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 <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, int flags)
  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     /* mmap the bitmap */
  97     s->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
  98     s->cow_bitmap_addr = mmap(get_mmap_addr(s->cow_bitmap_size),
  99                               s->cow_bitmap_size,
 100                               PROT_READ | PROT_WRITE,
 101                               MAP_SHARED, s->fd, 0);
 102     if (s->cow_bitmap_addr == MAP_FAILED)
 103         goto fail;
 104     s->cow_bitmap = s->cow_bitmap_addr + sizeof(cow_header);
 105     s->cow_sectors_offset = (s->cow_bitmap_size + 511) & ~511;
 106     return 0;
 107  fail:
 108     close(fd);
 109     return -1;
 110 }
 111
 112 static inline void cow_set_bit(uint8_t *bitmap, int64_t bitnum)
 113 {
 114     bitmap[bitnum / 8] |= (1 << (bitnum%8));
 115 }
 116
 117 static inline int is_bit_set(const uint8_t *bitmap, int64_t bitnum)
 118 {
 119     return !!(bitmap[bitnum / 8] & (1 << (bitnum%8)));
 120 }
 121
 122
 123 /* Return true if first block has been changed (ie. current version is
 124  * in COW file).  Set the number of continuous blocks for which that
 125  * is true. */
 126 static inline int is_changed(uint8_t *bitmap,
 127                              int64_t sector_num, int nb_sectors,
 128                              int *num_same)
 129 {
 130     int changed;
 131
 132     if (!bitmap || nb_sectors == 0) {
 133         *num_same = nb_sectors;
 134         return 0;
 135     }
 136
 137     changed = is_bit_set(bitmap, sector_num);
 138     for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
 139         if (is_bit_set(bitmap, sector_num + *num_same) != changed)
 140             break;
 141     }
 142
 143     return changed;
 144 }
 145
 146 static int cow_is_allocated(BlockDriverState *bs, int64_t sector_num,
 147                             int nb_sectors, int *pnum)
 148 {
 149     BDRVCowState *s = bs->opaque;
 150     return is_changed(s->cow_bitmap, sector_num, nb_sectors, pnum);
 151 }
 152
 153 static int cow_read(BlockDriverState *bs, int64_t sector_num,
 154                     uint8_t *buf, int nb_sectors)
 155 {
 156     BDRVCowState *s = bs->opaque;
 157     int ret, n;
 158
 159     while (nb_sectors > 0) {
 160         if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) {
 161             lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
 162             ret = read(s->fd, buf, n * 512);
 163             if (ret != n * 512)
 164                 return -1;
 165         } else {
 166             if (bs->backing_hd) {
 167                 /* read from the base image */
 168                 ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
 169                 if (ret < 0)
 170                     return -1;
 171             } else {
 172             memset(buf, 0, n * 512);
 173         }
 174         }
 175         nb_sectors -= n;
 176         sector_num += n;
 177         buf += n * 512;
 178     }
 179     return 0;
 180 }
 181
 182 static int cow_write(BlockDriverState *bs, int64_t sector_num,
 183                      const uint8_t *buf, int nb_sectors)
 184 {
 185     BDRVCowState *s = bs->opaque;
 186     int ret, i;
 187
 188     lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
 189     ret = write(s->fd, buf, nb_sectors * 512);
 190     if (ret != nb_sectors * 512)
 191         return -1;
 192     for (i = 0; i < nb_sectors; i++)
 193         cow_set_bit(s->cow_bitmap, sector_num + i);
 194     return 0;
 195 }
 196
 197 static void cow_close(BlockDriverState *bs)
 198 {
 199     BDRVCowState *s = bs->opaque;
 200     munmap(s->cow_bitmap_addr, s->cow_bitmap_size);
 201     close(s->fd);
 202 }
 203
 204 static int cow_create(const char *filename, int64_t image_sectors,
 205                       const char *image_filename, int flags)
 206 {
 207     int fd, cow_fd;
 208     struct cow_header_v2 cow_header;
 209     struct stat st;
 210
 211     if (flags)
 212         return -ENOTSUP;
 213
 214     cow_fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
 215               0644);
 216     if (cow_fd < 0)
 217         return -1;
 218     memset(&cow_header, 0, sizeof(cow_header));
 219     cow_header.magic = cpu_to_be32(COW_MAGIC);
 220     cow_header.version = cpu_to_be32(COW_VERSION);
 221     if (image_filename) {
 222         /* Note: if no file, we put a dummy mtime */
 223         cow_header.mtime = cpu_to_be32(0);
 224
 225         fd = open(image_filename, O_RDONLY | O_BINARY);
 226         if (fd < 0) {
 227             close(cow_fd);
 228             goto mtime_fail;
 229         }
 230         if (fstat(fd, &st) != 0) {
 231             close(fd);
 232             goto mtime_fail;
 233         }
 234         close(fd);
 235         cow_header.mtime = cpu_to_be32(st.st_mtime);
 236     mtime_fail:
 237         pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
 238                 image_filename);
 239     }
 240     cow_header.sectorsize = cpu_to_be32(512);
 241     cow_header.size = cpu_to_be64(image_sectors * 512);
 242     write(cow_fd, &cow_header, sizeof(cow_header));
 243     /* resize to include at least all the bitmap */
 244     ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));
 245     close(cow_fd);
 246     return 0;
 247 }
 248
 249 static void cow_flush(BlockDriverState *bs)
 250 {
 251     BDRVCowState *s = bs->opaque;
 252     fsync(s->fd);
 253 }
 254
 255 BlockDriver bdrv_cow = {
 256     "cow",
 257     sizeof(BDRVCowState),
 258     cow_probe,
 259     cow_open,
 260     cow_read,
 261     cow_write,
 262     cow_close,
 263     cow_create,
 264     cow_flush,
 265     cow_is_allocated,
 266 };
 267 #endif