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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 05:19:08 -0500 (EST) |
----- Original Message -----
> From: "Paolo Bonzini" <address@hidden>
> To: "Federico Simoncelli" <address@hidden>
> Cc: address@hidden, address@hidden, address@hidden
> Sent: Thursday, February 23, 2012 10:48:59 AM
> Subject: Re: [PATCH 3/3] Add nocreate option to snapshot_blkdev
>
> On 02/23/2012 10:39 AM, Federico Simoncelli wrote:
> > 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.
>
> True, on the other hand if we add this we will have to keep it
> forever.
>
> I'm worried that blkmirror does not satisfy _all_ mirroring needs,
> for
> example you cannot use block_stream to copy from the source to the
> destination, so perhaps in the future we want to change it to
> something
> else.
Are you talking about a mirroring where you block_stream the missing
clusters in the destination from the source?
I believe that it could be done without losing the blkmirror
modularity probably extending the BlockDriver structure with some
additional concepts.
> So while I appreciate the easier debugging, I'm afraid that we'll
> regret
> adding a command-line-visible feature.
>
> > 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).
>
> No, the format of the source and destination should be independent.
> It
> would be nice to have something like this:
>
> blkmirror:src=...,dst=...,srcformat=...,dstformat=...
>
> but commas are a pain because they need escaping.
I like that, one limitation we need to keep in mind is that it should
fit into the hard-coded filename limit of 1024 characters that (sadly) we
have in multiple places. Another thing is that at this stage the mirroring
is more an original/copy concept rather than source/destination.
What about:
blkmirror:...,copy=...,fmt=... (both images uses the same fmt)
blkmirror:...,copy=...,fmt=...,copyfmt=...
Or, eventually if you feel like that source/destination is more appropriate
for the future, then:
blkmirror:...,dst=...,fmt=...,dstfmt=...
--
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
Re: [Qemu-devel] [PATCH 1/3] Add blkmirror block driver, Stefan Hajnoczi, 2012/02/27
Re: [Qemu-devel] [PATCH 1/3] Add blkmirror block driver, Paolo Bonzini, 2012/02/27