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 "qemu-common.h"
  26 #include "block_int.h"
  27 #include "module.h"
  28 #include <sys/mman.h>
  29
  30 /**************************************************************/
  31 /* COW block driver using file system holes */
  32
  33 /* user mode linux compatible COW file */
  34 #define COW_MAGIC 0x4f4f4f4d  /* MOOO */
  35 #define COW_VERSION 2
  36
  37 struct cow_header_v2 {
  38     uint32_t magic;
  39     uint32_t version;
  40     char backing_file[1024];
  41     int32_t mtime;
  42     uint64_t size;
  43     uint32_t sectorsize;
  44 };
  45
  46 typedef struct BDRVCowState {
  47     int fd;
  48     uint8_t *cow_bitmap; /* if non NULL, COW mappings are used first */
  49     uint8_t *cow_bitmap_addr; /* mmap address of cow_bitmap */
  50     int cow_bitmap_size;
  51     int64_t cow_sectors_offset;
  52 } BDRVCowState;
  53
  54 static int cow_probe(const uint8_t *buf, int buf_size, const char *filename)
  55 {
  56     const struct cow_header_v2 *cow_header = (const void *)buf;
  57
  58     if (buf_size >= sizeof(struct cow_header_v2) &&
  59         be32_to_cpu(cow_header->magic) == COW_MAGIC &&
  60         be32_to_cpu(cow_header->version) == COW_VERSION)
  61         return 100;
  62     else
  63         return 0;
  64 }
  65
  66 static int cow_open(BlockDriverState *bs, const char *filename, int flags)
  67 {
  68     BDRVCowState *s = bs->opaque;
  69     int fd;
  70     struct cow_header_v2 cow_header;
  71     int64_t size;
  72
  73     fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
  74     if (fd < 0) {
  75         fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
  76         if (fd < 0)
  77             return -1;
  78     }
  79     s->fd = fd;
  80     /* see if it is a cow image */
  81     if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) {
  82         goto fail;
  83     }
  84
  85     if (be32_to_cpu(cow_header.magic) != COW_MAGIC ||
  86         be32_to_cpu(cow_header.version) != COW_VERSION) {
  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     /* mmap the bitmap */
  98     s->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
  99     s->cow_bitmap_addr = (void *)mmap(get_mmap_addr(s->cow_bitmap_size),
 100                                       s->cow_bitmap_size,
 101                                       PROT_READ | PROT_WRITE,
 102                                       MAP_SHARED, s->fd, 0);
 103     if (s->cow_bitmap_addr == MAP_FAILED)
 104         goto fail;
 105     s->cow_bitmap = s->cow_bitmap_addr + sizeof(cow_header);
 106     s->cow_sectors_offset = (s->cow_bitmap_size + 511) & ~511;
 107     return 0;
 108  fail:
 109     close(fd);
 110     return -1;
 111 }
 112
 113 static inline void cow_set_bit(uint8_t *bitmap, int64_t bitnum)
 114 {
 115     bitmap[bitnum / 8] |= (1 << (bitnum%8));
 116 }
 117
 118 static inline int is_bit_set(const uint8_t *bitmap, int64_t bitnum)
 119 {
 120     return !!(bitmap[bitnum / 8] & (1 << (bitnum%8)));
 121 }
 122
 123
 124 /* Return true if first block has been changed (ie. current version is
 125  * in COW file).  Set the number of continuous blocks for which that
 126  * is true. */
 127 static inline int is_changed(uint8_t *bitmap,
 128                              int64_t sector_num, int nb_sectors,
 129                              int *num_same)
 130 {
 131     int changed;
 132
 133     if (!bitmap || nb_sectors == 0) {
 134         *num_same = nb_sectors;
 135         return 0;
 136     }
 137
 138     changed = is_bit_set(bitmap, sector_num);
 139     for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
 140         if (is_bit_set(bitmap, sector_num + *num_same) != changed)
 141             break;
 142     }
 143
 144     return changed;
 145 }
 146
 147 static int cow_is_allocated(BlockDriverState *bs, int64_t sector_num,
 148                             int nb_sectors, int *pnum)
 149 {
 150     BDRVCowState *s = bs->opaque;
 151     return is_changed(s->cow_bitmap, sector_num, nb_sectors, pnum);
 152 }
 153
 154 static int cow_read(BlockDriverState *bs, int64_t sector_num,
 155                     uint8_t *buf, int nb_sectors)
 156 {
 157     BDRVCowState *s = bs->opaque;
 158     int ret, n;
 159
 160     while (nb_sectors > 0) {
 161         if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) {
 162             lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
 163             ret = read(s->fd, buf, n * 512);
 164             if (ret != n * 512)
 165                 return -1;
 166         } else {
 167             if (bs->backing_hd) {
 168                 /* read from the base image */
 169                 ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
 170                 if (ret < 0)
 171                     return -1;
 172             } else {
 173             memset(buf, 0, n * 512);
 174         }
 175         }
 176         nb_sectors -= n;
 177         sector_num += n;
 178         buf += n * 512;
 179     }
 180     return 0;
 181 }
 182
 183 static int cow_write(BlockDriverState *bs, int64_t sector_num,
 184                      const uint8_t *buf, int nb_sectors)
 185 {
 186     BDRVCowState *s = bs->opaque;
 187     int ret, i;
 188
 189     lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
 190     ret = write(s->fd, buf, nb_sectors * 512);
 191     if (ret != nb_sectors * 512)
 192         return -1;
 193     for (i = 0; i < nb_sectors; i++)
 194         cow_set_bit(s->cow_bitmap, sector_num + i);
 195     return 0;
 196 }
 197
 198 static void cow_close(BlockDriverState *bs)
 199 {
 200     BDRVCowState *s = bs->opaque;
 201     munmap((void *)s->cow_bitmap_addr, s->cow_bitmap_size);
 202     close(s->fd);
 203 }
 204
 205 static int cow_create(const char *filename, int64_t image_sectors,
 206                       const char *image_filename, int flags)
 207 {
 208     int fd, cow_fd;
 209     struct cow_header_v2 cow_header;
 210     struct stat st;
 211
 212     if (flags)
 213         return -ENOTSUP;
 214
 215     cow_fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
 216               0644);
 217     if (cow_fd < 0)
 218         return -1;
 219     memset(&cow_header, 0, sizeof(cow_header));
 220     cow_header.magic = cpu_to_be32(COW_MAGIC);
 221     cow_header.version = cpu_to_be32(COW_VERSION);
 222     if (image_filename) {
 223         /* Note: if no file, we put a dummy mtime */
 224         cow_header.mtime = cpu_to_be32(0);
 225
 226         fd = open(image_filename, O_RDONLY | O_BINARY);
 227         if (fd < 0) {
 228             close(cow_fd);
 229             goto mtime_fail;
 230         }
 231         if (fstat(fd, &st) != 0) {
 232             close(fd);
 233             goto mtime_fail;
 234         }
 235         close(fd);
 236         cow_header.mtime = cpu_to_be32(st.st_mtime);
 237     mtime_fail:
 238         pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
 239                 image_filename);
 240     }
 241     cow_header.sectorsize = cpu_to_be32(512);
 242     cow_header.size = cpu_to_be64(image_sectors * 512);
 243     write(cow_fd, &cow_header, sizeof(cow_header));
 244     /* resize to include at least all the bitmap */
 245     ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));
 246     close(cow_fd);
 247     return 0;
 248 }
 249
 250 static void cow_flush(BlockDriverState *bs)
 251 {
 252     BDRVCowState *s = bs->opaque;
 253     fsync(s->fd);
 254 }
 255
 256 static BlockDriver bdrv_cow = {
 257     .format_name        = "cow",
 258     .instance_size      = sizeof(BDRVCowState),
 259     .bdrv_probe         = cow_probe,
 260     .bdrv_open          = cow_open,
 261     .bdrv_read          = cow_read,
 262     .bdrv_write         = cow_write,
 263     .bdrv_close         = cow_close,
 264     .bdrv_create        = cow_create,
 265     .bdrv_flush         = cow_flush,
 266     .bdrv_is_allocated  = cow_is_allocated,
 267 };
 268
 269 static void bdrv_cow_init(void)
 270 {
 271     bdrv_register(&bdrv_cow);
 272 }
 273
 274 block_init(bdrv_cow_init);
 275 #endif