block/cow.c

   1 /*
   2  * Block driver for the COW format
   3  *
   4  * Copyright (c) 2004 Fabrice Bellard
   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 #include "qemu-common.h"
  25 #include "block/block_int.h"
  26 #include "qemu/module.h"
  27
  28 /**************************************************************/
  29 /* COW block driver using file system holes */
  30
  31 /* user mode linux compatible COW file */
  32 #define COW_MAGIC 0x4f4f4f4d  /* MOOO */
  33 #define COW_VERSION 2
  34
  35 struct cow_header_v2 {
  36     uint32_t magic;
  37     uint32_t version;
  38     char backing_file[1024];
  39     int32_t mtime;
  40     uint64_t size;
  41     uint32_t sectorsize;
  42 };
  43
  44 typedef struct BDRVCowState {
  45     CoMutex lock;
  46     int64_t cow_sectors_offset;
  47 } BDRVCowState;
  48
  49 static int cow_probe(const uint8_t *buf, int buf_size, const char *filename)
  50 {
  51     const struct cow_header_v2 *cow_header = (const void *)buf;
  52
  53     if (buf_size >= sizeof(struct cow_header_v2) &&
  54         be32_to_cpu(cow_header->magic) == COW_MAGIC &&
  55         be32_to_cpu(cow_header->version) == COW_VERSION)
  56         return 100;
  57     else
  58         return 0;
  59 }
  60
  61 static int cow_open(BlockDriverState *bs, QDict *options, int flags,
  62                     Error **errp)
  63 {
  64     BDRVCowState *s = bs->opaque;
  65     struct cow_header_v2 cow_header;
  66     int bitmap_size;
  67     int64_t size;
  68     int ret;
  69
  70     /* see if it is a cow image */
  71     ret = bdrv_pread(bs->file, 0, &cow_header, sizeof(cow_header));
  72     if (ret < 0) {
  73         goto fail;
  74     }
  75
  76     if (be32_to_cpu(cow_header.magic) != COW_MAGIC) {
  77         ret = -EMEDIUMTYPE;
  78         goto fail;
  79     }
  80
  81     if (be32_to_cpu(cow_header.version) != COW_VERSION) {
  82         char version[64];
  83         snprintf(version, sizeof(version),
  84                "COW version %d", cow_header.version);
  85         qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
  86             bs->device_name, "cow", version);
  87         ret = -ENOTSUP;
  88         goto fail;
  89     }
  90
  91     /* cow image found */
  92     size = be64_to_cpu(cow_header.size);
  93     bs->total_sectors = size / 512;
  94
  95     pstrcpy(bs->backing_file, sizeof(bs->backing_file),
  96             cow_header.backing_file);
  97
  98     bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
  99     s->cow_sectors_offset = (bitmap_size + 511) & ~511;
 100     qemu_co_mutex_init(&s->lock);
 101     return 0;
 102  fail:
 103     return ret;
 104 }
 105
 106 static inline void cow_set_bits(uint8_t *bitmap, int start, int64_t nb_sectors)
 107 {
 108     int64_t bitnum = start, last = start + nb_sectors;
 109     while (bitnum < last) {
 110         if ((bitnum & 7) == 0 && bitnum + 8 <= last) {
 111             bitmap[bitnum / 8] = 0xFF;
 112             bitnum += 8;
 113             continue;
 114         }
 115         bitmap[bitnum/8] |= (1 << (bitnum % 8));
 116         bitnum++;
 117     }
 118 }
 119
 120 #define BITS_PER_BITMAP_SECTOR (512 * 8)
 121
 122 /* Cannot use bitmap.c on big-endian machines.  */
 123 static int cow_test_bit(int64_t bitnum, const uint8_t *bitmap)
 124 {
 125     return (bitmap[bitnum / 8] & (1 << (bitnum & 7))) != 0;
 126 }
 127
 128 static int cow_find_streak(const uint8_t *bitmap, int value, int start, int nb_sectors)
 129 {
 130     int streak_value = value ? 0xFF : 0;
 131     int last = MIN(start + nb_sectors, BITS_PER_BITMAP_SECTOR);
 132     int bitnum = start;
 133     while (bitnum < last) {
 134         if ((bitnum & 7) == 0 && bitmap[bitnum / 8] == streak_value) {
 135             bitnum += 8;
 136             continue;
 137         }
 138         if (cow_test_bit(bitnum, bitmap) == value) {
 139             bitnum++;
 140             continue;
 141         }
 142         break;
 143     }
 144     return MIN(bitnum, last) - start;
 145 }
 146
 147 /* Return true if first block has been changed (ie. current version is
 148  * in COW file).  Set the number of continuous blocks for which that
 149  * is true. */
 150 static int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,
 151         int64_t sector_num, int nb_sectors, int *num_same)
 152 {
 153     int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
 154     uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
 155     bool first = true;
 156     int changed = 0, same = 0;
 157
 158     do {
 159         int ret;
 160         uint8_t bitmap[BDRV_SECTOR_SIZE];
 161
 162         bitnum &= BITS_PER_BITMAP_SECTOR - 1;
 163         int sector_bits = MIN(nb_sectors, BITS_PER_BITMAP_SECTOR - bitnum);
 164
 165         ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
 166         if (ret < 0) {
 167             return ret;
 168         }
 169
 170         if (first) {
 171             changed = cow_test_bit(bitnum, bitmap);
 172             first = false;
 173         }
 174
 175         same += cow_find_streak(bitmap, changed, bitnum, nb_sectors);
 176
 177         bitnum += sector_bits;
 178         nb_sectors -= sector_bits;
 179         offset += BDRV_SECTOR_SIZE;
 180     } while (nb_sectors);
 181
 182     *num_same = same;
 183     return changed;
 184 }
 185
 186 static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs,
 187         int64_t sector_num, int nb_sectors, int *num_same)
 188 {
 189     BDRVCowState *s = bs->opaque;
 190     int ret = cow_co_is_allocated(bs, sector_num, nb_sectors, num_same);
 191     int64_t offset = s->cow_sectors_offset + (sector_num << BDRV_SECTOR_BITS);
 192     if (ret < 0) {
 193         return ret;
 194     }
 195     return (ret ? BDRV_BLOCK_DATA : 0) | offset | BDRV_BLOCK_OFFSET_VALID;
 196 }
 197
 198 static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
 199         int nb_sectors)
 200 {
 201     int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
 202     uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
 203     bool first = true;
 204     int sector_bits;
 205
 206     for ( ; nb_sectors;
 207             bitnum += sector_bits,
 208             nb_sectors -= sector_bits,
 209             offset += BDRV_SECTOR_SIZE) {
 210         int ret, set;
 211         uint8_t bitmap[BDRV_SECTOR_SIZE];
 212
 213         bitnum &= BITS_PER_BITMAP_SECTOR - 1;
 214         sector_bits = MIN(nb_sectors, BITS_PER_BITMAP_SECTOR - bitnum);
 215
 216         ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
 217         if (ret < 0) {
 218             return ret;
 219         }
 220
 221         /* Skip over any already set bits */
 222         set = cow_find_streak(bitmap, 1, bitnum, sector_bits);
 223         bitnum += set;
 224         sector_bits -= set;
 225         nb_sectors -= set;
 226         if (!sector_bits) {
 227             continue;
 228         }
 229
 230         if (first) {
 231             ret = bdrv_flush(bs->file);
 232             if (ret < 0) {
 233                 return ret;
 234             }
 235             first = false;
 236         }
 237
 238         cow_set_bits(bitmap, bitnum, sector_bits);
 239
 240         ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap));
 241         if (ret < 0) {
 242             return ret;
 243         }
 244     }
 245
 246     return 0;
 247 }
 248
 249 static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num,
 250                                  uint8_t *buf, int nb_sectors)
 251 {
 252     BDRVCowState *s = bs->opaque;
 253     int ret, n;
 254
 255     while (nb_sectors > 0) {
 256         ret = cow_co_is_allocated(bs, sector_num, nb_sectors, &n);
 257         if (ret < 0) {
 258             return ret;
 259         }
 260         if (ret) {
 261             ret = bdrv_pread(bs->file,
 262                         s->cow_sectors_offset + sector_num * 512,
 263                         buf, n * 512);
 264             if (ret < 0) {
 265                 return ret;
 266             }
 267         } else {
 268             if (bs->backing_hd) {
 269                 /* read from the base image */
 270                 ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
 271                 if (ret < 0) {
 272                     return ret;
 273                 }
 274             } else {
 275                 memset(buf, 0, n * 512);
 276             }
 277         }
 278         nb_sectors -= n;
 279         sector_num += n;
 280         buf += n * 512;
 281     }
 282     return 0;
 283 }
 284
 285 static coroutine_fn int cow_co_read(BlockDriverState *bs, int64_t sector_num,
 286                                     uint8_t *buf, int nb_sectors)
 287 {
 288     int ret;
 289     BDRVCowState *s = bs->opaque;
 290     qemu_co_mutex_lock(&s->lock);
 291     ret = cow_read(bs, sector_num, buf, nb_sectors);
 292     qemu_co_mutex_unlock(&s->lock);
 293     return ret;
 294 }
 295
 296 static int cow_write(BlockDriverState *bs, int64_t sector_num,
 297                      const uint8_t *buf, int nb_sectors)
 298 {
 299     BDRVCowState *s = bs->opaque;
 300     int ret;
 301
 302     ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,
 303                       buf, nb_sectors * 512);
 304     if (ret < 0) {
 305         return ret;
 306     }
 307
 308     return cow_update_bitmap(bs, sector_num, nb_sectors);
 309 }
 310
 311 static coroutine_fn int cow_co_write(BlockDriverState *bs, int64_t sector_num,
 312                                      const uint8_t *buf, int nb_sectors)
 313 {
 314     int ret;
 315     BDRVCowState *s = bs->opaque;
 316     qemu_co_mutex_lock(&s->lock);
 317     ret = cow_write(bs, sector_num, buf, nb_sectors);
 318     qemu_co_mutex_unlock(&s->lock);
 319     return ret;
 320 }
 321
 322 static void cow_close(BlockDriverState *bs)
 323 {
 324 }
 325
 326 static int cow_create(const char *filename, QEMUOptionParameter *options,
 327                       Error **errp)
 328 {
 329     struct cow_header_v2 cow_header;
 330     struct stat st;
 331     int64_t image_sectors = 0;
 332     const char *image_filename = NULL;
 333     Error *local_err = NULL;
 334     int ret;
 335     BlockDriverState *cow_bs;
 336
 337     /* Read out options */
 338     while (options && options->name) {
 339         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
 340             image_sectors = options->value.n / 512;
 341         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
 342             image_filename = options->value.s;
 343         }
 344         options++;
 345     }
 346
 347     ret = bdrv_create_file(filename, options, &local_err);
 348     if (ret < 0) {
 349         qerror_report_err(local_err);
 350         error_free(local_err);
 351         return ret;
 352     }
 353
 354     ret = bdrv_file_open(&cow_bs, filename, NULL, NULL, BDRV_O_RDWR,
 355                          &local_err);
 356     if (ret < 0) {
 357         qerror_report_err(local_err);
 358         error_free(local_err);
 359         return ret;
 360     }
 361
 362     memset(&cow_header, 0, sizeof(cow_header));
 363     cow_header.magic = cpu_to_be32(COW_MAGIC);
 364     cow_header.version = cpu_to_be32(COW_VERSION);
 365     if (image_filename) {
 366         /* Note: if no file, we put a dummy mtime */
 367         cow_header.mtime = cpu_to_be32(0);
 368
 369         if (stat(image_filename, &st) != 0) {
 370             goto mtime_fail;
 371         }
 372         cow_header.mtime = cpu_to_be32(st.st_mtime);
 373     mtime_fail:
 374         pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
 375                 image_filename);
 376     }
 377     cow_header.sectorsize = cpu_to_be32(512);
 378     cow_header.size = cpu_to_be64(image_sectors * 512);
 379     ret = bdrv_pwrite(cow_bs, 0, &cow_header, sizeof(cow_header));
 380     if (ret < 0) {
 381         goto exit;
 382     }
 383
 384     /* resize to include at least all the bitmap */
 385     ret = bdrv_truncate(cow_bs,
 386         sizeof(cow_header) + ((image_sectors + 7) >> 3));
 387     if (ret < 0) {
 388         goto exit;
 389     }
 390
 391 exit:
 392     bdrv_unref(cow_bs);
 393     return ret;
 394 }
 395
 396 static QEMUOptionParameter cow_create_options[] = {
 397     {
 398         .name = BLOCK_OPT_SIZE,
 399         .type = OPT_SIZE,
 400         .help = "Virtual disk size"
 401     },
 402     {
 403         .name = BLOCK_OPT_BACKING_FILE,
 404         .type = OPT_STRING,
 405         .help = "File name of a base image"
 406     },
 407     { NULL }
 408 };
 409
 410 static BlockDriver bdrv_cow = {
 411     .format_name    = "cow",
 412     .instance_size  = sizeof(BDRVCowState),
 413
 414     .bdrv_probe     = cow_probe,
 415     .bdrv_open      = cow_open,
 416     .bdrv_close     = cow_close,
 417     .bdrv_create    = cow_create,
 418     .bdrv_has_zero_init     = bdrv_has_zero_init_1,
 419
 420     .bdrv_read              = cow_co_read,
 421     .bdrv_write             = cow_co_write,
 422     .bdrv_co_get_block_status   = cow_co_get_block_status,
 423
 424     .create_options = cow_create_options,
 425 };
 426
 427 static void bdrv_cow_init(void)
 428 {
 429     bdrv_register(&bdrv_cow);
 430 }
 431
 432 block_init(bdrv_cow_init);