block/qcow2-cache.c

   1 /*
   2  * L2/refcount table cache for the QCOW2 format
   3  *
   4  * Copyright (c) 2010 Kevin Wolf <kwolf@redhat.com>
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include "qemu/osdep.h"
  26 #include "qemu/memalign.h"
  27 #include "qcow2.h"
  28 #include "trace.h"
  29
  30 typedef struct Qcow2CachedTable {
  31     int64_t  offset;
  32     uint64_t lru_counter;
  33     int      ref;
  34     bool     dirty;
  35 } Qcow2CachedTable;
  36
  37 struct Qcow2Cache {
  38     Qcow2CachedTable       *entries;
  39     struct Qcow2Cache      *depends;
  40     int                     size;
  41     int                     table_size;
  42     bool                    depends_on_flush;
  43     void                   *table_array;
  44     uint64_t                lru_counter;
  45     uint64_t                cache_clean_lru_counter;
  46 };
  47
  48 static inline void *qcow2_cache_get_table_addr(Qcow2Cache *c, int table)
  49 {
  50     return (uint8_t *) c->table_array + (size_t) table * c->table_size;
  51 }
  52
  53 static inline int qcow2_cache_get_table_idx(Qcow2Cache *c, void *table)
  54 {
  55     ptrdiff_t table_offset = (uint8_t *) table - (uint8_t *) c->table_array;
  56     int idx = table_offset / c->table_size;
  57     assert(idx >= 0 && idx < c->size && table_offset % c->table_size == 0);
  58     return idx;
  59 }
  60
  61 static inline const char *qcow2_cache_get_name(BDRVQcow2State *s, Qcow2Cache *c)
  62 {
  63     if (c == s->refcount_block_cache) {
  64         return "refcount block";
  65     } else if (c == s->l2_table_cache) {
  66         return "L2 table";
  67     } else {
  68         /* Do not abort, because this is not critical */
  69         return "unknown";
  70     }
  71 }
  72
  73 static void qcow2_cache_table_release(Qcow2Cache *c, int i, int num_tables)
  74 {
  75 /* Using MADV_DONTNEED to discard memory is a Linux-specific feature */
  76 #ifdef CONFIG_LINUX
  77     void *t = qcow2_cache_get_table_addr(c, i);
  78     int align = qemu_real_host_page_size();
  79     size_t mem_size = (size_t) c->table_size * num_tables;
  80     size_t offset = QEMU_ALIGN_UP((uintptr_t) t, align) - (uintptr_t) t;
  81     size_t length = QEMU_ALIGN_DOWN(mem_size - offset, align);
  82     if (mem_size > offset && length > 0) {
  83         madvise((uint8_t *) t + offset, length, MADV_DONTNEED);
  84     }
  85 #endif
  86 }
  87
  88 static inline bool can_clean_entry(Qcow2Cache *c, int i)
  89 {
  90     Qcow2CachedTable *t = &c->entries[i];
  91     return t->ref == 0 && !t->dirty && t->offset != 0 &&
  92         t->lru_counter <= c->cache_clean_lru_counter;
  93 }
  94
  95 void qcow2_cache_clean_unused(Qcow2Cache *c)
  96 {
  97     int i = 0;
  98     while (i < c->size) {
  99         int to_clean = 0;
 100
 101         /* Skip the entries that we don't need to clean */
 102         while (i < c->size && !can_clean_entry(c, i)) {
 103             i++;
 104         }
 105
 106         /* And count how many we can clean in a row */
 107         while (i < c->size && can_clean_entry(c, i)) {
 108             c->entries[i].offset = 0;
 109             c->entries[i].lru_counter = 0;
 110             i++;
 111             to_clean++;
 112         }
 113
 114         if (to_clean > 0) {
 115             qcow2_cache_table_release(c, i - to_clean, to_clean);
 116         }
 117     }
 118
 119     c->cache_clean_lru_counter = c->lru_counter;
 120 }
 121
 122 Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables,
 123                                unsigned table_size)
 124 {
 125     BDRVQcow2State *s = bs->opaque;
 126     Qcow2Cache *c;
 127
 128     assert(num_tables > 0);
 129     assert(is_power_of_2(table_size));
 130     assert(table_size >= (1 << MIN_CLUSTER_BITS));
 131     assert(table_size <= s->cluster_size);
 132
 133     c = g_new0(Qcow2Cache, 1);
 134     c->size = num_tables;
 135     c->table_size = table_size;
 136     c->entries = g_try_new0(Qcow2CachedTable, num_tables);
 137     c->table_array = qemu_try_blockalign(bs->file->bs,
 138                                          (size_t) num_tables * c->table_size);
 139
 140     if (!c->entries || !c->table_array) {
 141         qemu_vfree(c->table_array);
 142         g_free(c->entries);
 143         g_free(c);
 144         c = NULL;
 145     }
 146
 147     return c;
 148 }
 149
 150 int qcow2_cache_destroy(Qcow2Cache *c)
 151 {
 152     int i;
 153
 154     for (i = 0; i < c->size; i++) {
 155         assert(c->entries[i].ref == 0);
 156     }
 157
 158     qemu_vfree(c->table_array);
 159     g_free(c->entries);
 160     g_free(c);
 161
 162     return 0;
 163 }
 164
 165 static int qcow2_cache_flush_dependency(BlockDriverState *bs, Qcow2Cache *c)
 166 {
 167     int ret;
 168
 169     ret = qcow2_cache_flush(bs, c->depends);
 170     if (ret < 0) {
 171         return ret;
 172     }
 173
 174     c->depends = NULL;
 175     c->depends_on_flush = false;
 176
 177     return 0;
 178 }
 179
 180 static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i)
 181 {
 182     BDRVQcow2State *s = bs->opaque;
 183     int ret = 0;
 184
 185     if (!c->entries[i].dirty || !c->entries[i].offset) {
 186         return 0;
 187     }
 188
 189     trace_qcow2_cache_entry_flush(qemu_coroutine_self(),
 190                                   c == s->l2_table_cache, i);
 191
 192     if (c->depends) {
 193         ret = qcow2_cache_flush_dependency(bs, c);
 194     } else if (c->depends_on_flush) {
 195         ret = bdrv_flush(bs->file->bs);
 196         if (ret >= 0) {
 197             c->depends_on_flush = false;
 198         }
 199     }
 200
 201     if (ret < 0) {
 202         return ret;
 203     }
 204
 205     if (c == s->refcount_block_cache) {
 206         ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_REFCOUNT_BLOCK,
 207                 c->entries[i].offset, c->table_size, false);
 208     } else if (c == s->l2_table_cache) {
 209         ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L2,
 210                 c->entries[i].offset, c->table_size, false);
 211     } else {
 212         ret = qcow2_pre_write_overlap_check(bs, 0,
 213                 c->entries[i].offset, c->table_size, false);
 214     }
 215
 216     if (ret < 0) {
 217         return ret;
 218     }
 219
 220     if (c == s->refcount_block_cache) {
 221         BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_UPDATE_PART);
 222     } else if (c == s->l2_table_cache) {
 223         BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE);
 224     }
 225
 226     ret = bdrv_pwrite(bs->file, c->entries[i].offset,
 227                       qcow2_cache_get_table_addr(c, i), c->table_size);
 228     if (ret < 0) {
 229         return ret;
 230     }
 231
 232     c->entries[i].dirty = false;
 233
 234     return 0;
 235 }
 236
 237 int qcow2_cache_write(BlockDriverState *bs, Qcow2Cache *c)
 238 {
 239     BDRVQcow2State *s = bs->opaque;
 240     int result = 0;
 241     int ret;
 242     int i;
 243
 244     trace_qcow2_cache_flush(qemu_coroutine_self(), c == s->l2_table_cache);
 245
 246     for (i = 0; i < c->size; i++) {
 247         ret = qcow2_cache_entry_flush(bs, c, i);
 248         if (ret < 0 && result != -ENOSPC) {
 249             result = ret;
 250         }
 251     }
 252
 253     return result;
 254 }
 255
 256 int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c)
 257 {
 258     int result = qcow2_cache_write(bs, c);
 259
 260     if (result == 0) {
 261         int ret = bdrv_flush(bs->file->bs);
 262         if (ret < 0) {
 263             result = ret;
 264         }
 265     }
 266
 267     return result;
 268 }
 269
 270 int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c,
 271     Qcow2Cache *dependency)
 272 {
 273     int ret;
 274
 275     if (dependency->depends) {
 276         ret = qcow2_cache_flush_dependency(bs, dependency);
 277         if (ret < 0) {
 278             return ret;
 279         }
 280     }
 281
 282     if (c->depends && (c->depends != dependency)) {
 283         ret = qcow2_cache_flush_dependency(bs, c);
 284         if (ret < 0) {
 285             return ret;
 286         }
 287     }
 288
 289     c->depends = dependency;
 290     return 0;
 291 }
 292
 293 void qcow2_cache_depends_on_flush(Qcow2Cache *c)
 294 {
 295     c->depends_on_flush = true;
 296 }
 297
 298 int qcow2_cache_empty(BlockDriverState *bs, Qcow2Cache *c)
 299 {
 300     int ret, i;
 301
 302     ret = qcow2_cache_flush(bs, c);
 303     if (ret < 0) {
 304         return ret;
 305     }
 306
 307     for (i = 0; i < c->size; i++) {
 308         assert(c->entries[i].ref == 0);
 309         c->entries[i].offset = 0;
 310         c->entries[i].lru_counter = 0;
 311     }
 312
 313     qcow2_cache_table_release(c, 0, c->size);
 314
 315     c->lru_counter = 0;
 316
 317     return 0;
 318 }
 319
 320 static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c,
 321     uint64_t offset, void **table, bool read_from_disk)
 322 {
 323     BDRVQcow2State *s = bs->opaque;
 324     int i;
 325     int ret;
 326     int lookup_index;
 327     uint64_t min_lru_counter = UINT64_MAX;
 328     int min_lru_index = -1;
 329
 330     assert(offset != 0);
 331
 332     trace_qcow2_cache_get(qemu_coroutine_self(), c == s->l2_table_cache,
 333                           offset, read_from_disk);
 334
 335     if (!QEMU_IS_ALIGNED(offset, c->table_size)) {
 336         qcow2_signal_corruption(bs, true, -1, -1, "Cannot get entry from %s "
 337                                 "cache: Offset %#" PRIx64 " is unaligned",
 338                                 qcow2_cache_get_name(s, c), offset);
 339         return -EIO;
 340     }
 341
 342     /* Check if the table is already cached */
 343     i = lookup_index = (offset / c->table_size * 4) % c->size;
 344     do {
 345         const Qcow2CachedTable *t = &c->entries[i];
 346         if (t->offset == offset) {
 347             goto found;
 348         }
 349         if (t->ref == 0 && t->lru_counter < min_lru_counter) {
 350             min_lru_counter = t->lru_counter;
 351             min_lru_index = i;
 352         }
 353         if (++i == c->size) {
 354             i = 0;
 355         }
 356     } while (i != lookup_index);
 357
 358     if (min_lru_index == -1) {
 359         /* This can't happen in current synchronous code, but leave the check
 360          * here as a reminder for whoever starts using AIO with the cache */
 361         abort();
 362     }
 363
 364     /* Cache miss: write a table back and replace it */
 365     i = min_lru_index;
 366     trace_qcow2_cache_get_replace_entry(qemu_coroutine_self(),
 367                                         c == s->l2_table_cache, i);
 368
 369     ret = qcow2_cache_entry_flush(bs, c, i);
 370     if (ret < 0) {
 371         return ret;
 372     }
 373
 374     trace_qcow2_cache_get_read(qemu_coroutine_self(),
 375                                c == s->l2_table_cache, i);
 376     c->entries[i].offset = 0;
 377     if (read_from_disk) {
 378         if (c == s->l2_table_cache) {
 379             BLKDBG_EVENT(bs->file, BLKDBG_L2_LOAD);
 380         }
 381
 382         ret = bdrv_pread(bs->file, offset,
 383                          qcow2_cache_get_table_addr(c, i),
 384                          c->table_size);
 385         if (ret < 0) {
 386             return ret;
 387         }
 388     }
 389
 390     c->entries[i].offset = offset;
 391
 392     /* And return the right table */
 393 found:
 394     c->entries[i].ref++;
 395     *table = qcow2_cache_get_table_addr(c, i);
 396
 397     trace_qcow2_cache_get_done(qemu_coroutine_self(),
 398                                c == s->l2_table_cache, i);
 399
 400     return 0;
 401 }
 402
 403 int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
 404     void **table)
 405 {
 406     return qcow2_cache_do_get(bs, c, offset, table, true);
 407 }
 408
 409 int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
 410     void **table)
 411 {
 412     return qcow2_cache_do_get(bs, c, offset, table, false);
 413 }
 414
 415 void qcow2_cache_put(Qcow2Cache *c, void **table)
 416 {
 417     int i = qcow2_cache_get_table_idx(c, *table);
 418
 419     c->entries[i].ref--;
 420     *table = NULL;
 421
 422     if (c->entries[i].ref == 0) {
 423         c->entries[i].lru_counter = ++c->lru_counter;
 424     }
 425
 426     assert(c->entries[i].ref >= 0);
 427 }
 428
 429 void qcow2_cache_entry_mark_dirty(Qcow2Cache *c, void *table)
 430 {
 431     int i = qcow2_cache_get_table_idx(c, table);
 432     assert(c->entries[i].offset != 0);
 433     c->entries[i].dirty = true;
 434 }
 435
 436 void *qcow2_cache_is_table_offset(Qcow2Cache *c, uint64_t offset)
 437 {
 438     int i;
 439
 440     for (i = 0; i < c->size; i++) {
 441         if (c->entries[i].offset == offset) {
 442             return qcow2_cache_get_table_addr(c, i);
 443         }
 444     }
 445     return NULL;
 446 }
 447
 448 void qcow2_cache_discard(Qcow2Cache *c, void *table)
 449 {
 450     int i = qcow2_cache_get_table_idx(c, table);
 451
 452     assert(c->entries[i].ref == 0);
 453
 454     c->entries[i].offset = 0;
 455     c->entries[i].lru_counter = 0;
 456     c->entries[i].dirty = false;
 457
 458     qcow2_cache_table_release(c, i, 1);
 459 }