On 07/14/2016 07:03 AM, Daniel P. Berrange wrote: >>> I'm not really a huge fan of the approach there. IMHO the >>> input visitor should strictly operate in "all native types" >>> or "all string types" mode. The way you've done it here >>> means that users can actually mix & match strings vs native >>> types for each individual parameter :-( >>> >>> IMHO, I'd suggest you try to parse netdev_add args with >>> it in "all native types" mode, if that fails, then re-parse >>> in "all string types" mode. >> >> Sadly, this idea won't work. Without this series, the existing QMP >> command 'netdev_add' takes mixed integers and strings in a single call, >> by virtue of converting QObject into QemuOpts and back into QObject. > > Ok, so lemme check I understand. The original QObject has properties > which are integers, but with existing code QMP allows them to be passed > as strings or ints, converts them to QemuOpts which makes them all > strings and converts them back to QObject leaving them all as strings.
Yes, the existing code (using 'gen':false) just passes an entire QObject to hand-written code; the hand-written code converted everything to QemuOpts (which flattens both integers and strings into options), then expanded QemuOpts back into QObject (strings-only). > > You've now got rid of the QObject -> QemuOpts conversion, so we're > not string-ifying everything, and so have to cope with arbitrary > mix directly. Yes. > >> Forcing the parser to allow only integers or only strings would reject >> current uses of netdev_add, and we don't yet have a good idea whether >> any existing clients were depending on that behavior. >> >> Also, see patch 17/17 - the easiest way to implement a relaxed QMP parse >> is by setting a single flag which controls which visitor constructor is >> used. Your idea of parsing once with integer-only, then falling back to >> parse a second time with string-only, would complicate the generator to >> have to create two different visitors, rather than passing a single >> boolean parameter through to the single visitor constructor. > > So I don't think a simple boolean flag is desirable, as we have 3 distinct > scenarios: > > 1. Strongly typed only > 2. String conversion only > 3. Strongly typed, with string conversion fallback > > My current patch provides 1 + 2, your alternative patch provides 1 + 3. > If we use option 3, in cases which only actually need option 2, then we > are potentially introducing more scenarios where arbitrarily mixed > types are accepted. IOW, I think we must implement 1, 2 and 3 and avoid > using 3 except where absolutely needed. 3 is a superset of 2, and your command-line conversion is the only case where we can achieve 2. That is, code dealing with QMP can only choose between 1 and 3, based on whether the QAPI .json file used 'autocast':true for back-compat reasons (the only candidates are 'netdev_add' and 'device_add'). And code dealing with command line parsing can only choose 2 (QemuOpts is string-only), but parsing string-only via 2 is no different than the result achieved from parsing strongly-typed with string fallback via 3. I still don't buy the fact that we need a string-only parser at the moment, but it would not be hard to change the 'bool autocast' into a tri-state enum, and then make the implementation specifically honor 1, 2, or 3 based on the enum value. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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