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From: Markus Armbruster <armbru@redhat.com>
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Date: Fri, 19 Dec 2014 15:24:52 +0100
In-Reply-To: <87mw6l9e04.fsf@blackfin.pond.sub.org> (Markus Armbruster's
	message of "Thu, 18 Dec 2014 16:25:15 +0100")
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Subject: Re: [Qemu-devel] Review of ways to create BDSes
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To: qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>

Markus Armbruster <armbru@redhat.com> writes:

> = Introduction =
>
> BDSes can be opened in various ways.  Some of them don't provide for
> user configuration.  Some of them should.
>
> Example: -drive format=qcow2,file=foo.qcow2 where foo.qcow2 has a raw
> backing file foo.raw.  This creates the the following tree of BDSes:
>
>             (qcow2,foo.qcow2)
>               /            \
>     (file,foo.qcow2)    (raw,foo.raw)
>                             |
>                        (file,foo.raw)
>
> Before Kevin added driver-specific options, -drive let you configure
> basically just the root.  Configuration for the others was inferred from
> the root's configuration and the images.  Driver-specific options let
> you configure all the nodes.  Defaults are still inferred as before.
>
> Example: blockdev-snapshot-sync provides only a small subset of the full
> configuration options for the BDS it creates.  Could be fixed by
> duplicating the full options, i.e. blockdev-add's.  But a command that
> just snapshots and leaves BDS creation to blockdev-add would be cleaner.
>
> This is a systematic review of all the ways you can open BDSes in qemu
> proper, i.e. not in qemu-{img,io,nbd}.  I tracked them down by following
> the call chains leading to bdrv_open().

Forgot to mention: I ignored HMP commands, too.

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