On 2018-03-10 23:34, Eric Blake wrote:
> On 02/24/2018 09:40 AM, Max Reitz wrote:
>> Currently, we try to rewrite every occurrence of "backing": null into
>> "backing": "" in qmp_blockdev_add().  However, that breaks using the
>> same "backing": null construction in json:{} file names (which do not go
>> through qmp_blockdev_add()).  Currently, these then just behave as if
>> the option has not been specified.
>>
>> Since there is actually only one place where we evaluate the @backing
>> option to find out whether not to use a backing file, we can instead
>> just check for null there.  It doesn't matter that this changes the
>> runtime state of the option from "" to null, because nobody really does
>> anything with that runtime state anyway (except put it into qemu again,
>> but qemu doesn't care whether it's "" or null).
>>
>> And in the future, it's much better if we get it to be null in that
>> runtime state sooner than later -- see patch 7.
>>
>>
>> Note that it was Markus (who's away having a good time, I hope) who
>> proposed qobject_to(), so I guess he won't object too much to seeing the
>> concept having landed in his tree once he returns.
>> (Although he hasn't reviewed the previous iteration of this series,
>>   which included it already.)
>>
> 
> Thanks, applied to my QAPI staging tree (with qobject_to(type, obj)
> reordering - it didn't take me too long after all):
> git://repo.or.cz/qemu/ericb.git qapi
> http://repo.or.cz/qemu/ericb.git/shortlog/refs/heads/qapi

Thanks!

Max

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