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 #ifndef _WIN32
  25 #include "vl.h"
  26 #include "block_int.h"
  27 #include <sys/mman.h>
  28
  29 /**************************************************************/
  30 /* COW block driver using file system holes */
  31
  32 /* user mode linux compatible COW file */
  33 #define COW_MAGIC 0x4f4f4f4d  /* MOOO */
  34 #define COW_VERSION 2
  35
  36 struct cow_header_v2 {
  37     uint32_t magic;
  38     uint32_t version;
  39     char backing_file[1024];
  40     int32_t mtime;
  41     uint64_t size;
  42     uint32_t sectorsize;
  43 };
  44
  45 typedef struct BDRVCowState {
  46     int fd;
  47     uint8_t *cow_bitmap; /* if non NULL, COW mappings are used first */
  48     uint8_t *cow_bitmap_addr; /* mmap address of cow_bitmap */
  49     int cow_bitmap_size;
  50     int64_t cow_sectors_offset;
  51 } BDRVCowState;
  52
  53 static int cow_probe(const uint8_t *buf, int buf_size, const char *filename)
  54 {
  55     const struct cow_header_v2 *cow_header = (const void *)buf;
  56
  57     if (be32_to_cpu(cow_header->magic) == COW_MAGIC &&
  58         be32_to_cpu(cow_header->version) == COW_VERSION)
  59         return 100;
  60     else
  61         return 0;
  62 }
  63
  64 static int cow_open(BlockDriverState *bs, const char *filename)
  65 {
  66     BDRVCowState *s = bs->opaque;
  67     int fd;
  68     struct cow_header_v2 cow_header;
  69     int64_t size;
  70
  71     fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
  72     if (fd < 0) {
  73         fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
  74         if (fd < 0)
  75             return -1;
  76     }
  77     s->fd = fd;
  78     /* see if it is a cow image */
  79     if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) {
  80         goto fail;
  81     }
  82
  83     if (be32_to_cpu(cow_header.magic) != COW_MAGIC ||
  84         be32_to_cpu(cow_header.version) != COW_VERSION) {
  85         goto fail;
  86     }
  87
  88     /* cow image found */
  89     size = be64_to_cpu(cow_header.size);
  90     bs->total_sectors = size / 512;
  91
  92     pstrcpy(bs->backing_file, sizeof(bs->backing_file),
  93             cow_header.backing_file);
  94
  95 #if 0
  96     if (cow_header.backing_file[0] != '\0') {
  97         if (stat(cow_header.backing_file, &st) != 0) {
  98             fprintf(stderr, "%s: could not find original disk image '%s'\n", filename, cow_header.backing_file);
  99             goto fail;
 100         }
 101         if (st.st_mtime != be32_to_cpu(cow_header.mtime)) {
 102             fprintf(stderr, "%s: original raw disk image '%s' does not match saved timestamp\n", filename, cow_header.backing_file);
 103             goto fail;
 104             }
 105         fd = open(cow_header.backing_file, O_RDONLY | O_LARGEFILE);
 106         if (fd < 0)
 107             goto fail;
 108         bs->fd = fd;
 109     }
 110 #endif
 111     /* mmap the bitmap */
 112     s->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
 113     s->cow_bitmap_addr = mmap(get_mmap_addr(s->cow_bitmap_size),
 114                               s->cow_bitmap_size,
 115                               PROT_READ | PROT_WRITE,
 116                               MAP_SHARED, s->fd, 0);
 117     if (s->cow_bitmap_addr == MAP_FAILED)
 118         goto fail;
 119     s->cow_bitmap = s->cow_bitmap_addr + sizeof(cow_header);
 120     s->cow_sectors_offset = (s->cow_bitmap_size + 511) & ~511;
 121     return 0;
 122  fail:
 123     close(fd);
 124     return -1;
 125 }
 126
 127 static inline void cow_set_bit(uint8_t *bitmap, int64_t bitnum)
 128 {
 129     bitmap[bitnum / 8] |= (1 << (bitnum%8));
 130 }
 131
 132 static inline int is_bit_set(const uint8_t *bitmap, int64_t bitnum)
 133 {
 134     return !!(bitmap[bitnum / 8] & (1 << (bitnum%8)));
 135 }
 136
 137
 138 /* Return true if first block has been changed (ie. current version is
 139  * in COW file).  Set the number of continuous blocks for which that
 140  * is true. */
 141 static inline int is_changed(uint8_t *bitmap,
 142                              int64_t sector_num, int nb_sectors,
 143                              int *num_same)
 144 {
 145     int changed;
 146
 147     if (!bitmap || nb_sectors == 0) {
 148         *num_same = nb_sectors;
 149         return 0;
 150     }
 151
 152     changed = is_bit_set(bitmap, sector_num);
 153     for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
 154         if (is_bit_set(bitmap, sector_num + *num_same) != changed)
 155             break;
 156     }
 157
 158     return changed;
 159 }
 160
 161 static int cow_is_allocated(BlockDriverState *bs, int64_t sector_num,
 162                             int nb_sectors, int *pnum)
 163 {
 164     BDRVCowState *s = bs->opaque;
 165     return is_changed(s->cow_bitmap, sector_num, nb_sectors, pnum);
 166 }
 167
 168 static int cow_read(BlockDriverState *bs, int64_t sector_num,
 169                     uint8_t *buf, int nb_sectors)
 170 {
 171     BDRVCowState *s = bs->opaque;
 172     int ret, n;
 173
 174     while (nb_sectors > 0) {
 175         if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) {
 176             lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
 177             ret = read(s->fd, buf, n * 512);
 178             if (ret != n * 512)
 179                 return -1;
 180         } else {
 181             memset(buf, 0, n * 512);
 182         }
 183         nb_sectors -= n;
 184         sector_num += n;
 185         buf += n * 512;
 186     }
 187     return 0;
 188 }
 189
 190 static int cow_write(BlockDriverState *bs, int64_t sector_num,
 191                      const uint8_t *buf, int nb_sectors)
 192 {
 193     BDRVCowState *s = bs->opaque;
 194     int ret, i;
 195
 196     lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
 197     ret = write(s->fd, buf, nb_sectors * 512);
 198     if (ret != nb_sectors * 512)
 199         return -1;
 200     for (i = 0; i < nb_sectors; i++)
 201         cow_set_bit(s->cow_bitmap, sector_num + i);
 202     return 0;
 203 }
 204
 205 static void cow_close(BlockDriverState *bs)
 206 {
 207     BDRVCowState *s = bs->opaque;
 208     munmap(s->cow_bitmap_addr, s->cow_bitmap_size);
 209     close(s->fd);
 210 }
 211
 212 static int cow_create(const char *filename, int64_t image_sectors,
 213                       const char *image_filename, int flags)
 214 {
 215     int fd, cow_fd;
 216     struct cow_header_v2 cow_header;
 217     struct stat st;
 218
 219     if (flags)
 220         return -ENOTSUP;
 221
 222     cow_fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE,
 223               0644);
 224     if (cow_fd < 0)
 225         return -1;
 226     memset(&cow_header, 0, sizeof(cow_header));
 227     cow_header.magic = cpu_to_be32(COW_MAGIC);
 228     cow_header.version = cpu_to_be32(COW_VERSION);
 229     if (image_filename) {
 230         fd = open(image_filename, O_RDONLY | O_BINARY);
 231         if (fd < 0) {
 232             close(cow_fd);
 233             return -1;
 234         }
 235         if (fstat(fd, &st) != 0) {
 236             close(fd);
 237             return -1;
 238         }
 239         close(fd);
 240         cow_header.mtime = cpu_to_be32(st.st_mtime);
 241         realpath(image_filename, cow_header.backing_file);
 242     }
 243     cow_header.sectorsize = cpu_to_be32(512);
 244     cow_header.size = cpu_to_be64(image_sectors * 512);
 245     write(cow_fd, &cow_header, sizeof(cow_header));
 246     /* resize to include at least all the bitmap */
 247     ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));
 248     close(cow_fd);
 249     return 0;
 250 }
 251
 252 BlockDriver bdrv_cow = {
 253     "cow",
 254     sizeof(BDRVCowState),
 255     cow_probe,
 256     cow_open,
 257     cow_read,
 258     cow_write,
 259     cow_close,
 260     cow_create,
 261     cow_is_allocated,
 262 };
 263 #endif