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qemu/block/replication.c
Kevin Wolf 6bc0bcc89f block: Fix deadlocks in bdrv_graph_wrunlock() 
bdrv_graph_wrunlock() calls aio_poll(), which may run callbacks that
have a nested event loop. Nested event loops can depend on other
iothreads making progress, so in order to allow them to make progress it
must not hold the AioContext lock of another thread while calling
aio_poll().

This introduces a @bs parameter to bdrv_graph_wrunlock() whose
AioContext is temporarily dropped (which matches bdrv_graph_wrlock()),
and a bdrv_graph_wrunlock_ctx() that can be used if the BlockDriverState
doesn't necessarily exist any more when unlocking.

This also requires a change to bdrv_schedule_unref(), which was relying
on the incorrectly taken lock. It needs to take the lock itself now.
While this is a separate bug, it can't be fixed a separate patch because
otherwise the intermediate state would either deadlock or try to release
a lock that we don't even hold.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20231115172012.112727-3-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
[kwolf: Fixed up bdrv_schedule_unref()]
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2023-11-21 12:45:21 +01:00

804 lines
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/*
* Replication Block filter
*
* Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
* Copyright (c) 2016 Intel Corporation
* Copyright (c) 2016 FUJITSU LIMITED
*
* Author:
* Wen Congyang <wency@cn.fujitsu.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 "qemu/module.h"
#include "qemu/option.h"
#include "block/nbd.h"
#include "block/blockjob.h"
#include "block/block_int.h"
#include "block/block_backup.h"
#include "sysemu/block-backend.h"
#include "qapi/error.h"
#include "qapi/qmp/qdict.h"
#include "block/replication.h"
typedef enum {
BLOCK_REPLICATION_NONE, /* block replication is not started */
BLOCK_REPLICATION_RUNNING, /* block replication is running */
BLOCK_REPLICATION_FAILOVER, /* failover is running in background */
BLOCK_REPLICATION_FAILOVER_FAILED, /* failover failed */
BLOCK_REPLICATION_DONE, /* block replication is done */
} ReplicationStage;
typedef struct BDRVReplicationState {
ReplicationMode mode;
ReplicationStage stage;
BlockJob *commit_job;
BdrvChild *hidden_disk;
BdrvChild *secondary_disk;
BlockJob *backup_job;
char *top_id;
ReplicationState *rs;
Error *blocker;
bool orig_hidden_read_only;
bool orig_secondary_read_only;
int error;
} BDRVReplicationState;
static void replication_start(ReplicationState *rs, ReplicationMode mode,
Error **errp);
static void replication_do_checkpoint(ReplicationState *rs, Error **errp);
static void replication_get_error(ReplicationState *rs, Error **errp);
static void replication_stop(ReplicationState *rs, bool failover,
Error **errp);
#define REPLICATION_MODE "mode"
#define REPLICATION_TOP_ID "top-id"
static QemuOptsList replication_runtime_opts = {
.name = "replication",
.head = QTAILQ_HEAD_INITIALIZER(replication_runtime_opts.head),
.desc = {
{
.name = REPLICATION_MODE,
.type = QEMU_OPT_STRING,
},
{
.name = REPLICATION_TOP_ID,
.type = QEMU_OPT_STRING,
},
{ /* end of list */ }
},
};
static ReplicationOps replication_ops = {
.start = replication_start,
.checkpoint = replication_do_checkpoint,
.get_error = replication_get_error,
.stop = replication_stop,
};
static int replication_open(BlockDriverState *bs, QDict *options,
int flags, Error **errp)
{
int ret;
BDRVReplicationState *s = bs->opaque;
QemuOpts *opts = NULL;
const char *mode;
const char *top_id;
ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
if (ret < 0) {
return ret;
}
ret = -EINVAL;
opts = qemu_opts_create(&replication_runtime_opts, NULL, 0, &error_abort);
if (!qemu_opts_absorb_qdict(opts, options, errp)) {
goto fail;
}
mode = qemu_opt_get(opts, REPLICATION_MODE);
if (!mode) {
error_setg(errp, "Missing the option mode");
goto fail;
}
if (!strcmp(mode, "primary")) {
s->mode = REPLICATION_MODE_PRIMARY;
top_id = qemu_opt_get(opts, REPLICATION_TOP_ID);
if (top_id) {
error_setg(errp,
"The primary side does not support option top-id");
goto fail;
}
} else if (!strcmp(mode, "secondary")) {
s->mode = REPLICATION_MODE_SECONDARY;
top_id = qemu_opt_get(opts, REPLICATION_TOP_ID);
s->top_id = g_strdup(top_id);
if (!s->top_id) {
error_setg(errp, "Missing the option top-id");
goto fail;
}
} else {
error_setg(errp,
"The option mode's value should be primary or secondary");
goto fail;
}
s->rs = replication_new(bs, &replication_ops);
ret = 0;
fail:
qemu_opts_del(opts);
return ret;
}
static void replication_close(BlockDriverState *bs)
{
BDRVReplicationState *s = bs->opaque;
Job *commit_job;
GLOBAL_STATE_CODE();
if (s->stage == BLOCK_REPLICATION_RUNNING) {
replication_stop(s->rs, false, NULL);
}
if (s->stage == BLOCK_REPLICATION_FAILOVER) {
commit_job = &s->commit_job->job;
assert(commit_job->aio_context == qemu_get_current_aio_context());
job_cancel_sync(commit_job, false);
}
if (s->mode == REPLICATION_MODE_SECONDARY) {
g_free(s->top_id);
}
replication_remove(s->rs);
}
static void replication_child_perm(BlockDriverState *bs, BdrvChild *c,
BdrvChildRole role,
BlockReopenQueue *reopen_queue,
uint64_t perm, uint64_t shared,
uint64_t *nperm, uint64_t *nshared)
{
if (role & BDRV_CHILD_PRIMARY) {
*nperm = BLK_PERM_CONSISTENT_READ;
} else {
*nperm = 0;
}
if ((bs->open_flags & (BDRV_O_INACTIVE | BDRV_O_RDWR)) == BDRV_O_RDWR) {
*nperm |= BLK_PERM_WRITE;
}
*nshared = BLK_PERM_CONSISTENT_READ
| BLK_PERM_WRITE
| BLK_PERM_WRITE_UNCHANGED;
return;
}
static int64_t coroutine_fn GRAPH_RDLOCK
replication_co_getlength(BlockDriverState *bs)
{
return bdrv_co_getlength(bs->file->bs);
}
static int replication_get_io_status(BDRVReplicationState *s)
{
switch (s->stage) {
case BLOCK_REPLICATION_NONE:
return -EIO;
case BLOCK_REPLICATION_RUNNING:
return 0;
case BLOCK_REPLICATION_FAILOVER:
return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 0;
case BLOCK_REPLICATION_FAILOVER_FAILED:
return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 1;
case BLOCK_REPLICATION_DONE:
/*
* active commit job completes, and active disk and secondary_disk
* is swapped, so we can operate bs->file directly
*/
return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 0;
default:
abort();
}
}
static int replication_return_value(BDRVReplicationState *s, int ret)
{
if (s->mode == REPLICATION_MODE_SECONDARY) {
return ret;
}
if (ret < 0) {
s->error = ret;
ret = 0;
}
return ret;
}
static int coroutine_fn GRAPH_RDLOCK
replication_co_readv(BlockDriverState *bs, int64_t sector_num,
int remaining_sectors, QEMUIOVector *qiov)
{
BDRVReplicationState *s = bs->opaque;
int ret;
if (s->mode == REPLICATION_MODE_PRIMARY) {
/* We only use it to forward primary write requests */
return -EIO;
}
ret = replication_get_io_status(s);
if (ret < 0) {
return ret;
}
ret = bdrv_co_preadv(bs->file, sector_num * BDRV_SECTOR_SIZE,
remaining_sectors * BDRV_SECTOR_SIZE, qiov, 0);
return replication_return_value(s, ret);
}
static int coroutine_fn GRAPH_RDLOCK
replication_co_writev(BlockDriverState *bs, int64_t sector_num,
int remaining_sectors, QEMUIOVector *qiov, int flags)
{
BDRVReplicationState *s = bs->opaque;
QEMUIOVector hd_qiov;
uint64_t bytes_done = 0;
BdrvChild *top = bs->file;
BdrvChild *base = s->secondary_disk;
BdrvChild *target;
int ret;
int64_t n;
ret = replication_get_io_status(s);
if (ret < 0) {
goto out;
}
if (ret == 0) {
ret = bdrv_co_pwritev(top, sector_num * BDRV_SECTOR_SIZE,
remaining_sectors * BDRV_SECTOR_SIZE, qiov, 0);
return replication_return_value(s, ret);
}
/*
* Failover failed, only write to active disk if the sectors
* have already been allocated in active disk/hidden disk.
*/
qemu_iovec_init(&hd_qiov, qiov->niov);
while (remaining_sectors > 0) {
int64_t count;
ret = bdrv_co_is_allocated_above(top->bs, base->bs, false,
sector_num * BDRV_SECTOR_SIZE,
remaining_sectors * BDRV_SECTOR_SIZE,
&count);
if (ret < 0) {
goto out1;
}
assert(QEMU_IS_ALIGNED(count, BDRV_SECTOR_SIZE));
n = count >> BDRV_SECTOR_BITS;
qemu_iovec_reset(&hd_qiov);
qemu_iovec_concat(&hd_qiov, qiov, bytes_done, count);
target = ret ? top : base;
ret = bdrv_co_pwritev(target, sector_num * BDRV_SECTOR_SIZE,
n * BDRV_SECTOR_SIZE, &hd_qiov, 0);
if (ret < 0) {
goto out1;
}
remaining_sectors -= n;
sector_num += n;
bytes_done += count;
}
out1:
qemu_iovec_destroy(&hd_qiov);
out:
return ret;
}
static void GRAPH_UNLOCKED
secondary_do_checkpoint(BlockDriverState *bs, Error **errp)
{
BDRVReplicationState *s = bs->opaque;
BdrvChild *active_disk;
Error *local_err = NULL;
int ret;
GRAPH_RDLOCK_GUARD_MAINLOOP();
if (!s->backup_job) {
error_setg(errp, "Backup job was cancelled unexpectedly");
return;
}
backup_do_checkpoint(s->backup_job, &local_err);
if (local_err) {
error_propagate(errp, local_err);
return;
}
active_disk = bs->file;
if (!active_disk->bs->drv) {
error_setg(errp, "Active disk %s is ejected",
active_disk->bs->node_name);
return;
}
ret = bdrv_make_empty(active_disk, errp);
if (ret < 0) {
return;
}
if (!s->hidden_disk->bs->drv) {
error_setg(errp, "Hidden disk %s is ejected",
s->hidden_disk->bs->node_name);
return;
}
ret = bdrv_make_empty(s->hidden_disk, errp);
if (ret < 0) {
return;
}
}
/* This function is supposed to be called twice:
* first with writable = true, then with writable = false.
* The first call puts s->hidden_disk and s->secondary_disk in
* r/w mode, and the second puts them back in their original state.
*/
static void reopen_backing_file(BlockDriverState *bs, bool writable,
Error **errp)
{
BDRVReplicationState *s = bs->opaque;
BdrvChild *hidden_disk, *secondary_disk;
BlockReopenQueue *reopen_queue = NULL;
GLOBAL_STATE_CODE();
GRAPH_RDLOCK_GUARD_MAINLOOP();
/*
* s->hidden_disk and s->secondary_disk may not be set yet, as they will
* only be set after the children are writable.
*/
hidden_disk = bs->file->bs->backing;
secondary_disk = hidden_disk->bs->backing;
if (writable) {
s->orig_hidden_read_only = bdrv_is_read_only(hidden_disk->bs);
s->orig_secondary_read_only = bdrv_is_read_only(secondary_disk->bs);
}
if (s->orig_hidden_read_only) {
QDict *opts = qdict_new();
qdict_put_bool(opts, BDRV_OPT_READ_ONLY, !writable);
reopen_queue = bdrv_reopen_queue(reopen_queue, hidden_disk->bs,
opts, true);
}
if (s->orig_secondary_read_only) {
QDict *opts = qdict_new();
qdict_put_bool(opts, BDRV_OPT_READ_ONLY, !writable);
reopen_queue = bdrv_reopen_queue(reopen_queue, secondary_disk->bs,
opts, true);
}
if (reopen_queue) {
AioContext *ctx = bdrv_get_aio_context(bs);
if (ctx != qemu_get_aio_context()) {
aio_context_release(ctx);
}
bdrv_reopen_multiple(reopen_queue, errp);
if (ctx != qemu_get_aio_context()) {
aio_context_acquire(ctx);
}
}
}
static void backup_job_cleanup(BlockDriverState *bs)
{
BDRVReplicationState *s = bs->opaque;
BlockDriverState *top_bs;
s->backup_job = NULL;
top_bs = bdrv_lookup_bs(s->top_id, s->top_id, NULL);
if (!top_bs) {
return;
}
bdrv_op_unblock_all(top_bs, s->blocker);
error_free(s->blocker);
reopen_backing_file(bs, false, NULL);
}
static void backup_job_completed(void *opaque, int ret)
{
BlockDriverState *bs = opaque;
BDRVReplicationState *s = bs->opaque;
if (s->stage != BLOCK_REPLICATION_FAILOVER) {
/* The backup job is cancelled unexpectedly */
s->error = -EIO;
}
backup_job_cleanup(bs);
}
static bool GRAPH_RDLOCK
check_top_bs(BlockDriverState *top_bs, BlockDriverState *bs)
{
BdrvChild *child;
/* The bs itself is the top_bs */
if (top_bs == bs) {
return true;
}
/* Iterate over top_bs's children */
QLIST_FOREACH(child, &top_bs->children, next) {
if (child->bs == bs || check_top_bs(child->bs, bs)) {
return true;
}
}
return false;
}
static void replication_start(ReplicationState *rs, ReplicationMode mode,
Error **errp)
{
BlockDriverState *bs = rs->opaque;
BDRVReplicationState *s;
BlockDriverState *top_bs;
BdrvChild *active_disk, *hidden_disk, *secondary_disk;
int64_t active_length, hidden_length, disk_length;
AioContext *aio_context;
Error *local_err = NULL;
BackupPerf perf = { .use_copy_range = true, .max_workers = 1 };
GLOBAL_STATE_CODE();
aio_context = bdrv_get_aio_context(bs);
aio_context_acquire(aio_context);
s = bs->opaque;
if (s->stage == BLOCK_REPLICATION_DONE ||
s->stage == BLOCK_REPLICATION_FAILOVER) {
/*
* This case happens when a secondary is promoted to primary.
* Ignore the request because the secondary side of replication
* doesn't have to do anything anymore.
*/
aio_context_release(aio_context);
return;
}
if (s->stage != BLOCK_REPLICATION_NONE) {
error_setg(errp, "Block replication is running or done");
aio_context_release(aio_context);
return;
}
if (s->mode != mode) {
error_setg(errp, "The parameter mode's value is invalid, needs %d,"
" but got %d", s->mode, mode);
aio_context_release(aio_context);
return;
}
switch (s->mode) {
case REPLICATION_MODE_PRIMARY:
break;
case REPLICATION_MODE_SECONDARY:
bdrv_graph_rdlock_main_loop();
active_disk = bs->file;
if (!active_disk || !active_disk->bs || !active_disk->bs->backing) {
error_setg(errp, "Active disk doesn't have backing file");
bdrv_graph_rdunlock_main_loop();
aio_context_release(aio_context);
return;
}
hidden_disk = active_disk->bs->backing;
if (!hidden_disk->bs || !hidden_disk->bs->backing) {
error_setg(errp, "Hidden disk doesn't have backing file");
bdrv_graph_rdunlock_main_loop();
aio_context_release(aio_context);
return;
}
secondary_disk = hidden_disk->bs->backing;
if (!secondary_disk->bs || !bdrv_has_blk(secondary_disk->bs)) {
error_setg(errp, "The secondary disk doesn't have block backend");
bdrv_graph_rdunlock_main_loop();
aio_context_release(aio_context);
return;
}
bdrv_graph_rdunlock_main_loop();
/* verify the length */
active_length = bdrv_getlength(active_disk->bs);
hidden_length = bdrv_getlength(hidden_disk->bs);
disk_length = bdrv_getlength(secondary_disk->bs);
if (active_length < 0 || hidden_length < 0 || disk_length < 0 ||
active_length != hidden_length || hidden_length != disk_length) {
error_setg(errp, "Active disk, hidden disk, secondary disk's length"
" are not the same");
aio_context_release(aio_context);
return;
}
/* Must be true, or the bdrv_getlength() calls would have failed */
assert(active_disk->bs->drv && hidden_disk->bs->drv);
bdrv_graph_rdlock_main_loop();
if (!active_disk->bs->drv->bdrv_make_empty ||
!hidden_disk->bs->drv->bdrv_make_empty) {
error_setg(errp,
"Active disk or hidden disk doesn't support make_empty");
aio_context_release(aio_context);
bdrv_graph_rdunlock_main_loop();
return;
}
bdrv_graph_rdunlock_main_loop();
/* reopen the backing file in r/w mode */
reopen_backing_file(bs, true, &local_err);
if (local_err) {
error_propagate(errp, local_err);
aio_context_release(aio_context);
return;
}
bdrv_graph_wrlock(bs);
bdrv_ref(hidden_disk->bs);
s->hidden_disk = bdrv_attach_child(bs, hidden_disk->bs, "hidden disk",
&child_of_bds, BDRV_CHILD_DATA,
&local_err);
if (local_err) {
error_propagate(errp, local_err);
bdrv_graph_wrunlock(bs);
aio_context_release(aio_context);
return;
}
bdrv_ref(secondary_disk->bs);
s->secondary_disk = bdrv_attach_child(bs, secondary_disk->bs,
"secondary disk", &child_of_bds,
BDRV_CHILD_DATA, &local_err);
if (local_err) {
error_propagate(errp, local_err);
bdrv_graph_wrunlock(bs);
aio_context_release(aio_context);
return;
}
/* start backup job now */
error_setg(&s->blocker,
"Block device is in use by internal backup job");
top_bs = bdrv_lookup_bs(s->top_id, s->top_id, NULL);
if (!top_bs || !bdrv_is_root_node(top_bs) ||
!check_top_bs(top_bs, bs)) {
error_setg(errp, "No top_bs or it is invalid");
bdrv_graph_wrunlock(bs);
reopen_backing_file(bs, false, NULL);
aio_context_release(aio_context);
return;
}
bdrv_op_block_all(top_bs, s->blocker);
bdrv_op_unblock(top_bs, BLOCK_OP_TYPE_DATAPLANE, s->blocker);
bdrv_graph_wrunlock(bs);
s->backup_job = backup_job_create(
NULL, s->secondary_disk->bs, s->hidden_disk->bs,
0, MIRROR_SYNC_MODE_NONE, NULL, 0, false, NULL,
&perf,
BLOCKDEV_ON_ERROR_REPORT,
BLOCKDEV_ON_ERROR_REPORT, JOB_INTERNAL,
backup_job_completed, bs, NULL, &local_err);
if (local_err) {
error_propagate(errp, local_err);
backup_job_cleanup(bs);
aio_context_release(aio_context);
return;
}
job_start(&s->backup_job->job);
break;
default:
aio_context_release(aio_context);
abort();
}
s->stage = BLOCK_REPLICATION_RUNNING;
if (s->mode == REPLICATION_MODE_SECONDARY) {
secondary_do_checkpoint(bs, errp);
}
s->error = 0;
aio_context_release(aio_context);
}
static void replication_do_checkpoint(ReplicationState *rs, Error **errp)
{
BlockDriverState *bs = rs->opaque;
BDRVReplicationState *s;
AioContext *aio_context;
aio_context = bdrv_get_aio_context(bs);
aio_context_acquire(aio_context);
s = bs->opaque;
if (s->stage == BLOCK_REPLICATION_DONE ||
s->stage == BLOCK_REPLICATION_FAILOVER) {
/*
* This case happens when a secondary was promoted to primary.
* Ignore the request because the secondary side of replication
* doesn't have to do anything anymore.
*/
aio_context_release(aio_context);
return;
}
if (s->mode == REPLICATION_MODE_SECONDARY) {
secondary_do_checkpoint(bs, errp);
}
aio_context_release(aio_context);
}
static void replication_get_error(ReplicationState *rs, Error **errp)
{
BlockDriverState *bs = rs->opaque;
BDRVReplicationState *s;
AioContext *aio_context;
aio_context = bdrv_get_aio_context(bs);
aio_context_acquire(aio_context);
s = bs->opaque;
if (s->stage == BLOCK_REPLICATION_NONE) {
error_setg(errp, "Block replication is not running");
aio_context_release(aio_context);
return;
}
if (s->error) {
error_setg(errp, "I/O error occurred");
aio_context_release(aio_context);
return;
}
aio_context_release(aio_context);
}
static void replication_done(void *opaque, int ret)
{
BlockDriverState *bs = opaque;
BDRVReplicationState *s = bs->opaque;
if (ret == 0) {
s->stage = BLOCK_REPLICATION_DONE;
bdrv_graph_wrlock(NULL);
bdrv_unref_child(bs, s->secondary_disk);
s->secondary_disk = NULL;
bdrv_unref_child(bs, s->hidden_disk);
s->hidden_disk = NULL;
bdrv_graph_wrunlock(NULL);
s->error = 0;
} else {
s->stage = BLOCK_REPLICATION_FAILOVER_FAILED;
s->error = -EIO;
}
}
static void replication_stop(ReplicationState *rs, bool failover, Error **errp)
{
BlockDriverState *bs = rs->opaque;
BDRVReplicationState *s;
AioContext *aio_context;
aio_context = bdrv_get_aio_context(bs);
aio_context_acquire(aio_context);
s = bs->opaque;
if (s->stage == BLOCK_REPLICATION_DONE ||
s->stage == BLOCK_REPLICATION_FAILOVER) {
/*
* This case happens when a secondary was promoted to primary.
* Ignore the request because the secondary side of replication
* doesn't have to do anything anymore.
*/
aio_context_release(aio_context);
return;
}
if (s->stage != BLOCK_REPLICATION_RUNNING) {
error_setg(errp, "Block replication is not running");
aio_context_release(aio_context);
return;
}
switch (s->mode) {
case REPLICATION_MODE_PRIMARY:
s->stage = BLOCK_REPLICATION_DONE;
s->error = 0;
break;
case REPLICATION_MODE_SECONDARY:
/*
* This BDS will be closed, and the job should be completed
* before the BDS is closed, because we will access hidden
* disk, secondary disk in backup_job_completed().
*/
if (s->backup_job) {
aio_context_release(aio_context);
job_cancel_sync(&s->backup_job->job, true);
aio_context_acquire(aio_context);
}
if (!failover) {
secondary_do_checkpoint(bs, errp);
s->stage = BLOCK_REPLICATION_DONE;
aio_context_release(aio_context);
return;
}
bdrv_graph_rdlock_main_loop();
s->stage = BLOCK_REPLICATION_FAILOVER;
s->commit_job = commit_active_start(
NULL, bs->file->bs, s->secondary_disk->bs,
JOB_INTERNAL, 0, BLOCKDEV_ON_ERROR_REPORT,
NULL, replication_done, bs, true, errp);
bdrv_graph_rdunlock_main_loop();
break;
default:
aio_context_release(aio_context);
abort();
}
aio_context_release(aio_context);
}
static const char *const replication_strong_runtime_opts[] = {
REPLICATION_MODE,
REPLICATION_TOP_ID,
NULL
};
static BlockDriver bdrv_replication = {
.format_name = "replication",
.instance_size = sizeof(BDRVReplicationState),
.bdrv_open = replication_open,
.bdrv_close = replication_close,
.bdrv_child_perm = replication_child_perm,
.bdrv_co_getlength = replication_co_getlength,
.bdrv_co_readv = replication_co_readv,
.bdrv_co_writev = replication_co_writev,
.is_filter = true,
.strong_runtime_opts = replication_strong_runtime_opts,
};
static void bdrv_replication_init(void)
{
bdrv_register(&bdrv_replication);
}
block_init(bdrv_replication_init);
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