Re: [Qemu-devel] [PATCH 3/3] Add nocreate option to snapshot_blkdev

[Paolo Bonzini <pbonzini@redhat.com>]

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.

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.

Paolo