Re: [Qemu-devel] [PATCH 3/4] qcow2: add a migration blocker

[Kevin Wolf <kwolf@redhat.com>]

Am 14.11.2011 17:25, schrieb Anthony Liguori:
> On 11/14/2011 09:51 AM, Stefan Hajnoczi wrote:
>> On Fri, Nov 11, 2011 at 8:29 PM, Anthony Liguori<aliguori@us.ibm.com>  wrote:
>>> +#define QERR_BLOCK_FORMAT_FEATURE_NOT_SUPPORTED \
>>> +    "{ 'class': 'BlockFormatFeatureNotSupported', 'data': { 'format': %s, 'name': %s, 'feature': %s } }"
>>> +
>>
>> Isn't having a separate error going to make life harder for management
>> tool writers?  I would have expected one "migration not supported"
>> error, regardless of whether the reason is ivshmem, qcow2, or anything
>> else.
> 
> Errors shouldn't be tied to verbs.  IOW, if you have a migrate command, you 
> don't want to have a MigrationFailed error because that's tied to a specific verb.
> 
> Instead, you want the errors to provide additional information about the verb 
> failed.  In this case, the verb is failing because you're requesting to use a 
> feature that is not supported by this particular block format.

We already have QERR_UNKNOWN_BLOCK_FORMAT_FEATURE which is very similar
(in fact, FEATURE_NOT_SUPPORTED is a much better name which we should
have used from the beginning).

"unknown feature" doesn't really fit here and it's too late to change
the name of the existing error. We'll probably have to live with two
different error messages.

Kevin