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 {
  63     BDRVCowState *s = bs->opaque;
  64     struct cow_header_v2 cow_header;
  65     int bitmap_size;
  66     int64_t size;
  67     int ret;
  68
  69     /* see if it is a cow image */
  70     ret = bdrv_pread(bs->file, 0, &cow_header, sizeof(cow_header));
  71     if (ret < 0) {
  72         goto fail;
  73     }
  74
  75     if (be32_to_cpu(cow_header.magic) != COW_MAGIC) {
  76         ret = -EMEDIUMTYPE;
  77         goto fail;
  78     }
  79
  80     if (be32_to_cpu(cow_header.version) != COW_VERSION) {
  81         char version[64];
  82         snprintf(version, sizeof(version),
  83                "COW version %d", cow_header.version);
  84         qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
  85             bs->device_name, "cow", version);
  86         ret = -ENOTSUP;
  87         goto fail;
  88     }
  89
  90     /* cow image found */
  91     size = be64_to_cpu(cow_header.size);
  92     bs->total_sectors = size / 512;
  93
  94     pstrcpy(bs->backing_file, sizeof(bs->backing_file),
  95             cow_header.backing_file);
  96
  97     bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
  98     s->cow_sectors_offset = (bitmap_size + 511) & ~511;
  99     qemu_co_mutex_init(&s->lock);
 100     return 0;
 101  fail:
 102     return ret;
 103 }
 104
 105 /*
 106  * XXX(hch): right now these functions are extremely inefficient.
 107  * We should just read the whole bitmap we'll need in one go instead.
 108  */
 109 static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum, bool *first)
 110 {
 111     uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
 112     uint8_t bitmap;
 113     int ret;
 114
 115     ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
 116     if (ret < 0) {
 117        return ret;
 118     }
 119
 120     if (bitmap & (1 << (bitnum % 8))) {
 121         return 0;
 122     }
 123
 124     if (*first) {
 125         ret = bdrv_flush(bs->file);
 126         if (ret < 0) {
 127             return ret;
 128         }
 129         *first = false;
 130     }
 131
 132     bitmap |= (1 << (bitnum % 8));
 133
 134     ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap));
 135     if (ret < 0) {
 136        return ret;
 137     }
 138     return 0;
 139 }
 140
 141 #define BITS_PER_BITMAP_SECTOR (512 * 8)
 142
 143 /* Cannot use bitmap.c on big-endian machines.  */
 144 static int cow_test_bit(int64_t bitnum, const uint8_t *bitmap)
 145 {
 146     return (bitmap[bitnum / 8] & (1 << (bitnum & 7))) != 0;
 147 }
 148
 149 static int cow_find_streak(const uint8_t *bitmap, int value, int start, int nb_sectors)
 150 {
 151     int streak_value = value ? 0xFF : 0;
 152     int last = MIN(start + nb_sectors, BITS_PER_BITMAP_SECTOR);
 153     int bitnum = start;
 154     while (bitnum < last) {
 155         if ((bitnum & 7) == 0 && bitmap[bitnum / 8] == streak_value) {
 156             bitnum += 8;
 157             continue;
 158         }
 159         if (cow_test_bit(bitnum, bitmap) == value) {
 160             bitnum++;
 161             continue;
 162         }
 163         break;
 164     }
 165     return MIN(bitnum, last) - start;
 166 }
 167
 168 /* Return true if first block has been changed (ie. current version is
 169  * in COW file).  Set the number of continuous blocks for which that
 170  * is true. */
 171 static int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,
 172         int64_t sector_num, int nb_sectors, int *num_same)
 173 {
 174     int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
 175     uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
 176     uint8_t bitmap[BDRV_SECTOR_SIZE];
 177     int ret;
 178     int changed;
 179
 180     ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
 181     if (ret < 0) {
 182         return ret;
 183     }
 184
 185     bitnum &= BITS_PER_BITMAP_SECTOR - 1;
 186     changed = cow_test_bit(bitnum, bitmap);
 187     *num_same = cow_find_streak(bitmap, changed, bitnum, nb_sectors);
 188     return changed;
 189 }
 190
 191 static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs,
 192         int64_t sector_num, int nb_sectors, int *num_same)
 193 {
 194     BDRVCowState *s = bs->opaque;
 195     int ret = cow_co_is_allocated(bs, sector_num, nb_sectors, num_same);
 196     int64_t offset = s->cow_sectors_offset + (sector_num << BDRV_SECTOR_BITS);
 197     if (ret < 0) {
 198         return ret;
 199     }
 200     return (ret ? BDRV_BLOCK_DATA : 0) | offset | BDRV_BLOCK_OFFSET_VALID;
 201 }
 202
 203 static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
 204         int nb_sectors)
 205 {
 206     int error = 0;
 207     int i;
 208     bool first = true;
 209
 210     for (i = 0; i < nb_sectors; i++) {
 211         error = cow_set_bit(bs, sector_num + i, &first);
 212         if (error) {
 213             break;
 214         }
 215     }
 216
 217     return error;
 218 }
 219
 220 static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num,
 221                                  uint8_t *buf, int nb_sectors)
 222 {
 223     BDRVCowState *s = bs->opaque;
 224     int ret, n;
 225
 226     while (nb_sectors > 0) {
 227         ret = cow_co_is_allocated(bs, sector_num, nb_sectors, &n);
 228         if (ret < 0) {
 229             return ret;
 230         }
 231         if (ret) {
 232             ret = bdrv_pread(bs->file,
 233                         s->cow_sectors_offset + sector_num * 512,
 234                         buf, n * 512);
 235             if (ret < 0) {
 236                 return ret;
 237             }
 238         } else {
 239             if (bs->backing_hd) {
 240                 /* read from the base image */
 241                 ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
 242                 if (ret < 0) {
 243                     return ret;
 244                 }
 245             } else {
 246                 memset(buf, 0, n * 512);
 247             }
 248         }
 249         nb_sectors -= n;
 250         sector_num += n;
 251         buf += n * 512;
 252     }
 253     return 0;
 254 }
 255
 256 static coroutine_fn int cow_co_read(BlockDriverState *bs, int64_t sector_num,
 257                                     uint8_t *buf, int nb_sectors)
 258 {
 259     int ret;
 260     BDRVCowState *s = bs->opaque;
 261     qemu_co_mutex_lock(&s->lock);
 262     ret = cow_read(bs, sector_num, buf, nb_sectors);
 263     qemu_co_mutex_unlock(&s->lock);
 264     return ret;
 265 }
 266
 267 static int cow_write(BlockDriverState *bs, int64_t sector_num,
 268                      const uint8_t *buf, int nb_sectors)
 269 {
 270     BDRVCowState *s = bs->opaque;
 271     int ret;
 272
 273     ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,
 274                       buf, nb_sectors * 512);
 275     if (ret < 0) {
 276         return ret;
 277     }
 278
 279     return cow_update_bitmap(bs, sector_num, nb_sectors);
 280 }
 281
 282 static coroutine_fn int cow_co_write(BlockDriverState *bs, int64_t sector_num,
 283                                      const uint8_t *buf, int nb_sectors)
 284 {
 285     int ret;
 286     BDRVCowState *s = bs->opaque;
 287     qemu_co_mutex_lock(&s->lock);
 288     ret = cow_write(bs, sector_num, buf, nb_sectors);
 289     qemu_co_mutex_unlock(&s->lock);
 290     return ret;
 291 }
 292
 293 static void cow_close(BlockDriverState *bs)
 294 {
 295 }
 296
 297 static int cow_create(const char *filename, QEMUOptionParameter *options)
 298 {
 299     struct cow_header_v2 cow_header;
 300     struct stat st;
 301     int64_t image_sectors = 0;
 302     const char *image_filename = NULL;
 303     int ret;
 304     BlockDriverState *cow_bs;
 305
 306     /* Read out options */
 307     while (options && options->name) {
 308         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
 309             image_sectors = options->value.n / 512;
 310         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
 311             image_filename = options->value.s;
 312         }
 313         options++;
 314     }
 315
 316     ret = bdrv_create_file(filename, options);
 317     if (ret < 0) {
 318         return ret;
 319     }
 320
 321     ret = bdrv_file_open(&cow_bs, filename, NULL, BDRV_O_RDWR);
 322     if (ret < 0) {
 323         return ret;
 324     }
 325
 326     memset(&cow_header, 0, sizeof(cow_header));
 327     cow_header.magic = cpu_to_be32(COW_MAGIC);
 328     cow_header.version = cpu_to_be32(COW_VERSION);
 329     if (image_filename) {
 330         /* Note: if no file, we put a dummy mtime */
 331         cow_header.mtime = cpu_to_be32(0);
 332
 333         if (stat(image_filename, &st) != 0) {
 334             goto mtime_fail;
 335         }
 336         cow_header.mtime = cpu_to_be32(st.st_mtime);
 337     mtime_fail:
 338         pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
 339                 image_filename);
 340     }
 341     cow_header.sectorsize = cpu_to_be32(512);
 342     cow_header.size = cpu_to_be64(image_sectors * 512);
 343     ret = bdrv_pwrite(cow_bs, 0, &cow_header, sizeof(cow_header));
 344     if (ret < 0) {
 345         goto exit;
 346     }
 347
 348     /* resize to include at least all the bitmap */
 349     ret = bdrv_truncate(cow_bs,
 350         sizeof(cow_header) + ((image_sectors + 7) >> 3));
 351     if (ret < 0) {
 352         goto exit;
 353     }
 354
 355 exit:
 356     bdrv_unref(cow_bs);
 357     return ret;
 358 }
 359
 360 static QEMUOptionParameter cow_create_options[] = {
 361     {
 362         .name = BLOCK_OPT_SIZE,
 363         .type = OPT_SIZE,
 364         .help = "Virtual disk size"
 365     },
 366     {
 367         .name = BLOCK_OPT_BACKING_FILE,
 368         .type = OPT_STRING,
 369         .help = "File name of a base image"
 370     },
 371     { NULL }
 372 };
 373
 374 static BlockDriver bdrv_cow = {
 375     .format_name    = "cow",
 376     .instance_size  = sizeof(BDRVCowState),
 377
 378     .bdrv_probe     = cow_probe,
 379     .bdrv_open      = cow_open,
 380     .bdrv_close     = cow_close,
 381     .bdrv_create    = cow_create,
 382     .bdrv_has_zero_init     = bdrv_has_zero_init_1,
 383
 384     .bdrv_read              = cow_co_read,
 385     .bdrv_write             = cow_co_write,
 386     .bdrv_co_get_block_status   = cow_co_get_block_status,
 387
 388     .create_options = cow_create_options,
 389 };
 390
 391 static void bdrv_cow_init(void)
 392 {
 393     bdrv_register(&bdrv_cow);
 394 }
 395
 396 block_init(bdrv_cow_init);