Re: [Qemu-devel] [PATCH 2/2 v2] Add the blockdev-reopen and blockdev-migrate commands

[Paolo Bonzini]

On 02/24/2012 06:46 PM, Eric Blake wrote:
> I think you need to be more explicit that @new-image-file MUST have
> identical contents as the current image file, for this to be useful, and
> that qemu does not validate whether the new image met those conditions.
>  Possible ways to achieve this:

Not necessarily, you could always do this on a paused machine.

>> > +# @destination: the destination of the block migration.
> Where do you list what format the destination is?  Shouldn't this have
> an optional format, defaulting to qcow2?  Does qemu create the
> destination file, or must it already be existing?

I think no default, raw makes as much or more sense in the
non-incremental case.  Anyway either autodetect, or no default.

>> > +#
>> > +# @new-image-file: #optional an existing image file that will replace
>> > +#                  the current one in the device.
> Where do you list what format the new-image-file is?  Shouldn't this
> have an optional format, defaulting to qcow2?  Does qemu create the
> new-image-file, or can one already be existing?

qemu does not create the file now, but in the future we may add a flag
to create a snapshot.  I think no default is better here too, or autodetect.

> I know that this patch is only implementing the case where incremental
> is true and new-image-file is provided; but I'm not quite sure what
> semantics are intended if incremental is false.  Is that still a case
> where this sets up mirroring (writes go to two images) but additionally
> the contents from the current image are (asynchronously) streamed into
> the destination?

Yes.  The image should already be there also in this case, and
new-image-file will usually be omitted.

Paolo