The backup job must only copy areas that the copy_bitmap reports as dirty. This is always the case when using traditional non-offloading backup, because it copies each cluster separately. When offloading the copy operation, we sometimes copy more than one cluster at a time, but we only check whether the first one is dirty.
Therefore, whenever copy offloading is possible, the backup job currently produces wrong output when the guest writes to an area of which an inner part has already been backed up, because that inner part will be re-copied. Fixes: 9ded4a0114968e98b41494fc035ba14f84cdf700 Signed-off-by: Max Reitz <mre...@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> --- block/backup.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/block/backup.c b/block/backup.c index 715e1d3be8..1ee271f9f1 100644 --- a/block/backup.c +++ b/block/backup.c @@ -202,22 +202,31 @@ static int coroutine_fn backup_do_cow(BackupBlockJob *job, cow_request_begin(&cow_request, job, start, end); while (start < end) { + int64_t dirty_end; + if (!hbitmap_get(job->copy_bitmap, start)) { trace_backup_do_cow_skip(job, start); start += job->cluster_size; continue; /* already copied */ } + dirty_end = hbitmap_next_zero(job->copy_bitmap, start, (end - start)); + if (dirty_end < 0) { + dirty_end = end; + } + trace_backup_do_cow_process(job, start); if (job->use_copy_range) { - ret = backup_cow_with_offload(job, start, end, is_write_notifier); + ret = backup_cow_with_offload(job, start, dirty_end, + is_write_notifier); if (ret < 0) { job->use_copy_range = false; } } if (!job->use_copy_range) { - ret = backup_cow_with_bounce_buffer(job, start, end, is_write_notifier, + ret = backup_cow_with_bounce_buffer(job, start, dirty_end, + is_write_notifier, error_is_read, &bounce_buffer); } if (ret < 0) { -- 2.21.0