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 int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
 192         int nb_sectors)
 193 {
 194     int error = 0;
 195     int i;
 196     bool first = true;
 197
 198     for (i = 0; i < nb_sectors; i++) {
 199         error = cow_set_bit(bs, sector_num + i, &first);
 200         if (error) {
 201             break;
 202         }
 203     }
 204
 205     return error;
 206 }
 207
 208 static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num,
 209                                  uint8_t *buf, int nb_sectors)
 210 {
 211     BDRVCowState *s = bs->opaque;
 212     int ret, n;
 213
 214     while (nb_sectors > 0) {
 215         if (cow_co_is_allocated(bs, sector_num, nb_sectors, &n)) {
 216             ret = bdrv_pread(bs->file,
 217                         s->cow_sectors_offset + sector_num * 512,
 218                         buf, n * 512);
 219             if (ret < 0) {
 220                 return ret;
 221             }
 222         } else {
 223             if (bs->backing_hd) {
 224                 /* read from the base image */
 225                 ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
 226                 if (ret < 0) {
 227                     return ret;
 228                 }
 229             } else {
 230                 memset(buf, 0, n * 512);
 231             }
 232         }
 233         nb_sectors -= n;
 234         sector_num += n;
 235         buf += n * 512;
 236     }
 237     return 0;
 238 }
 239
 240 static coroutine_fn int cow_co_read(BlockDriverState *bs, int64_t sector_num,
 241                                     uint8_t *buf, int nb_sectors)
 242 {
 243     int ret;
 244     BDRVCowState *s = bs->opaque;
 245     qemu_co_mutex_lock(&s->lock);
 246     ret = cow_read(bs, sector_num, buf, nb_sectors);
 247     qemu_co_mutex_unlock(&s->lock);
 248     return ret;
 249 }
 250
 251 static int cow_write(BlockDriverState *bs, int64_t sector_num,
 252                      const uint8_t *buf, int nb_sectors)
 253 {
 254     BDRVCowState *s = bs->opaque;
 255     int ret;
 256
 257     ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,
 258                       buf, nb_sectors * 512);
 259     if (ret < 0) {
 260         return ret;
 261     }
 262
 263     return cow_update_bitmap(bs, sector_num, nb_sectors);
 264 }
 265
 266 static coroutine_fn int cow_co_write(BlockDriverState *bs, int64_t sector_num,
 267                                      const uint8_t *buf, int nb_sectors)
 268 {
 269     int ret;
 270     BDRVCowState *s = bs->opaque;
 271     qemu_co_mutex_lock(&s->lock);
 272     ret = cow_write(bs, sector_num, buf, nb_sectors);
 273     qemu_co_mutex_unlock(&s->lock);
 274     return ret;
 275 }
 276
 277 static void cow_close(BlockDriverState *bs)
 278 {
 279 }
 280
 281 static int cow_create(const char *filename, QEMUOptionParameter *options)
 282 {
 283     struct cow_header_v2 cow_header;
 284     struct stat st;
 285     int64_t image_sectors = 0;
 286     const char *image_filename = NULL;
 287     int ret;
 288     BlockDriverState *cow_bs;
 289
 290     /* Read out options */
 291     while (options && options->name) {
 292         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
 293             image_sectors = options->value.n / 512;
 294         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
 295             image_filename = options->value.s;
 296         }
 297         options++;
 298     }
 299
 300     ret = bdrv_create_file(filename, options);
 301     if (ret < 0) {
 302         return ret;
 303     }
 304
 305     ret = bdrv_file_open(&cow_bs, filename, NULL, BDRV_O_RDWR);
 306     if (ret < 0) {
 307         return ret;
 308     }
 309
 310     memset(&cow_header, 0, sizeof(cow_header));
 311     cow_header.magic = cpu_to_be32(COW_MAGIC);
 312     cow_header.version = cpu_to_be32(COW_VERSION);
 313     if (image_filename) {
 314         /* Note: if no file, we put a dummy mtime */
 315         cow_header.mtime = cpu_to_be32(0);
 316
 317         if (stat(image_filename, &st) != 0) {
 318             goto mtime_fail;
 319         }
 320         cow_header.mtime = cpu_to_be32(st.st_mtime);
 321     mtime_fail:
 322         pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
 323                 image_filename);
 324     }
 325     cow_header.sectorsize = cpu_to_be32(512);
 326     cow_header.size = cpu_to_be64(image_sectors * 512);
 327     ret = bdrv_pwrite(cow_bs, 0, &cow_header, sizeof(cow_header));
 328     if (ret < 0) {
 329         goto exit;
 330     }
 331
 332     /* resize to include at least all the bitmap */
 333     ret = bdrv_truncate(cow_bs,
 334         sizeof(cow_header) + ((image_sectors + 7) >> 3));
 335     if (ret < 0) {
 336         goto exit;
 337     }
 338
 339 exit:
 340     bdrv_unref(cow_bs);
 341     return ret;
 342 }
 343
 344 static QEMUOptionParameter cow_create_options[] = {
 345     {
 346         .name = BLOCK_OPT_SIZE,
 347         .type = OPT_SIZE,
 348         .help = "Virtual disk size"
 349     },
 350     {
 351         .name = BLOCK_OPT_BACKING_FILE,
 352         .type = OPT_STRING,
 353         .help = "File name of a base image"
 354     },
 355     { NULL }
 356 };
 357
 358 static BlockDriver bdrv_cow = {
 359     .format_name    = "cow",
 360     .instance_size  = sizeof(BDRVCowState),
 361
 362     .bdrv_probe     = cow_probe,
 363     .bdrv_open      = cow_open,
 364     .bdrv_close     = cow_close,
 365     .bdrv_create    = cow_create,
 366     .bdrv_has_zero_init     = bdrv_has_zero_init_1,
 367
 368     .bdrv_read              = cow_co_read,
 369     .bdrv_write             = cow_co_write,
 370     .bdrv_co_is_allocated   = cow_co_is_allocated,
 371
 372     .create_options = cow_create_options,
 373 };
 374
 375 static void bdrv_cow_init(void)
 376 {
 377     bdrv_register(&bdrv_cow);
 378 }
 379
 380 block_init(bdrv_cow_init);