qemu: process: Don't redetect backing chain on reconnect

Skip purging the backing chain and redetecting it when it was not going
to change during the time we were not present.

The decision is based on the new flag which records whether there were
blockjobs running to the status XML.

src/qemu/qemu_process.c

@@ -6975,12 +6975,16 @@ qemuProcessReconnect(void *opaque)
         if (virStorageTranslateDiskSourcePool(conn, disk) < 0)
             goto error;
 
-        /* XXX we should be able to restore all data from XML in the future.
-         * This should be the only place that calls qemuDomainDetermineDiskChain
-         * with @report_broken == false to guarantee best-effort domain
-         * reconnect */
-        if (qemuDomainDetermineDiskChain(driver, obj, disk, true, false) < 0)
-            goto error;
+        /* backing chains need to be refreshed only if they could change */
+        if (priv->reconnectBlockjobs != VIR_TRISTATE_BOOL_NO) {
+            /* This should be the only place that calls
+             * qemuDomainDetermineDiskChain with @report_broken == false
+             * to guarantee best-effort domain reconnect */
+            if (qemuDomainDetermineDiskChain(driver, obj, disk, true, false) < 0)
+                goto error;
+        } else {
+            VIR_DEBUG("skipping backing chain detection for '%s'", disk->dst);
+        }
 
         dev.type = VIR_DOMAIN_DEVICE_DISK;
         dev.data.disk = disk;