Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver

[Dietmar Maurer]

> Hmm, right.  But do we need the bitmap at all?  We can just use
> bdrv_is_allocated like bdrv_co_do_readv does.

If a write occur, we read and backup that cluster immediately (out of order). So
I am quite sure we need the bitmap.