[Qemu-block] block migration and dirty bitmap reset

[Peter Lieven]

Hi,

while looking at the code I wonder if the blk_aio_preadv and the 
bdrv_reset_dirty_bitmap order must
be swapped in mig_save_device_bulk:

    qemu_mutex_lock_iothread();
    aio_context_acquire(blk_get_aio_context(bmds->blk));
    blk->aiocb = blk_aio_preadv(bb, cur_sector * BDRV_SECTOR_SIZE, &blk->qiov,
                                0, blk_mig_read_cb, blk);

    bdrv_reset_dirty_bitmap(bmds->dirty_bitmap, cur_sector * BDRV_SECTOR_SIZE,
                            nr_sectors * BDRV_SECTOR_SIZE);
    aio_context_release(blk_get_aio_context(bmds->blk));
    qemu_mutex_unlock_iothread();

In mig_save_device_dirty we first reset the dirty bitmap and read then which 
shoulds like
a better idea. Maybe it doesn't matter while we acquire the aioctx and the 
iothread lock...

Peter