qemu: backup: Merge bitmaps accross the backing chain

To allow backups work across external snapshots we need to improve the
algorithm which calculates which bitmaps to merge.

The algorithm must look for appropriately named bitmaps in the image and
possibly descend into a backing image if the current image does not have
the bitmap.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

src/qemu/qemu_backup.c

@@ -173,24 +173,70 @@ qemuBackupDiskDataCleanup(virDomainObjPtr vm,
 virJSONValuePtr
 qemuBackupDiskPrepareOneBitmapsChain(virDomainMomentDefPtr *incremental,
                                      virStorageSourcePtr backingChain,
-                                     virHashTablePtr blockNamedNodeData G_GNUC_UNUSED,
-                                     const char *diskdst G_GNUC_UNUSED)
+                                     virHashTablePtr blockNamedNodeData,
+                                     const char *diskdst)
 {
+    qemuBlockNamedNodeDataBitmapPtr bitmap;
     g_autoptr(virJSONValue) ret = NULL;
+    size_t incridx = 0;
 
     if (!(ret = virJSONValueNewArray()))
         return NULL;
 
-    /* TODO: this code works only if the bitmaps are present on a single node.
-     * The algorithm needs to be changed so that it looks into the backing chain
-     * so that we can combine all relevant bitmaps for a given backing chain */
-    while (*incremental) {
+    if (!(bitmap = qemuBlockNamedNodeDataGetBitmapByName(blockNamedNodeData,
+                                                         backingChain,
+                                                         incremental[0]->name))) {
+        virReportError(VIR_ERR_INVALID_ARG,
+                       _("failed to find bitmap '%s' in image '%s%u'"),
+                       incremental[0]->name, diskdst, backingChain->id);
+        return NULL;
+    }
+
+    while (bitmap) {
+        if (bitmap->inconsistent) {
+            virReportError(VIR_ERR_INVALID_ARG,
+                           _("bitmap '%s' for image '%s%u' is inconsistent"),
+                           bitmap->name, diskdst, backingChain->id);
+            return NULL;
+        }
+
         if (qemuMonitorTransactionBitmapMergeSourceAddBitmap(ret,
                                                              backingChain->nodeformat,
-                                                             (*incremental)->name) < 0)
+                                                             bitmap->name) < 0)
             return NULL;
 
-        incremental++;
+        if (backingChain->backingStore &&
+            (bitmap = qemuBlockNamedNodeDataGetBitmapByName(blockNamedNodeData,
+                                                            backingChain->backingStore,
+                                                            incremental[incridx]->name))) {
+            backingChain = backingChain->backingStore;
+            continue;
+        }
+
+        if (incremental[incridx + 1]) {
+            if ((bitmap = qemuBlockNamedNodeDataGetBitmapByName(blockNamedNodeData,
+                                                                backingChain,
+                                                                incremental[incridx + 1]->name))) {
+                incridx++;
+                continue;
+            }
+
+            if (backingChain->backingStore &&
+                (bitmap = qemuBlockNamedNodeDataGetBitmapByName(blockNamedNodeData,
+                                                                backingChain->backingStore,
+                                                                incremental[incridx + 1]->name))) {
+                incridx++;
+                backingChain = backingChain->backingStore;
+                continue;
+            }
+
+            virReportError(VIR_ERR_INVALID_ARG,
+                           _("failed to find bitmap '%s' in image '%s%u'"),
+                           incremental[incridx]->name, diskdst, backingChain->id);
+            return NULL;
+        } else {
+            break;
+        }
     }
 
     return g_steal_pointer(&ret);