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qemu/block/backup.c
Vladimir Sementsov-Ogievskiy f8d59dfb40 block/backup: fix fleecing scheme: use serialized writes 
Fleecing scheme works as follows: we want a kind of temporary snapshot
of active drive A. We create temporary image B, with B->backing = A.
Then we start backup(sync=none) from A to B. From this point, B reads
as point-in-time snapshot of A (A continues to be active drive,
accepting guest IO).

This scheme needs some additional synchronization between reads from B
and backup COW operations, otherwise, the following situation is
theoretically possible:

(assume B is qcow2, client is NBD client, reading from B)

1. client starts reading and take qcow2 mutex in qcow2_co_preadv, and
   goes up to l2 table loading (assume cache miss)

2) guest write => backup COW => qcow2 write =>
   try to take qcow2 mutex => waiting

3. l2 table loaded, we see that cluster is UNALLOCATED, go to
   "case QCOW2_CLUSTER_UNALLOCATED" and unlock mutex before
   bdrv_co_preadv(bs->backing, ...)

4) aha, mutex unlocked, backup COW continues, and we finally finish
   guest write and change cluster in our active disk A

5. actually, do bdrv_co_preadv(bs->backing, ...) and read
   _new updated_ data.

To avoid this, let's make backup writes serializing, to not intersect
with reads from B.

Note: we expand range of handled cases from (sync=none and
B->backing = A) to just (A in backing chain of B), to finally allow
safe reading from B during backup for all cases when A in backing chain
of B, i.e. B formally looks like point-in-time snapshot of A.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2018-07-10 13:10:29 +02:00

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/*
* QEMU backup
*
* Copyright (C) 2013 Proxmox Server Solutions
*
* Authors:
* Dietmar Maurer (dietmar@proxmox.com)
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "trace.h"
#include "block/block.h"
#include "block/block_int.h"
#include "block/blockjob_int.h"
#include "block/block_backup.h"
#include "qapi/error.h"
#include "qapi/qmp/qerror.h"
#include "qemu/ratelimit.h"
#include "qemu/cutils.h"
#include "sysemu/block-backend.h"
#include "qemu/bitmap.h"
#include "qemu/error-report.h"
#define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
typedef struct BackupBlockJob {
BlockJob common;
BlockBackend *target;
/* bitmap for sync=incremental */
BdrvDirtyBitmap *sync_bitmap;
MirrorSyncMode sync_mode;
BlockdevOnError on_source_error;
BlockdevOnError on_target_error;
CoRwlock flush_rwlock;
uint64_t len;
uint64_t bytes_read;
int64_t cluster_size;
bool compress;
NotifierWithReturn before_write;
QLIST_HEAD(, CowRequest) inflight_reqs;
HBitmap *copy_bitmap;
bool use_copy_range;
int64_t copy_range_size;
bool serialize_target_writes;
} BackupBlockJob;
static const BlockJobDriver backup_job_driver;
/* See if in-flight requests overlap and wait for them to complete */
static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,
int64_t start,
int64_t end)
{
CowRequest *req;
bool retry;
do {
retry = false;
QLIST_FOREACH(req, &job->inflight_reqs, list) {
if (end > req->start_byte && start < req->end_byte) {
qemu_co_queue_wait(&req->wait_queue, NULL);
retry = true;
break;
}
}
} while (retry);
}
/* Keep track of an in-flight request */
static void cow_request_begin(CowRequest *req, BackupBlockJob *job,
int64_t start, int64_t end)
{
req->start_byte = start;
req->end_byte = end;
qemu_co_queue_init(&req->wait_queue);
QLIST_INSERT_HEAD(&job->inflight_reqs, req, list);
}
/* Forget about a completed request */
static void cow_request_end(CowRequest *req)
{
QLIST_REMOVE(req, list);
qemu_co_queue_restart_all(&req->wait_queue);
}
/* Copy range to target with a bounce buffer and return the bytes copied. If
* error occured, return a negative error number */
static int coroutine_fn backup_cow_with_bounce_buffer(BackupBlockJob *job,
int64_t start,
int64_t end,
bool is_write_notifier,
bool *error_is_read,
void **bounce_buffer)
{
int ret;
struct iovec iov;
QEMUIOVector qiov;
BlockBackend *blk = job->common.blk;
int nbytes;
int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0;
hbitmap_reset(job->copy_bitmap, start / job->cluster_size, 1);
nbytes = MIN(job->cluster_size, job->len - start);
if (!*bounce_buffer) {
*bounce_buffer = blk_blockalign(blk, job->cluster_size);
}
iov.iov_base = *bounce_buffer;
iov.iov_len = nbytes;
qemu_iovec_init_external(&qiov, &iov, 1);
ret = blk_co_preadv(blk, start, qiov.size, &qiov, read_flags);
if (ret < 0) {
trace_backup_do_cow_read_fail(job, start, ret);
if (error_is_read) {
*error_is_read = true;
}
goto fail;
}
if (qemu_iovec_is_zero(&qiov)) {
ret = blk_co_pwrite_zeroes(job->target, start,
qiov.size, write_flags | BDRV_REQ_MAY_UNMAP);
} else {
ret = blk_co_pwritev(job->target, start,
qiov.size, &qiov, write_flags |
(job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0));
}
if (ret < 0) {
trace_backup_do_cow_write_fail(job, start, ret);
if (error_is_read) {
*error_is_read = false;
}
goto fail;
}
return nbytes;
fail:
hbitmap_set(job->copy_bitmap, start / job->cluster_size, 1);
return ret;
}
/* Copy range to target and return the bytes copied. If error occured, return a
* negative error number. */
static int coroutine_fn backup_cow_with_offload(BackupBlockJob *job,
int64_t start,
int64_t end,
bool is_write_notifier)
{
int ret;
int nr_clusters;
BlockBackend *blk = job->common.blk;
int nbytes;
int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0;
assert(QEMU_IS_ALIGNED(job->copy_range_size, job->cluster_size));
nbytes = MIN(job->copy_range_size, end - start);
nr_clusters = DIV_ROUND_UP(nbytes, job->cluster_size);
hbitmap_reset(job->copy_bitmap, start / job->cluster_size,
nr_clusters);
ret = blk_co_copy_range(blk, start, job->target, start, nbytes,
read_flags, write_flags);
if (ret < 0) {
trace_backup_do_cow_copy_range_fail(job, start, ret);
hbitmap_set(job->copy_bitmap, start / job->cluster_size,
nr_clusters);
return ret;
}
return nbytes;
}
static int coroutine_fn backup_do_cow(BackupBlockJob *job,
int64_t offset, uint64_t bytes,
bool *error_is_read,
bool is_write_notifier)
{
CowRequest cow_request;
int ret = 0;
int64_t start, end; /* bytes */
void *bounce_buffer = NULL;
qemu_co_rwlock_rdlock(&job->flush_rwlock);
start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
trace_backup_do_cow_enter(job, start, offset, bytes);
wait_for_overlapping_requests(job, start, end);
cow_request_begin(&cow_request, job, start, end);
while (start < end) {
if (!hbitmap_get(job->copy_bitmap, start / job->cluster_size)) {
trace_backup_do_cow_skip(job, start);
start += job->cluster_size;
continue; /* already copied */
}
trace_backup_do_cow_process(job, start);
if (job->use_copy_range) {
ret = backup_cow_with_offload(job, start, end, is_write_notifier);
if (ret < 0) {
job->use_copy_range = false;
}
}
if (!job->use_copy_range) {
ret = backup_cow_with_bounce_buffer(job, start, end, is_write_notifier,
error_is_read, &bounce_buffer);
}
if (ret < 0) {
break;
}
/* Publish progress, guest I/O counts as progress too. Note that the
* offset field is an opaque progress value, it is not a disk offset.
*/
start += ret;
job->bytes_read += ret;
job_progress_update(&job->common.job, ret);
ret = 0;
}
if (bounce_buffer) {
qemu_vfree(bounce_buffer);
}
cow_request_end(&cow_request);
trace_backup_do_cow_return(job, offset, bytes, ret);
qemu_co_rwlock_unlock(&job->flush_rwlock);
return ret;
}
static int coroutine_fn backup_before_write_notify(
NotifierWithReturn *notifier,
void *opaque)
{
BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
BdrvTrackedRequest *req = opaque;
assert(req->bs == blk_bs(job->common.blk));
assert(QEMU_IS_ALIGNED(req->offset, BDRV_SECTOR_SIZE));
assert(QEMU_IS_ALIGNED(req->bytes, BDRV_SECTOR_SIZE));
return backup_do_cow(job, req->offset, req->bytes, NULL, true);
}
static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
{
BdrvDirtyBitmap *bm;
BlockDriverState *bs = blk_bs(job->common.blk);
if (ret < 0) {
/* Merge the successor back into the parent, delete nothing. */
bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
assert(bm);
} else {
/* Everything is fine, delete this bitmap and install the backup. */
bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
assert(bm);
}
}
static void backup_commit(Job *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
if (s->sync_bitmap) {
backup_cleanup_sync_bitmap(s, 0);
}
}
static void backup_abort(Job *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
if (s->sync_bitmap) {
backup_cleanup_sync_bitmap(s, -1);
}
}
static void backup_clean(Job *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
assert(s->target);
blk_unref(s->target);
s->target = NULL;
}
static void backup_attached_aio_context(BlockJob *job, AioContext *aio_context)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common);
blk_set_aio_context(s->target, aio_context);
}
void backup_do_checkpoint(BlockJob *job, Error **errp)
{
BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
int64_t len;
assert(block_job_driver(job) == &backup_job_driver);
if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
error_setg(errp, "The backup job only supports block checkpoint in"
" sync=none mode");
return;
}
len = DIV_ROUND_UP(backup_job->len, backup_job->cluster_size);
hbitmap_set(backup_job->copy_bitmap, 0, len);
}
void backup_wait_for_overlapping_requests(BlockJob *job, int64_t offset,
uint64_t bytes)
{
BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
int64_t start, end;
assert(block_job_driver(job) == &backup_job_driver);
start = QEMU_ALIGN_DOWN(offset, backup_job->cluster_size);
end = QEMU_ALIGN_UP(offset + bytes, backup_job->cluster_size);
wait_for_overlapping_requests(backup_job, start, end);
}
void backup_cow_request_begin(CowRequest *req, BlockJob *job,
int64_t offset, uint64_t bytes)
{
BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
int64_t start, end;
assert(block_job_driver(job) == &backup_job_driver);
start = QEMU_ALIGN_DOWN(offset, backup_job->cluster_size);
end = QEMU_ALIGN_UP(offset + bytes, backup_job->cluster_size);
cow_request_begin(req, backup_job, start, end);
}
void backup_cow_request_end(CowRequest *req)
{
cow_request_end(req);
}
static void backup_drain(BlockJob *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common);
/* Need to keep a reference in case blk_drain triggers execution
* of backup_complete...
*/
if (s->target) {
BlockBackend *target = s->target;
blk_ref(target);
blk_drain(target);
blk_unref(target);
}
}
static BlockErrorAction backup_error_action(BackupBlockJob *job,
bool read, int error)
{
if (read) {
return block_job_error_action(&job->common, job->on_source_error,
true, error);
} else {
return block_job_error_action(&job->common, job->on_target_error,
false, error);
}
}
typedef struct {
int ret;
} BackupCompleteData;
static void backup_complete(Job *job, void *opaque)
{
BackupCompleteData *data = opaque;
job_completed(job, data->ret, NULL);
g_free(data);
}
static bool coroutine_fn yield_and_check(BackupBlockJob *job)
{
uint64_t delay_ns;
if (job_is_cancelled(&job->common.job)) {
return true;
}
/* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
* return. Without a yield, the VM would not reboot. */
delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
job->bytes_read = 0;
job_sleep_ns(&job->common.job, delay_ns);
if (job_is_cancelled(&job->common.job)) {
return true;
}
return false;
}
static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
{
int ret;
bool error_is_read;
int64_t cluster;
HBitmapIter hbi;
hbitmap_iter_init(&hbi, job->copy_bitmap, 0);
while ((cluster = hbitmap_iter_next(&hbi, true)) != -1) {
do {
if (yield_and_check(job)) {
return 0;
}
ret = backup_do_cow(job, cluster * job->cluster_size,
job->cluster_size, &error_is_read, false);
if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
BLOCK_ERROR_ACTION_REPORT)
{
return ret;
}
} while (ret < 0);
}
return 0;
}
/* init copy_bitmap from sync_bitmap */
static void backup_incremental_init_copy_bitmap(BackupBlockJob *job)
{
BdrvDirtyBitmapIter *dbi;
int64_t offset;
int64_t end = DIV_ROUND_UP(bdrv_dirty_bitmap_size(job->sync_bitmap),
job->cluster_size);
dbi = bdrv_dirty_iter_new(job->sync_bitmap);
while ((offset = bdrv_dirty_iter_next(dbi)) != -1) {
int64_t cluster = offset / job->cluster_size;
int64_t next_cluster;
offset += bdrv_dirty_bitmap_granularity(job->sync_bitmap);
if (offset >= bdrv_dirty_bitmap_size(job->sync_bitmap)) {
hbitmap_set(job->copy_bitmap, cluster, end - cluster);
break;
}
offset = bdrv_dirty_bitmap_next_zero(job->sync_bitmap, offset);
if (offset == -1) {
hbitmap_set(job->copy_bitmap, cluster, end - cluster);
break;
}
next_cluster = DIV_ROUND_UP(offset, job->cluster_size);
hbitmap_set(job->copy_bitmap, cluster, next_cluster - cluster);
if (next_cluster >= end) {
break;
}
bdrv_set_dirty_iter(dbi, next_cluster * job->cluster_size);
}
/* TODO job_progress_set_remaining() would make more sense */
job_progress_update(&job->common.job,
job->len - hbitmap_count(job->copy_bitmap) * job->cluster_size);
bdrv_dirty_iter_free(dbi);
}
static void coroutine_fn backup_run(void *opaque)
{
BackupBlockJob *job = opaque;
BackupCompleteData *data;
BlockDriverState *bs = blk_bs(job->common.blk);
int64_t offset, nb_clusters;
int ret = 0;
QLIST_INIT(&job->inflight_reqs);
qemu_co_rwlock_init(&job->flush_rwlock);
nb_clusters = DIV_ROUND_UP(job->len, job->cluster_size);
job_progress_set_remaining(&job->common.job, job->len);
job->copy_bitmap = hbitmap_alloc(nb_clusters, 0);
if (job->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
backup_incremental_init_copy_bitmap(job);
} else {
hbitmap_set(job->copy_bitmap, 0, nb_clusters);
}
job->before_write.notify = backup_before_write_notify;
bdrv_add_before_write_notifier(bs, &job->before_write);
if (job->sync_mode == MIRROR_SYNC_MODE_NONE) {
/* All bits are set in copy_bitmap to allow any cluster to be copied.
* This does not actually require them to be copied. */
while (!job_is_cancelled(&job->common.job)) {
/* Yield until the job is cancelled. We just let our before_write
* notify callback service CoW requests. */
job_yield(&job->common.job);
}
} else if (job->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
ret = backup_run_incremental(job);
} else {
/* Both FULL and TOP SYNC_MODE's require copying.. */
for (offset = 0; offset < job->len;
offset += job->cluster_size) {
bool error_is_read;
int alloced = 0;
if (yield_and_check(job)) {
break;
}
if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
int i;
int64_t n;
/* Check to see if these blocks are already in the
* backing file. */
for (i = 0; i < job->cluster_size;) {
/* bdrv_is_allocated() only returns true/false based
* on the first set of sectors it comes across that
* are are all in the same state.
* For that reason we must verify each sector in the
* backup cluster length. We end up copying more than
* needed but at some point that is always the case. */
alloced =
bdrv_is_allocated(bs, offset + i,
job->cluster_size - i, &n);
i += n;
if (alloced || n == 0) {
break;
}
}
/* If the above loop never found any sectors that are in
* the topmost image, skip this backup. */
if (alloced == 0) {
continue;
}
}
/* FULL sync mode we copy the whole drive. */
if (alloced < 0) {
ret = alloced;
} else {
ret = backup_do_cow(job, offset, job->cluster_size,
&error_is_read, false);
}
if (ret < 0) {
/* Depending on error action, fail now or retry cluster */
BlockErrorAction action =
backup_error_action(job, error_is_read, -ret);
if (action == BLOCK_ERROR_ACTION_REPORT) {
break;
} else {
offset -= job->cluster_size;
continue;
}
}
}
}
notifier_with_return_remove(&job->before_write);
/* wait until pending backup_do_cow() calls have completed */
qemu_co_rwlock_wrlock(&job->flush_rwlock);
qemu_co_rwlock_unlock(&job->flush_rwlock);
hbitmap_free(job->copy_bitmap);
data = g_malloc(sizeof(*data));
data->ret = ret;
job_defer_to_main_loop(&job->common.job, backup_complete, data);
}
static const BlockJobDriver backup_job_driver = {
.job_driver = {
.instance_size = sizeof(BackupBlockJob),
.job_type = JOB_TYPE_BACKUP,
.free = block_job_free,
.user_resume = block_job_user_resume,
.drain = block_job_drain,
.start = backup_run,
.commit = backup_commit,
.abort = backup_abort,
.clean = backup_clean,
},
.attached_aio_context = backup_attached_aio_context,
.drain = backup_drain,
};
BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
BlockDriverState *target, int64_t speed,
MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
bool compress,
BlockdevOnError on_source_error,
BlockdevOnError on_target_error,
int creation_flags,
BlockCompletionFunc *cb, void *opaque,
JobTxn *txn, Error **errp)
{
int64_t len;
BlockDriverInfo bdi;
BackupBlockJob *job = NULL;
int ret;
assert(bs);
assert(target);
if (bs == target) {
error_setg(errp, "Source and target cannot be the same");
return NULL;
}
if (!bdrv_is_inserted(bs)) {
error_setg(errp, "Device is not inserted: %s",
bdrv_get_device_name(bs));
return NULL;
}
if (!bdrv_is_inserted(target)) {
error_setg(errp, "Device is not inserted: %s",
bdrv_get_device_name(target));
return NULL;
}
if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
error_setg(errp, "Compression is not supported for this drive %s",
bdrv_get_device_name(target));
return NULL;
}
if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
return NULL;
}
if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
return NULL;
}
if (sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
if (!sync_bitmap) {
error_setg(errp, "must provide a valid bitmap name for "
"\"incremental\" sync mode");
return NULL;
}
/* Create a new bitmap, and freeze/disable this one. */
if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
return NULL;
}
} else if (sync_bitmap) {
error_setg(errp,
"a sync_bitmap was provided to backup_run, "
"but received an incompatible sync_mode (%s)",
MirrorSyncMode_str(sync_mode));
return NULL;
}
len = bdrv_getlength(bs);
if (len < 0) {
error_setg_errno(errp, -len, "unable to get length for '%s'",
bdrv_get_device_name(bs));
goto error;
}
/* job->len is fixed, so we can't allow resize */
job = block_job_create(job_id, &backup_job_driver, txn, bs,
BLK_PERM_CONSISTENT_READ,
BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD,
speed, creation_flags, cb, opaque, errp);
if (!job) {
goto error;
}
/* The target must match the source in size, so no resize here either */
job->target = blk_new(BLK_PERM_WRITE,
BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD);
ret = blk_insert_bs(job->target, target, errp);
if (ret < 0) {
goto error;
}
job->on_source_error = on_source_error;
job->on_target_error = on_target_error;
job->sync_mode = sync_mode;
job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_INCREMENTAL ?
sync_bitmap : NULL;
job->compress = compress;
/* Detect image-fleecing (and similar) schemes */
job->serialize_target_writes = bdrv_chain_contains(target, bs);
/* If there is no backing file on the target, we cannot rely on COW if our
* backup cluster size is smaller than the target cluster size. Even for
* targets with a backing file, try to avoid COW if possible. */
ret = bdrv_get_info(target, &bdi);
if (ret == -ENOTSUP && !target->backing) {
/* Cluster size is not defined */
warn_report("The target block device doesn't provide "
"information about the block size and it doesn't have a "
"backing file. The default block size of %u bytes is "
"used. If the actual block size of the target exceeds "
"this default, the backup may be unusable",
BACKUP_CLUSTER_SIZE_DEFAULT);
job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
} else if (ret < 0 && !target->backing) {
error_setg_errno(errp, -ret,
"Couldn't determine the cluster size of the target image, "
"which has no backing file");
error_append_hint(errp,
"Aborting, since this may create an unusable destination image\n");
goto error;
} else if (ret < 0 && target->backing) {
/* Not fatal; just trudge on ahead. */
job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
} else {
job->cluster_size = MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
}
job->use_copy_range = true;
job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
blk_get_max_transfer(job->target));
job->copy_range_size = MAX(job->cluster_size,
QEMU_ALIGN_UP(job->copy_range_size,
job->cluster_size));
/* Required permissions are already taken with target's blk_new() */
block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
&error_abort);
job->len = len;
return &job->common;
error:
if (sync_bitmap) {
bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
}
if (job) {
backup_clean(&job->common.job);
job_early_fail(&job->common.job);
}
return NULL;
}
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