@@ -2367,6 +2367,85 @@ void qmp_block_job_complete(const char *device, Error **errp)
block_job_complete(job, errp);
}
+void qmp_change_backing_file(const char *device,
+ const char *image_node_name,
+ const char *backing_file,
+ Error **errp)
+{
+ BlockDriverState *bs = NULL;
+ BlockDriverState *image_bs = NULL;
+ Error *local_err = NULL;
+ bool ro;
+ int open_flags;
+ int ret;
+
+ /* find the top layer BDS of the chain */
+ bs = bdrv_find(device);
+ if (!bs) {
+ error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+ return;
+ }
+
+ image_bs = bdrv_lookup_bs(NULL, image_node_name, &local_err);
+ if (local_err) {
+ error_propagate(errp, local_err);
+ return;
+ }
+
+ if (!image_bs) {
+ error_setg(errp, "image file not found");
+ return;
+ }
+
+ if (bdrv_find_base(image_bs) == image_bs) {
+ error_setg(errp, "not allowing backing file change on an image "
+ "without a backing file");
+ return;
+ }
+
+ /* even though we are not necessarily operating on bs, we need it to
+ * determine if block ops are currently prohibited on the chain */
+ if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_CHANGE, errp)) {
+ return;
+ }
+
+ /* final sanity check */
+ if (!bdrv_chain_contains(bs, image_bs)) {
+ error_setg(errp, "'%s' and image file are not in the same chain",
+ device);
+ return;
+ }
+
+ /* if not r/w, reopen to make r/w */
+ open_flags = image_bs->open_flags;
+ ro = bdrv_is_read_only(image_bs);
+
+ if (ro) {
+ bdrv_reopen(image_bs, open_flags | BDRV_O_RDWR, &local_err);
+ if (local_err) {
+ error_propagate(errp, local_err);
+ return;
+ }
+ }
+
+ ret = bdrv_change_backing_file(image_bs, backing_file,
+ image_bs->drv ? image_bs->drv->format_name : "");
+
+ if (ret < 0) {
+ error_setg_errno(errp, -ret, "Could not change backing file to '%s'",
+ backing_file);
+ /* don't exit here, so we can try to restore open flags if
+ * appropriate */
+ }
+
+ if (ro) {
+ bdrv_reopen(image_bs, open_flags, &local_err);
+ if (local_err) {
+ error_propagate(errp, local_err); /* will preserve prior errp */
+ }
+ }
+}
+
void qmp_blockdev_add(BlockdevOptions *options, Error **errp)
{
QmpOutputVisitor *ov = qmp_output_visitor_new();
@@ -680,6 +680,32 @@
'data': 'BlockdevSnapshot' }
##
+# @change-backing-file
+#
+# Change the backing file in the image file metadata. This does not
+# cause QEMU to reopen the image file to reparse the backing filename
+# (it may, however, perform a reopen to change permissions from
+# r/o -> r/w -> r/o, if needed). The new backing file string is written
+# into the image file metadata, and the QEMU internal strings are
+# updated.
+#
+# @image-node-name: The name of the block driver state node of the
+# image to modify.
+#
+# @device: The name of the device that owns image-node-name.
+#
+# @backing-file: The string to write as the backing file. This
+# string is not validated, so care should be taken
+# when specifying the string or the image chain may
+# not be able to be reopened again.
+#
+# Since: 2.1
+##
+{ 'command': 'change-backing-file',
+ 'data': { 'device': 'str', 'image-node-name': 'str',
+ 'backing-file': 'str' } }
+
+##
# @block-commit
#
# Live commit of data from overlay image nodes into backing nodes - i.e.,
@@ -1353,6 +1353,45 @@ Example:
EQMP
{
+ .name = "change-backing-file",
+ .args_type = "device:s,image-node-name:s,backing-file:s",
+ .mhandler.cmd_new = qmp_marshal_input_change_backing_file,
+ },
+
+SQMP
+change-backing-file
+-------------------
+Since: 2.1
+
+Change the backing file in the image file metadata. This does not cause
+QEMU to reopen the image file to reparse the backing filename (it may,
+however, perform a reopen to change permissions from r/o -> r/w -> r/o,
+if needed). The new backing file string is written into the image file
+metadata, and the QEMU internal strings are updated.
+
+Arguments:
+
+- "image-node-name": The name of the block driver state node of the
+ image to modify. The "device" is argument is used to
+ verify "image-node-name" is in the chain described by
+ "device".
+ (json-string, optional)
+
+- "device": The name of the device.
+ (json-string)
+
+- "backing-file": The string to write as the backing file. This string is
+ not validated, so care should be taken when specifying
+ the string or the image chain may not be able to be
+ reopened again.
+ (json-string)
+
+Returns: Nothing on success
+ If "device" does not exist or cannot be determined, DeviceNotFound
+
+EQMP
+
+ {
.name = "balloon",
.args_type = "value:M",
.mhandler.cmd_new = qmp_marshal_input_balloon,