summaryrefslogtreecommitdiff
path: root/block/cow.c
blob: a5a00eb9ca548d334e8431d6e33d322e569296e9 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
/*
 * Block driver for the COW format
 *
 * Copyright (c) 2004 Fabrice Bellard
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#include "qemu-common.h"
#include "block_int.h"
#include "module.h"

/**************************************************************/
/* COW block driver using file system holes */

/* user mode linux compatible COW file */
#define COW_MAGIC 0x4f4f4f4d  /* MOOO */
#define COW_VERSION 2

struct cow_header_v2 {
    uint32_t magic;
    uint32_t version;
    char backing_file[1024];
    int32_t mtime;
    uint64_t size;
    uint32_t sectorsize;
};

typedef struct BDRVCowState {
    CoMutex lock;
    int64_t cow_sectors_offset;
} BDRVCowState;

static int cow_probe(const uint8_t *buf, int buf_size, const char *filename)
{
    const struct cow_header_v2 *cow_header = (const void *)buf;

    if (buf_size >= sizeof(struct cow_header_v2) &&
        be32_to_cpu(cow_header->magic) == COW_MAGIC &&
        be32_to_cpu(cow_header->version) == COW_VERSION)
        return 100;
    else
        return 0;
}

static int cow_open(BlockDriverState *bs, int flags)
{
    BDRVCowState *s = bs->opaque;
    struct cow_header_v2 cow_header;
    int bitmap_size;
    int64_t size;
    int ret;

    /* see if it is a cow image */
    ret = bdrv_pread(bs->file, 0, &cow_header, sizeof(cow_header));
    if (ret < 0) {
        goto fail;
    }

    if (be32_to_cpu(cow_header.magic) != COW_MAGIC) {
        ret = -EINVAL;
        goto fail;
    }

    if (be32_to_cpu(cow_header.version) != COW_VERSION) {
        char version[64];
        snprintf(version, sizeof(version),
               "COW version %d", cow_header.version);
        qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
            bs->device_name, "cow", version);
        ret = -ENOTSUP;
        goto fail;
    }

    /* cow image found */
    size = be64_to_cpu(cow_header.size);
    bs->total_sectors = size / 512;

    pstrcpy(bs->backing_file, sizeof(bs->backing_file),
            cow_header.backing_file);

    bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
    s->cow_sectors_offset = (bitmap_size + 511) & ~511;
    qemu_co_mutex_init(&s->lock);
    return 0;
 fail:
    return ret;
}

/*
 * XXX(hch): right now these functions are extremely inefficient.
 * We should just read the whole bitmap we'll need in one go instead.
 */
static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum)
{
    uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
    uint8_t bitmap;
    int ret;

    ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
    if (ret < 0) {
       return ret;
    }

    bitmap |= (1 << (bitnum % 8));

    ret = bdrv_pwrite_sync(bs->file, offset, &bitmap, sizeof(bitmap));
    if (ret < 0) {
       return ret;
    }
    return 0;
}

static inline int is_bit_set(BlockDriverState *bs, int64_t bitnum)
{
    uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
    uint8_t bitmap;
    int ret;

    ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));
    if (ret < 0) {
       return ret;
    }

    return !!(bitmap & (1 << (bitnum % 8)));
}

/* Return true if first block has been changed (ie. current version is
 * in COW file).  Set the number of continuous blocks for which that
 * is true. */
static int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,
        int64_t sector_num, int nb_sectors, int *num_same)
{
    int changed;

    if (nb_sectors == 0) {
	*num_same = nb_sectors;
	return 0;
    }

    changed = is_bit_set(bs, sector_num);
    if (changed < 0) {
        return 0; /* XXX: how to return I/O errors? */
    }

    for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
	if (is_bit_set(bs, sector_num + *num_same) != changed)
	    break;
    }

    return changed;
}

static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
        int nb_sectors)
{
    int error = 0;
    int i;

    for (i = 0; i < nb_sectors; i++) {
        error = cow_set_bit(bs, sector_num + i);
        if (error) {
            break;
        }
    }

    return error;
}

static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num,
                                 uint8_t *buf, int nb_sectors)
{
    BDRVCowState *s = bs->opaque;
    int ret, n;

    while (nb_sectors > 0) {
        if (bdrv_co_is_allocated(bs, sector_num, nb_sectors, &n)) {
            ret = bdrv_pread(bs->file,
                        s->cow_sectors_offset + sector_num * 512,
                        buf, n * 512);
            if (ret < 0) {
                return ret;
            }
        } else {
            if (bs->backing_hd) {
                /* read from the base image */
                ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
                if (ret < 0) {
                    return ret;
                }
            } else {
                memset(buf, 0, n * 512);
            }
        }
        nb_sectors -= n;
        sector_num += n;
        buf += n * 512;
    }
    return 0;
}

static coroutine_fn int cow_co_read(BlockDriverState *bs, int64_t sector_num,
                                    uint8_t *buf, int nb_sectors)
{
    int ret;
    BDRVCowState *s = bs->opaque;
    qemu_co_mutex_lock(&s->lock);
    ret = cow_read(bs, sector_num, buf, nb_sectors);
    qemu_co_mutex_unlock(&s->lock);
    return ret;
}

static int cow_write(BlockDriverState *bs, int64_t sector_num,
                     const uint8_t *buf, int nb_sectors)
{
    BDRVCowState *s = bs->opaque;
    int ret;

    ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,
                      buf, nb_sectors * 512);
    if (ret < 0) {
        return ret;
    }

    return cow_update_bitmap(bs, sector_num, nb_sectors);
}

static coroutine_fn int cow_co_write(BlockDriverState *bs, int64_t sector_num,
                                     const uint8_t *buf, int nb_sectors)
{
    int ret;
    BDRVCowState *s = bs->opaque;
    qemu_co_mutex_lock(&s->lock);
    ret = cow_write(bs, sector_num, buf, nb_sectors);
    qemu_co_mutex_unlock(&s->lock);
    return ret;
}

static void cow_close(BlockDriverState *bs)
{
}

static int cow_create(const char *filename, QEMUOptionParameter *options)
{
    struct cow_header_v2 cow_header;
    struct stat st;
    int64_t image_sectors = 0;
    const char *image_filename = NULL;
    int ret;
    BlockDriverState *cow_bs;

    /* Read out options */
    while (options && options->name) {
        if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
            image_sectors = options->value.n / 512;
        } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
            image_filename = options->value.s;
        }
        options++;
    }

    ret = bdrv_create_file(filename, options);
    if (ret < 0) {
        return ret;
    }

    ret = bdrv_file_open(&cow_bs, filename, BDRV_O_RDWR);
    if (ret < 0) {
        return ret;
    }

    memset(&cow_header, 0, sizeof(cow_header));
    cow_header.magic = cpu_to_be32(COW_MAGIC);
    cow_header.version = cpu_to_be32(COW_VERSION);
    if (image_filename) {
        /* Note: if no file, we put a dummy mtime */
        cow_header.mtime = cpu_to_be32(0);

        if (stat(image_filename, &st) != 0) {
            goto mtime_fail;
        }
        cow_header.mtime = cpu_to_be32(st.st_mtime);
    mtime_fail:
        pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
                image_filename);
    }
    cow_header.sectorsize = cpu_to_be32(512);
    cow_header.size = cpu_to_be64(image_sectors * 512);
    ret = bdrv_pwrite(cow_bs, 0, &cow_header, sizeof(cow_header));
    if (ret < 0) {
        goto exit;
    }

    /* resize to include at least all the bitmap */
    ret = bdrv_truncate(cow_bs,
        sizeof(cow_header) + ((image_sectors + 7) >> 3));
    if (ret < 0) {
        goto exit;
    }

exit:
    bdrv_delete(cow_bs);
    return ret;
}

static QEMUOptionParameter cow_create_options[] = {
    {
        .name = BLOCK_OPT_SIZE,
        .type = OPT_SIZE,
        .help = "Virtual disk size"
    },
    {
        .name = BLOCK_OPT_BACKING_FILE,
        .type = OPT_STRING,
        .help = "File name of a base image"
    },
    { NULL }
};

static BlockDriver bdrv_cow = {
    .format_name    = "cow",
    .instance_size  = sizeof(BDRVCowState),

    .bdrv_probe     = cow_probe,
    .bdrv_open      = cow_open,
    .bdrv_close     = cow_close,
    .bdrv_create    = cow_create,

    .bdrv_read              = cow_co_read,
    .bdrv_write             = cow_co_write,
    .bdrv_co_is_allocated   = cow_co_is_allocated,

    .create_options = cow_create_options,
};

static void bdrv_cow_init(void)
{
    bdrv_register(&bdrv_cow);
}

block_init(bdrv_cow_init);