Re: [Qemu-devel] [PATCH 1/5] RFC: Efficient VM backup for qemu (v1)

[Dietmar Maurer]

> > >> Filters would be implemented as BlockDrivers, i.e. you could
> > >> implement
> > >> .bdrv_co_write() in a filter to intercept all writes to an image.
> > >
> > > I am quite unsure if that make things easier.
> >
> > At least it would make for a much cleaner design compared to putting
> > code for every feature you can think of into bdrv_co_do_readv/writev().
> 
> So if you want to add a filter, you simply modify bs->drv to point to the 
> filter?

Seems the BlockDriver struct does not contain any 'state' (I guess that is by 
design),
so where do you store filter related dynamic data?