qemu: capabilities: Introduce QEMU_CAPS_BLOCKDEV_SNAPSHOT_ALLOW_WRITE_ONLY

The capability is based on qemu's support of using blockdev-snapshot to
install backing chain also for images which are in use by a block-copy
job.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

src/qemu/qemu_capabilities.c

@@ -565,6 +565,7 @@ VIR_ENUM_IMPL(virQEMUCaps,
               /* 355 */
               "vhost-user-fs",
               "query-named-block-nodes.flat",
+              "blockdev-snapshot.allow-write-only-overlay",
     );
 
 
@@ -1441,6 +1442,7 @@ static struct virQEMUCapsStringFlags virQEMUCapsQMPSchemaQueries[] = {
     { "human-monitor-command/$savevm-monitor-nodes", QEMU_CAPS_SAVEVM_MONITOR_NODES },
     { "blockdev-add/arg-type/+nvme", QEMU_CAPS_DRIVE_NVME },
     { "query-named-block-nodes/arg-type/flat", QEMU_CAPS_QMP_QUERY_NAMED_BLOCK_NODES_FLAT },
+    { "blockdev-snapshot/$allow-write-only-overlay", QEMU_CAPS_BLOCKDEV_SNAPSHOT_ALLOW_WRITE_ONLY },
 };
 
 typedef struct _virQEMUCapsObjectTypeProps virQEMUCapsObjectTypeProps;

src/qemu/qemu_capabilities.h

@@ -546,6 +546,7 @@ typedef enum { /* virQEMUCapsFlags grouping marker for syntax-check */
     /* 355 */
     QEMU_CAPS_DEVICE_VHOST_USER_FS, /* -device vhost-user-fs */
     QEMU_CAPS_QMP_QUERY_NAMED_BLOCK_NODES_FLAT, /* query-named-block-nodes supports the 'flat' option */
+    QEMU_CAPS_BLOCKDEV_SNAPSHOT_ALLOW_WRITE_ONLY, /* blockdev-snapshot has the 'allow-write-only-overlay' feature */
 
     QEMU_CAPS_LAST /* this must always be the last item */
 } virQEMUCapsFlags;

tests/qemucapabilitiesdata/caps_5.0.0.x86_64.xml

@@ -225,6 +225,7 @@
   <flag name='virtio-net.failover'/>
   <flag name='vhost-user-fs'/>
   <flag name='query-named-block-nodes.flat'/>
+  <flag name='blockdev-snapshot.allow-write-only-overlay'/>
   <version>4002050</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>43100241</microcodeVersion>