snapshot: affect persistent xml after disk snapshot

For external snapshots to be useful on persistent domains, we must
alter the persistent definition alongside the running definition.
Thanks to the possibility of disk hotplug as well as of edits that
only affect the persistent xml, we can't assume that vm->def and
vm->newDef have the same disk at the same index, so we can only
update the persistent copy if the device destination matches up.

* src/qemu/qemu_driver.c (qemuDomainSnapshotCreateDiskActive)
(qemuDomainSnapshotCreateSingleDiskActive): Also affect newDef, if
present.

src/qemu/qemu_driver.c

@@ -9107,12 +9107,15 @@ static int
 qemuDomainSnapshotCreateSingleDiskActive(struct qemud_driver *driver,
                                          virDomainObjPtr vm,
                                          virDomainSnapshotDiskDefPtr snap,
-                                         virDomainDiskDefPtr disk)
+                                         virDomainDiskDefPtr disk,
+                                         virDomainDiskDefPtr persistDisk)
 {
     qemuDomainObjPrivatePtr priv = vm->privateData;
     char *device = NULL;
     char *source = NULL;
     char *driverType = NULL;
+    char *persistSource = NULL;
+    char *persistDriverType = NULL;
     int ret = -1;
     int fd = -1;
     char *origsrc = NULL;
@@ -9128,7 +9131,11 @@ qemuDomainSnapshotCreateSingleDiskActive(struct qemud_driver *driver,
     if (virAsprintf(&device, "drive-%s", disk->info.alias) < 0 ||
         !(source = strdup(snap->file)) ||
         (STRNEQ_NULLABLE(disk->driverType, "qcow2") &&
-         !(driverType = strdup("qcow2")))) {
+         !(driverType = strdup("qcow2"))) ||
+        (persistDisk &&
+         (!(persistSource = strdup(source)) ||
+          (STRNEQ_NULLABLE(persistDisk->driverType, "qcow2") &&
+           !(persistDriverType = strdup("qcow2")))))) {
         virReportOOMError();
         goto cleanup;
     }
@@ -9176,9 +9183,16 @@ qemuDomainSnapshotCreateSingleDiskActive(struct qemud_driver *driver,
         disk->driverType = driverType;
         driverType = NULL;
     }
-
-    /* XXX Do we also need to update vm->newDef if there are pending
-     * configuration changes awaiting the next boot?  */
+    if (persistDisk) {
+        VIR_FREE(persistDisk->src);
+        persistDisk->src = persistSource;
+        persistSource = NULL;
+        if (persistDriverType) {
+            VIR_FREE(persistDisk->driverType);
+            persistDisk->driverType = persistDriverType;
+            persistDriverType = NULL;
+        }
+    }
 
 cleanup:
     if (origsrc) {
@@ -9190,6 +9204,8 @@ cleanup:
     VIR_FREE(device);
     VIR_FREE(source);
     VIR_FREE(driverType);
+    VIR_FREE(persistSource);
+    VIR_FREE(persistDriverType);
     return ret;
 }
 
@@ -9205,6 +9221,7 @@ qemuDomainSnapshotCreateDiskActive(virConnectPtr conn,
     bool resume = false;
     int ret = -1;
     int i;
+    bool persist = false;
 
     if (qemuDomainObjBeginJobWithDriver(driver, vm, QEMU_JOB_MODIFY) < 0)
         return -1;
@@ -9235,12 +9252,24 @@ qemuDomainSnapshotCreateDiskActive(virConnectPtr conn,
      * SNAPSHOT_EXTERNAL with a valid file name and qcow2 format.  */
     qemuDomainObjEnterMonitorWithDriver(driver, vm);
     for (i = 0; i < snap->def->ndisks; i++) {
+        virDomainDiskDefPtr persistDisk = NULL;
+
         if (snap->def->disks[i].snapshot == VIR_DOMAIN_DISK_SNAPSHOT_NO)
             continue;
+        if (vm->newDef) {
+            int indx = virDomainDiskIndexByName(vm->newDef,
+                                                vm->def->disks[i]->dst,
+                                                false);
+            if (indx >= 0) {
+                persistDisk = vm->newDef->disks[indx];
+                persist = true;
+            }
+        }
 
         ret = qemuDomainSnapshotCreateSingleDiskActive(driver, vm,
                                                        &snap->def->disks[i],
-                                                       vm->def->disks[i]);
+                                                       vm->def->disks[i],
+                                                       persistDisk);
         if (ret < 0)
             break;
     }
@@ -9275,7 +9304,9 @@ cleanup:
     }
 
     if (vm) {
-        if (virDomainSaveStatus(driver->caps, driver->stateDir, vm) < 0)
+        if (virDomainSaveStatus(driver->caps, driver->stateDir, vm) < 0 ||
+            (persist &&
+             virDomainSaveConfig(driver->configDir, vm->newDef) < 0))
             ret = -1;
         if (qemuDomainObjEndJob(driver, vm) == 0) {
             /* Only possible if a transient vm quit while our locks were down,