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