[PATCH v3 3/3] qapi: Allow introspecting fix for savevm's cooperation with blockdev

[Peter Krempa]

'savevm' was buggy as it considered all monitor-owned block device nodes
for snapshot. With introduction of -blockdev the common usage made all
nodes including protocol and backing file nodes monitor-owned and thus
considered for snapshot.

This is a problem since the 'file' protocol nodes can't have internal
snapshots and it does not make sense to take snapshot of nodes
representing backing files.

This was fixed by commit 05f4aced658a02b02 clients need to be able to
detect whether this fix is present.

Since savevm does not have an QMP alternative, add the feature for the
'human-monitor-command' backdoor which is used to call this command in
modern use.

Signed-off-by: Peter Krempa <address@hidden>
---
 qapi/misc.json | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/qapi/misc.json b/qapi/misc.json
index 6bd11f50e6..5d0070aa43 100644
--- a/qapi/misc.json
+++ b/qapi/misc.json
@@ -1020,6 +1020,12 @@
 #
 # @cpu-index: The CPU to use for commands that require an implicit CPU
 #
+# Features:
+# @savevm-blockdev-monitor-nodes: If present, the HMP command savevm only
+#                                 snapshots monitor-owned nodes if they have no
+#                                 parents. This allows to use 'savevm' with
+#                                 -blockdev. (since 4.2)
+#
 # Returns: the output of the command as a string
 #
 # Since: 0.14.0
@@ -1047,7 +1053,8 @@
 ##
 { 'command': 'human-monitor-command',
   'data': {'command-line': 'str', '*cpu-index': 'int'},
-  'returns': 'str' }
+  'returns': 'str',
+  'features': [ 'savevm-blockdev-monitor-nodes' ] }

 ##
 # @change:
-- 
2.21.0