[Libguestfs] Can I specify qcow2 preallocation method with virt-builder?

[Richard W.M. Jones]

On Tue, May 17, 2016 at 03:41:53PM +0100, Richard W.M. Jones wrote:
> On Tue, May 17, 2016 at 05:15:57PM +0300, Yaniv Kaul wrote:
> > When creating qcow2 images using virt-builder, is there a way to specify
> > the qcow2 preallocation, as possible with qemu-img create -o
> > preallocation=metada , for example?
> 
> No .. but .. it does default to preallocation=metadata provided that
> the output format is qcow2:
> 
> https://github.com/libguestfs/libguestfs/blob/master/builder/builder.ml#L582-L585

I should say this only applies when the image needs to be resized
(ie. you supply a --size parameter which != the size of the template),
AND if the resize is the final step that the planner comes up with.

https://rwmj.wordpress.com/2013/12/14/writing-a-planner-to-solve-a-tricky-programming-optimization-problem/

In the general case implementing this is more complicated.  I think it
would require another planner transition.

Rich.

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