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, 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 = -EINVAL;
  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)
 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     bitmap |= (1 << (bitnum % 8));
 121
 122     ret = bdrv_pwrite_sync(bs->file, offset, &bitmap, sizeof(bitmap));
 123     if (ret < 0) {
 124        return ret;
 125     }
 126     return 0;
 127 }
 128
 129 static inline int is_bit_set(BlockDriverState *bs, int64_t bitnum)
 130 {
 131     uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
 132     uint8_t bitmap;
 133     int ret;
 134
 135     ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
 136     if (ret < 0) {
 137        return ret;
 138     }
 139
 140     return !!(bitmap & (1 << (bitnum % 8)));
 141 }
 142
 143 /* Return true if first block has been changed (ie. current version is
 144  * in COW file).  Set the number of continuous blocks for which that
 145  * is true. */
 146 static int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,
 147         int64_t sector_num, int nb_sectors, int *num_same)
 148 {
 149     int changed;
 150
 151     if (nb_sectors == 0) {
 152         *num_same = nb_sectors;
 153         return 0;
 154     }
 155
 156     changed = is_bit_set(bs, sector_num);
 157     if (changed < 0) {
 158         return 0; /* XXX: how to return I/O errors? */
 159     }
 160
 161     for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
 162         if (is_bit_set(bs, sector_num + *num_same) != changed)
 163             break;
 164     }
 165
 166     return changed;
 167 }
 168
 169 static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
 170         int nb_sectors)
 171 {
 172     int error = 0;
 173     int i;
 174
 175     for (i = 0; i < nb_sectors; i++) {
 176         error = cow_set_bit(bs, sector_num + i);
 177         if (error) {
 178             break;
 179         }
 180     }
 181
 182     return error;
 183 }
 184
 185 static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num,
 186                                  uint8_t *buf, int nb_sectors)
 187 {
 188     BDRVCowState *s = bs->opaque;
 189     int ret, n;
 190
 191     while (nb_sectors > 0) {
 192         if (bdrv_co_is_allocated(bs, sector_num, nb_sectors, &n)) {
 193             ret = bdrv_pread(bs->file,
 194                         s->cow_sectors_offset + sector_num * 512,
 195                         buf, n * 512);
 196             if (ret < 0) {
 197                 return ret;
 198             }
 199         } else {
 200             if (bs->backing_hd) {
 201                 /* read from the base image */
 202                 ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
 203                 if (ret < 0) {
 204                     return ret;
 205                 }
 206             } else {
 207                 memset(buf, 0, n * 512);
 208             }
 209         }
 210         nb_sectors -= n;
 211         sector_num += n;
 212         buf += n * 512;
 213     }
 214     return 0;
 215 }
 216
 217 static coroutine_fn int cow_co_read(BlockDriverState *bs, int64_t sector_num,
 218                                     uint8_t *buf, int nb_sectors)
 219 {
 220     int ret;
 221     BDRVCowState *s = bs->opaque;
 222     qemu_co_mutex_lock(&s->lock);
 223     ret = cow_read(bs, sector_num, buf, nb_sectors);
 224     qemu_co_mutex_unlock(&s->lock);
 225     return ret;
 226 }
 227
 228 static int cow_write(BlockDriverState *bs, int64_t sector_num,
 229                      const uint8_t *buf, int nb_sectors)
 230 {
 231     BDRVCowState *s = bs->opaque;
 232     int ret;
 233
 234     ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,
 235                       buf, nb_sectors * 512);
 236     if (ret < 0) {
 237         return ret;
 238     }
 239
 240     return cow_update_bitmap(bs, sector_num, nb_sectors);
 241 }
 242
 243 static coroutine_fn int cow_co_write(BlockDriverState *bs, int64_t sector_num,
 244                                      const uint8_t *buf, int nb_sectors)
 245 {
 246     int ret;
 247     BDRVCowState *s = bs->opaque;
 248     qemu_co_mutex_lock(&s->lock);
 249     ret = cow_write(bs, sector_num, buf, nb_sectors);
 250     qemu_co_mutex_unlock(&s->lock);
 251     return ret;
 252 }
 253
 254 static void cow_close(BlockDriverState *bs)
 255 {
 256 }
 257
 258 static int cow_create(const char *filename, QEMUOptionParameter *options)
 259 {
 260     struct cow_header_v2 cow_header;
 261     struct stat st;
 262     int64_t image_sectors = 0;
 263     const char *image_filename = NULL;
 264     int ret;
 265     BlockDriverState *cow_bs;
 266
 267     /* Read out options */
 268     while (options && options->name) {
 269         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
 270             image_sectors = options->value.n / 512;
 271         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
 272             image_filename = options->value.s;
 273         }
 274         options++;
 275     }
 276
 277     ret = bdrv_create_file(filename, options);
 278     if (ret < 0) {
 279         return ret;
 280     }
 281
 282     ret = bdrv_file_open(&cow_bs, filename, BDRV_O_RDWR);
 283     if (ret < 0) {
 284         return ret;
 285     }
 286
 287     memset(&cow_header, 0, sizeof(cow_header));
 288     cow_header.magic = cpu_to_be32(COW_MAGIC);
 289     cow_header.version = cpu_to_be32(COW_VERSION);
 290     if (image_filename) {
 291         /* Note: if no file, we put a dummy mtime */
 292         cow_header.mtime = cpu_to_be32(0);
 293
 294         if (stat(image_filename, &st) != 0) {
 295             goto mtime_fail;
 296         }
 297         cow_header.mtime = cpu_to_be32(st.st_mtime);
 298     mtime_fail:
 299         pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
 300                 image_filename);
 301     }
 302     cow_header.sectorsize = cpu_to_be32(512);
 303     cow_header.size = cpu_to_be64(image_sectors * 512);
 304     ret = bdrv_pwrite(cow_bs, 0, &cow_header, sizeof(cow_header));
 305     if (ret < 0) {
 306         goto exit;
 307     }
 308
 309     /* resize to include at least all the bitmap */
 310     ret = bdrv_truncate(cow_bs,
 311         sizeof(cow_header) + ((image_sectors + 7) >> 3));
 312     if (ret < 0) {
 313         goto exit;
 314     }
 315
 316 exit:
 317     bdrv_delete(cow_bs);
 318     return ret;
 319 }
 320
 321 static QEMUOptionParameter cow_create_options[] = {
 322     {
 323         .name = BLOCK_OPT_SIZE,
 324         .type = OPT_SIZE,
 325         .help = "Virtual disk size"
 326     },
 327     {
 328         .name = BLOCK_OPT_BACKING_FILE,
 329         .type = OPT_STRING,
 330         .help = "File name of a base image"
 331     },
 332     { NULL }
 333 };
 334
 335 static BlockDriver bdrv_cow = {
 336     .format_name    = "cow",
 337     .instance_size  = sizeof(BDRVCowState),
 338
 339     .bdrv_probe     = cow_probe,
 340     .bdrv_open      = cow_open,
 341     .bdrv_close     = cow_close,
 342     .bdrv_create    = cow_create,
 343
 344     .bdrv_read              = cow_co_read,
 345     .bdrv_write             = cow_co_write,
 346     .bdrv_co_is_allocated   = cow_co_is_allocated,
 347
 348     .create_options = cow_create_options,
 349 };
 350
 351 static void bdrv_cow_init(void)
 352 {
 353     bdrv_register(&bdrv_cow);
 354 }
 355
 356 block_init(bdrv_cow_init);