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

From: Stefan Hajnoczi
Subject: Re: [Qemu-block] [Qemu-devel] Minutes from the "Stuttgart block Gipfele"
Date: Mon, 4 Jan 2016 13:16:34 +0800
User-agent: Mutt/1.5.24 (2015-08-30)

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

Does anything perform I/O to BB[d1]?

If nothing is writing to/reading from BB[d1], then I don't understand
the purpose of the pull filter.


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