@@ -353,6 +353,11 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
BlockDriverState *bs);
BlockDriverState *bdrv_find_base(BlockDriverState *bs);
+bool bdrv_is_backing_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
+ Error **errp);
+int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
+ Error **errp);
+void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState *base);
typedef struct BdrvCheckResult {
@@ -711,6 +711,12 @@ struct BdrvChild {
uint64_t backup_perm;
uint64_t backup_shared_perm;
+ /*
+ * This link is frozen: the child can neither be replaced nor
+ * detached from the parent.
+ */
+ bool frozen;
+
QLIST_ENTRY(BdrvChild) next;
QLIST_ENTRY(BdrvChild) next_parent;
};
@@ -2126,6 +2126,8 @@ static void bdrv_replace_child_noperm(BdrvChild *child,
BlockDriverState *old_bs = child->bs;
int i;
+ assert(!child->frozen);
+
if (old_bs && new_bs) {
assert(bdrv_get_aio_context(old_bs) == bdrv_get_aio_context(new_bs));
}
@@ -2342,6 +2344,10 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
bool update_inherits_from = bdrv_chain_contains(bs, backing_hd) &&
bdrv_inherits_from_recursive(backing_hd, bs);
+ if (bdrv_is_backing_chain_frozen(bs, backing_bs(bs), errp)) {
+ return;
+ }
+
if (backing_hd) {
bdrv_ref(backing_hd);
}
@@ -3721,6 +3727,11 @@ void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
if (!should_update_child(c, to)) {
continue;
}
+ if (c->frozen) {
+ error_setg(errp, "Cannot change '%s' link to '%s'",
+ c->name, from->node_name);
+ goto out;
+ }
list = g_slist_prepend(list, c);
perm |= c->perm;
shared &= c->shared_perm;
@@ -3932,6 +3943,63 @@ BlockDriverState *bdrv_find_base(BlockDriverState *bs)
return bdrv_find_overlay(bs, NULL);
}
+/*
+ * Return true if at least one of the backing links between @bs and
+ * @base is frozen. @errp is set if that's the case.
+ */
+bool bdrv_is_backing_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
+ Error **errp)
+{
+ BlockDriverState *i;
+
+ for (i = bs; i != base && i->backing; i = backing_bs(i)) {
+ if (i->backing->frozen) {
+ error_setg(errp, "Cannot change '%s' link from '%s' to '%s'",
+ i->backing->name, i->node_name,
+ backing_bs(i)->node_name);
+ return true;
+ }
+ }
+
+ return false;
+}
+
+/*
+ * Freeze all backing links between @bs and @base.
+ * If any of the links is already frozen the operation is aborted and
+ * none of the links are modified.
+ * Returns 0 on success. On failure returns < 0 and sets @errp.
+ */
+int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
+ Error **errp)
+{
+ BlockDriverState *i;
+
+ if (bdrv_is_backing_chain_frozen(bs, base, errp)) {
+ return -EPERM;
+ }
+
+ for (i = bs; i != base && i->backing; i = backing_bs(i)) {
+ i->backing->frozen = true;
+ }
+
+ return 0;
+}
+
+/*
+ * Unfreeze all backing links between @bs and @base. The caller must
+ * ensure that all links are frozen before using this function.
+ */
+void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState *base)
+{
+ BlockDriverState *i;
+
+ for (i = bs; i != base && i->backing; i = backing_bs(i)) {
+ assert(i->backing->frozen);
+ i->backing->frozen = false;
+ }
+}
+
/*
* Drops images above 'base' up to and including 'top', and sets the image
* above 'top' to have base as its backing file.
@@ -3981,6 +4049,14 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
goto exit;
}
+ /* This function changes all links that point to top and makes
+ * them point to base. Check that none of them is frozen. */
+ QLIST_FOREACH(c, &top->parents, next_parent) {
+ if (c->frozen) {
+ goto exit;
+ }
+ }
+
/* If 'base' recursively inherits from 'top' then we should set
* base->inherits_from to top->inherits_from after 'top' and all
* other intermediate nodes have been dropped.