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 /*
 107  * XXX(hch): right now these functions are extremely inefficient.
 108  * We should just read the whole bitmap we'll need in one go instead.
 109  */
 110 static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum, bool *first)
 111 {
 112     uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
 113     uint8_t bitmap;
 114     int ret;
 115
 116     ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
 117     if (ret < 0) {
 118        return ret;
 119     }
 120
 121     if (bitmap & (1 << (bitnum % 8))) {
 122         return 0;
 123     }
 124
 125     if (*first) {
 126         ret = bdrv_flush(bs->file);
 127         if (ret < 0) {
 128             return ret;
 129         }
 130         *first = false;
 131     }
 132
 133     bitmap |= (1 << (bitnum % 8));
 134
 135     ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap));
 136     if (ret < 0) {
 137        return ret;
 138     }
 139     return 0;
 140 }
 141
 142 #define BITS_PER_BITMAP_SECTOR (512 * 8)
 143
 144 /* Cannot use bitmap.c on big-endian machines.  */
 145 static int cow_test_bit(int64_t bitnum, const uint8_t *bitmap)
 146 {
 147     return (bitmap[bitnum / 8] & (1 << (bitnum & 7))) != 0;
 148 }
 149
 150 static int cow_find_streak(const uint8_t *bitmap, int value, int start, int nb_sectors)
 151 {
 152     int streak_value = value ? 0xFF : 0;
 153     int last = MIN(start + nb_sectors, BITS_PER_BITMAP_SECTOR);
 154     int bitnum = start;
 155     while (bitnum < last) {
 156         if ((bitnum & 7) == 0 && bitmap[bitnum / 8] == streak_value) {
 157             bitnum += 8;
 158             continue;
 159         }
 160         if (cow_test_bit(bitnum, bitmap) == value) {
 161             bitnum++;
 162             continue;
 163         }
 164         break;
 165     }
 166     return MIN(bitnum, last) - start;
 167 }
 168
 169 /* Return true if first block has been changed (ie. current version is
 170  * in COW file).  Set the number of continuous blocks for which that
 171  * is true. */
 172 static int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,
 173         int64_t sector_num, int nb_sectors, int *num_same)
 174 {
 175     int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;
 176     uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;
 177     uint8_t bitmap[BDRV_SECTOR_SIZE];
 178     int ret;
 179     int changed;
 180
 181     ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
 182     if (ret < 0) {
 183         return ret;
 184     }
 185
 186     bitnum &= BITS_PER_BITMAP_SECTOR - 1;
 187     changed = cow_test_bit(bitnum, bitmap);
 188     *num_same = cow_find_streak(bitmap, changed, bitnum, nb_sectors);
 189     return changed;
 190 }
 191
 192 static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs,
 193         int64_t sector_num, int nb_sectors, int *num_same)
 194 {
 195     BDRVCowState *s = bs->opaque;
 196     int ret = cow_co_is_allocated(bs, sector_num, nb_sectors, num_same);
 197     int64_t offset = s->cow_sectors_offset + (sector_num << BDRV_SECTOR_BITS);
 198     if (ret < 0) {
 199         return ret;
 200     }
 201     return (ret ? BDRV_BLOCK_DATA : 0) | offset | BDRV_BLOCK_OFFSET_VALID;
 202 }
 203
 204 static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
 205         int nb_sectors)
 206 {
 207     int error = 0;
 208     int i;
 209     bool first = true;
 210
 211     for (i = 0; i < nb_sectors; i++) {
 212         error = cow_set_bit(bs, sector_num + i, &first);
 213         if (error) {
 214             break;
 215         }
 216     }
 217
 218     return error;
 219 }
 220
 221 static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num,
 222                                  uint8_t *buf, int nb_sectors)
 223 {
 224     BDRVCowState *s = bs->opaque;
 225     int ret, n;
 226
 227     while (nb_sectors > 0) {
 228         ret = cow_co_is_allocated(bs, sector_num, nb_sectors, &n);
 229         if (ret < 0) {
 230             return ret;
 231         }
 232         if (ret) {
 233             ret = bdrv_pread(bs->file,
 234                         s->cow_sectors_offset + sector_num * 512,
 235                         buf, n * 512);
 236             if (ret < 0) {
 237                 return ret;
 238             }
 239         } else {
 240             if (bs->backing_hd) {
 241                 /* read from the base image */
 242                 ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
 243                 if (ret < 0) {
 244                     return ret;
 245                 }
 246             } else {
 247                 memset(buf, 0, n * 512);
 248             }
 249         }
 250         nb_sectors -= n;
 251         sector_num += n;
 252         buf += n * 512;
 253     }
 254     return 0;
 255 }
 256
 257 static coroutine_fn int cow_co_read(BlockDriverState *bs, int64_t sector_num,
 258                                     uint8_t *buf, int nb_sectors)
 259 {
 260     int ret;
 261     BDRVCowState *s = bs->opaque;
 262     qemu_co_mutex_lock(&s->lock);
 263     ret = cow_read(bs, sector_num, buf, nb_sectors);
 264     qemu_co_mutex_unlock(&s->lock);
 265     return ret;
 266 }
 267
 268 static int cow_write(BlockDriverState *bs, int64_t sector_num,
 269                      const uint8_t *buf, int nb_sectors)
 270 {
 271     BDRVCowState *s = bs->opaque;
 272     int ret;
 273
 274     ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,
 275                       buf, nb_sectors * 512);
 276     if (ret < 0) {
 277         return ret;
 278     }
 279
 280     return cow_update_bitmap(bs, sector_num, nb_sectors);
 281 }
 282
 283 static coroutine_fn int cow_co_write(BlockDriverState *bs, int64_t sector_num,
 284                                      const uint8_t *buf, int nb_sectors)
 285 {
 286     int ret;
 287     BDRVCowState *s = bs->opaque;
 288     qemu_co_mutex_lock(&s->lock);
 289     ret = cow_write(bs, sector_num, buf, nb_sectors);
 290     qemu_co_mutex_unlock(&s->lock);
 291     return ret;
 292 }
 293
 294 static void cow_close(BlockDriverState *bs)
 295 {
 296 }
 297
 298 static int cow_create(const char *filename, QEMUOptionParameter *options,
 299                       Error **errp)
 300 {
 301     struct cow_header_v2 cow_header;
 302     struct stat st;
 303     int64_t image_sectors = 0;
 304     const char *image_filename = NULL;
 305     Error *local_err = NULL;
 306     int ret;
 307     BlockDriverState *cow_bs;
 308
 309     /* Read out options */
 310     while (options && options->name) {
 311         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
 312             image_sectors = options->value.n / 512;
 313         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
 314             image_filename = options->value.s;
 315         }
 316         options++;
 317     }
 318
 319     ret = bdrv_create_file(filename, options, &local_err);
 320     if (ret < 0) {
 321         qerror_report_err(local_err);
 322         error_free(local_err);
 323         return ret;
 324     }
 325
 326     ret = bdrv_file_open(&cow_bs, filename, NULL, BDRV_O_RDWR, &local_err);
 327     if (ret < 0) {
 328         qerror_report_err(local_err);
 329         error_free(local_err);
 330         return ret;
 331     }
 332
 333     memset(&cow_header, 0, sizeof(cow_header));
 334     cow_header.magic = cpu_to_be32(COW_MAGIC);
 335     cow_header.version = cpu_to_be32(COW_VERSION);
 336     if (image_filename) {
 337         /* Note: if no file, we put a dummy mtime */
 338         cow_header.mtime = cpu_to_be32(0);
 339
 340         if (stat(image_filename, &st) != 0) {
 341             goto mtime_fail;
 342         }
 343         cow_header.mtime = cpu_to_be32(st.st_mtime);
 344     mtime_fail:
 345         pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
 346                 image_filename);
 347     }
 348     cow_header.sectorsize = cpu_to_be32(512);
 349     cow_header.size = cpu_to_be64(image_sectors * 512);
 350     ret = bdrv_pwrite(cow_bs, 0, &cow_header, sizeof(cow_header));
 351     if (ret < 0) {
 352         goto exit;
 353     }
 354
 355     /* resize to include at least all the bitmap */
 356     ret = bdrv_truncate(cow_bs,
 357         sizeof(cow_header) + ((image_sectors + 7) >> 3));
 358     if (ret < 0) {
 359         goto exit;
 360     }
 361
 362 exit:
 363     bdrv_unref(cow_bs);
 364     return ret;
 365 }
 366
 367 static QEMUOptionParameter cow_create_options[] = {
 368     {
 369         .name = BLOCK_OPT_SIZE,
 370         .type = OPT_SIZE,
 371         .help = "Virtual disk size"
 372     },
 373     {
 374         .name = BLOCK_OPT_BACKING_FILE,
 375         .type = OPT_STRING,
 376         .help = "File name of a base image"
 377     },
 378     { NULL }
 379 };
 380
 381 static BlockDriver bdrv_cow = {
 382     .format_name    = "cow",
 383     .instance_size  = sizeof(BDRVCowState),
 384
 385     .bdrv_probe     = cow_probe,
 386     .bdrv_open      = cow_open,
 387     .bdrv_close     = cow_close,
 388     .bdrv_create    = cow_create,
 389     .bdrv_has_zero_init     = bdrv_has_zero_init_1,
 390
 391     .bdrv_read              = cow_co_read,
 392     .bdrv_write             = cow_co_write,
 393     .bdrv_co_get_block_status   = cow_co_get_block_status,
 394
 395     .create_options = cow_create_options,
 396 };
 397
 398 static void bdrv_cow_init(void)
 399 {
 400     bdrv_register(&bdrv_cow);
 401 }
 402
 403 block_init(bdrv_cow_init);