snapshot: improve disk align checking

There were not previous callers with require_match set to true.
I originally implemented this bool with the intent of supporting
ESX snapshot semantics, where the choice of internal vs. external
vs. non-checkpointable must be made at domain start, but as ESX
has not been wired up to use it yet, we might as well fix it to
work with our next qemu patch for now, and worry about any further
improvements (changing the bool to a flags argument) if the ESX
driver decides to use this function in the future.

* src/conf/snapshot_conf.c (virDomainSnapshotAlignDisks): Alter
logic when require_match is true to deal with new XML.

src/conf/snapshot_conf.c

@@ -368,9 +368,8 @@ disksorter(const void *a, const void *b)
  * the domain, with a fallback to a passed in default.  Convert paths
  * to disk targets for uniformity.  Issue an error and return -1 if
  * any def->disks[n]->name appears more than once or does not map to
- * dom->disks.  If require_match, also require that existing
- * def->disks snapshot states do not override explicit def->dom
- * settings.  */
+ * dom->disks.  If require_match, also ensure that there is no
+ * conflicting requests for both internal and external snapshots.  */
 int
 virDomainSnapshotAlignDisks(virDomainSnapshotDefPtr def,
                             int default_snapshot,
@@ -416,7 +415,6 @@ virDomainSnapshotAlignDisks(virDomainSnapshotDefPtr def,
                            _("no disk named '%s'"), disk->name);
             goto cleanup;
         }
-        disk_snapshot = def->dom->disks[idx]->snapshot;
 
         if (virBitmapGetBit(map, idx, &inuse) < 0 || inuse) {
             virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
@@ -426,15 +424,22 @@ virDomainSnapshotAlignDisks(virDomainSnapshotDefPtr def,
         }
         ignore_value(virBitmapSetBit(map, idx));
         disk->index = idx;
-        if (!disk_snapshot)
-            disk_snapshot = default_snapshot;
+
+        disk_snapshot = def->dom->disks[idx]->snapshot;
         if (!disk->snapshot) {
-            disk->snapshot = disk_snapshot;
-        } else if (disk_snapshot && require_match &&
-                   disk->snapshot != disk_snapshot) {
+            if (disk_snapshot &&
+                (!require_match ||
+                 disk_snapshot == VIR_DOMAIN_SNAPSHOT_LOCATION_NONE))
+                disk->snapshot = disk_snapshot;
+            else
+                disk->snapshot = default_snapshot;
+        } else if (require_match &&
+                   disk->snapshot != default_snapshot &&
+                   !(disk->snapshot == VIR_DOMAIN_SNAPSHOT_LOCATION_NONE &&
+                     disk_snapshot == VIR_DOMAIN_SNAPSHOT_LOCATION_NONE)) {
             const char *tmp;
 
-            tmp = virDomainSnapshotLocationTypeToString(disk_snapshot);
+            tmp = virDomainSnapshotLocationTypeToString(default_snapshot);
             virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
                            _("disk '%s' must use snapshot mode '%s'"),
                            disk->name, tmp);