Re: RFC: Qemu backup interface plans

18.05.2021 19:39, Max Reitz wrote:

> On 17.05.21 14:07, Vladimir Sementsov-Ogievskiy wrote:

>> Not also, that there is another benefit of such thing: we'll >> implement this callback in qcow2 driver, so that backup will read >> clusters not in guest cluster order, but in host cluster order, to >> read more sequentially, which should bring better performance on >> rotating disks. > > I’m not exactly sure how you envision this to work, but block_status > also already gives you the host offset in *map. > But block-status doesn't give a possibility to read sequentially. For this, user should call block-status several times until the whole disk covered, then sort the segments by host offset. I wonder, could it be implemented as some iterator, like read_iter = bdrv_get_sequential_read_iter(source) while (extents = bdrv_read_next(read_iter)):   for ext in extents:     start_writing_task(target, ext.offset, ext.bytes, ext.qiov) where bdrv_read_next will read guest data in host-cluster-sequence..