qemu: domain: Add helper to generate indexed backing store names

The code is currently simple, but if we later add node names, it will be
necessary to generate the names based on the node name. Add a helper so
that there's a central point to fix once we add self-generated node
names.

src/qemu/qemu_domain.c

@@ -8558,3 +8558,25 @@ qemuDomainDiskLookupByNodename(virDomainDefPtr def,
 
     return NULL;
 }
+
+
+/**
+ * qemuDomainDiskBackingStoreGetName:
+ *
+ * Creates a name using the indexed syntax (vda[1])for the given backing store
+ * entry for a disk.
+ */
+char *
+qemuDomainDiskBackingStoreGetName(virDomainDiskDefPtr disk,
+                                  virStorageSourcePtr src ATTRIBUTE_UNUSED,
+                                  unsigned int idx)
+{
+    char *ret = NULL;
+
+    if (idx)
+        ignore_value(virAsprintf(&ret, "%s[%d]", disk->dst, idx));
+    else
+        ignore_value(VIR_STRDUP(ret, disk->dst));
+
+    return ret;
+}

src/qemu/qemu_domain.h

@@ -883,4 +883,8 @@ virDomainDiskDefPtr qemuDomainDiskLookupByNodename(virDomainDefPtr def,
                                                    virStorageSourcePtr *src,
                                                    unsigned int *idx);
 
+char *qemuDomainDiskBackingStoreGetName(virDomainDiskDefPtr disk,
+                                        virStorageSourcePtr src,
+                                        unsigned int idx);
+
 #endif /* __QEMU_DOMAIN_H__ */