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Re: [libvirt] [PATCH] virterror: Add error message for unsupported operations.



On 08/09/12 15:38, Eric Blake wrote:
On 08/09/2012 07:31 AM, Peter Krempa wrote:
This patch introduces a new error code VIR_ERR_OPERATION_UNSUPPORTED to
mark error messages regarding operations that failed due to lack of
support on the hypervisor or other than libvirt issues.

The code is first used in reporting error if qemu does not support block
IO tuning variables yielding error message:
error: Unable to get block I/O throttle parameters
error: Operation not supported: block_io_throttle field
'total_bytes_sec' missing in qemu's output

instead of:
error: Unable to get block I/O throttle parameters
error: internal error cannot read total_bytes_sec
---

In the past, we have used VIR_ERR_CONFIG_UNSUPPORTED for messages about
a qemu binary that doesn't support something; would that be any better
than inventing a new error here?  Or are all of those errors worth
switching over to this new code?

Using VIR_ERR_CONFIG_UNSUPPORTED seems reasonable to me in cases where the unsupported feature is requested by the user. Eg. when setting something or requesting some weird configuration or even if the hypervisor doesn't support it.

On the other hand It doesn't make sense to me to use it on getter-type APIs where the user isn't setting anything just wants some information back. In this case I'd rather like to see a new message, as stating that config isn't supported is a little bit strange.


As written, your patch seems fine, but only if we agree that a new error
is the way to go.

Thanks for reviewing.



Peter


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