release/src/router/tor/src/common/memarea.c

   1 /* Copyright (c) 2008-2013, The Tor Project, Inc. */
   2 /* See LICENSE for licensing information */
   3
   4 /** \file memarea.c
   5  * \brief Implementation for memarea_t, an allocator for allocating lots of
   6  * small objects that will be freed all at once.
   7  */
   8
   9 #include "orconfig.h"
  10 #include <stdlib.h>
  11 #include "memarea.h"
  12 #include "util.h"
  13 #include "compat.h"
  14 #include "torlog.h"
  15
  16 /** If true, we try to detect any attempts to write beyond the length of a
  17  * memarea. */
  18 #define USE_SENTINELS
  19
  20 /** All returned pointers should be aligned to the nearest multiple of this
  21  * value. */
  22 #define MEMAREA_ALIGN SIZEOF_VOID_P
  23
  24 #if MEMAREA_ALIGN == 4
  25 #define MEMAREA_ALIGN_MASK 3lu
  26 #elif MEMAREA_ALIGN == 8
  27 #define MEMAREA_ALIGN_MASK 7lu
  28 #else
  29 #error "void* is neither 4 nor 8 bytes long. I don't know how to align stuff."
  30 #endif
  31
  32 #if defined(__GNUC__) && defined(FLEXIBLE_ARRAY_MEMBER)
  33 #define USE_ALIGNED_ATTRIBUTE
  34 #define U_MEM mem
  35 #else
  36 #define U_MEM u.mem
  37 #endif
  38
  39 #ifdef USE_SENTINELS
  40 /** Magic value that we stick at the end of a memarea so we can make sure
  41  * there are no run-off-the-end bugs. */
  42 #define SENTINEL_VAL 0x90806622u
  43 /** How many bytes per area do we devote to the sentinel? */
  44 #define SENTINEL_LEN sizeof(uint32_t)
  45 /** Given a mem_area_chunk_t with SENTINEL_LEN extra bytes allocated at the
  46  * end, set those bytes. */
  47 #define SET_SENTINEL(chunk)                                     \
  48   STMT_BEGIN                                                    \
  49   set_uint32( &(chunk)->U_MEM[chunk->mem_size], SENTINEL_VAL ); \
  50   STMT_END
  51 /** Assert that the sentinel on a memarea is set correctly. */
  52 #define CHECK_SENTINEL(chunk)                                           \
  53   STMT_BEGIN                                                            \
  54   uint32_t sent_val = get_uint32(&(chunk)->U_MEM[chunk->mem_size]);     \
  55   tor_assert(sent_val == SENTINEL_VAL);                                 \
  56   STMT_END
  57 #else
  58 #define SENTINEL_LEN 0
  59 #define SET_SENTINEL(chunk) STMT_NIL
  60 #define CHECK_SENTINEL(chunk) STMT_NIL
  61 #endif
  62
  63 /** Increment <b>ptr</b> until it is aligned to MEMAREA_ALIGN. */
  64 static INLINE void *
  65 realign_pointer(void *ptr)
  66 {
  67   uintptr_t x = (uintptr_t)ptr;
  68   x = (x+MEMAREA_ALIGN_MASK) & ~MEMAREA_ALIGN_MASK;
  69   /* Reinstate this if bug 930 ever reappears
  70   tor_assert(((void*)x) >= ptr);
  71   */
  72   return (void*)x;
  73 }
  74
  75 /** Implements part of a memarea.  New memory is carved off from chunk->mem in
  76  * increasing order until a request is too big, at which point a new chunk is
  77  * allocated. */
  78 typedef struct memarea_chunk_t {
  79   /** Next chunk in this area. Only kept around so we can free it. */
  80   struct memarea_chunk_t *next_chunk;
  81   size_t mem_size; /**< How much RAM is available in mem, total? */
  82   char *next_mem; /**< Next position in mem to allocate data at.  If it's
  83                    * greater than or equal to mem+mem_size, this chunk is
  84                    * full. */
  85 #ifdef USE_ALIGNED_ATTRIBUTE
  86   char mem[FLEXIBLE_ARRAY_MEMBER] __attribute__((aligned(MEMAREA_ALIGN)));
  87 #else
  88   union {
  89     char mem[1]; /**< Memory space in this chunk.  */
  90     void *void_for_alignment_; /**< Dummy; used to make sure mem is aligned. */
  91   } u;
  92 #endif
  93 } memarea_chunk_t;
  94
  95 /** How many bytes are needed for overhead before we get to the memory part
  96  * of a chunk? */
  97 #define CHUNK_HEADER_SIZE STRUCT_OFFSET(memarea_chunk_t, U_MEM)
  98
  99 /** What's the smallest that we'll allocate a chunk? */
 100 #define CHUNK_SIZE 4096
 101
 102 /** A memarea_t is an allocation region for a set of small memory requests
 103  * that will all be freed at once. */
 104 struct memarea_t {
 105   memarea_chunk_t *first; /**< Top of the chunk stack: never NULL. */
 106 };
 107
 108 /** How many chunks will we put into the freelist before freeing them? */
 109 #define MAX_FREELIST_LEN 4
 110 /** The number of memarea chunks currently in our freelist. */
 111 static int freelist_len=0;
 112 /** A linked list of unused memory area chunks.  Used to prevent us from
 113  * spinning in malloc/free loops. */
 114 static memarea_chunk_t *freelist = NULL;
 115
 116 /** Helper: allocate a new memarea chunk of around <b>chunk_size</b> bytes. */
 117 static memarea_chunk_t *
 118 alloc_chunk(size_t sz, int freelist_ok)
 119 {
 120   tor_assert(sz < SIZE_T_CEILING);
 121   if (freelist && freelist_ok) {
 122     memarea_chunk_t *res = freelist;
 123     freelist = res->next_chunk;
 124     res->next_chunk = NULL;
 125     --freelist_len;
 126     CHECK_SENTINEL(res);
 127     return res;
 128   } else {
 129     size_t chunk_size = freelist_ok ? CHUNK_SIZE : sz;
 130     memarea_chunk_t *res;
 131     chunk_size += SENTINEL_LEN;
 132     res = tor_malloc(chunk_size);
 133     res->next_chunk = NULL;
 134     res->mem_size = chunk_size - CHUNK_HEADER_SIZE - SENTINEL_LEN;
 135     res->next_mem = res->U_MEM;
 136     tor_assert(res->next_mem+res->mem_size+SENTINEL_LEN ==
 137                ((char*)res)+chunk_size);
 138     tor_assert(realign_pointer(res->next_mem) == res->next_mem);
 139     SET_SENTINEL(res);
 140     return res;
 141   }
 142 }
 143
 144 /** Release <b>chunk</b> from a memarea, either by adding it to the freelist
 145  * or by freeing it if the freelist is already too big. */
 146 static void
 147 chunk_free_unchecked(memarea_chunk_t *chunk)
 148 {
 149   CHECK_SENTINEL(chunk);
 150   if (freelist_len < MAX_FREELIST_LEN) {
 151     ++freelist_len;
 152     chunk->next_chunk = freelist;
 153     freelist = chunk;
 154     chunk->next_mem = chunk->U_MEM;
 155   } else {
 156     tor_free(chunk);
 157   }
 158 }
 159
 160 /** Allocate and return new memarea. */
 161 memarea_t *
 162 memarea_new(void)
 163 {
 164   memarea_t *head = tor_malloc(sizeof(memarea_t));
 165   head->first = alloc_chunk(CHUNK_SIZE, 1);
 166   return head;
 167 }
 168
 169 /** Free <b>area</b>, invalidating all pointers returned from memarea_alloc()
 170  * and friends for this area */
 171 void
 172 memarea_drop_all(memarea_t *area)
 173 {
 174   memarea_chunk_t *chunk, *next;
 175   for (chunk = area->first; chunk; chunk = next) {
 176     next = chunk->next_chunk;
 177     chunk_free_unchecked(chunk);
 178   }
 179   area->first = NULL; /*fail fast on */
 180   tor_free(area);
 181 }
 182
 183 /** Forget about having allocated anything in <b>area</b>, and free some of
 184  * the backing storage associated with it, as appropriate. Invalidates all
 185  * pointers returned from memarea_alloc() for this area. */
 186 void
 187 memarea_clear(memarea_t *area)
 188 {
 189   memarea_chunk_t *chunk, *next;
 190   if (area->first->next_chunk) {
 191     for (chunk = area->first->next_chunk; chunk; chunk = next) {
 192       next = chunk->next_chunk;
 193       chunk_free_unchecked(chunk);
 194     }
 195     area->first->next_chunk = NULL;
 196   }
 197   area->first->next_mem = area->first->U_MEM;
 198 }
 199
 200 /** Remove all unused memarea chunks from the internal freelist. */
 201 void
 202 memarea_clear_freelist(void)
 203 {
 204   memarea_chunk_t *chunk, *next;
 205   freelist_len = 0;
 206   for (chunk = freelist; chunk; chunk = next) {
 207     next = chunk->next_chunk;
 208     tor_free(chunk);
 209   }
 210   freelist = NULL;
 211 }
 212
 213 /** Return true iff <b>p</b> is in a range that has been returned by an
 214  * allocation from <b>area</b>. */
 215 int
 216 memarea_owns_ptr(const memarea_t *area, const void *p)
 217 {
 218   memarea_chunk_t *chunk;
 219   const char *ptr = p;
 220   for (chunk = area->first; chunk; chunk = chunk->next_chunk) {
 221     if (ptr >= chunk->U_MEM && ptr < chunk->next_mem)
 222       return 1;
 223   }
 224   return 0;
 225 }
 226
 227 /** Return a pointer to a chunk of memory in <b>area</b> of at least <b>sz</b>
 228  * bytes.  <b>sz</b> should be significantly smaller than the area's chunk
 229  * size, though we can deal if it isn't. */
 230 void *
 231 memarea_alloc(memarea_t *area, size_t sz)
 232 {
 233   memarea_chunk_t *chunk = area->first;
 234   char *result;
 235   tor_assert(chunk);
 236   CHECK_SENTINEL(chunk);
 237   tor_assert(sz < SIZE_T_CEILING);
 238   if (sz == 0)
 239     sz = 1;
 240   if (chunk->next_mem+sz > chunk->U_MEM+chunk->mem_size) {
 241     if (sz+CHUNK_HEADER_SIZE >= CHUNK_SIZE) {
 242       /* This allocation is too big.  Stick it in a special chunk, and put
 243        * that chunk second in the list. */
 244       memarea_chunk_t *new_chunk = alloc_chunk(sz+CHUNK_HEADER_SIZE, 0);
 245       new_chunk->next_chunk = chunk->next_chunk;
 246       chunk->next_chunk = new_chunk;
 247       chunk = new_chunk;
 248     } else {
 249       memarea_chunk_t *new_chunk = alloc_chunk(CHUNK_SIZE, 1);
 250       new_chunk->next_chunk = chunk;
 251       area->first = chunk = new_chunk;
 252     }
 253     tor_assert(chunk->mem_size >= sz);
 254   }
 255   result = chunk->next_mem;
 256   chunk->next_mem = chunk->next_mem + sz;
 257   /* Reinstate these if bug 930 ever comes back
 258   tor_assert(chunk->next_mem >= chunk->U_MEM);
 259   tor_assert(chunk->next_mem <= chunk->U_MEM+chunk->mem_size);
 260   */
 261   chunk->next_mem = realign_pointer(chunk->next_mem);
 262   return result;
 263 }
 264
 265 /** As memarea_alloc(), but clears the memory it returns. */
 266 void *
 267 memarea_alloc_zero(memarea_t *area, size_t sz)
 268 {
 269   void *result = memarea_alloc(area, sz);
 270   memset(result, 0, sz);
 271   return result;
 272 }
 273
 274 /** As memdup, but returns the memory from <b>area</b>. */
 275 void *
 276 memarea_memdup(memarea_t *area, const void *s, size_t n)
 277 {
 278   char *result = memarea_alloc(area, n);
 279   memcpy(result, s, n);
 280   return result;
 281 }
 282
 283 /** As strdup, but returns the memory from <b>area</b>. */
 284 char *
 285 memarea_strdup(memarea_t *area, const char *s)
 286 {
 287   return memarea_memdup(area, s, strlen(s)+1);
 288 }
 289
 290 /** As strndup, but returns the memory from <b>area</b>. */
 291 char *
 292 memarea_strndup(memarea_t *area, const char *s, size_t n)
 293 {
 294   size_t ln = 0;
 295   char *result;
 296   tor_assert(n < SIZE_T_CEILING);
 297   for (ln = 0; ln < n && s[ln]; ++ln)
 298     ;
 299   result = memarea_alloc(area, ln+1);
 300   memcpy(result, s, ln);
 301   result[ln]='\0';
 302   return result;
 303 }
 304
 305 /** Set <b>allocated_out</b> to the number of bytes allocated in <b>area</b>,
 306  * and <b>used_out</b> to the number of bytes currently used. */
 307 void
 308 memarea_get_stats(memarea_t *area, size_t *allocated_out, size_t *used_out)
 309 {
 310   size_t a = 0, u = 0;
 311   memarea_chunk_t *chunk;
 312   for (chunk = area->first; chunk; chunk = chunk->next_chunk) {
 313     CHECK_SENTINEL(chunk);
 314     a += CHUNK_HEADER_SIZE + chunk->mem_size;
 315     tor_assert(chunk->next_mem >= chunk->U_MEM);
 316     u += CHUNK_HEADER_SIZE + (chunk->next_mem - chunk->U_MEM);
 317   }
 318   *allocated_out = a;
 319   *used_out = u;
 320 }
 321
 322 /** Assert that <b>area</b> is okay. */
 323 void
 324 memarea_assert_ok(memarea_t *area)
 325 {
 326   memarea_chunk_t *chunk;
 327   tor_assert(area->first);
 328
 329   for (chunk = area->first; chunk; chunk = chunk->next_chunk) {
 330     CHECK_SENTINEL(chunk);
 331     tor_assert(chunk->next_mem >= chunk->U_MEM);
 332     tor_assert(chunk->next_mem <=
 333           (char*) realign_pointer(chunk->U_MEM+chunk->mem_size));
 334   }
 335 }
 336