Re: [Qemu-devel] [PATCHv4] add qemu-img convert -C option (skip target volume creation)

[Stefan Hajnoczi]

On Thu, Aug 22, 2013 at 08:27:12PM +0100, Alex Bligh wrote:
> 
> On 22 Aug 2013, at 12:45, Stefan Hajnoczi wrote:
> The behaviour of the current code appears to be as follows
> (Alexandre's code not mine):
> 
> a) if the target volume size > the converted volume size, convert
>    leaving the remaining data on the target volume as is. This
>    is I believe useful, as on (e.g.) rbd, the target volume size
>    may be larger than required due to rounding requirements.

Seems ok.

> b) if the target volume size < the converted volume size, convert
>    truncates it but does not error. I'm torn between whether this
>    continue to do exactly as it asked, attempt to expand the
>    volume, or error. These all seem reasonably easy (the expand
>    option presumably being a call to bdrv_truncate).

Silently truncating can be a problem, e.g. the user deletes the original
file after conversion completes and later discovers not all data was
copied.

I think we should fail here.

Stefan