[libvirt] [PATCH] qemu: Refactor parsing of block device IO tuning parameters.

[Jiri Denemark]

On Thu, Aug 09, 2012 at 10:48:43 +0100, Daniel P. Berrange wrote:
> On Thu, Aug 09, 2012 at 11:39:57AM +0200, Jiri Denemark wrote:
> > On Thu, Aug 09, 2012 at 10:48:42 +0200, Peter Krempa wrote:
> > > # virsh blkdeviotune asdf hda
> > > error: Unable to get block I/O throttle parameters
> > > error: internal error block_io_throttle field 'total_bytes_sec' missing in qemu's output
> > 
> > I think the old/new error messages can be included directly in the commit
> > message. Anyway, I wonder if we should take this as an opportunity to fix the
> > "internal error", however I'm not sure what is the best code to use. It seems
> > we use OPERATION_INVALID in such cases, which could be good enough.
> 
> No, OPERATION_INVALID is for scenarios where the API request cannot
> be performed because the object is in the wrong state.
> 
> eg when you request to pause a VM that is shutoff.
> 
> 
> This is a case where the data we receive back from QEMU is incorrect.
> I don't think we have a current error code that is suitable for this
> kind of scenario, so we ought to invent a new one.
> 
> Some ideas
> 
>    MISSING_DATA
>    DATA_INVALID
>    UNEXPECTED_DATA
>    ...insert others...
> 
> my favour is probably DATA_INVALID

The data is actually correct, just the fields required for this functionality
are missing because QEMU is too old to support them. Perhaps
OPERATION_UNSUPPORTED (which doesn't currently exist either) could be the
right choice.

Jirka