From: Peter Krempa <pkrempa@redhat.com>

Anounce that 'blockdev-snapshot' command's permissions allow changing
of the backing file if the 'consistent_read' permission is not required.

This is useful for libvirt to allow late opening of the backing chain
during a blockdev-mirror.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200310113831.27293-8-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qapi/block-core.json | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 9758fc48d2..91586fb1fb 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1472,6 +1472,12 @@
 #
 # For the arguments, see the documentation of BlockdevSnapshot.
 #
+# Features:
+# @allow-write-only-overlay: If present, the check whether this operation is safe
+#                            was relaxed so that it can be used to change
+#                            backing file of a destination of a blockdev-mirror.
+#                            (since 5.0)
+#
 # Since: 2.5
 #
 # Example:
@@ -1492,7 +1498,8 @@
 #
 ##
 { 'command': 'blockdev-snapshot',
-  'data': 'BlockdevSnapshot' }
+  'data': 'BlockdevSnapshot',
+  'features': [ 'allow-write-only-overlay' ] }
 
 ##
 # @change-backing-file:
-- 
2.20.1