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