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Re: [PULL 04/12] hmp: Simplify qom-set

From: David Hildenbrand
Subject: Re: [PULL 04/12] hmp: Simplify qom-set
Date: Wed, 3 Jun 2020 14:26:50 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0

On 03.06.20 14:24, Dr. David Alan Gilbert wrote:
> * David Hildenbrand (david@redhat.com) wrote:
>> On 03.06.20 13:43, Dr. David Alan Gilbert wrote:
>>> * David Hildenbrand (david@redhat.com) wrote:
>>>> On 03.06.20 12:43, Dr. David Alan Gilbert wrote:
>>>>> * David Hildenbrand (david@redhat.com) wrote:
>>>>>> On 02.06.20 11:26, Dr. David Alan Gilbert wrote:
>>>>>>> * Markus Armbruster (armbru@redhat.com) wrote:
>>>>>>>> "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> writes:
>>>>>>>>> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>>>>>>>>> Simplify qom_set by making it use qmp_qom_set and the JSON parser.
>>>>>>>>> (qemu) qom-get /machine smm
>>>>>>>>> "auto"
>>>>>>>>> (qemu) qom-set /machine smm "auto"
>>>>>>>>> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>>>>>>>>> Message-Id: <20200520151108.160598-3-dgilbert@redhat.com>
>>>>>>>>> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>>>>>>> Reviewed-by: Markus Armbruster <armbru@redhat.com>
>>>>>>>>> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>>>>>>>>>   With 's'->'S' type change suggested by Paolo and Markus
>>>>>>>> This is actually more than just simplification, it's disarming a bear
>>>>>>>> trap: the string visitor is restricted to a subset of the QAPI types,
>>>>>>>> and when you qom-set a property with a type it can't handle, QEMU
>>>>>>>> aborts.  I mentioned this in the discussion of possible ways out of the
>>>>>>>> qom-get impasse, but missed reraising it in patch review.
>>>>>>>> A suitably amended commit would be nice, but respinning the PR just for
>>>>>>>> that may not be worthwhile.
>>>>>>> A bit late; still as long as we're removing bear traps not adding them.
>>>>>> This breaks qom-set for my (virtio-mem) use case:
>>>>>> echo "qom-set vm0 requested-size 300M" | sudo nc -U /var/tmp/mon_src
>>>>>> QEMU 5.0.50 monitor - type 'help' for more information
>>>>>> (qemu) qom-set vm0 requested-size 300M
>>>>>> Error: Expecting at most one JSON value
>>>>> Does qom-set vm0 requested-size 300e6 do the same thing?
>>>> The property is defined to be of type "size".
>>>> (qemu) qom-set vm0 requested-size 300e6
>>>> Error: Parameter 'requested-size' expects uint64
>>>> (not sure how "size" and "uint64" are mapped here)
>>> I think the problem here is that the JSON parser is converting anything
>>> with an 'e' as a float; JSON itself doesn't have the distinction
>>> between int and float.
>> (and just to clarify - I assume you are aware - 300e6 != 300M. So the
>> interface becomes way harder to use in case one wants to specify
>> properly aligned sizes - 300M vs 314572800)
> Oops, yes, good point.
> I think on balance it's probably best that this keeps supporting JSON;
> although tbh I'm not convinced there are any complex types that can be
> set.
> I'm not seeing a prettier answer.

So, I have to use a calculator from now on to set a property that I can
set on the QEMU cmdline just fine without it? :(

This feels like a step backwards, @Markus any way to keep supporting sizes?


David / dhildenb

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