Re: [Qemu-devel] [PATCH v12 07/17] qmp: Add support of "dirty-bitmap" sync mode for drive-backup

[Vladimir Sementsov-Ogievskiy]

On 10.02.2015 04:35, John Snow wrote:

......

@@ -278,28 +305,61 @@ static void coroutine_fn backup_run(void *opaque)

              qemu_coroutine_yield();
              job->common.busy = true;
          }
+    } else if (job->sync_mode == MIRROR_SYNC_MODE_DIRTY_BITMAP) {
+        /* Dirty Bitmap sync has a slightly different iteration method */
+        HBitmapIter hbi;
+        int64_t sector;
+        int64_t cluster;
+        int64_t last_cluster = -1;
+        bool polyrhythmic;
+
+        bdrv_dirty_iter_init(bs, job->sync_bitmap, &hbi);
+        /* Does the granularity happen to match our backup cluster size? */
+        polyrhythmic = (bdrv_dirty_bitmap_granularity(job->sync_bitmap) !=
+                        BACKUP_CLUSTER_SIZE);

let it be false, i.e. granularity == cluster

+
+        /* Find the next dirty /sector/ and copy that /cluster/ */
+        while ((sector = hbitmap_iter_next(&hbi)) != -1) {

then, don't we skip here the very first cluster, if it is dirty?

+            if (yield_and_check(job)) {
+                goto leave;
+            }
+            cluster = sector / BACKUP_SECTORS_PER_CLUSTER;
+
+            /* Play some catchup with the progress meter */
+            if (cluster != last_cluster + 1) {
+                job->common.offset += ((cluster - last_cluster - 1) *
+                                       BACKUP_CLUSTER_SIZE);
+            }
+
+            do {
+                ret = backup_do_cow(bs, cluster * BACKUP_SECTORS_PER_CLUSTER,
+                                    BACKUP_SECTORS_PER_CLUSTER, 
&error_is_read);
+                if ((ret < 0) &&
+                    backup_error_action(job, error_is_read, -ret) ==
+                    BLOCK_ERROR_ACTION_REPORT) {
+                    goto leave;
+                }
+            } while (ret < 0);
+
+            /* Advance (or rewind) our iterator if we need to. */
+            if (polyrhythmic) {
+                bdrv_set_dirty_iter(&hbi,
+                                    (cluster + 1) * 
BACKUP_SECTORS_PER_CLUSTER);
+            }
+
+            last_cluster = cluster;
+        }
+
+        /* Play some final catchup with the progress meter */
+        if (last_cluster + 1 < end) {
+            job->common.offset += ((end - last_cluster - 1) *
+                                   BACKUP_CLUSTER_SIZE);
+        }
+
      } else {

--
Best regards,
Vladimir