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