Commit 4a5b91ca authored by Max Reitz's avatar Max Reitz
Browse files

backup: Copy only dirty areas 



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: 9ded4a01
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
Reviewed-by: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20190801173900.23851-2-mreitz@redhat.com
Cc: qemu-stable@nongnu.org
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
parent 9bb68d34

block/backup.c

+11 −2
Original line number Diff line number Diff line
@@ -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) {