Re: [Qemu-devel] [Qemu-block] Minutes from the "Stuttgart block Gipfele"

[Stefan Hajnoczi]

On Mon, Jan 04, 2016 at 03:28:36PM +0800, Fam Zheng wrote:
> On Mon, 01/04 13:16, Stefan Hajnoczi wrote:
> > On Wed, Dec 23, 2015 at 06:15:20PM +0800, Fam Zheng wrote:
> > > On Fri, 12/18 14:15, Markus Armbruster wrote:
> > > In that theory, all other block job types, mirror/stream/commit, fit into 
> > > a
> > > "pull" model, which follows a specified dirty bitmap and copies data from 
> > > a
> > > specified src BDS. In this pull model,
> > > 
> > > mirror (device=d0 target=d1) becomes a pull fileter:
> > > 
> > >         BB[d0]            BB[d1]
> > >            |                 |
> > >         throttle        [pull,src=d0]
> > >            |                 |
> > >        detect-zero       detect-zero
> > >            |                 |
> > >       copy-on-read      copy-on-read
> > >            |                 |
> > >           BDS               BDS
> > > 
> > > Note: the pull reuses most of the block/mirror.c code except the
> > > s->dirty_bitmap will be initialized depending on the block job type. In 
> > > the
> > > case of mirror, it is trivially the same as now.
> > 
> > I don't understand the pull filter.  Is there also a mirror block job
> > coroutine?
> > 
> > Does anything perform I/O to BB[d1]?
> 
> Yes, the filter will have a mirror block job coroutine, and it writes to the
> BDS behind BB[d1]. This is conceptually different from the "block jobs have
> their own BBs" design.

Are any of the pull filter's callbacks (.bdrv_co_readv(),
.bdrv_co_writev()) being invoked?

I still don't understand your idea because it seems like the coroutine
is doing all the work and the filter serves no purpose.

Stefan

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