On Fri, Mar 20, 2015 at 03:16:53PM -0400, John Snow wrote:
> + } 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);
> +
> + /* Find the next dirty /sector/ and copy that /cluster/ */
> + while ((sector = hbitmap_iter_next(&hbi)) != -1) {
> + cluster = sector / BACKUP_SECTORS_PER_CLUSTER;
> +
> + /* Fake progress updates for any clusters we skipped,
> + * excluding this current cluster. */
> + if (cluster != last_cluster + 1) {
> + job->common.offset += ((cluster - last_cluster - 1) *
> + BACKUP_CLUSTER_SIZE);
> + }
> +
> + if (yield_and_check(job)) {
> + goto leave;
> + }
> +
> + 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;
> + }
What happens when the dirty bitmap granularity is larger than
BACKUP_SECTORS_PER_CLUSTER?
|-----bitmap granularity-----|
|---backup cluster---|
~~~~~~~
Will these sectors ever be copied?
I think this case causes an infinite loop:
cluster = hbitmap_iter_next(&hbi) / BACKUP_SECTORS_PER_CLUSTER
The iterator is reset:
bdrv_set_dirty_iter(&hbi, (cluster + 1) * BACKUP_SECTORS_PER_CLUSTER);
So we get the same cluster ever time and never advance?
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