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Re: [libvirt] [PATCH] Drop UML driver



On 12/14/18 3:53 PM, Daniel P. Berrangé wrote:
> On Fri, Dec 14, 2018 at 03:46:16PM +0100, Michal Privoznik wrote:
>> On 12/14/18 3:35 PM, Daniel P. Berrangé wrote:
>>> On Fri, Dec 14, 2018 at 03:30:17PM +0100, Michal Privoznik wrote:
>>>> The driver is unmaintained, untested and severely broken for
>>>> quite some time now. Since nobody even reported any issue with it
>>>> let us drop it.
>>>>
>>>> Signed-off-by: Michal Privoznik <mprivozn redhat com>
>>>> ---
>>>
>>>>  docs/schemas/capability.rng          |    2 -
>>>>  docs/schemas/domaincommon.rng        |    3 -
>>>
>>>
>>>>  src/conf/domain_conf.c               |   11 +-
>>>>  src/conf/domain_conf.h               |    4 -
>>>
>>> We shouldn't be deleting stuff from the XML schemas. IMHO the schemas
>>> are an append only source object. If some parts happen to not be used
>>> by current code that's fine, but they are a record of the ABI promise
>>> of the schema.
>>
>> So we should be able to validate <domain type="uml"/> even though there
>> is no longer any driver that would define such domain? I don't see much
>> point in that.
> 
> The point is that the schema definition is independent of the driver
> implementations. Implementations in libvirt come & go, but the schema
> that they adhere to must remain constant.
> 
>> Also, removing a driver is breaking the ABI promise.
> 
> To some extent, but I don't consider that equivalent to the promise of
> stability of our library ELF API or XML schema. Implementations of
> a feature may have a finite lifetime. The way a feature is described
> remains the same forever, which is what the XML schema declares. As
> such its inappropriate to remove something from the schema, just
> because the feature doesn't exist.
> 
> This can affect downstream applications, even if they are not actively
> using the UML driver. For example libraries that provide an API around
> our XML schema may be validating their implementation against our RNG
> schemas & thus removing it can break those impls.

Okay, Fair enough. But what about the domain_conf.c? I think it's safe
to remove "uml" from there, isn't it? I mean, does it matter whether we
fail parsing the domain because of unknown domain type or unsupported
domain type?

Michal


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