returns the "ptr", given the id. A NULL return indicates that the
* id is not valid (or you passed NULL in the idr_get_new(), shame on
* you). This function must be called with a spinlock that prevents
* calling either idr_get_new() or idr_remove() or idr_find() while it
* is working.
* void idr_remove(struct idr *idp, int id);
* removes the given id, freeing that slot and any memory that may
* now be unused. See idr_find() for locking restrictions.
*/
#ifndef TEST // to test in user space...
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/module.h>
#endif
#include <linux/string.h>
#include <linux/idr.h>
static kmem_cache_t *idr_layer_cache;
static inline struct idr_layer *alloc_layer(struct idr *idp)
{
struct idr_layer *p;
spin_lock(&idp->lock);
if (!(p = idp->id_free))
BUG();
idp->id_free = p->ary[0];
idp->id_free_cnt--;
p->ary[0] = 0;
spin_unlock(&idp->lock);
return(p);
}
static inline void free_layer(struct idr *idp, struct idr_layer *p)
{
/*
* Depends on the return element being zeroed.
*/
spin_lock(&idp->lock);
p->ary[0] = idp->id_free;
idp->id_free = p;
idp->id_free_cnt++;
spin_unlock(&idp->lock);
}
int idr_pre_get(struct idr *idp)
{
while (idp->id_free_cnt < idp->layers + 1) {
struct idr_layer *new;
new = kmem_cache_alloc(idr_layer_cache, GFP_KERNEL);
if(new == NULL)
return (0);
free_layer(idp, new);
}
return 1;
}
EXPORT_SYMBOL(idr_pre_get);
static inline int sub_alloc(struct idr *idp, int shift, void *ptr)
{
int n, v = 0;
struct idr_layer *p;
struct idr_layer **pa[MAX_LEVEL];
struct idr_layer ***paa = &pa[0];
*paa = NULL;
*++paa = &idp->top;
/*
* By keeping each pointer in an array we can do the
* "after" recursion processing. In this case, that means
* we can update the upper level bit map.
*/
while (1){
p = **paa;
n = ffz(p->bitmap);
if (shift){
/*
* We run around this while until we
* reach the leaf node...
*/
if (!p->ary[n]){
/*
* If no node, allocate one, AFTER
* we insure that we will not
* intrude on the reserved bit field.
*/
if ((n << shift) >= MAX_ID_BIT)
return -1;
p->ary[n] = alloc_layer(idp);
p->count++;
}
*++paa = &p->ary[n];
v += (n << shift);
shift -= IDR_BITS;
} else {
/*
* We have reached the leaf node, plant the
* users pointer and return the raw id.
*/
p->ary[n] = (struct idr_layer *)ptr;
__set_bit(n, &p->bitmap);
v += n;
p->count++;
/*
* This is the post recursion processing. Once
* we find a bitmap that is not full we are
* done
*/
while (*(paa-1) && (**paa)->bitmap == IDR_FULL){
n = *paa - &(**(paa-1))->ary[0];
__set_bit(n, &(**--paa)->bitmap);
}
return(v);
}
}
}
int idr_get_new(struct idr *idp, void *ptr)
{
int v;
if (idp->id_free_cnt < idp->layers + 1)
return (-1);
/*
* Add a new layer if the array is full
*/
if (unlikely(!idp->top || idp->top->bitmap == IDR_FULL)){
/*
* This is a bit different than the lower layers because
* we have one branch already allocated and full.
*/
struct idr_layer *new = alloc_layer(idp);
new->ary[0] = idp->top;
if ( idp->top)
++new->count;
idp->top = new;
if ( idp->layers++ )
__set_bit(0, &new->bitmap);
}
v = sub_alloc(idp, (idp->layers - 1) * IDR_BITS, ptr);
if ( likely(v >= 0 )){
idp->count++;
v += (idp->count << MAX_ID_SHIFT);
if ( unlikely( v == -1 ))
v += (1L << MAX_ID_SHIFT);
}
return(v);
}
EXPORT_SYMBOL(idr_get_new);
static inline 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 (likely(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;
}
}
void idr_remove(struct idr *idp, int id)
{
struct idr_layer *p;
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);
kmem_cache_free(idr_layer_cache, p);
return;
}
}
EXPORT_SYMBOL(idr_remove);
void *idr_find(struct idr *idp, int id)
{
int n;
struct idr_layer *p;
n = idp->layers * IDR_BITS;
p = idp->top;
#if 0
/*
* This tests to see if bits outside the current tree are
* present. If so, tain't one of ours!
*/
if ( unlikely( (id & ~(~0 << MAX_ID_SHIFT)) >> (n + IDR_BITS)))
return NULL;
#endif
while (n > 0 && p) {
n -= IDR_BITS;
p = p->ary[(id >> n) & IDR_MASK];
}
return((void *)p);
}
EXPORT_SYMBOL(idr_find);
static void idr_cache_ctor(void * idr_layer,
kmem_cache_t *idr_layer_cache, unsigned long flags)
{
memset(idr_layer, 0, sizeof(struct idr_layer));
}
static int init_id_cache(void)
{
if (!idr_layer_cache)
idr_layer_cache = kmem_cache_create("idr_layer_cache",
sizeof(struct idr_layer), 0, 0, idr_cache_ctor, 0);
return 0;
}
void idr_init(struct idr *idp)
{
init_id_cache();
memset(idp, 0, sizeof(struct idr));
spin_lock_init(&idp->lock);
}
EXPORT_SYMBOL(idr_init);
|