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         error_setg(errp, "Image not in COW format");
  78         ret = -EINVAL;
  79         goto fail;
  80     }
  81
  82     if (be32_to_cpu(cow_header.version) != COW_VERSION) {
  83         char version[64];
  84         snprintf(version, sizeof(version),
  85                "COW version %d", cow_header.version);
  86         error_set(errp, QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
  87             bs->device_name, "cow", version);
  88         ret = -ENOTSUP;
  89         goto fail;
  90     }
  91
  92     /* cow image found */
  93     size = be64_to_cpu(cow_header.size);
  94     bs->total_sectors = size / 512;
  95
  96     pstrcpy(bs->backing_file, sizeof(bs->backing_file),
  97             cow_header.backing_file);
  98
  99     bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
 100     s->cow_sectors_offset = (bitmap_size + 511) & ~511;
 101     qemu_co_mutex_init(&s->lock);
 102     return 0;
 103  fail:
 104     return ret;
 105 }
 106
 107 static inline void cow_set_bits(uint8_t *bitmap, int start, int64_t nb_sectors)
 108 {
 109     int64_t bitnum = start, last = start + nb_sectors;
 110     while (bitnum < last) {
 111         if ((bitnum & 7) == 0 && bitnum + 8 <= last) {
 112             bitmap[bitnum / 8] = 0xFF;
 113             bitnum += 8;
 114             continue;
 115         }
 116         bitmap[bitnum/8] |= (1 << (bitnum % 8));
 117         bitnum++;
 118     }
 119 }
 120
 121 #define BITS_PER_BITMAP_SECTOR (512 * 8)
 122
 123 /* Cannot use bitmap.c on big-endian machines.  */
 124 static int cow_test_bit(int64_t bitnum, const uint8_t *bitmap)
 125 {
 126     return (bitmap[bitnum / 8] & (1 << (bitnum & 7))) != 0;
 127 }
 128
 129 static int cow_find_streak(const uint8_t *bitmap, int value, int start, int nb_sectors)
 130 {
 131     int streak_value = value ? 0xFF : 0;
 132     int last = MIN(start + nb_sectors, BITS_PER_BITMAP_SECTOR);
 133     int bitnum = start;
 134     while (bitnum < last) {
 135         if ((bitnum & 7) == 0 && bitmap[bitnum / 8] == streak_value) {
 136             bitnum += 8;
 137             continue;
 138         }
 139         if (cow_test_bit(bitnum, bitmap) == value) {
 140             bitnum++;
 141             continue;
 142         }
 143         break;
 144     }
 145     return MIN(bitnum, last) - start;
 146 }
 147
 148 /* Return true if first block has been changed (ie. current version is
 149  * in COW file).  Set the number of continuous blocks for which that
 150  * is true. */
 151 static int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,
 152         int64_t sector_num, int nb_sectors, int *num_same)
 153 {
 154     int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
 155     uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
 156     bool first = true;
 157     int changed = 0, same = 0;
 158
 159     do {
 160         int ret;
 161         uint8_t bitmap[BDRV_SECTOR_SIZE];
 162
 163         bitnum &= BITS_PER_BITMAP_SECTOR - 1;
 164         int sector_bits = MIN(nb_sectors, BITS_PER_BITMAP_SECTOR - bitnum);
 165
 166         ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
 167         if (ret < 0) {
 168             return ret;
 169         }
 170
 171         if (first) {
 172             changed = cow_test_bit(bitnum, bitmap);
 173             first = false;
 174         }
 175
 176         same += cow_find_streak(bitmap, changed, bitnum, nb_sectors);
 177
 178         bitnum += sector_bits;
 179         nb_sectors -= sector_bits;
 180         offset += BDRV_SECTOR_SIZE;
 181     } while (nb_sectors);
 182
 183     *num_same = same;
 184     return changed;
 185 }
 186
 187 static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs,
 188         int64_t sector_num, int nb_sectors, int *num_same)
 189 {
 190     BDRVCowState *s = bs->opaque;
 191     int ret = cow_co_is_allocated(bs, sector_num, nb_sectors, num_same);
 192     int64_t offset = s->cow_sectors_offset + (sector_num << BDRV_SECTOR_BITS);
 193     if (ret < 0) {
 194         return ret;
 195     }
 196     return (ret ? BDRV_BLOCK_DATA : 0) | offset | BDRV_BLOCK_OFFSET_VALID;
 197 }
 198
 199 static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
 200         int nb_sectors)
 201 {
 202     int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
 203     uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
 204     bool first = true;
 205     int sector_bits;
 206
 207     for ( ; nb_sectors;
 208             bitnum += sector_bits,
 209             nb_sectors -= sector_bits,
 210             offset += BDRV_SECTOR_SIZE) {
 211         int ret, set;
 212         uint8_t bitmap[BDRV_SECTOR_SIZE];
 213
 214         bitnum &= BITS_PER_BITMAP_SECTOR - 1;
 215         sector_bits = MIN(nb_sectors, BITS_PER_BITMAP_SECTOR - bitnum);
 216
 217         ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
 218         if (ret < 0) {
 219             return ret;
 220         }
 221
 222         /* Skip over any already set bits */
 223         set = cow_find_streak(bitmap, 1, bitnum, sector_bits);
 224         bitnum += set;
 225         sector_bits -= set;
 226         nb_sectors -= set;
 227         if (!sector_bits) {
 228             continue;
 229         }
 230
 231         if (first) {
 232             ret = bdrv_flush(bs->file);
 233             if (ret < 0) {
 234                 return ret;
 235             }
 236             first = false;
 237         }
 238
 239         cow_set_bits(bitmap, bitnum, sector_bits);
 240
 241         ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap));
 242         if (ret < 0) {
 243             return ret;
 244         }
 245     }
 246
 247     return 0;
 248 }
 249
 250 static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num,
 251                                  uint8_t *buf, int nb_sectors)
 252 {
 253     BDRVCowState *s = bs->opaque;
 254     int ret, n;
 255
 256     while (nb_sectors > 0) {
 257         ret = cow_co_is_allocated(bs, sector_num, nb_sectors, &n);
 258         if (ret < 0) {
 259             return ret;
 260         }
 261         if (ret) {
 262             ret = bdrv_pread(bs->file,
 263                         s->cow_sectors_offset + sector_num * 512,
 264                         buf, n * 512);
 265             if (ret < 0) {
 266                 return ret;
 267             }
 268         } else {
 269             if (bs->backing_hd) {
 270                 /* read from the base image */
 271                 ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
 272                 if (ret < 0) {
 273                     return ret;
 274                 }
 275             } else {
 276                 memset(buf, 0, n * 512);
 277             }
 278         }
 279         nb_sectors -= n;
 280         sector_num += n;
 281         buf += n * 512;
 282     }
 283     return 0;
 284 }
 285
 286 static coroutine_fn int cow_co_read(BlockDriverState *bs, int64_t sector_num,
 287                                     uint8_t *buf, int nb_sectors)
 288 {
 289     int ret;
 290     BDRVCowState *s = bs->opaque;
 291     qemu_co_mutex_lock(&s->lock);
 292     ret = cow_read(bs, sector_num, buf, nb_sectors);
 293     qemu_co_mutex_unlock(&s->lock);
 294     return ret;
 295 }
 296
 297 static int cow_write(BlockDriverState *bs, int64_t sector_num,
 298                      const uint8_t *buf, int nb_sectors)
 299 {
 300     BDRVCowState *s = bs->opaque;
 301     int ret;
 302
 303     ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,
 304                       buf, nb_sectors * 512);
 305     if (ret < 0) {
 306         return ret;
 307     }
 308
 309     return cow_update_bitmap(bs, sector_num, nb_sectors);
 310 }
 311
 312 static coroutine_fn int cow_co_write(BlockDriverState *bs, int64_t sector_num,
 313                                      const uint8_t *buf, int nb_sectors)
 314 {
 315     int ret;
 316     BDRVCowState *s = bs->opaque;
 317     qemu_co_mutex_lock(&s->lock);
 318     ret = cow_write(bs, sector_num, buf, nb_sectors);
 319     qemu_co_mutex_unlock(&s->lock);
 320     return ret;
 321 }
 322
 323 static void cow_close(BlockDriverState *bs)
 324 {
 325 }
 326
 327 static int cow_create(const char *filename, QEMUOptionParameter *options,
 328                       Error **errp)
 329 {
 330     struct cow_header_v2 cow_header;
 331     struct stat st;
 332     int64_t image_sectors = 0;
 333     const char *image_filename = NULL;
 334     Error *local_err = NULL;
 335     int ret;
 336     BlockDriverState *cow_bs;
 337
 338     /* Read out options */
 339     while (options && options->name) {
 340         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
 341             image_sectors = options->value.n / 512;
 342         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
 343             image_filename = options->value.s;
 344         }
 345         options++;
 346     }
 347
 348     ret = bdrv_create_file(filename, options, &local_err);
 349     if (ret < 0) {
 350         error_propagate(errp, local_err);
 351         return ret;
 352     }
 353
 354     cow_bs = NULL;
 355     ret = bdrv_open(&cow_bs, filename, NULL, NULL,
 356                     BDRV_O_RDWR | BDRV_O_PROTOCOL, NULL, &local_err);
 357     if (ret < 0) {
 358         error_propagate(errp, 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);