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 /* Needed for CONFIG_MADVISE */
  26 #include "config-host.h"
  27
  28 #if defined(CONFIG_MADVISE) || defined(CONFIG_POSIX_MADVISE)
  29 #include <sys/mman.h>
  30 #endif
  31
  32 #include "block/block_int.h"
  33 #include "qemu-common.h"
  34 #include "qemu/osdep.h"
  35 #include "qcow2.h"
  36 #include "trace.h"
  37
  38 typedef struct Qcow2CachedTable {
  39     int64_t  offset;
  40     bool     dirty;
  41     uint64_t lru_counter;
  42     int      ref;
  43 } Qcow2CachedTable;
  44
  45 struct Qcow2Cache {
  46     Qcow2CachedTable       *entries;
  47     struct Qcow2Cache      *depends;
  48     int                     size;
  49     bool                    depends_on_flush;
  50     void                   *table_array;
  51     uint64_t                lru_counter;
  52     uint64_t                cache_clean_lru_counter;
  53 };
  54
  55 static inline void *qcow2_cache_get_table_addr(BlockDriverState *bs,
  56                     Qcow2Cache *c, int table)
  57 {
  58     BDRVQcowState *s = bs->opaque;
  59     return (uint8_t *) c->table_array + (size_t) table * s->cluster_size;
  60 }
  61
  62 static inline int qcow2_cache_get_table_idx(BlockDriverState *bs,
  63                   Qcow2Cache *c, void *table)
  64 {
  65     BDRVQcowState *s = bs->opaque;
  66     ptrdiff_t table_offset = (uint8_t *) table - (uint8_t *) c->table_array;
  67     int idx = table_offset / s->cluster_size;
  68     assert(idx >= 0 && idx < c->size && table_offset % s->cluster_size == 0);
  69     return idx;
  70 }
  71
  72 static void qcow2_cache_table_release(BlockDriverState *bs, Qcow2Cache *c,
  73                                       int i, int num_tables)
  74 {
  75 #if QEMU_MADV_DONTNEED != QEMU_MADV_INVALID
  76     BDRVQcowState *s = bs->opaque;
  77     void *t = qcow2_cache_get_table_addr(bs, c, i);
  78     int align = getpagesize();
  79     size_t mem_size = (size_t) s->cluster_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 (length > 0) {
  83         qemu_madvise((uint8_t *) t + offset, length, QEMU_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(BlockDriverState *bs, 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(bs, 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 {
 124     BDRVQcowState *s = bs->opaque;
 125     Qcow2Cache *c;
 126
 127     c = g_new0(Qcow2Cache, 1);
 128     c->size = num_tables;
 129     c->entries = g_try_new0(Qcow2CachedTable, num_tables);
 130     c->table_array = qemu_try_blockalign(bs->file,
 131                                          (size_t) num_tables * s->cluster_size);
 132
 133     if (!c->entries || !c->table_array) {
 134         qemu_vfree(c->table_array);
 135         g_free(c->entries);
 136         g_free(c);
 137         c = NULL;
 138     }
 139
 140     return c;
 141 }
 142
 143 int qcow2_cache_destroy(BlockDriverState *bs, Qcow2Cache *c)
 144 {
 145     int i;
 146
 147     for (i = 0; i < c->size; i++) {
 148         assert(c->entries[i].ref == 0);
 149     }
 150
 151     qemu_vfree(c->table_array);
 152     g_free(c->entries);
 153     g_free(c);
 154
 155     return 0;
 156 }
 157
 158 static int qcow2_cache_flush_dependency(BlockDriverState *bs, Qcow2Cache *c)
 159 {
 160     int ret;
 161
 162     ret = qcow2_cache_flush(bs, c->depends);
 163     if (ret < 0) {
 164         return ret;
 165     }
 166
 167     c->depends = NULL;
 168     c->depends_on_flush = false;
 169
 170     return 0;
 171 }
 172
 173 static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i)
 174 {
 175     BDRVQcowState *s = bs->opaque;
 176     int ret = 0;
 177
 178     if (!c->entries[i].dirty || !c->entries[i].offset) {
 179         return 0;
 180     }
 181
 182     trace_qcow2_cache_entry_flush(qemu_coroutine_self(),
 183                                   c == s->l2_table_cache, i);
 184
 185     if (c->depends) {
 186         ret = qcow2_cache_flush_dependency(bs, c);
 187     } else if (c->depends_on_flush) {
 188         ret = bdrv_flush(bs->file);
 189         if (ret >= 0) {
 190             c->depends_on_flush = false;
 191         }
 192     }
 193
 194     if (ret < 0) {
 195         return ret;
 196     }
 197
 198     if (c == s->refcount_block_cache) {
 199         ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_REFCOUNT_BLOCK,
 200                 c->entries[i].offset, s->cluster_size);
 201     } else if (c == s->l2_table_cache) {
 202         ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L2,
 203                 c->entries[i].offset, s->cluster_size);
 204     } else {
 205         ret = qcow2_pre_write_overlap_check(bs, 0,
 206                 c->entries[i].offset, s->cluster_size);
 207     }
 208
 209     if (ret < 0) {
 210         return ret;
 211     }
 212
 213     if (c == s->refcount_block_cache) {
 214         BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_UPDATE_PART);
 215     } else if (c == s->l2_table_cache) {
 216         BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE);
 217     }
 218
 219     ret = bdrv_pwrite(bs->file, c->entries[i].offset,
 220                       qcow2_cache_get_table_addr(bs, c, i), s->cluster_size);
 221     if (ret < 0) {
 222         return ret;
 223     }
 224
 225     c->entries[i].dirty = false;
 226
 227     return 0;
 228 }
 229
 230 int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c)
 231 {
 232     BDRVQcowState *s = bs->opaque;
 233     int result = 0;
 234     int ret;
 235     int i;
 236
 237     trace_qcow2_cache_flush(qemu_coroutine_self(), c == s->l2_table_cache);
 238
 239     for (i = 0; i < c->size; i++) {
 240         ret = qcow2_cache_entry_flush(bs, c, i);
 241         if (ret < 0 && result != -ENOSPC) {
 242             result = ret;
 243         }
 244     }
 245
 246     if (result == 0) {
 247         ret = bdrv_flush(bs->file);
 248         if (ret < 0) {
 249             result = ret;
 250         }
 251     }
 252
 253     return result;
 254 }
 255
 256 int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c,
 257     Qcow2Cache *dependency)
 258 {
 259     int ret;
 260
 261     if (dependency->depends) {
 262         ret = qcow2_cache_flush_dependency(bs, dependency);
 263         if (ret < 0) {
 264             return ret;
 265         }
 266     }
 267
 268     if (c->depends && (c->depends != dependency)) {
 269         ret = qcow2_cache_flush_dependency(bs, c);
 270         if (ret < 0) {
 271             return ret;
 272         }
 273     }
 274
 275     c->depends = dependency;
 276     return 0;
 277 }
 278
 279 void qcow2_cache_depends_on_flush(Qcow2Cache *c)
 280 {
 281     c->depends_on_flush = true;
 282 }
 283
 284 int qcow2_cache_empty(BlockDriverState *bs, Qcow2Cache *c)
 285 {
 286     int ret, i;
 287
 288     ret = qcow2_cache_flush(bs, c);
 289     if (ret < 0) {
 290         return ret;
 291     }
 292
 293     for (i = 0; i < c->size; i++) {
 294         assert(c->entries[i].ref == 0);
 295         c->entries[i].offset = 0;
 296         c->entries[i].lru_counter = 0;
 297     }
 298
 299     qcow2_cache_table_release(bs, c, 0, c->size);
 300
 301     c->lru_counter = 0;
 302
 303     return 0;
 304 }
 305
 306 static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c,
 307     uint64_t offset, void **table, bool read_from_disk)
 308 {
 309     BDRVQcowState *s = bs->opaque;
 310     int i;
 311     int ret;
 312     int lookup_index;
 313     uint64_t min_lru_counter = UINT64_MAX;
 314     int min_lru_index = -1;
 315
 316     trace_qcow2_cache_get(qemu_coroutine_self(), c == s->l2_table_cache,
 317                           offset, read_from_disk);
 318
 319     /* Check if the table is already cached */
 320     i = lookup_index = (offset / s->cluster_size * 4) % c->size;
 321     do {
 322         const Qcow2CachedTable *t = &c->entries[i];
 323         if (t->offset == offset) {
 324             goto found;
 325         }
 326         if (t->ref == 0 && t->lru_counter < min_lru_counter) {
 327             min_lru_counter = t->lru_counter;
 328             min_lru_index = i;
 329         }
 330         if (++i == c->size) {
 331             i = 0;
 332         }
 333     } while (i != lookup_index);
 334
 335     if (min_lru_index == -1) {
 336         /* This can't happen in current synchronous code, but leave the check
 337          * here as a reminder for whoever starts using AIO with the cache */
 338         abort();
 339     }
 340
 341     /* Cache miss: write a table back and replace it */
 342     i = min_lru_index;
 343     trace_qcow2_cache_get_replace_entry(qemu_coroutine_self(),
 344                                         c == s->l2_table_cache, i);
 345
 346     ret = qcow2_cache_entry_flush(bs, c, i);
 347     if (ret < 0) {
 348         return ret;
 349     }
 350
 351     trace_qcow2_cache_get_read(qemu_coroutine_self(),
 352                                c == s->l2_table_cache, i);
 353     c->entries[i].offset = 0;
 354     if (read_from_disk) {
 355         if (c == s->l2_table_cache) {
 356             BLKDBG_EVENT(bs->file, BLKDBG_L2_LOAD);
 357         }
 358
 359         ret = bdrv_pread(bs->file, offset, qcow2_cache_get_table_addr(bs, c, i),
 360                          s->cluster_size);
 361         if (ret < 0) {
 362             return ret;
 363         }
 364     }
 365
 366     c->entries[i].offset = offset;
 367
 368     /* And return the right table */
 369 found:
 370     c->entries[i].ref++;
 371     *table = qcow2_cache_get_table_addr(bs, c, i);
 372
 373     trace_qcow2_cache_get_done(qemu_coroutine_self(),
 374                                c == s->l2_table_cache, i);
 375
 376     return 0;
 377 }
 378
 379 int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
 380     void **table)
 381 {
 382     return qcow2_cache_do_get(bs, c, offset, table, true);
 383 }
 384
 385 int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
 386     void **table)
 387 {
 388     return qcow2_cache_do_get(bs, c, offset, table, false);
 389 }
 390
 391 void qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table)
 392 {
 393     int i = qcow2_cache_get_table_idx(bs, c, *table);
 394
 395     c->entries[i].ref--;
 396     *table = NULL;
 397
 398     if (c->entries[i].ref == 0) {
 399         c->entries[i].lru_counter = ++c->lru_counter;
 400     }
 401
 402     assert(c->entries[i].ref >= 0);
 403 }
 404
 405 void qcow2_cache_entry_mark_dirty(BlockDriverState *bs, Qcow2Cache *c,
 406      void *table)
 407 {
 408     int i = qcow2_cache_get_table_idx(bs, c, table);
 409     assert(c->entries[i].offset != 0);
 410     c->entries[i].dirty = true;
 411 }