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block/snapshot: Fix fallback 

If the top node's driver does not provide snapshot functionality and we
want to fall back to a node down the chain, we need to snapshot all
non-COW children.  For simplicity's sake, just do not fall back if there
is more than one such child.  Furthermore, we really only can fall back
to bs->file and bs->backing, because bdrv_snapshot_goto() has to modify
the child link (notably, set it to NULL).

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
master
Max Reitz 2019-06-12 18:21:07 +02:00 committed by Kevin Wolf
parent c4db2e25df
commit c8af87573f
1 changed files with 83 additions and 21 deletions
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104
block/snapshot.c
View File

@ -147,6 +147,56 @@ bool bdrv_snapshot_find_by_id_and_name(BlockDriverState *bs,
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;
@ -155,8 +205,9 @@ int bdrv_can_snapshot(BlockDriverState *bs)
}
if (!drv->bdrv_snapshot_create) {
if (bs->file != NULL) {
return bdrv_can_snapshot(bs->file->bs);
BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
if (fallback_bs) {
return bdrv_can_snapshot(fallback_bs);
}
return 0;
}
@ -168,14 +219,15 @@ 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 (bs->file) {
return bdrv_snapshot_create(bs->file->bs, sn_info);
if (fallback_bs) {
return bdrv_snapshot_create(fallback_bs, sn_info);
}
return -ENOTSUP;
}
@ -185,6 +237,7 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
Error **errp)
{
BlockDriver *drv = bs->drv;
BdrvChild **fallback_ptr;
int ret, open_ret;
if (!drv) {
@ -205,39 +258,46 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
return ret;
}
if (bs->file) {
BlockDriverState *file;
QDict *options = qdict_clone_shallow(bs->options);
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);
file = bs->file->bs;
/* Prevent it from getting deleted when detached from bs */
bdrv_ref(file);
bdrv_ref(fallback_bs);
qdict_extract_subqdict(options, &file_options, "file.");
qdict_extract_subqdict(options, &file_options, subqdict_prefix);
qobject_unref(file_options);
qdict_put_str(options, "file", bdrv_get_node_name(file));
g_free(subqdict_prefix);
qdict_put_str(options, (*fallback_ptr)->name,
bdrv_get_node_name(fallback_bs));
if (drv->bdrv_close) {
drv->bdrv_close(bs);
}
bdrv_unref_child(bs, bs->file);
bs->file = NULL;
ret = bdrv_snapshot_goto(file, snapshot_id, errp);
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(file);
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;
}
assert(bs->file->bs == file);
bdrv_unref(file);
assert(fallback_bs == (*fallback_ptr)->bs);
bdrv_unref(fallback_bs);
return ret;
}
@ -273,6 +333,7 @@ int bdrv_snapshot_delete(BlockDriverState *bs,
Error **errp)
{
BlockDriver *drv = bs->drv;
BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
int ret;
if (!drv) {
@ -289,8 +350,8 @@ int bdrv_snapshot_delete(BlockDriverState *bs,
if (drv->bdrv_snapshot_delete) {
ret = drv->bdrv_snapshot_delete(bs, snapshot_id, name, errp);
} else if (bs->file) {
ret = bdrv_snapshot_delete(bs->file->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",
@ -306,14 +367,15 @@ 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 (bs->file) {
return bdrv_snapshot_list(bs->file->bs, psn_info);
if (fallback_bs) {
return bdrv_snapshot_list(fallback_bs, psn_info);
}
return -ENOTSUP;
}