qemu: capabilities: Lock out incremental backup capability without blockdev

Blockdev is required to do incremental backups properly. Add a helper
function for locking out capabilities and export it to allow re-doing
the processing if a different code path modifies capabilities.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NCole Robinson <crobinso@redhat.com>

src/qemu/qemu_capabilities.c

@@ -4577,6 +4577,21 @@ virQEMUCapsInitQMPVersionCaps(virQEMUCapsPtr qemuCaps)
 }
 
 
+/**
+ * virQEMUCapsInitProcessCapsInterlock:
+ * @qemuCaps: QEMU capabilities
+ *
+ * A capability which requires a different capability being present in order
+ * for libvirt to be able to drive it properly should be processed here.
+ */
+void
+virQEMUCapsInitProcessCapsInterlock(virQEMUCapsPtr qemuCaps)
+{
+    if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_BLOCKDEV))
+        virQEMUCapsClear(qemuCaps, QEMU_CAPS_INCREMENTAL_BACKUP);
+}
+
+
 /**
  * virQEMUCapsInitProcessCaps:
  * @qemuCaps: QEMU capabilities
@@ -4627,6 +4642,8 @@ virQEMUCapsInitProcessCaps(virQEMUCapsPtr qemuCaps)
         virQEMUCapsGet(qemuCaps, QEMU_CAPS_SCSI_DISK_DEVICE_ID) &&
         virQEMUCapsGet(qemuCaps, QEMU_CAPS_SAVEVM_MONITOR_NODES))
         virQEMUCapsSet(qemuCaps, QEMU_CAPS_BLOCKDEV);
+
+    virQEMUCapsInitProcessCapsInterlock(qemuCaps);
 }
 
 

src/qemu/qemu_capabilities.h

@@ -555,6 +555,8 @@ void virQEMUCapsClear(virQEMUCapsPtr qemuCaps,
 bool virQEMUCapsGet(virQEMUCapsPtr qemuCaps,
                     virQEMUCapsFlags flag);
 
+void virQEMUCapsInitProcessCapsInterlock(virQEMUCapsPtr qemuCaps);
+
 bool virQEMUCapsHasPCIMultiBus(virQEMUCapsPtr qemuCaps,
                                const virDomainDef *def);