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qemu-e2k/block/snapshot.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

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/*
* Block layer snapshot related functions
*
* Copyright (c) 2003-2008 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/osdep.h"
#include "block/snapshot.h"
#include "block/block_int.h"
#include "block/qdict.h"
#include "qapi/error.h"
#include "qapi/qmp/qdict.h"
#include "qapi/qmp/qerror.h"
#include "qapi/qmp/qstring.h"
#include "qemu/option.h"
#include "sysemu/block-backend.h"
QemuOptsList internal_snapshot_opts = {
.name = "snapshot",
.head = QTAILQ_HEAD_INITIALIZER(internal_snapshot_opts.head),
.desc = {
{
.name = SNAPSHOT_OPT_ID,
.type = QEMU_OPT_STRING,
.help = "snapshot id"
},{
.name = SNAPSHOT_OPT_NAME,
.type = QEMU_OPT_STRING,
.help = "snapshot name"
},{
/* end of list */
}
},
};
int bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
const char *name)
{
QEMUSnapshotInfo *sn_tab, *sn;
int nb_sns, i, ret;
GLOBAL_STATE_CODE();
ret = -ENOENT;
nb_sns = bdrv_snapshot_list(bs, &sn_tab);
if (nb_sns < 0) {
return ret;
}
for (i = 0; i < nb_sns; i++) {
sn = &sn_tab[i];
if (!strcmp(sn->name, name)) {
*sn_info = *sn;
ret = 0;
break;
}
}
g_free(sn_tab);
return ret;
}
/**
* Look up an internal snapshot by @id and @name.
* @bs: block device to search
* @id: unique snapshot ID, or NULL
* @name: snapshot name, or NULL
* @sn_info: location to store information on the snapshot found
* @errp: location to store error, will be set only for exception
*
* This function will traverse snapshot list in @bs to search the matching
* one, @id and @name are the matching condition:
* If both @id and @name are specified, find the first one with id @id and
* name @name.
* If only @id is specified, find the first one with id @id.
* If only @name is specified, find the first one with name @name.
* if none is specified, abort().
*
* Returns: true when a snapshot is found and @sn_info will be filled, false
* when error or not found. If all operation succeed but no matching one is
* found, @errp will NOT be set.
*/
bool bdrv_snapshot_find_by_id_and_name(BlockDriverState *bs,
const char *id,
const char *name,
QEMUSnapshotInfo *sn_info,
Error **errp)
{
QEMUSnapshotInfo *sn_tab, *sn;
int nb_sns, i;
bool ret = false;
assert(id || name);
GLOBAL_STATE_CODE();
nb_sns = bdrv_snapshot_list(bs, &sn_tab);
if (nb_sns < 0) {
error_setg_errno(errp, -nb_sns, "Failed to get a snapshot list");
return false;
} else if (nb_sns == 0) {
return false;
}
if (id && name) {
for (i = 0; i < nb_sns; i++) {
sn = &sn_tab[i];
if (!strcmp(sn->id_str, id) && !strcmp(sn->name, name)) {
*sn_info = *sn;
ret = true;
break;
}
}
} else if (id) {
for (i = 0; i < nb_sns; i++) {
sn = &sn_tab[i];
if (!strcmp(sn->id_str, id)) {
*sn_info = *sn;
ret = true;
break;
}
}
} else if (name) {
for (i = 0; i < nb_sns; i++) {
sn = &sn_tab[i];
if (!strcmp(sn->name, name)) {
*sn_info = *sn;
ret = true;
break;
}
}
}
g_free(sn_tab);
return ret;
}
/**
* Return a pointer to child of given BDS to which we can fall
* back if the given BDS does not support snapshots.
* Return NULL if there is no BDS to (safely) fall back to.
*/
static BdrvChild * GRAPH_RDLOCK
bdrv_snapshot_fallback_child(BlockDriverState *bs)
{
BdrvChild *fallback = bdrv_primary_child(bs);
BdrvChild *child;
GLOBAL_STATE_CODE();
assert_bdrv_graph_readable();
/* We allow fallback only to primary child */
if (!fallback) {
return NULL;
}
/*
* Check that there are no other children that would need to be
* snapshotted. If there are, it is not safe to fall back to
* fallback.
*/
QLIST_FOREACH(child, &bs->children, next) {
if (child->role & (BDRV_CHILD_DATA | BDRV_CHILD_METADATA |
BDRV_CHILD_FILTERED) &&
child != fallback)
{
return NULL;
}
}
return fallback;
}
static BlockDriverState * GRAPH_RDLOCK
bdrv_snapshot_fallback(BlockDriverState *bs)
{
GLOBAL_STATE_CODE();
return child_bs(bdrv_snapshot_fallback_child(bs));
}
int bdrv_can_snapshot(BlockDriverState *bs)
{
BlockDriver *drv = bs->drv;
GLOBAL_STATE_CODE();
if (!drv || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
return 0;
}
if (!drv->bdrv_snapshot_create) {
BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
if (fallback_bs) {
return bdrv_can_snapshot(fallback_bs);
}
return 0;
}
return 1;
}
int bdrv_snapshot_create(BlockDriverState *bs,
QEMUSnapshotInfo *sn_info)
{
BlockDriver *drv = bs->drv;
BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
GLOBAL_STATE_CODE();
if (!drv) {
return -ENOMEDIUM;
}
if (drv->bdrv_snapshot_create) {
return drv->bdrv_snapshot_create(bs, sn_info);
}
if (fallback_bs) {
return bdrv_snapshot_create(fallback_bs, sn_info);
}
return -ENOTSUP;
}
int bdrv_snapshot_goto(BlockDriverState *bs,
const char *snapshot_id,
Error **errp)
{
BlockDriver *drv = bs->drv;
BdrvChild *fallback;
int ret, open_ret;
GLOBAL_STATE_CODE();
if (!drv) {
error_setg(errp, "Block driver is closed");
return -ENOMEDIUM;
}
if (!QLIST_EMPTY(&bs->dirty_bitmaps)) {
error_setg(errp, "Device has active dirty bitmaps");
return -EBUSY;
}
if (drv->bdrv_snapshot_goto) {
ret = drv->bdrv_snapshot_goto(bs, snapshot_id);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to load snapshot");
}
return ret;
}
bdrv_graph_rdlock_main_loop();
fallback = bdrv_snapshot_fallback_child(bs);
bdrv_graph_rdunlock_main_loop();
if (fallback) {
QDict *options;
QDict *file_options;
Error *local_err = NULL;
BlockDriverState *fallback_bs = fallback->bs;
char *subqdict_prefix = g_strdup_printf("%s.", fallback->name);
options = qdict_clone_shallow(bs->options);
/* Prevent it from getting deleted when detached from bs */
bdrv_ref(fallback_bs);
qdict_extract_subqdict(options, &file_options, subqdict_prefix);
qobject_unref(file_options);
g_free(subqdict_prefix);
/* Force .bdrv_open() below to re-attach fallback_bs on fallback */
qdict_put_str(options, fallback->name,
bdrv_get_node_name(fallback_bs));
/* Now close bs, apply the snapshot on fallback_bs, and re-open bs */
if (drv->bdrv_close) {
drv->bdrv_close(bs);
}
/* .bdrv_open() will re-attach it */
bdrv_graph_wrlock(NULL);
bdrv_unref_child(bs, fallback);
bdrv_graph_wrunlock(NULL);
ret = bdrv_snapshot_goto(fallback_bs, snapshot_id, errp);
open_ret = drv->bdrv_open(bs, options, bs->open_flags, &local_err);
qobject_unref(options);
if (open_ret < 0) {
bdrv_unref(fallback_bs);
bs->drv = NULL;
/* A bdrv_snapshot_goto() error takes precedence */
error_propagate(errp, local_err);
return ret < 0 ? ret : open_ret;
}
/*
* fallback was a primary child. It was closed above and set to NULL,
* but the .bdrv_open() call has opened it again, because we set the
* respective option (with the qdict_put_str() call above).
* Assert that .bdrv_open() has attached the right BDS as primary child.
*/
bdrv_graph_rdlock_main_loop();
assert(bdrv_primary_bs(bs) == fallback_bs);
bdrv_graph_rdunlock_main_loop();
bdrv_unref(fallback_bs);
return ret;
}
error_setg(errp, "Block driver does not support snapshots");
return -ENOTSUP;
}
/**
* Delete an internal snapshot by @snapshot_id and @name.
* @bs: block device used in the operation
* @snapshot_id: unique snapshot ID, or NULL
* @name: snapshot name, or NULL
* @errp: location to store error
*
* If both @snapshot_id and @name are specified, delete the first one with
* id @snapshot_id and name @name.
* If only @snapshot_id is specified, delete the first one with id
* @snapshot_id.
* If only @name is specified, delete the first one with name @name.
* if none is specified, return -EINVAL.
*
* Returns: 0 on success, -errno on failure. If @bs is not inserted, return
* -ENOMEDIUM. If @snapshot_id and @name are both NULL, return -EINVAL. If @bs
* does not support internal snapshot deletion, return -ENOTSUP. If @bs does
* not support parameter @snapshot_id or @name, or one of them is not correctly
* specified, return -EINVAL. If @bs can't find one matching @id and @name,
* return -ENOENT. If @errp != NULL, it will always be filled with error
* message on failure.
*/
int bdrv_snapshot_delete(BlockDriverState *bs,
const char *snapshot_id,
const char *name,
Error **errp)
{
BlockDriver *drv = bs->drv;
BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
int ret;
GLOBAL_STATE_CODE();
if (!drv) {
error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, bdrv_get_device_name(bs));
return -ENOMEDIUM;
}
if (!snapshot_id && !name) {
error_setg(errp, "snapshot_id and name are both NULL");
return -EINVAL;
}
/* drain all pending i/o before deleting snapshot */
bdrv_drained_begin(bs);
if (drv->bdrv_snapshot_delete) {
ret = drv->bdrv_snapshot_delete(bs, snapshot_id, name, errp);
} else if (fallback_bs) {
ret = bdrv_snapshot_delete(fallback_bs, snapshot_id, name, errp);
} else {
error_setg(errp, "Block format '%s' used by device '%s' "
"does not support internal snapshot deletion",
drv->format_name, bdrv_get_device_name(bs));
ret = -ENOTSUP;
}
bdrv_drained_end(bs);
return ret;
}
int bdrv_snapshot_list(BlockDriverState *bs,
QEMUSnapshotInfo **psn_info)
{
GLOBAL_STATE_CODE();
GRAPH_RDLOCK_GUARD_MAINLOOP();
BlockDriver *drv = bs->drv;
BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
if (!drv) {
return -ENOMEDIUM;
}
if (drv->bdrv_snapshot_list) {
return drv->bdrv_snapshot_list(bs, psn_info);
}
if (fallback_bs) {
return bdrv_snapshot_list(fallback_bs, psn_info);
}
return -ENOTSUP;
}
/**
* Temporarily load an internal snapshot by @snapshot_id and @name.
* @bs: block device used in the operation
* @snapshot_id: unique snapshot ID, or NULL
* @name: snapshot name, or NULL
* @errp: location to store error
*
* If both @snapshot_id and @name are specified, load the first one with
* id @snapshot_id and name @name.
* If only @snapshot_id is specified, load the first one with id
* @snapshot_id.
* If only @name is specified, load the first one with name @name.
* if none is specified, return -EINVAL.
*
* Returns: 0 on success, -errno on fail. If @bs is not inserted, return
* -ENOMEDIUM. If @bs is not readonly, return -EINVAL. If @bs did not support
* internal snapshot, return -ENOTSUP. If qemu can't find a matching @id and
* @name, return -ENOENT. If @errp != NULL, it will always be filled on
* failure.
*/
int bdrv_snapshot_load_tmp(BlockDriverState *bs,
const char *snapshot_id,
const char *name,
Error **errp)
{
BlockDriver *drv = bs->drv;
GLOBAL_STATE_CODE();
GRAPH_RDLOCK_GUARD_MAINLOOP();
if (!drv) {
error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, bdrv_get_device_name(bs));
return -ENOMEDIUM;
}
if (!snapshot_id && !name) {
error_setg(errp, "snapshot_id and name are both NULL");
return -EINVAL;
}
if (!bdrv_is_read_only(bs)) {
error_setg(errp, "Device is not readonly");
return -EINVAL;
}
if (drv->bdrv_snapshot_load_tmp) {
return drv->bdrv_snapshot_load_tmp(bs, snapshot_id, name, errp);
}
error_setg(errp, "Block format '%s' used by device '%s' "
"does not support temporarily loading internal snapshots",
drv->format_name, bdrv_get_device_name(bs));
return -ENOTSUP;
}
int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
const char *id_or_name,
Error **errp)
{
int ret;
Error *local_err = NULL;
GLOBAL_STATE_CODE();
ret = bdrv_snapshot_load_tmp(bs, id_or_name, NULL, &local_err);
if (ret == -ENOENT || ret == -EINVAL) {
error_free(local_err);
local_err = NULL;
ret = bdrv_snapshot_load_tmp(bs, NULL, id_or_name, &local_err);
}
error_propagate(errp, local_err);
return ret;
}
static int GRAPH_RDLOCK
bdrv_all_get_snapshot_devices(bool has_devices, strList *devices,
GList **all_bdrvs, Error **errp)
{
g_autoptr(GList) bdrvs = NULL;
if (has_devices) {
if (!devices) {
error_setg(errp, "At least one device is required for snapshot");
return -1;
}
while (devices) {
BlockDriverState *bs = bdrv_find_node(devices->value);
if (!bs) {
error_setg(errp, "No block device node '%s'", devices->value);
return -1;
}
bdrvs = g_list_append(bdrvs, bs);
devices = devices->next;
}
} else {
BlockDriverState *bs;
BdrvNextIterator it;
for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
bdrvs = g_list_append(bdrvs, bs);
}
}
*all_bdrvs = g_steal_pointer(&bdrvs);
return 0;
}
static bool GRAPH_RDLOCK bdrv_all_snapshots_includes_bs(BlockDriverState *bs)
{
GLOBAL_STATE_CODE();
assert_bdrv_graph_readable();
if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
return false;
}
/* Include all nodes that are either in use by a BlockBackend, or that
* aren't attached to any node, but owned by the monitor. */
return bdrv_has_blk(bs) || QLIST_EMPTY(&bs->parents);
}
/* Group operations. All block drivers are involved.
* These functions will properly handle dataplane (take aio_context_acquire
* when appropriate for appropriate block drivers) */
bool bdrv_all_can_snapshot(bool has_devices, strList *devices,
Error **errp)
{
g_autoptr(GList) bdrvs = NULL;
GList *iterbdrvs;
GLOBAL_STATE_CODE();
GRAPH_RDLOCK_GUARD_MAINLOOP();
if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
return false;
}
iterbdrvs = bdrvs;
while (iterbdrvs) {
BlockDriverState *bs = iterbdrvs->data;
AioContext *ctx = bdrv_get_aio_context(bs);
bool ok = true;
aio_context_acquire(ctx);
if (devices || bdrv_all_snapshots_includes_bs(bs)) {
ok = bdrv_can_snapshot(bs);
}
aio_context_release(ctx);
if (!ok) {
error_setg(errp, "Device '%s' is writable but does not support "
"snapshots", bdrv_get_device_or_node_name(bs));
return false;
}
iterbdrvs = iterbdrvs->next;
}
return true;
}
int bdrv_all_delete_snapshot(const char *name,
bool has_devices, strList *devices,
Error **errp)
{
g_autoptr(GList) bdrvs = NULL;
GList *iterbdrvs;
GLOBAL_STATE_CODE();
GRAPH_RDLOCK_GUARD_MAINLOOP();
if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
return -1;
}
iterbdrvs = bdrvs;
while (iterbdrvs) {
BlockDriverState *bs = iterbdrvs->data;
AioContext *ctx = bdrv_get_aio_context(bs);
QEMUSnapshotInfo sn1, *snapshot = &sn1;
int ret = 0;
aio_context_acquire(ctx);
if ((devices || bdrv_all_snapshots_includes_bs(bs)) &&
bdrv_snapshot_find(bs, snapshot, name) >= 0)
{
ret = bdrv_snapshot_delete(bs, snapshot->id_str,
snapshot->name, errp);
}
aio_context_release(ctx);
if (ret < 0) {
error_prepend(errp, "Could not delete snapshot '%s' on '%s': ",
name, bdrv_get_device_or_node_name(bs));
return -1;
}
iterbdrvs = iterbdrvs->next;
}
return 0;
}
int bdrv_all_goto_snapshot(const char *name,
bool has_devices, strList *devices,
Error **errp)
{
g_autoptr(GList) bdrvs = NULL;
GList *iterbdrvs;
int ret;
GLOBAL_STATE_CODE();
bdrv_graph_rdlock_main_loop();
ret = bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp);
bdrv_graph_rdunlock_main_loop();
if (ret < 0) {
return -1;
}
iterbdrvs = bdrvs;
while (iterbdrvs) {
BlockDriverState *bs = iterbdrvs->data;
AioContext *ctx = bdrv_get_aio_context(bs);
bool all_snapshots_includes_bs;
aio_context_acquire(ctx);
bdrv_graph_rdlock_main_loop();
all_snapshots_includes_bs = bdrv_all_snapshots_includes_bs(bs);
bdrv_graph_rdunlock_main_loop();
ret = (devices || all_snapshots_includes_bs) ?
bdrv_snapshot_goto(bs, name, errp) : 0;
aio_context_release(ctx);
if (ret < 0) {
bdrv_graph_rdlock_main_loop();
error_prepend(errp, "Could not load snapshot '%s' on '%s': ",
name, bdrv_get_device_or_node_name(bs));
bdrv_graph_rdunlock_main_loop();
return -1;
}
iterbdrvs = iterbdrvs->next;
}
return 0;
}
int bdrv_all_has_snapshot(const char *name,
bool has_devices, strList *devices,
Error **errp)
{
g_autoptr(GList) bdrvs = NULL;
GList *iterbdrvs;
GLOBAL_STATE_CODE();
GRAPH_RDLOCK_GUARD_MAINLOOP();
if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
return -1;
}
iterbdrvs = bdrvs;
while (iterbdrvs) {
BlockDriverState *bs = iterbdrvs->data;
AioContext *ctx = bdrv_get_aio_context(bs);
QEMUSnapshotInfo sn;
int ret = 0;
aio_context_acquire(ctx);
if (devices || bdrv_all_snapshots_includes_bs(bs)) {
ret = bdrv_snapshot_find(bs, &sn, name);
}
aio_context_release(ctx);
if (ret < 0) {
if (ret == -ENOENT) {
return 0;
} else {
error_setg_errno(errp, errno,
"Could not check snapshot '%s' on '%s'",
name, bdrv_get_device_or_node_name(bs));
return -1;
}
}
iterbdrvs = iterbdrvs->next;
}
return 1;
}
int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
BlockDriverState *vm_state_bs,
uint64_t vm_state_size,
bool has_devices, strList *devices,
Error **errp)
{
g_autoptr(GList) bdrvs = NULL;
GList *iterbdrvs;
GLOBAL_STATE_CODE();
GRAPH_RDLOCK_GUARD_MAINLOOP();
if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
return -1;
}
iterbdrvs = bdrvs;
while (iterbdrvs) {
BlockDriverState *bs = iterbdrvs->data;
AioContext *ctx = bdrv_get_aio_context(bs);
int ret = 0;
aio_context_acquire(ctx);
if (bs == vm_state_bs) {
sn->vm_state_size = vm_state_size;
ret = bdrv_snapshot_create(bs, sn);
} else if (devices || bdrv_all_snapshots_includes_bs(bs)) {
sn->vm_state_size = 0;
ret = bdrv_snapshot_create(bs, sn);
}
aio_context_release(ctx);
if (ret < 0) {
error_setg(errp, "Could not create snapshot '%s' on '%s'",
sn->name, bdrv_get_device_or_node_name(bs));
return -1;
}
iterbdrvs = iterbdrvs->next;
}
return 0;
}
BlockDriverState *bdrv_all_find_vmstate_bs(const char *vmstate_bs,
bool has_devices, strList *devices,
Error **errp)
{
g_autoptr(GList) bdrvs = NULL;
GList *iterbdrvs;
GLOBAL_STATE_CODE();
GRAPH_RDLOCK_GUARD_MAINLOOP();
if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
return NULL;
}
iterbdrvs = bdrvs;
while (iterbdrvs) {
BlockDriverState *bs = iterbdrvs->data;
AioContext *ctx = bdrv_get_aio_context(bs);
bool found = false;
aio_context_acquire(ctx);
found = (devices || bdrv_all_snapshots_includes_bs(bs)) &&
bdrv_can_snapshot(bs);
aio_context_release(ctx);
if (vmstate_bs) {
if (g_str_equal(vmstate_bs,
bdrv_get_node_name(bs))) {
if (found) {
return bs;
} else {
error_setg(errp,
"vmstate block device '%s' does not support snapshots",
vmstate_bs);
return NULL;
}
}
} else if (found) {
return bs;
}
iterbdrvs = iterbdrvs->next;
}
if (vmstate_bs) {
error_setg(errp,
"vmstate block device '%s' does not exist", vmstate_bs);
} else {
error_setg(errp,
"no block device can store vmstate for snapshot");
}
return NULL;
}
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