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



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:
> > This patch refactors the JSON parsing function that extracts the block
> > IO tuning parameters from qemu's output. The most impacting change
> > concerns the error message that is returned if the reply from qemu does
> > not contain the needed data. The data for IO parameter tuning were added
> > in qemu 1.1 and the previous error message was confusing.
> > 
> > This patch also breaks long lines and extracts a multiple time used code
> > pattern to a macro.
> > ---
> > Old error message looks like:
> > # virsh blkdeviotune asdf hda
> > error: Unable to get block I/O throttle parameters
> > error: internal error cannot read total_bytes_sec
> > 
> > and the new:
> > # 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

Daniel
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