block: Add QMP support for streaming to an intermediate layer
This patch makes the 'device' parameter of the 'block-stream' command
accept a node name that is not a root node. The presence of this
feature can't be directly tested with introspection; soon we'll
introduce a 'base-node' parameter whose presence can be checked for
this purpose.
In addition to that, operation blockers will be checked in all
intermediate nodes between the top and the base node.
Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 0f2b703..d7a029c 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1464,6 +1464,13 @@
# with query-block-jobs. The operation can be stopped before it has completed
# using the block-job-cancel command.
#
+# The node that receives the data is called the top image, can be located in
+# any part of the chain (but always above the base image; see below) and can be
+# specified using its device or node name. Earlier qemu versions only allowed
+# 'device' to name the top level node; presence of the 'base-node' parameter
+# during introspection can be used as a witness of the enhanced semantics
+# of 'device'.
+#
# If a base file is specified then sectors are not copied from that base file and
# its backing chain. When streaming completes the image file will have the base
# file as its backing file. This can be used to stream a subset of the backing
@@ -1475,12 +1482,12 @@
# @job-id: #optional identifier for the newly-created block job. If
# omitted, the device name will be used. (Since 2.7)
#
-# @device: the device name or node-name of a root node
+# @device: the device or node name of the top image
#
# @base: #optional the common backing file name
#
-# @backing-file: #optional The backing file string to write into the active
-# layer. This filename is not validated.
+# @backing-file: #optional The backing file string to write into the top
+# image. This filename is not validated.
#
# If a pathname string is such that it cannot be
# resolved by QEMU, that means that subsequent QMP or
