Reopening a node's backing child needs a bit of special handling because
the "backing" child has different defaults than all other children
(among other things). Adding filter support here is a bit more
difficult than just using the child access functions. In fact, we often
have to directly use bs->backing because these functions are about the
"backing" child (which may or may not be the COW backing file).
Signed-off-by: Max Reitz
---
block.c | 45 ++---
1 file changed, 38 insertions(+), 7 deletions(-)
diff --git a/block.c b/block.c
index 42abbaf0ba..064cc99857 100644
--- a/block.c
+++ b/block.c
@@ -3660,25 +3660,56 @@ static int bdrv_reopen_parse_backing(BDRVReopenState
*reopen_state,
}
}
+/*
+ * Ensure that @bs can really handle backing files, because we are
+ * about to give it one (or swap the existing one)
+ */
+if (bs->drv->is_filter) {
+/* Filters always have a file or a backing child */
+if (!bs->backing) {
+error_setg(errp, "'%s' is a %s filter node that does not support a
"
+ "backing child", bs->node_name, bs->drv->format_name);
+return -EINVAL;
+}
+} else if (!bs->drv->supports_backing) {
+error_setg(errp, "Driver '%s' of node '%s' does not support backing "
+ "files", bs->drv->format_name, bs->node_name);
+return -EINVAL;
+}
+
/*
* Find the "actual" backing file by skipping all links that point
* to an implicit node, if any (e.g. a commit filter node).
+ * We cannot use any of the bdrv_skip_*() functions here because
+ * those return the first explicit node, while we are looking for
+ * its overlay here.
*/
overlay_bs = bs;
-while (backing_bs(overlay_bs) && backing_bs(overlay_bs)->implicit) {
-overlay_bs = backing_bs(overlay_bs);
+while (bdrv_filtered_bs(overlay_bs) &&
+ bdrv_filtered_bs(overlay_bs)->implicit)
+{
+overlay_bs = bdrv_filtered_bs(overlay_bs);
}
/* If we want to replace the backing file we need some extra checks */
-if (new_backing_bs != backing_bs(overlay_bs)) {
+if (new_backing_bs != bdrv_filtered_bs(overlay_bs)) {
/* Check for implicit nodes between bs and its backing file */
if (bs != overlay_bs) {
error_setg(errp, "Cannot change backing link if '%s' has "
"an implicit backing file", bs->node_name);
return -EPERM;
}
-/* Check if the backing link that we want to replace is frozen */
-if (bdrv_is_chain_frozen(overlay_bs, backing_bs(overlay_bs), errp)) {
+/*
+ * Check if the backing link that we want to replace is frozen.
+ * Note that
+ * bdrv_filtered_child(overlay_bs) == overlay_bs->backing,
+ * because we know that overlay_bs == bs, and that @bs
+ * either is an R/W filter that uses ->backing or a COW format
+ * with bs->drv->supports_backing == true.
+ */
+if (bdrv_is_chain_frozen(overlay_bs, child_bs(overlay_bs->backing),
+ errp))
+{
return -EPERM;
}
reopen_state->replace_backing_bs = true;
@@ -3829,7 +3860,7 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state,
BlockReopenQueue *queue,
* its metadata. Otherwise the 'backing' option can be omitted.
*/
if (drv->supports_backing && reopen_state->backing_missing &&
-(backing_bs(reopen_state->bs) || reopen_state->bs->backing_file[0])) {
+(reopen_state->bs->backing || reopen_state->bs->backing_file[0])) {
error_setg(errp, "backing is missing for '%s'",
reopen_state->bs->node_name);
ret = -EINVAL;
@@ -3974,7 +4005,7 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state)
* from bdrv_set_backing_hd()) has the new values.
*/
if (reopen_state->replace_backing_bs) {
-BlockDriverState *old_backing_bs = backing_bs(bs);
+BlockDriverState *old_backing_bs = child_bs(bs->backing);
assert(!old_backing_bs || !old_backing_bs->implicit);
/* Abort the permission update on the backing bs we're detaching */
if (old_backing_bs) {
--
2.21.0
