Re: [Qemu-devel] [PATCH V2 3/4] blockdev: Allow snapshoting of protocols.

[Kevin Wolf]

Am 29.01.2013 17:24, schrieb Eric Blake:
> On 01/29/2013 07:27 AM, Benoît Canet wrote:
>>> base1 [file] --- base1 [qcow2] --- snap1.qcow2 --\
>>> base2 [file] --- base2 [qcow2] --- snap2.qcow2 --->-- quorum
>>> base3 [file] --- base3 [qcow2] --- snap3.qcow2 --/
> 
> For that matter, I think it would be useful to have a quorum where the
> data is duplicated between different formats, such as:
> 
> file1 [raw]                         --\
> base2 [raw] --- snap2.qcow2 [qcow2] -->-- quorum
> base3 [qed] --- snap3.qed [qed]     --/
> 
> In that case, you NEED to be able to pass in the protocol of each
> underlying device _as part of opening the quorum_, something like:
> 
> quorum:2/3:file1[raw]:snap2.qcow2[qcow2]:snap3.qed[qed]
> 
> or some such punctuation.  And of course, that means you'd have to
> extend your escaping mechanism to allow escaping of whatever syntax you
> use for declaring a per-member format.

Let me rephrase that: quorum really needs -blockdev. And quite possibly
the data that can be passed to the snapshot QMP commands today isn't
sufficient to describe what we want to describe. :-/

Kevin