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>
diff --git a/block/snapshot.c b/block/snapshot.c
index bd9fb01..a2bf3a5 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -147,6 +147,56 @@
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 @@
}
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 @@
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 @@
Error **errp)
{
BlockDriver *drv = bs->drv;
+ BdrvChild **fallback_ptr;
int ret, open_ret;
if (!drv) {
@@ -205,39 +258,46 @@
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);
- file = bs->file->bs;
+ options = qdict_clone_shallow(bs->options);
+
/* 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 @@
Error **errp)
{
BlockDriver *drv = bs->drv;
+ BlockDriverState *fallback_bs = bdrv_snapshot_fallback(bs);
int ret;
if (!drv) {
@@ -289,8 +350,8 @@
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 @@
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;
}
