mirror: Go through ready -> complete process for 0 len image
[qemu.git] / block / mirror.c
1 /*
2 * Image mirroring
3 *
4 * Copyright Red Hat, Inc. 2012
5 *
6 * Authors:
7 * Paolo Bonzini <pbonzini@redhat.com>
8 *
9 * This work is licensed under the terms of the GNU LGPL, version 2 or later.
10 * See the COPYING.LIB file in the top-level directory.
11 *
12 */
13
14 #include "trace.h"
15 #include "block/blockjob.h"
16 #include "block/block_int.h"
17 #include "qemu/ratelimit.h"
18 #include "qemu/bitmap.h"
19
20 #define SLICE_TIME 100000000ULL /* ns */
21 #define MAX_IN_FLIGHT 16
22
23 /* The mirroring buffer is a list of granularity-sized chunks.
24 * Free chunks are organized in a list.
25 */
26 typedef struct MirrorBuffer {
27 QSIMPLEQ_ENTRY(MirrorBuffer) next;
28 } MirrorBuffer;
29
30 typedef struct MirrorBlockJob {
31 BlockJob common;
32 RateLimit limit;
33 BlockDriverState *target;
34 BlockDriverState *base;
35 bool is_none_mode;
36 BlockdevOnError on_source_error, on_target_error;
37 bool synced;
38 bool should_complete;
39 int64_t sector_num;
40 int64_t granularity;
41 size_t buf_size;
42 unsigned long *cow_bitmap;
43 BdrvDirtyBitmap *dirty_bitmap;
44 HBitmapIter hbi;
45 uint8_t *buf;
46 QSIMPLEQ_HEAD(, MirrorBuffer) buf_free;
47 int buf_free_count;
48
49 unsigned long *in_flight_bitmap;
50 int in_flight;
51 int ret;
52 } MirrorBlockJob;
53
54 typedef struct MirrorOp {
55 MirrorBlockJob *s;
56 QEMUIOVector qiov;
57 int64_t sector_num;
58 int nb_sectors;
59 } MirrorOp;
60
61 static BlockErrorAction mirror_error_action(MirrorBlockJob *s, bool read,
62 int error)
63 {
64 s->synced = false;
65 if (read) {
66 return block_job_error_action(&s->common, s->common.bs,
67 s->on_source_error, true, error);
68 } else {
69 return block_job_error_action(&s->common, s->target,
70 s->on_target_error, false, error);
71 }
72 }
73
74 static void mirror_iteration_done(MirrorOp *op, int ret)
75 {
76 MirrorBlockJob *s = op->s;
77 struct iovec *iov;
78 int64_t chunk_num;
79 int i, nb_chunks, sectors_per_chunk;
80
81 trace_mirror_iteration_done(s, op->sector_num, op->nb_sectors, ret);
82
83 s->in_flight--;
84 iov = op->qiov.iov;
85 for (i = 0; i < op->qiov.niov; i++) {
86 MirrorBuffer *buf = (MirrorBuffer *) iov[i].iov_base;
87 QSIMPLEQ_INSERT_TAIL(&s->buf_free, buf, next);
88 s->buf_free_count++;
89 }
90
91 sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
92 chunk_num = op->sector_num / sectors_per_chunk;
93 nb_chunks = op->nb_sectors / sectors_per_chunk;
94 bitmap_clear(s->in_flight_bitmap, chunk_num, nb_chunks);
95 if (s->cow_bitmap && ret >= 0) {
96 bitmap_set(s->cow_bitmap, chunk_num, nb_chunks);
97 }
98
99 qemu_iovec_destroy(&op->qiov);
100 g_slice_free(MirrorOp, op);
101
102 /* Enter coroutine when it is not sleeping. The coroutine sleeps to
103 * rate-limit itself. The coroutine will eventually resume since there is
104 * a sleep timeout so don't wake it early.
105 */
106 if (s->common.busy) {
107 qemu_coroutine_enter(s->common.co, NULL);
108 }
109 }
110
111 static void mirror_write_complete(void *opaque, int ret)
112 {
113 MirrorOp *op = opaque;
114 MirrorBlockJob *s = op->s;
115 if (ret < 0) {
116 BlockDriverState *source = s->common.bs;
117 BlockErrorAction action;
118
119 bdrv_set_dirty(source, op->sector_num, op->nb_sectors);
120 action = mirror_error_action(s, false, -ret);
121 if (action == BLOCK_ERROR_ACTION_REPORT && s->ret >= 0) {
122 s->ret = ret;
123 }
124 }
125 mirror_iteration_done(op, ret);
126 }
127
128 static void mirror_read_complete(void *opaque, int ret)
129 {
130 MirrorOp *op = opaque;
131 MirrorBlockJob *s = op->s;
132 if (ret < 0) {
133 BlockDriverState *source = s->common.bs;
134 BlockErrorAction action;
135
136 bdrv_set_dirty(source, op->sector_num, op->nb_sectors);
137 action = mirror_error_action(s, true, -ret);
138 if (action == BLOCK_ERROR_ACTION_REPORT && s->ret >= 0) {
139 s->ret = ret;
140 }
141
142 mirror_iteration_done(op, ret);
143 return;
144 }
145 bdrv_aio_writev(s->target, op->sector_num, &op->qiov, op->nb_sectors,
146 mirror_write_complete, op);
147 }
148
149 static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
150 {
151 BlockDriverState *source = s->common.bs;
152 int nb_sectors, sectors_per_chunk, nb_chunks;
153 int64_t end, sector_num, next_chunk, next_sector, hbitmap_next_sector;
154 uint64_t delay_ns;
155 MirrorOp *op;
156
157 s->sector_num = hbitmap_iter_next(&s->hbi);
158 if (s->sector_num < 0) {
159 bdrv_dirty_iter_init(source, s->dirty_bitmap, &s->hbi);
160 s->sector_num = hbitmap_iter_next(&s->hbi);
161 trace_mirror_restart_iter(s,
162 bdrv_get_dirty_count(source, s->dirty_bitmap));
163 assert(s->sector_num >= 0);
164 }
165
166 hbitmap_next_sector = s->sector_num;
167 sector_num = s->sector_num;
168 sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
169 end = s->common.len >> BDRV_SECTOR_BITS;
170
171 /* Extend the QEMUIOVector to include all adjacent blocks that will
172 * be copied in this operation.
173 *
174 * We have to do this if we have no backing file yet in the destination,
175 * and the cluster size is very large. Then we need to do COW ourselves.
176 * The first time a cluster is copied, copy it entirely. Note that,
177 * because both the granularity and the cluster size are powers of two,
178 * the number of sectors to copy cannot exceed one cluster.
179 *
180 * We also want to extend the QEMUIOVector to include more adjacent
181 * dirty blocks if possible, to limit the number of I/O operations and
182 * run efficiently even with a small granularity.
183 */
184 nb_chunks = 0;
185 nb_sectors = 0;
186 next_sector = sector_num;
187 next_chunk = sector_num / sectors_per_chunk;
188
189 /* Wait for I/O to this cluster (from a previous iteration) to be done. */
190 while (test_bit(next_chunk, s->in_flight_bitmap)) {
191 trace_mirror_yield_in_flight(s, sector_num, s->in_flight);
192 qemu_coroutine_yield();
193 }
194
195 do {
196 int added_sectors, added_chunks;
197
198 if (!bdrv_get_dirty(source, s->dirty_bitmap, next_sector) ||
199 test_bit(next_chunk, s->in_flight_bitmap)) {
200 assert(nb_sectors > 0);
201 break;
202 }
203
204 added_sectors = sectors_per_chunk;
205 if (s->cow_bitmap && !test_bit(next_chunk, s->cow_bitmap)) {
206 bdrv_round_to_clusters(s->target,
207 next_sector, added_sectors,
208 &next_sector, &added_sectors);
209
210 /* On the first iteration, the rounding may make us copy
211 * sectors before the first dirty one.
212 */
213 if (next_sector < sector_num) {
214 assert(nb_sectors == 0);
215 sector_num = next_sector;
216 next_chunk = next_sector / sectors_per_chunk;
217 }
218 }
219
220 added_sectors = MIN(added_sectors, end - (sector_num + nb_sectors));
221 added_chunks = (added_sectors + sectors_per_chunk - 1) / sectors_per_chunk;
222
223 /* When doing COW, it may happen that there is not enough space for
224 * a full cluster. Wait if that is the case.
225 */
226 while (nb_chunks == 0 && s->buf_free_count < added_chunks) {
227 trace_mirror_yield_buf_busy(s, nb_chunks, s->in_flight);
228 qemu_coroutine_yield();
229 }
230 if (s->buf_free_count < nb_chunks + added_chunks) {
231 trace_mirror_break_buf_busy(s, nb_chunks, s->in_flight);
232 break;
233 }
234
235 /* We have enough free space to copy these sectors. */
236 bitmap_set(s->in_flight_bitmap, next_chunk, added_chunks);
237
238 nb_sectors += added_sectors;
239 nb_chunks += added_chunks;
240 next_sector += added_sectors;
241 next_chunk += added_chunks;
242 if (!s->synced && s->common.speed) {
243 delay_ns = ratelimit_calculate_delay(&s->limit, added_sectors);
244 } else {
245 delay_ns = 0;
246 }
247 } while (delay_ns == 0 && next_sector < end);
248
249 /* Allocate a MirrorOp that is used as an AIO callback. */
250 op = g_slice_new(MirrorOp);
251 op->s = s;
252 op->sector_num = sector_num;
253 op->nb_sectors = nb_sectors;
254
255 /* Now make a QEMUIOVector taking enough granularity-sized chunks
256 * from s->buf_free.
257 */
258 qemu_iovec_init(&op->qiov, nb_chunks);
259 next_sector = sector_num;
260 while (nb_chunks-- > 0) {
261 MirrorBuffer *buf = QSIMPLEQ_FIRST(&s->buf_free);
262 QSIMPLEQ_REMOVE_HEAD(&s->buf_free, next);
263 s->buf_free_count--;
264 qemu_iovec_add(&op->qiov, buf, s->granularity);
265
266 /* Advance the HBitmapIter in parallel, so that we do not examine
267 * the same sector twice.
268 */
269 if (next_sector > hbitmap_next_sector
270 && bdrv_get_dirty(source, s->dirty_bitmap, next_sector)) {
271 hbitmap_next_sector = hbitmap_iter_next(&s->hbi);
272 }
273
274 next_sector += sectors_per_chunk;
275 }
276
277 bdrv_reset_dirty(source, sector_num, nb_sectors);
278
279 /* Copy the dirty cluster. */
280 s->in_flight++;
281 trace_mirror_one_iteration(s, sector_num, nb_sectors);
282 bdrv_aio_readv(source, sector_num, &op->qiov, nb_sectors,
283 mirror_read_complete, op);
284 return delay_ns;
285 }
286
287 static void mirror_free_init(MirrorBlockJob *s)
288 {
289 int granularity = s->granularity;
290 size_t buf_size = s->buf_size;
291 uint8_t *buf = s->buf;
292
293 assert(s->buf_free_count == 0);
294 QSIMPLEQ_INIT(&s->buf_free);
295 while (buf_size != 0) {
296 MirrorBuffer *cur = (MirrorBuffer *)buf;
297 QSIMPLEQ_INSERT_TAIL(&s->buf_free, cur, next);
298 s->buf_free_count++;
299 buf_size -= granularity;
300 buf += granularity;
301 }
302 }
303
304 static void mirror_drain(MirrorBlockJob *s)
305 {
306 while (s->in_flight > 0) {
307 qemu_coroutine_yield();
308 }
309 }
310
311 static void coroutine_fn mirror_run(void *opaque)
312 {
313 MirrorBlockJob *s = opaque;
314 BlockDriverState *bs = s->common.bs;
315 int64_t sector_num, end, sectors_per_chunk, length;
316 uint64_t last_pause_ns;
317 BlockDriverInfo bdi;
318 char backing_filename[1024];
319 int ret = 0;
320 int n;
321
322 if (block_job_is_cancelled(&s->common)) {
323 goto immediate_exit;
324 }
325
326 s->common.len = bdrv_getlength(bs);
327 if (s->common.len < 0) {
328 ret = s->common.len;
329 goto immediate_exit;
330 } else if (s->common.len == 0) {
331 /* Report BLOCK_JOB_READY and wait for complete. */
332 block_job_event_ready(&s->common);
333 s->synced = true;
334 while (!block_job_is_cancelled(&s->common) && !s->should_complete) {
335 block_job_yield(&s->common);
336 }
337 s->common.cancelled = false;
338 goto immediate_exit;
339 }
340
341 length = DIV_ROUND_UP(s->common.len, s->granularity);
342 s->in_flight_bitmap = bitmap_new(length);
343
344 /* If we have no backing file yet in the destination, we cannot let
345 * the destination do COW. Instead, we copy sectors around the
346 * dirty data if needed. We need a bitmap to do that.
347 */
348 bdrv_get_backing_filename(s->target, backing_filename,
349 sizeof(backing_filename));
350 if (backing_filename[0] && !s->target->backing_hd) {
351 ret = bdrv_get_info(s->target, &bdi);
352 if (ret < 0) {
353 goto immediate_exit;
354 }
355 if (s->granularity < bdi.cluster_size) {
356 s->buf_size = MAX(s->buf_size, bdi.cluster_size);
357 s->cow_bitmap = bitmap_new(length);
358 }
359 }
360
361 end = s->common.len >> BDRV_SECTOR_BITS;
362 s->buf = qemu_blockalign(bs, s->buf_size);
363 sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
364 mirror_free_init(s);
365
366 if (!s->is_none_mode) {
367 /* First part, loop on the sectors and initialize the dirty bitmap. */
368 BlockDriverState *base = s->base;
369 for (sector_num = 0; sector_num < end; ) {
370 int64_t next = (sector_num | (sectors_per_chunk - 1)) + 1;
371 ret = bdrv_is_allocated_above(bs, base,
372 sector_num, next - sector_num, &n);
373
374 if (ret < 0) {
375 goto immediate_exit;
376 }
377
378 assert(n > 0);
379 if (ret == 1) {
380 bdrv_set_dirty(bs, sector_num, n);
381 sector_num = next;
382 } else {
383 sector_num += n;
384 }
385 }
386 }
387
388 bdrv_dirty_iter_init(bs, s->dirty_bitmap, &s->hbi);
389 last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
390 for (;;) {
391 uint64_t delay_ns = 0;
392 int64_t cnt;
393 bool should_complete;
394
395 if (s->ret < 0) {
396 ret = s->ret;
397 goto immediate_exit;
398 }
399
400 cnt = bdrv_get_dirty_count(bs, s->dirty_bitmap);
401
402 /* Note that even when no rate limit is applied we need to yield
403 * periodically with no pending I/O so that qemu_aio_flush() returns.
404 * We do so every SLICE_TIME nanoseconds, or when there is an error,
405 * or when the source is clean, whichever comes first.
406 */
407 if (qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - last_pause_ns < SLICE_TIME &&
408 s->common.iostatus == BLOCK_DEVICE_IO_STATUS_OK) {
409 if (s->in_flight == MAX_IN_FLIGHT || s->buf_free_count == 0 ||
410 (cnt == 0 && s->in_flight > 0)) {
411 trace_mirror_yield(s, s->in_flight, s->buf_free_count, cnt);
412 qemu_coroutine_yield();
413 continue;
414 } else if (cnt != 0) {
415 delay_ns = mirror_iteration(s);
416 if (delay_ns == 0) {
417 continue;
418 }
419 }
420 }
421
422 should_complete = false;
423 if (s->in_flight == 0 && cnt == 0) {
424 trace_mirror_before_flush(s);
425 ret = bdrv_flush(s->target);
426 if (ret < 0) {
427 if (mirror_error_action(s, false, -ret) ==
428 BLOCK_ERROR_ACTION_REPORT) {
429 goto immediate_exit;
430 }
431 } else {
432 /* We're out of the streaming phase. From now on, if the job
433 * is cancelled we will actually complete all pending I/O and
434 * report completion. This way, block-job-cancel will leave
435 * the target in a consistent state.
436 */
437 s->common.offset = end * BDRV_SECTOR_SIZE;
438 if (!s->synced) {
439 block_job_event_ready(&s->common);
440 s->synced = true;
441 }
442
443 should_complete = s->should_complete ||
444 block_job_is_cancelled(&s->common);
445 cnt = bdrv_get_dirty_count(bs, s->dirty_bitmap);
446 }
447 }
448
449 if (cnt == 0 && should_complete) {
450 /* The dirty bitmap is not updated while operations are pending.
451 * If we're about to exit, wait for pending operations before
452 * calling bdrv_get_dirty_count(bs), or we may exit while the
453 * source has dirty data to copy!
454 *
455 * Note that I/O can be submitted by the guest while
456 * mirror_populate runs.
457 */
458 trace_mirror_before_drain(s, cnt);
459 bdrv_drain_all();
460 cnt = bdrv_get_dirty_count(bs, s->dirty_bitmap);
461 }
462
463 ret = 0;
464 trace_mirror_before_sleep(s, cnt, s->synced, delay_ns);
465 if (!s->synced) {
466 /* Publish progress */
467 s->common.offset = (end - cnt) * BDRV_SECTOR_SIZE;
468 block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, delay_ns);
469 if (block_job_is_cancelled(&s->common)) {
470 break;
471 }
472 } else if (!should_complete) {
473 delay_ns = (s->in_flight == 0 && cnt == 0 ? SLICE_TIME : 0);
474 block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, delay_ns);
475 } else if (cnt == 0) {
476 /* The two disks are in sync. Exit and report successful
477 * completion.
478 */
479 assert(QLIST_EMPTY(&bs->tracked_requests));
480 s->common.cancelled = false;
481 break;
482 }
483 last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
484 }
485
486 immediate_exit:
487 if (s->in_flight > 0) {
488 /* We get here only if something went wrong. Either the job failed,
489 * or it was cancelled prematurely so that we do not guarantee that
490 * the target is a copy of the source.
491 */
492 assert(ret < 0 || (!s->synced && block_job_is_cancelled(&s->common)));
493 mirror_drain(s);
494 }
495
496 assert(s->in_flight == 0);
497 qemu_vfree(s->buf);
498 g_free(s->cow_bitmap);
499 g_free(s->in_flight_bitmap);
500 bdrv_release_dirty_bitmap(bs, s->dirty_bitmap);
501 bdrv_iostatus_disable(s->target);
502 if (s->should_complete && ret == 0) {
503 if (bdrv_get_flags(s->target) != bdrv_get_flags(s->common.bs)) {
504 bdrv_reopen(s->target, bdrv_get_flags(s->common.bs), NULL);
505 }
506 bdrv_swap(s->target, s->common.bs);
507 if (s->common.driver->job_type == BLOCK_JOB_TYPE_COMMIT) {
508 /* drop the bs loop chain formed by the swap: break the loop then
509 * trigger the unref from the top one */
510 BlockDriverState *p = s->base->backing_hd;
511 bdrv_set_backing_hd(s->base, NULL);
512 bdrv_unref(p);
513 }
514 }
515 bdrv_unref(s->target);
516 block_job_completed(&s->common, ret);
517 }
518
519 static void mirror_set_speed(BlockJob *job, int64_t speed, Error **errp)
520 {
521 MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
522
523 if (speed < 0) {
524 error_set(errp, QERR_INVALID_PARAMETER, "speed");
525 return;
526 }
527 ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE, SLICE_TIME);
528 }
529
530 static void mirror_iostatus_reset(BlockJob *job)
531 {
532 MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
533
534 bdrv_iostatus_reset(s->target);
535 }
536
537 static void mirror_complete(BlockJob *job, Error **errp)
538 {
539 MirrorBlockJob *s = container_of(job, MirrorBlockJob, common);
540 Error *local_err = NULL;
541 int ret;
542
543 ret = bdrv_open_backing_file(s->target, NULL, &local_err);
544 if (ret < 0) {
545 error_propagate(errp, local_err);
546 return;
547 }
548 if (!s->synced) {
549 error_set(errp, QERR_BLOCK_JOB_NOT_READY, job->bs->device_name);
550 return;
551 }
552
553 s->should_complete = true;
554 block_job_resume(job);
555 }
556
557 static const BlockJobDriver mirror_job_driver = {
558 .instance_size = sizeof(MirrorBlockJob),
559 .job_type = BLOCK_JOB_TYPE_MIRROR,
560 .set_speed = mirror_set_speed,
561 .iostatus_reset= mirror_iostatus_reset,
562 .complete = mirror_complete,
563 };
564
565 static const BlockJobDriver commit_active_job_driver = {
566 .instance_size = sizeof(MirrorBlockJob),
567 .job_type = BLOCK_JOB_TYPE_COMMIT,
568 .set_speed = mirror_set_speed,
569 .iostatus_reset
570 = mirror_iostatus_reset,
571 .complete = mirror_complete,
572 };
573
574 static void mirror_start_job(BlockDriverState *bs, BlockDriverState *target,
575 int64_t speed, int64_t granularity,
576 int64_t buf_size,
577 BlockdevOnError on_source_error,
578 BlockdevOnError on_target_error,
579 BlockDriverCompletionFunc *cb,
580 void *opaque, Error **errp,
581 const BlockJobDriver *driver,
582 bool is_none_mode, BlockDriverState *base)
583 {
584 MirrorBlockJob *s;
585
586 if (granularity == 0) {
587 /* Choose the default granularity based on the target file's cluster
588 * size, clamped between 4k and 64k. */
589 BlockDriverInfo bdi;
590 if (bdrv_get_info(target, &bdi) >= 0 && bdi.cluster_size != 0) {
591 granularity = MAX(4096, bdi.cluster_size);
592 granularity = MIN(65536, granularity);
593 } else {
594 granularity = 65536;
595 }
596 }
597
598 assert ((granularity & (granularity - 1)) == 0);
599
600 if ((on_source_error == BLOCKDEV_ON_ERROR_STOP ||
601 on_source_error == BLOCKDEV_ON_ERROR_ENOSPC) &&
602 !bdrv_iostatus_is_enabled(bs)) {
603 error_set(errp, QERR_INVALID_PARAMETER, "on-source-error");
604 return;
605 }
606
607
608 s = block_job_create(driver, bs, speed, cb, opaque, errp);
609 if (!s) {
610 return;
611 }
612
613 s->on_source_error = on_source_error;
614 s->on_target_error = on_target_error;
615 s->target = target;
616 s->is_none_mode = is_none_mode;
617 s->base = base;
618 s->granularity = granularity;
619 s->buf_size = MAX(buf_size, granularity);
620
621 s->dirty_bitmap = bdrv_create_dirty_bitmap(bs, granularity, errp);
622 if (!s->dirty_bitmap) {
623 return;
624 }
625 bdrv_set_enable_write_cache(s->target, true);
626 bdrv_set_on_error(s->target, on_target_error, on_target_error);
627 bdrv_iostatus_enable(s->target);
628 s->common.co = qemu_coroutine_create(mirror_run);
629 trace_mirror_start(bs, s, s->common.co, opaque);
630 qemu_coroutine_enter(s->common.co, s);
631 }
632
633 void mirror_start(BlockDriverState *bs, BlockDriverState *target,
634 int64_t speed, int64_t granularity, int64_t buf_size,
635 MirrorSyncMode mode, BlockdevOnError on_source_error,
636 BlockdevOnError on_target_error,
637 BlockDriverCompletionFunc *cb,
638 void *opaque, Error **errp)
639 {
640 bool is_none_mode;
641 BlockDriverState *base;
642
643 is_none_mode = mode == MIRROR_SYNC_MODE_NONE;
644 base = mode == MIRROR_SYNC_MODE_TOP ? bs->backing_hd : NULL;
645 mirror_start_job(bs, target, speed, granularity, buf_size,
646 on_source_error, on_target_error, cb, opaque, errp,
647 &mirror_job_driver, is_none_mode, base);
648 }
649
650 void commit_active_start(BlockDriverState *bs, BlockDriverState *base,
651 int64_t speed,
652 BlockdevOnError on_error,
653 BlockDriverCompletionFunc *cb,
654 void *opaque, Error **errp)
655 {
656 int64_t length, base_length;
657 int orig_base_flags;
658 int ret;
659 Error *local_err = NULL;
660
661 orig_base_flags = bdrv_get_flags(base);
662
663 if (bdrv_reopen(base, bs->open_flags, errp)) {
664 return;
665 }
666
667 length = bdrv_getlength(bs);
668 if (length < 0) {
669 error_setg_errno(errp, -length,
670 "Unable to determine length of %s", bs->filename);
671 goto error_restore_flags;
672 }
673
674 base_length = bdrv_getlength(base);
675 if (base_length < 0) {
676 error_setg_errno(errp, -base_length,
677 "Unable to determine length of %s", base->filename);
678 goto error_restore_flags;
679 }
680
681 if (length > base_length) {
682 ret = bdrv_truncate(base, length);
683 if (ret < 0) {
684 error_setg_errno(errp, -ret,
685 "Top image %s is larger than base image %s, and "
686 "resize of base image failed",
687 bs->filename, base->filename);
688 goto error_restore_flags;
689 }
690 }
691
692 bdrv_ref(base);
693 mirror_start_job(bs, base, speed, 0, 0,
694 on_error, on_error, cb, opaque, &local_err,
695 &commit_active_job_driver, false, base);
696 if (local_err) {
697 error_propagate(errp, local_err);
698 goto error_restore_flags;
699 }
700
701 return;
702
703 error_restore_flags:
704 /* ignore error and errp for bdrv_reopen, because we want to propagate
705 * the original error */
706 bdrv_reopen(base, orig_base_flags, NULL);
707 return;
708 }