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qemu/block/snapshot.c
Max Reitz 32a9a245d7 block/snapshot: Clarify goto fallback behavior 
In the bdrv_snapshot_goto() fallback code, we work with a pointer to
either bs->file or bs->backing.  We detach that child, close the node
(with .bdrv_close()), apply the snapshot on the child node, and then
re-open the node (with .bdrv_open()).

In order for .bdrv_open() to attach the same child node that we had
before, we pass "file={child-node}" or "backing={child-node}" to it.
Therefore, when .bdrv_open() has returned success, we can assume that
bs->file or bs->backing (respectively) points to our original child
again.  This is verified by an assertion.

All of this is not immediately clear from a quick glance at the code,
so add a comment to the assertion what it is for, and why it is valid.
It certainly confused Coverity.

Reported-by: Coverity (CID 1452774)
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20210503095418.31521-1-mreitz@redhat.com>
[mreitz: s/close/detach/]
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
2021-06-24 09:49:04 +02:00

749 lines
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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;
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);
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 the child BDS pointer 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.
*
* We need to return an indirect pointer because bdrv_snapshot_goto()
* has to modify the BdrvChild pointer.
*/
static BdrvChild **bdrv_snapshot_fallback_ptr(BlockDriverState *bs)
{
BdrvChild **fallback;
BdrvChild *child;
/*
* The only BdrvChild pointers that are safe to modify (and which
* we can thus return a reference to) are bs->file and
* bs->backing.
*/
fallback = &bs->file;
if (!*fallback && bs->drv && bs->drv->is_filter) {
fallback = &bs->backing;
}
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 *bdrv_snapshot_fallback(BlockDriverState *bs)
{
BdrvChild **child_ptr = bdrv_snapshot_fallback_ptr(bs);
return child_ptr ? (*child_ptr)->bs : NULL;
}
int bdrv_can_snapshot(BlockDriverState *bs)
{
BlockDriver *drv = bs->drv;
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);
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_ptr;
int ret, open_ret;
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;
}
fallback_ptr = bdrv_snapshot_fallback_ptr(bs);
if (fallback_ptr) {
QDict *options;
QDict *file_options;
Error *local_err = NULL;
BlockDriverState *fallback_bs = (*fallback_ptr)->bs;
char *subqdict_prefix = g_strdup_printf("%s.", (*fallback_ptr)->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_ptr */
qdict_put_str(options, (*fallback_ptr)->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_unref_child(bs, *fallback_ptr);
*fallback_ptr = 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_ptr is &bs->file or &bs->backing. *fallback_ptr
* 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 some child on
* *fallback_ptr, and that it has attached the one we wanted
* it to (i.e., fallback_bs).
*/
assert(*fallback_ptr && fallback_bs == (*fallback_ptr)->bs);
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;
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)
{
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;
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;
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 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 bdrv_all_snapshots_includes_bs(BlockDriverState *bs)
{
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;
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;
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;
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 (devices || bdrv_all_snapshots_includes_bs(bs)) {
ret = bdrv_snapshot_goto(bs, name, errp);
}
aio_context_release(ctx);
if (ret < 0) {
error_prepend(errp, "Could not load snapshot '%s' on '%s': ",
name, bdrv_get_device_or_node_name(bs));
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;
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;
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;
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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