snapshot: Don't leak moment obj list metaroot to callers

virDomainSnapshotFindByName(list, NULL) should return NULL, rather
than the internal-use-only metaroot.  Most existing callers pass in a
non-NULL name; the few external callers that don't are immediately
calling virDomainMomentSetParent (which indeed needs the metaroot
rather than NULL if the parent name is NULL); but as the leaky
abstraction is ugly, it is worth instead making
virDomainMomentSetParent static and adding a new function for
resolving the parent link of a brand new moment within its list.  The
existing external uses of virDomainMomentSetParent always succeed
(either the new moment has parent_name of NULL to become a new root,
or has parent_name set to a strdup of the previous current moment);
hence, our new function does not need a return value (but it still has
a VIR_WARN in case future uses break our assumptions about failure
being impossible).

Missed when commit 02c4e24d refactored things to attempt to remove
direct metaroot manipulations out of the qemu and test drivers into
internal-only details, and made more obvious when commit dc8d3dc6
factored it out into a separate file.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

src/conf/virdomainmomentobjlist.c

@@ -151,7 +151,7 @@ virDomainMomentDropChildren(virDomainMomentObjPtr moment)
 
 
 /* Add @moment to @parent's list of children. */
-void
+static void
 virDomainMomentSetParent(virDomainMomentObjPtr moment,
                          virDomainMomentObjPtr parent)
 {
@@ -162,6 +162,27 @@ virDomainMomentSetParent(virDomainMomentObjPtr moment,
 }
 
 
+/* Add @moment to the appropriate parent's list of children. The
+ * caller must ensure that moment->def->parent_name is either NULL
+ * (for a new root) or set to an existing moment already in the
+ * list. */
+void
+virDomainMomentLinkParent(virDomainMomentObjListPtr moments,
+                          virDomainMomentObjPtr moment)
+{
+    virDomainMomentObjPtr parent;
+
+    parent = virDomainMomentFindByName(moments, moment->def->parent_name);
+    if (!parent) {
+        parent = &moments->metaroot;
+        if (moment->def->parent_name)
+            VIR_WARN("moment %s lacks parent %s", moment->def->name,
+                     moment->def->parent_name);
+    }
+    virDomainMomentSetParent(moment, parent);
+}
+
+
 /* Take all children of @from and convert them into children of @to. */
 void
 virDomainMomentMoveChildren(virDomainMomentObjPtr from,
@@ -390,7 +411,9 @@ virDomainMomentObjPtr
 virDomainMomentFindByName(virDomainMomentObjListPtr moments,
                           const char *name)
 {
-    return name ? virHashLookup(moments->objs, name) : &moments->metaroot;
+    if (name)
+        return virHashLookup(moments->objs, name);
+    return NULL;
 }
 
 
@@ -484,9 +507,12 @@ virDomainMomentSetRelations(void *payload,
 
     parent = virDomainMomentFindByName(curr->moments, obj->def->parent_name);
     if (!parent) {
-        curr->err = -1;
         parent = &curr->moments->metaroot;
-        VIR_WARN("moment %s lacks parent", obj->def->name);
+        if (obj->def->parent_name) {
+            curr->err = -1;
+            VIR_WARN("moment %s lacks parent %s", obj->def->name,
+                     obj->def->parent_name);
+        }
     } else {
         tmp = parent;
         while (tmp && tmp->def) {

src/conf/virdomainmomentobjlist.h

@@ -60,8 +60,8 @@ void virDomainMomentDropParent(virDomainMomentObjPtr moment);
 void virDomainMomentDropChildren(virDomainMomentObjPtr moment);
 void virDomainMomentMoveChildren(virDomainMomentObjPtr from,
                                  virDomainMomentObjPtr to);
-void virDomainMomentSetParent(virDomainMomentObjPtr moment,
-                              virDomainMomentObjPtr parent);
+void virDomainMomentLinkParent(virDomainMomentObjListPtr moments,
+                               virDomainMomentObjPtr moment);
 
 virDomainMomentObjListPtr virDomainMomentObjListNew(void);
 void virDomainMomentObjListFree(virDomainMomentObjListPtr moments);

src/conf/virdomainsnapshotobjlist.c

@@ -223,6 +223,15 @@ virDomainSnapshotForEach(virDomainSnapshotObjListPtr snapshots,
 }
 
 
+/* Populate parent link of a given snapshot. */
+void
+virDomainSnapshotLinkParent(virDomainSnapshotObjListPtr snapshots,
+                            virDomainMomentObjPtr snap)
+{
+    return virDomainMomentLinkParent(snapshots->base, snap);
+}
+
+
 /* Populate parent link and child count of all snapshots, with all
  * assigned defs having relations starting as 0/NULL. Return 0 on
  * success, -1 if a parent is missing or if a circular relationship

src/conf/virdomainsnapshotobjlist.h

@@ -51,6 +51,8 @@ void virDomainSnapshotObjListRemoveAll(virDomainSnapshotObjListPtr snapshots);
 int virDomainSnapshotForEach(virDomainSnapshotObjListPtr snapshots,
                              virHashIterator iter,
                              void *data);
+void virDomainSnapshotLinkParent(virDomainSnapshotObjListPtr snapshots,
+                                 virDomainMomentObjPtr moment);
 int virDomainSnapshotUpdateRelations(virDomainSnapshotObjListPtr snapshots);
 int virDomainSnapshotCheckCycles(virDomainSnapshotObjListPtr snapshots,
                                  virDomainSnapshotDefPtr def,

src/libvirt_private.syms

@@ -978,7 +978,6 @@ virDomainMomentDropParent;
 virDomainMomentForEachChild;
 virDomainMomentForEachDescendant;
 virDomainMomentMoveChildren;
-virDomainMomentSetParent;
 
 
 # conf/virdomainobjlist.h
@@ -1007,6 +1006,7 @@ virDomainSnapshotFindByName;
 virDomainSnapshotForEach;
 virDomainSnapshotGetCurrent;
 virDomainSnapshotGetCurrentName;
+virDomainSnapshotLinkParent;
 virDomainSnapshotObjListFree;
 virDomainSnapshotObjListGetNames;
 virDomainSnapshotObjListNew;

src/qemu/qemu_driver.c

@@ -15540,7 +15540,6 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
     bool update_current = true;
     bool redefine = flags & VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE;
     unsigned int parse_flags = VIR_DOMAIN_SNAPSHOT_PARSE_DISKS;
-    virDomainMomentObjPtr other = NULL;
     int align_location = VIR_DOMAIN_SNAPSHOT_LOCATION_INTERNAL;
     bool align_match = true;
     virQEMUDriverConfigPtr cfg = NULL;
@@ -15807,9 +15806,7 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
                            snap->def->name);
             virDomainSnapshotObjListRemove(vm->snapshots, snap);
         } else {
-            other = virDomainSnapshotFindByName(vm->snapshots,
-                                                snap->def->parent_name);
-            virDomainMomentSetParent(snap, other);
+            virDomainSnapshotLinkParent(vm->snapshots, snap);
         }
     } else if (snap) {
         virDomainSnapshotObjListRemove(vm->snapshots, snap);

src/test/test_driver.c

@@ -7663,12 +7663,9 @@ testDomainSnapshotCreateXML(virDomainPtr domain,
  cleanup:
     if (vm) {
         if (snapshot) {
-            virDomainMomentObjPtr other;
             if (update_current)
                 virDomainSnapshotSetCurrent(vm->snapshots, snap);
-            other = virDomainSnapshotFindByName(vm->snapshots,
-                                                snap->def->parent_name);
-            virDomainMomentSetParent(snap, other);
+            virDomainSnapshotLinkParent(vm->snapshots, snap);
         }
         virDomainObjEndAPI(&vm);
     }