"Daniel P. Berrange" <berra...@redhat.com> writes:
> On Thu, Oct 13, 2016 at 10:31:37AM +0200, Markus Armbruster wrote:
>> "Daniel P. Berrange" <berra...@redhat.com> writes:
>>
>> > If given an option string such as
>> >
>> > size=1024,nodes=10,nodes=4-5,nodes=1-2,policy=bind
>> >
>> > the qemu_opts_to_qdict() method will currently overwrite
>> > the values for repeated option keys, so only the last
>> > value is in the returned dict:
>> >
>> > size=QString("1024")
>> > nodes=QString("1-2")
>> > policy=QString("bind")
>> >
>> > With this change the caller can optionally ask for all
>> > the repeated values to be stored in a QList. In the
>> > above example that would result in 'nodes' being a
>> > QList, so the returned dict would contain
>> >
>> > size=QString("1024")
>> > nodes=QList([QString("10"),
>> > QString("4-5"),
>> > QString("1-2")])
>> > policy=QString("bind")
>> >
>> > Note that the conversion has no way of knowing whether
>> > any given key is expected to be a list upfront - it can
>> > only figure that out when seeing the first duplicated
>> > key. Thus the caller has to be prepared to deal with the
>> > fact that if a key 'foo' is a list, then the returned
>> > qdict may contain either a QString or a QList for the
>> > key 'foo'.
>>
>> Actually three cases, not two:
>>
>> 0. qdict does not contain the key means empty list.
>>
>> 1. qdict contains the key with a QString value means list of one
>> element.
>>
>> 2. qdict contains the key with a QList value means list of more than one
>> element.
>>
>> I consider this weird. However, it's usefully weird with at least your
>> QObject input visitor.
>>
>> > In a third mode, it is possible to ask for repeated
>> > options to be reported as an error, rather than silently
>> > dropping all but the last one.
>>
>> Got users for this policy in the pipeline?
>
> I in fact used it in the QObjectInputVisitor, when the
> autocreate_list is not set.
>
> I guess strictly speaking this is not back-compatible
> if someone is passing repeated keys, but I judged that
> rather than silently ignoring this incorrect usage, it
> was acceptable to report an error.
While usage like
-machine usb=on,usb=off
could perhaps be declared erroneous post hoc, the "last one wins"
feature also has genuinely useful applications. For instance, tack a
correction to a long command line:
-machine usb=on [... lots of other stuff ...] -machine usb=off
Or modify canned configuration:
-readconfig vm1.config -machine usb=off
# vm1.config sets usb=on, -machine overrides
-readconfig vm1.config -set drive.disk0.file=tmp.qcow2
# vm1.config defines drive "disk0", -set overrides its image file
I don't think we can break them all.
[...]
