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Re: [Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev
From: |
Federico Simoncelli |
Subject: |
Re: [Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev |
Date: |
Thu, 23 Feb 2012 04:39:04 -0500 (EST) |
----- Original Message -----
> From: "Paolo Bonzini" <address@hidden>
> Cc: "Federico Simoncelli" <address@hidden>, address@hidden, address@hidden,
> address@hidden
> Sent: Thursday, February 23, 2012 8:38:55 AM
> Subject: Re: [PATCH 3/3] Add nocreate option to snapshot_blkdev
>
> On 02/23/2012 08:19 AM, Paolo Bonzini wrote:
> >> > Signed-off-by: Federico Simoncelli <address@hidden>
> > What is the usecase, and how can this be tested?
>
> Oops, you explained it in part 0.
>
> > Step 5 - Final Switch to Destination
> > ====================================
> > VM1 is now able to switch to the destination for both read and
> > write
> > operations.
> >
> > [src/hd0base] <- [src/hd0snap1] <= VM1(read-write)
> >
> > (qemu) snapshot_blkdev -n ide0-hd0 /tmp/dst/hd0snap1.qcow2
>
> It seems to me that reusing the snapshot_blkdev command is a bit of a
> misnomer. It also forces you to use format autodetection for the
> destination in the blkmirror phase.
>
> I see two possibilities:
>
> 1) you can make a new command block_reopen; this fixes only the
> naming
> problem.
>
> 2) you can hide the new format behind a new command to be used like
> this:
>
> block_migrate --mirror ide-hd0 /tmp/dst/hd0snap1.qcow2
> ...
> block_migrate --switch ide-hd0
>
> This leave the possibility to specify the format in the future:
>
> block_migrate --mirror ide-hd0 /tmp/dst/hd0snap1.qcow2 qcow2
>
> And we could have another sub-command
>
> block_mirror --stream ide-hd0 /tmp/dst/hd0.raw
>
> to migrate block devices without shared storage and without an
> intermediate snapshot.
I agree on the fact that using snapshot_blkdev is a misnomer but at
the same time I like very much how blkmirror is modular and it can
be used as a regular image filename.
I'm worried that making it explicit with a "--mirror" option would
take away its flexibility.
What about adding block_reopen and extending the blkmirror string:
(qemu) block_reopen ide-hd0 \
blkmirror:qcow2:/tmp/src/hd0snap1.qcow2:/tmp/dst/hd0snap1.qcow2
so that the format is passed as first argument (and if it's empty we
would use the auto-detection).
--
Federico
[Qemu-devel] [PATCH 1/3] Add blkmirror block driver, Federico Simoncelli, 2012/02/22
Re: [Qemu-devel] [PATCH 1/3] Add blkmirror block driver, Federico Simoncelli, 2012/02/23