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

[Alex Bligh]

On 22 Aug 2013, at 12:45, Stefan Hajnoczi wrote:

> Looks good but please include a new qemu-iotest test case that checks:
> 
> 1. Error if the target volume does not exist.

Can do

> 2. Success if a correctly sized target volume exists.
> 
> 3. ?? if an incorrectly sized target volume exists.

Good catch re size.

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.

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).

Before we get to testing, I'm guessing we should establish
whether (a) is correct (I think yes), and what the correct
behaviour is for (b).

-- 
Alex Bligh