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