qemu: caps: Add capability for change-backing-file command

This command allows to change the backing file name recorded in the
metadata of a qcow (or other) image. The capability also notifies that
the "block-stream" and "block-commit" commands understand the
"backing-file" attribute.

src/qemu/qemu_capabilities.c

@@ -258,6 +258,7 @@ VIR_ENUM_IMPL(virQEMUCaps, QEMU_CAPS_LAST,
               "host-pci-multidomain",
               "msg-timestamp",
               "active-commit",
+              "change-backing-file",
     );
 
 
@@ -1415,6 +1416,7 @@ struct virQEMUCapsStringFlags virQEMUCapsCommands[] = {
     { "blockdev-snapshot-sync", QEMU_CAPS_DISK_SNAPSHOT },
     { "add-fd", QEMU_CAPS_ADD_FD },
     { "nbd-server-start", QEMU_CAPS_NBD_SERVER },
+    { "change-backing-file", QEMU_CAPS_CHANGE_BACKING_FILE },
 };
 
 struct virQEMUCapsStringFlags virQEMUCapsEvents[] = {

src/qemu/qemu_capabilities.h

@@ -208,6 +208,7 @@ typedef enum {
     QEMU_CAPS_HOST_PCI_MULTIDOMAIN = 166, /* support domain > 0 in host pci address */
     QEMU_CAPS_MSG_TIMESTAMP      = 167, /* -msg timestamp */
     QEMU_CAPS_ACTIVE_COMMIT      = 168, /* block-commit works without 'top' */
+    QEMU_CAPS_CHANGE_BACKING_FILE = 169, /* change name of backing file in metadata */
 
     QEMU_CAPS_LAST,                   /* this must always be the last item */
 } virQEMUCapsFlags;