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



On 08/09/12 13:00, Daniel P. Berrange wrote:
On Thu, Aug 09, 2012 at 12:52:16PM +0200, Jiri Denemark wrote:
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.

We do have a VIR_ERR_NO_SUPPORT, but its probably wise to restrict that
to only the case where the public API is not provided by the current
driver. So agree that a new OPERATION_UNSUPPORTED would be reasonable

Daniel


I've pushed this patch and I'll follow up with a separate one adding VIR_ERR_OPERATION_UNSUPPORTED and changing the error message type in that particular case.

Peter


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