[PATCH v3 00/15] Introduce virtio-mem <memory/> model

[David Hildenbrand]

On 17.06.21 14:42, Peter Krempa wrote:
> On Thu, Jun 17, 2021 at 14:34:21 +0200, David Hildenbrand wrote:
>> On 17.06.21 14:17, Peter Krempa wrote:
>>> On Thu, Jun 17, 2021 at 14:03:44 +0200, David Hildenbrand wrote:
> 
> [...]
> 
>>
>> 4. QEMU does no longer require a "slots" specification when maxmem is set
>> (because virtio-based memory devices don't require ACPI memory module
>> slots).
>>
>> Specifying "<maxMemory unit='KiB'>20971520</maxMemory>" results in (IMHO
>> confusing) error:
>>
>>    "error: XML document failed to validate against schema: Unable to
>>     validate doc against /usr/local/share/libvirt/schemas/domain.rng
>>     Extra element maxMemory in interleave
>>     Invalid sequence in interleave
>>     Element domain failed to validate content"
>>
>>
>> "Extra element maxMemory in interleave
>> Invalid sequence in interleave
>> Element domain failed to validate content"
> 
> This is because the XML schema for maxMemory requires the element.
> Unfortunately the XML schema validator from libxml2 has extremely
> user-unfriendly errors.
> 
>> Specifying "<maxMemory slots='0' unit='KiB'>20971520</maxMemory>" results in
>>    "error: XML error: both maximum memory size and memory slot count must
>>     be specified"
> 
> This is the error from the XML parser which has human-crafter errors.
> 
>> However, older QEMU version have that requirement. Supported since 3.0 I
>> think:
>>
>> $ git tag --contains 951f2269af2
>> ...
>> v3.0.0
>> ...
> 
> Is there a way how to detect that it's not needed? E.g. via the QMP
> schema or such?
> 
> In this instance we could perhaps drop it and let qemu report the error
> ... well if it's reasonable though.
> 

I guess only implicitly, for example, if virtio-mem-pci or 
virtio-pmem-pci are possible (I assume supported devices can be queried 
via QMP). And without these devices, it doesn't make sense to have 
"slots=0".

virtio-pmem-pci was introduced with v4.1.0, virtio-mem-pci was 
introduced with v5.1.0.

-- 
Thanks,

David / dhildenb