QMP: Add qmp command for blockdev-group-snapshot-sync

This adds the QMP command for blockdev-group-snapshot-sync. It
takes an array in as the input, for the argument devlist.  The
array consists of the following elements:

    + device:        device to snapshot. e.g. "ide-hd0", "virtio0"
    + snapshot-file: path & file for the snapshot image. e.g. "/tmp/file.img"
    + format:        snapshot format. e.g., "qcow2". Optional

There is no HMP equivalent for the command.
Signed-off-by: NJeff Cody <jcody@redhat.com>
Acked-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

qmp-commands.hx

@@ -686,6 +686,45 @@ EQMP
         .args_type  = "device:B",
         .mhandler.cmd_new = qmp_marshal_input_block_job_cancel,
     },
+    {
+        .name       = "blockdev-group-snapshot-sync",
+        .args_type  = "devlist:O",
+        .params  = "device:B,snapshot-file:s,format:s?",
+        .mhandler.cmd_new = qmp_marshal_input_blockdev_group_snapshot_sync,
+    },
+
+SQMP
+blockdev-group-snapshot-sync
+----------------------
+
+Synchronous snapshot of one or more block devices.  A list array input
+is accepted, that contains the device and snapshot file information for
+each device in group. The default format, if not specified, is qcow2.
+
+If there is any failure creating or opening a new snapshot, all snapshots
+for the group are abandoned, and the original disks pre-snapshot attempt
+are used.
+
+
+Arguments:
+
+devlist array:
+    - "device": device name to snapshot (json-string)
+    - "snapshot-file": name of new image file (json-string)
+    - "format": format of new image (json-string, optional)
+
+Example:
+
+-> { "execute": "blockdev-group-snapshot-sync", "arguments":
+                      { "devlist": [{ "device": "ide-hd0",
+                                      "snapshot-file": "/some/place/my-image",
+                                      "format": "qcow2" },
+                                    { "device": "ide-hd1",
+                                      "snapshot-file": "/some/place/my-image2",
+                                      "format": "qcow2" }] } }
+<- { "return": {} }
+
+EQMP
 
     {
         .name       = "blockdev-snapshot-sync",