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 "block_int.h"
  26 #include "qemu-common.h"
  27 #include "qcow2.h"
  28
  29 typedef struct Qcow2CachedTable {
  30     void*   table;
  31     int64_t offset;
  32     bool    dirty;
  33     int     cache_hits;
  34     int     ref;
  35 } Qcow2CachedTable;
  36
  37 struct Qcow2Cache {
  38     Qcow2CachedTable*       entries;
  39     struct Qcow2Cache*      depends;
  40     int                     size;
  41     bool                    depends_on_flush;
  42     bool                    writethrough;
  43 };
  44
  45 Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables,
  46     bool writethrough)
  47 {
  48     BDRVQcowState *s = bs->opaque;
  49     Qcow2Cache *c;
  50     int i;
  51
  52     c = qemu_mallocz(sizeof(*c));
  53     c->size = num_tables;
  54     c->entries = qemu_mallocz(sizeof(*c->entries) * num_tables);
  55     c->writethrough = writethrough;
  56
  57     for (i = 0; i < c->size; i++) {
  58         c->entries[i].table = qemu_blockalign(bs, s->cluster_size);
  59     }
  60
  61     return c;
  62 }
  63
  64 int qcow2_cache_destroy(BlockDriverState* bs, Qcow2Cache *c)
  65 {
  66     int i;
  67
  68     for (i = 0; i < c->size; i++) {
  69         assert(c->entries[i].ref == 0);
  70         qemu_vfree(c->entries[i].table);
  71     }
  72
  73     qemu_free(c->entries);
  74     qemu_free(c);
  75
  76     return 0;
  77 }
  78
  79 static int qcow2_cache_flush_dependency(BlockDriverState *bs, Qcow2Cache *c)
  80 {
  81     int ret;
  82
  83     ret = qcow2_cache_flush(bs, c->depends);
  84     if (ret < 0) {
  85         return ret;
  86     }
  87
  88     c->depends = NULL;
  89     c->depends_on_flush = false;
  90
  91     return 0;
  92 }
  93
  94 static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i)
  95 {
  96     BDRVQcowState *s = bs->opaque;
  97     int ret = 0;
  98
  99     if (!c->entries[i].dirty || !c->entries[i].offset) {
 100         return 0;
 101     }
 102
 103     if (c->depends) {
 104         ret = qcow2_cache_flush_dependency(bs, c);
 105     } else if (c->depends_on_flush) {
 106         ret = bdrv_flush(bs->file);
 107         if (ret >= 0) {
 108             c->depends_on_flush = false;
 109         }
 110     }
 111
 112     if (ret < 0) {
 113         return ret;
 114     }
 115
 116     if (c == s->refcount_block_cache) {
 117         BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_UPDATE_PART);
 118     } else if (c == s->l2_table_cache) {
 119         BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE);
 120     }
 121
 122     ret = bdrv_pwrite(bs->file, c->entries[i].offset, c->entries[i].table,
 123         s->cluster_size);
 124     if (ret < 0) {
 125         return ret;
 126     }
 127
 128     c->entries[i].dirty = false;
 129
 130     return 0;
 131 }
 132
 133 int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c)
 134 {
 135     int result = 0;
 136     int ret;
 137     int i;
 138
 139     for (i = 0; i < c->size; i++) {
 140         ret = qcow2_cache_entry_flush(bs, c, i);
 141         if (ret < 0 && result != -ENOSPC) {
 142             result = ret;
 143         }
 144     }
 145
 146     if (result == 0) {
 147         ret = bdrv_flush(bs->file);
 148         if (ret < 0) {
 149             result = ret;
 150         }
 151     }
 152
 153     return result;
 154 }
 155
 156 int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c,
 157     Qcow2Cache *dependency)
 158 {
 159     int ret;
 160
 161     if (dependency->depends) {
 162         ret = qcow2_cache_flush_dependency(bs, dependency);
 163         if (ret < 0) {
 164             return ret;
 165         }
 166     }
 167
 168     if (c->depends && (c->depends != dependency)) {
 169         ret = qcow2_cache_flush_dependency(bs, c);
 170         if (ret < 0) {
 171             return ret;
 172         }
 173     }
 174
 175     c->depends = dependency;
 176     return 0;
 177 }
 178
 179 void qcow2_cache_depends_on_flush(Qcow2Cache *c)
 180 {
 181     c->depends_on_flush = true;
 182 }
 183
 184 static int qcow2_cache_find_entry_to_replace(Qcow2Cache *c)
 185 {
 186     int i;
 187     int min_count = INT_MAX;
 188     int min_index = -1;
 189
 190
 191     for (i = 0; i < c->size; i++) {
 192         if (c->entries[i].ref) {
 193             continue;
 194         }
 195
 196         if (c->entries[i].cache_hits < min_count) {
 197             min_index = i;
 198             min_count = c->entries[i].cache_hits;
 199         }
 200
 201         /* Give newer hits priority */
 202         /* TODO Check how to optimize the replacement strategy */
 203         c->entries[i].cache_hits /= 2;
 204     }
 205
 206     if (min_index == -1) {
 207         /* This can't happen in current synchronous code, but leave the check
 208          * here as a reminder for whoever starts using AIO with the cache */
 209         abort();
 210     }
 211     return min_index;
 212 }
 213
 214 static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c,
 215     uint64_t offset, void **table, bool read_from_disk)
 216 {
 217     BDRVQcowState *s = bs->opaque;
 218     int i;
 219     int ret;
 220
 221     /* Check if the table is already cached */
 222     for (i = 0; i < c->size; i++) {
 223         if (c->entries[i].offset == offset) {
 224             goto found;
 225         }
 226     }
 227
 228     /* If not, write a table back and replace it */
 229     i = qcow2_cache_find_entry_to_replace(c);
 230     if (i < 0) {
 231         return i;
 232     }
 233
 234     ret = qcow2_cache_entry_flush(bs, c, i);
 235     if (ret < 0) {
 236         return ret;
 237     }
 238
 239     c->entries[i].offset = 0;
 240     if (read_from_disk) {
 241         if (c == s->l2_table_cache) {
 242             BLKDBG_EVENT(bs->file, BLKDBG_L2_LOAD);
 243         }
 244
 245         ret = bdrv_pread(bs->file, offset, c->entries[i].table, s->cluster_size);
 246         if (ret < 0) {
 247             return ret;
 248         }
 249     }
 250
 251     /* Give the table some hits for the start so that it won't be replaced
 252      * immediately. The number 32 is completely arbitrary. */
 253     c->entries[i].cache_hits = 32;
 254     c->entries[i].offset = offset;
 255
 256     /* And return the right table */
 257 found:
 258     c->entries[i].cache_hits++;
 259     c->entries[i].ref++;
 260     *table = c->entries[i].table;
 261     return 0;
 262 }
 263
 264 int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
 265     void **table)
 266 {
 267     return qcow2_cache_do_get(bs, c, offset, table, true);
 268 }
 269
 270 int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
 271     void **table)
 272 {
 273     return qcow2_cache_do_get(bs, c, offset, table, false);
 274 }
 275
 276 int qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table)
 277 {
 278     int i;
 279
 280     for (i = 0; i < c->size; i++) {
 281         if (c->entries[i].table == *table) {
 282             goto found;
 283         }
 284     }
 285     return -ENOENT;
 286
 287 found:
 288     c->entries[i].ref--;
 289     *table = NULL;
 290
 291     assert(c->entries[i].ref >= 0);
 292
 293     if (c->writethrough) {
 294         return qcow2_cache_entry_flush(bs, c, i);
 295     } else {
 296         return 0;
 297     }
 298 }
 299
 300 void qcow2_cache_entry_mark_dirty(Qcow2Cache *c, void *table)
 301 {
 302     int i;
 303
 304     for (i = 0; i < c->size; i++) {
 305         if (c->entries[i].table == table) {
 306             goto found;
 307         }
 308     }
 309     abort();
 310
 311 found:
 312     c->entries[i].dirty = true;
 313 }
 314