Statistics
| Branch: | Revision:

root / block-cow.c @ 5fafdf24

History | View | Annotate | Download (7.7 kB)

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, 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