Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging
[qemu.git] / block / qcow2-snapshot.c
1 /*
2 * Block driver for the QCOW version 2 format
3 *
4 * Copyright (c) 2004-2006 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
25 #include "qemu-common.h"
26 #include "block/block_int.h"
27 #include "block/qcow2.h"
28
29 typedef struct QEMU_PACKED QCowSnapshotHeader {
30 /* header is 8 byte aligned */
31 uint64_t l1_table_offset;
32
33 uint32_t l1_size;
34 uint16_t id_str_size;
35 uint16_t name_size;
36
37 uint32_t date_sec;
38 uint32_t date_nsec;
39
40 uint64_t vm_clock_nsec;
41
42 uint32_t vm_state_size;
43 uint32_t extra_data_size; /* for extension */
44 /* extra data follows */
45 /* id_str follows */
46 /* name follows */
47 } QCowSnapshotHeader;
48
49 typedef struct QEMU_PACKED QCowSnapshotExtraData {
50 uint64_t vm_state_size_large;
51 uint64_t disk_size;
52 } QCowSnapshotExtraData;
53
54 void qcow2_free_snapshots(BlockDriverState *bs)
55 {
56 BDRVQcowState *s = bs->opaque;
57 int i;
58
59 for(i = 0; i < s->nb_snapshots; i++) {
60 g_free(s->snapshots[i].name);
61 g_free(s->snapshots[i].id_str);
62 }
63 g_free(s->snapshots);
64 s->snapshots = NULL;
65 s->nb_snapshots = 0;
66 }
67
68 int qcow2_read_snapshots(BlockDriverState *bs)
69 {
70 BDRVQcowState *s = bs->opaque;
71 QCowSnapshotHeader h;
72 QCowSnapshotExtraData extra;
73 QCowSnapshot *sn;
74 int i, id_str_size, name_size;
75 int64_t offset;
76 uint32_t extra_data_size;
77 int ret;
78
79 if (!s->nb_snapshots) {
80 s->snapshots = NULL;
81 s->snapshots_size = 0;
82 return 0;
83 }
84
85 offset = s->snapshots_offset;
86 s->snapshots = g_malloc0(s->nb_snapshots * sizeof(QCowSnapshot));
87
88 for(i = 0; i < s->nb_snapshots; i++) {
89 /* Read statically sized part of the snapshot header */
90 offset = align_offset(offset, 8);
91 ret = bdrv_pread(bs->file, offset, &h, sizeof(h));
92 if (ret < 0) {
93 goto fail;
94 }
95
96 offset += sizeof(h);
97 sn = s->snapshots + i;
98 sn->l1_table_offset = be64_to_cpu(h.l1_table_offset);
99 sn->l1_size = be32_to_cpu(h.l1_size);
100 sn->vm_state_size = be32_to_cpu(h.vm_state_size);
101 sn->date_sec = be32_to_cpu(h.date_sec);
102 sn->date_nsec = be32_to_cpu(h.date_nsec);
103 sn->vm_clock_nsec = be64_to_cpu(h.vm_clock_nsec);
104 extra_data_size = be32_to_cpu(h.extra_data_size);
105
106 id_str_size = be16_to_cpu(h.id_str_size);
107 name_size = be16_to_cpu(h.name_size);
108
109 /* Read extra data */
110 ret = bdrv_pread(bs->file, offset, &extra,
111 MIN(sizeof(extra), extra_data_size));
112 if (ret < 0) {
113 goto fail;
114 }
115 offset += extra_data_size;
116
117 if (extra_data_size >= 8) {
118 sn->vm_state_size = be64_to_cpu(extra.vm_state_size_large);
119 }
120
121 if (extra_data_size >= 16) {
122 sn->disk_size = be64_to_cpu(extra.disk_size);
123 } else {
124 sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
125 }
126
127 /* Read snapshot ID */
128 sn->id_str = g_malloc(id_str_size + 1);
129 ret = bdrv_pread(bs->file, offset, sn->id_str, id_str_size);
130 if (ret < 0) {
131 goto fail;
132 }
133 offset += id_str_size;
134 sn->id_str[id_str_size] = '\0';
135
136 /* Read snapshot name */
137 sn->name = g_malloc(name_size + 1);
138 ret = bdrv_pread(bs->file, offset, sn->name, name_size);
139 if (ret < 0) {
140 goto fail;
141 }
142 offset += name_size;
143 sn->name[name_size] = '\0';
144 }
145
146 s->snapshots_size = offset - s->snapshots_offset;
147 return 0;
148
149 fail:
150 qcow2_free_snapshots(bs);
151 return ret;
152 }
153
154 /* add at the end of the file a new list of snapshots */
155 static int qcow2_write_snapshots(BlockDriverState *bs)
156 {
157 BDRVQcowState *s = bs->opaque;
158 QCowSnapshot *sn;
159 QCowSnapshotHeader h;
160 QCowSnapshotExtraData extra;
161 int i, name_size, id_str_size, snapshots_size;
162 struct {
163 uint32_t nb_snapshots;
164 uint64_t snapshots_offset;
165 } QEMU_PACKED header_data;
166 int64_t offset, snapshots_offset;
167 int ret;
168
169 /* compute the size of the snapshots */
170 offset = 0;
171 for(i = 0; i < s->nb_snapshots; i++) {
172 sn = s->snapshots + i;
173 offset = align_offset(offset, 8);
174 offset += sizeof(h);
175 offset += sizeof(extra);
176 offset += strlen(sn->id_str);
177 offset += strlen(sn->name);
178 }
179 snapshots_size = offset;
180
181 /* Allocate space for the new snapshot list */
182 snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
183 offset = snapshots_offset;
184 if (offset < 0) {
185 ret = offset;
186 goto fail;
187 }
188 ret = bdrv_flush(bs);
189 if (ret < 0) {
190 goto fail;
191 }
192
193 /* The snapshot list position has not yet been updated, so these clusters
194 * must indeed be completely free */
195 ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size);
196 if (ret < 0) {
197 goto fail;
198 }
199
200
201 /* Write all snapshots to the new list */
202 for(i = 0; i < s->nb_snapshots; i++) {
203 sn = s->snapshots + i;
204 memset(&h, 0, sizeof(h));
205 h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
206 h.l1_size = cpu_to_be32(sn->l1_size);
207 /* If it doesn't fit in 32 bit, older implementations should treat it
208 * as a disk-only snapshot rather than truncate the VM state */
209 if (sn->vm_state_size <= 0xffffffff) {
210 h.vm_state_size = cpu_to_be32(sn->vm_state_size);
211 }
212 h.date_sec = cpu_to_be32(sn->date_sec);
213 h.date_nsec = cpu_to_be32(sn->date_nsec);
214 h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);
215 h.extra_data_size = cpu_to_be32(sizeof(extra));
216
217 memset(&extra, 0, sizeof(extra));
218 extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
219 extra.disk_size = cpu_to_be64(sn->disk_size);
220
221 id_str_size = strlen(sn->id_str);
222 name_size = strlen(sn->name);
223 assert(id_str_size <= UINT16_MAX && name_size <= UINT16_MAX);
224 h.id_str_size = cpu_to_be16(id_str_size);
225 h.name_size = cpu_to_be16(name_size);
226 offset = align_offset(offset, 8);
227
228 ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
229 if (ret < 0) {
230 goto fail;
231 }
232 offset += sizeof(h);
233
234 ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
235 if (ret < 0) {
236 goto fail;
237 }
238 offset += sizeof(extra);
239
240 ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
241 if (ret < 0) {
242 goto fail;
243 }
244 offset += id_str_size;
245
246 ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
247 if (ret < 0) {
248 goto fail;
249 }
250 offset += name_size;
251 }
252
253 /*
254 * Update the header to point to the new snapshot table. This requires the
255 * new table and its refcounts to be stable on disk.
256 */
257 ret = bdrv_flush(bs);
258 if (ret < 0) {
259 goto fail;
260 }
261
262 QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
263 offsetof(QCowHeader, nb_snapshots) + sizeof(header_data.nb_snapshots));
264
265 header_data.nb_snapshots = cpu_to_be32(s->nb_snapshots);
266 header_data.snapshots_offset = cpu_to_be64(snapshots_offset);
267
268 ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
269 &header_data, sizeof(header_data));
270 if (ret < 0) {
271 goto fail;
272 }
273
274 /* free the old snapshot table */
275 qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size,
276 QCOW2_DISCARD_SNAPSHOT);
277 s->snapshots_offset = snapshots_offset;
278 s->snapshots_size = snapshots_size;
279 return 0;
280
281 fail:
282 if (snapshots_offset > 0) {
283 qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
284 QCOW2_DISCARD_ALWAYS);
285 }
286 return ret;
287 }
288
289 static void find_new_snapshot_id(BlockDriverState *bs,
290 char *id_str, int id_str_size)
291 {
292 BDRVQcowState *s = bs->opaque;
293 QCowSnapshot *sn;
294 int i;
295 unsigned long id, id_max = 0;
296
297 for(i = 0; i < s->nb_snapshots; i++) {
298 sn = s->snapshots + i;
299 id = strtoul(sn->id_str, NULL, 10);
300 if (id > id_max)
301 id_max = id;
302 }
303 snprintf(id_str, id_str_size, "%lu", id_max + 1);
304 }
305
306 static int find_snapshot_by_id_and_name(BlockDriverState *bs,
307 const char *id,
308 const char *name)
309 {
310 BDRVQcowState *s = bs->opaque;
311 int i;
312
313 if (id && name) {
314 for (i = 0; i < s->nb_snapshots; i++) {
315 if (!strcmp(s->snapshots[i].id_str, id) &&
316 !strcmp(s->snapshots[i].name, name)) {
317 return i;
318 }
319 }
320 } else if (id) {
321 for (i = 0; i < s->nb_snapshots; i++) {
322 if (!strcmp(s->snapshots[i].id_str, id)) {
323 return i;
324 }
325 }
326 } else if (name) {
327 for (i = 0; i < s->nb_snapshots; i++) {
328 if (!strcmp(s->snapshots[i].name, name)) {
329 return i;
330 }
331 }
332 }
333
334 return -1;
335 }
336
337 static int find_snapshot_by_id_or_name(BlockDriverState *bs,
338 const char *id_or_name)
339 {
340 int ret;
341
342 ret = find_snapshot_by_id_and_name(bs, id_or_name, NULL);
343 if (ret >= 0) {
344 return ret;
345 }
346 return find_snapshot_by_id_and_name(bs, NULL, id_or_name);
347 }
348
349 /* if no id is provided, a new one is constructed */
350 int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
351 {
352 BDRVQcowState *s = bs->opaque;
353 QCowSnapshot *new_snapshot_list = NULL;
354 QCowSnapshot *old_snapshot_list = NULL;
355 QCowSnapshot sn1, *sn = &sn1;
356 int i, ret;
357 uint64_t *l1_table = NULL;
358 int64_t l1_table_offset;
359
360 memset(sn, 0, sizeof(*sn));
361
362 /* Generate an ID if it wasn't passed */
363 if (sn_info->id_str[0] == '\0') {
364 find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
365 }
366
367 /* Check that the ID is unique */
368 if (find_snapshot_by_id_and_name(bs, sn_info->id_str, NULL) >= 0) {
369 return -EEXIST;
370 }
371
372 /* Populate sn with passed data */
373 sn->id_str = g_strdup(sn_info->id_str);
374 sn->name = g_strdup(sn_info->name);
375
376 sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
377 sn->vm_state_size = sn_info->vm_state_size;
378 sn->date_sec = sn_info->date_sec;
379 sn->date_nsec = sn_info->date_nsec;
380 sn->vm_clock_nsec = sn_info->vm_clock_nsec;
381
382 /* Allocate the L1 table of the snapshot and copy the current one there. */
383 l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * sizeof(uint64_t));
384 if (l1_table_offset < 0) {
385 ret = l1_table_offset;
386 goto fail;
387 }
388
389 sn->l1_table_offset = l1_table_offset;
390 sn->l1_size = s->l1_size;
391
392 l1_table = g_malloc(s->l1_size * sizeof(uint64_t));
393 for(i = 0; i < s->l1_size; i++) {
394 l1_table[i] = cpu_to_be64(s->l1_table[i]);
395 }
396
397 ret = qcow2_pre_write_overlap_check(bs, 0, sn->l1_table_offset,
398 s->l1_size * sizeof(uint64_t));
399 if (ret < 0) {
400 goto fail;
401 }
402
403 ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
404 s->l1_size * sizeof(uint64_t));
405 if (ret < 0) {
406 goto fail;
407 }
408
409 g_free(l1_table);
410 l1_table = NULL;
411
412 /*
413 * Increase the refcounts of all clusters and make sure everything is
414 * stable on disk before updating the snapshot table to contain a pointer
415 * to the new L1 table.
416 */
417 ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
418 if (ret < 0) {
419 goto fail;
420 }
421
422 /* Append the new snapshot to the snapshot list */
423 new_snapshot_list = g_malloc((s->nb_snapshots + 1) * sizeof(QCowSnapshot));
424 if (s->snapshots) {
425 memcpy(new_snapshot_list, s->snapshots,
426 s->nb_snapshots * sizeof(QCowSnapshot));
427 old_snapshot_list = s->snapshots;
428 }
429 s->snapshots = new_snapshot_list;
430 s->snapshots[s->nb_snapshots++] = *sn;
431
432 ret = qcow2_write_snapshots(bs);
433 if (ret < 0) {
434 g_free(s->snapshots);
435 s->snapshots = old_snapshot_list;
436 s->nb_snapshots--;
437 goto fail;
438 }
439
440 g_free(old_snapshot_list);
441
442 /* The VM state isn't needed any more in the active L1 table; in fact, it
443 * hurts by causing expensive COW for the next snapshot. */
444 qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),
445 align_offset(sn->vm_state_size, s->cluster_size)
446 >> BDRV_SECTOR_BITS,
447 QCOW2_DISCARD_NEVER);
448
449 #ifdef DEBUG_ALLOC
450 {
451 BdrvCheckResult result = {0};
452 qcow2_check_refcounts(bs, &result, 0);
453 }
454 #endif
455 return 0;
456
457 fail:
458 g_free(sn->id_str);
459 g_free(sn->name);
460 g_free(l1_table);
461
462 return ret;
463 }
464
465 /* copy the snapshot 'snapshot_name' into the current disk image */
466 int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
467 {
468 BDRVQcowState *s = bs->opaque;
469 QCowSnapshot *sn;
470 int i, snapshot_index;
471 int cur_l1_bytes, sn_l1_bytes;
472 int ret;
473 uint64_t *sn_l1_table = NULL;
474
475 /* Search the snapshot */
476 snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
477 if (snapshot_index < 0) {
478 return -ENOENT;
479 }
480 sn = &s->snapshots[snapshot_index];
481
482 if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
483 error_report("qcow2: Loading snapshots with different disk "
484 "size is not implemented");
485 ret = -ENOTSUP;
486 goto fail;
487 }
488
489 /*
490 * Make sure that the current L1 table is big enough to contain the whole
491 * L1 table of the snapshot. If the snapshot L1 table is smaller, the
492 * current one must be padded with zeros.
493 */
494 ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
495 if (ret < 0) {
496 goto fail;
497 }
498
499 cur_l1_bytes = s->l1_size * sizeof(uint64_t);
500 sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
501
502 /*
503 * Copy the snapshot L1 table to the current L1 table.
504 *
505 * Before overwriting the old current L1 table on disk, make sure to
506 * increase all refcounts for the clusters referenced by the new one.
507 * Decrease the refcount referenced by the old one only when the L1
508 * table is overwritten.
509 */
510 sn_l1_table = g_malloc0(cur_l1_bytes);
511
512 ret = bdrv_pread(bs->file, sn->l1_table_offset, sn_l1_table, sn_l1_bytes);
513 if (ret < 0) {
514 goto fail;
515 }
516
517 ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
518 sn->l1_size, 1);
519 if (ret < 0) {
520 goto fail;
521 }
522
523 ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
524 s->l1_table_offset, cur_l1_bytes);
525 if (ret < 0) {
526 goto fail;
527 }
528
529 ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
530 cur_l1_bytes);
531 if (ret < 0) {
532 goto fail;
533 }
534
535 /*
536 * Decrease refcount of clusters of current L1 table.
537 *
538 * At this point, the in-memory s->l1_table points to the old L1 table,
539 * whereas on disk we already have the new one.
540 *
541 * qcow2_update_snapshot_refcount special cases the current L1 table to use
542 * the in-memory data instead of really using the offset to load a new one,
543 * which is why this works.
544 */
545 ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
546 s->l1_size, -1);
547
548 /*
549 * Now update the in-memory L1 table to be in sync with the on-disk one. We
550 * need to do this even if updating refcounts failed.
551 */
552 for(i = 0;i < s->l1_size; i++) {
553 s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
554 }
555
556 if (ret < 0) {
557 goto fail;
558 }
559
560 g_free(sn_l1_table);
561 sn_l1_table = NULL;
562
563 /*
564 * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
565 * when we decreased the refcount of the old snapshot.
566 */
567 ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
568 if (ret < 0) {
569 goto fail;
570 }
571
572 #ifdef DEBUG_ALLOC
573 {
574 BdrvCheckResult result = {0};
575 qcow2_check_refcounts(bs, &result, 0);
576 }
577 #endif
578 return 0;
579
580 fail:
581 g_free(sn_l1_table);
582 return ret;
583 }
584
585 int qcow2_snapshot_delete(BlockDriverState *bs,
586 const char *snapshot_id,
587 const char *name,
588 Error **errp)
589 {
590 BDRVQcowState *s = bs->opaque;
591 QCowSnapshot sn;
592 int snapshot_index, ret;
593
594 /* Search the snapshot */
595 snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
596 if (snapshot_index < 0) {
597 error_setg(errp, "Can't find the snapshot");
598 return -ENOENT;
599 }
600 sn = s->snapshots[snapshot_index];
601
602 /* Remove it from the snapshot list */
603 memmove(s->snapshots + snapshot_index,
604 s->snapshots + snapshot_index + 1,
605 (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
606 s->nb_snapshots--;
607 ret = qcow2_write_snapshots(bs);
608 if (ret < 0) {
609 error_setg_errno(errp, -ret,
610 "Failed to remove snapshot from snapshot list");
611 return ret;
612 }
613
614 /*
615 * The snapshot is now unused, clean up. If we fail after this point, we
616 * won't recover but just leak clusters.
617 */
618 g_free(sn.id_str);
619 g_free(sn.name);
620
621 /*
622 * Now decrease the refcounts of clusters referenced by the snapshot and
623 * free the L1 table.
624 */
625 ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
626 sn.l1_size, -1);
627 if (ret < 0) {
628 error_setg_errno(errp, -ret, "Failed to free the cluster and L1 table");
629 return ret;
630 }
631 qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * sizeof(uint64_t),
632 QCOW2_DISCARD_SNAPSHOT);
633
634 /* must update the copied flag on the current cluster offsets */
635 ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
636 if (ret < 0) {
637 error_setg_errno(errp, -ret,
638 "Failed to update snapshot status in disk");
639 return ret;
640 }
641
642 #ifdef DEBUG_ALLOC
643 {
644 BdrvCheckResult result = {0};
645 qcow2_check_refcounts(bs, &result, 0);
646 }
647 #endif
648 return 0;
649 }
650
651 int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
652 {
653 BDRVQcowState *s = bs->opaque;
654 QEMUSnapshotInfo *sn_tab, *sn_info;
655 QCowSnapshot *sn;
656 int i;
657
658 if (!s->nb_snapshots) {
659 *psn_tab = NULL;
660 return s->nb_snapshots;
661 }
662
663 sn_tab = g_malloc0(s->nb_snapshots * sizeof(QEMUSnapshotInfo));
664 for(i = 0; i < s->nb_snapshots; i++) {
665 sn_info = sn_tab + i;
666 sn = s->snapshots + i;
667 pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
668 sn->id_str);
669 pstrcpy(sn_info->name, sizeof(sn_info->name),
670 sn->name);
671 sn_info->vm_state_size = sn->vm_state_size;
672 sn_info->date_sec = sn->date_sec;
673 sn_info->date_nsec = sn->date_nsec;
674 sn_info->vm_clock_nsec = sn->vm_clock_nsec;
675 }
676 *psn_tab = sn_tab;
677 return s->nb_snapshots;
678 }
679
680 int qcow2_snapshot_load_tmp(BlockDriverState *bs,
681 const char *snapshot_id,
682 const char *name,
683 Error **errp)
684 {
685 int i, snapshot_index;
686 BDRVQcowState *s = bs->opaque;
687 QCowSnapshot *sn;
688 uint64_t *new_l1_table;
689 int new_l1_bytes;
690 int ret;
691
692 assert(bs->read_only);
693
694 /* Search the snapshot */
695 snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
696 if (snapshot_index < 0) {
697 error_setg(errp,
698 "Can't find snapshot");
699 return -ENOENT;
700 }
701 sn = &s->snapshots[snapshot_index];
702
703 /* Allocate and read in the snapshot's L1 table */
704 new_l1_bytes = s->l1_size * sizeof(uint64_t);
705 new_l1_table = g_malloc0(align_offset(new_l1_bytes, 512));
706
707 ret = bdrv_pread(bs->file, sn->l1_table_offset, new_l1_table, new_l1_bytes);
708 if (ret < 0) {
709 error_setg(errp, "Failed to read l1 table for snapshot");
710 g_free(new_l1_table);
711 return ret;
712 }
713
714 /* Switch the L1 table */
715 g_free(s->l1_table);
716
717 s->l1_size = sn->l1_size;
718 s->l1_table_offset = sn->l1_table_offset;
719 s->l1_table = new_l1_table;
720
721 for(i = 0;i < s->l1_size; i++) {
722 be64_to_cpus(&s->l1_table[i]);
723 }
724
725 return 0;
726 }