Am 14.08.2019 um 23:08 hat Eric Blake geschrieben: > On 8/14/19 3:22 PM, Maxim Levitsky wrote: > > > This is an issue that was raised today on IRC with Kevin Wolf. Really thanks > > for the idea! > > > > We agreed that this new qmp interface should take the same options as > > blockdev-create does, however since we want to be able to edit the > > encryption > > slots separately, this implies that we sort of need to allow this on > > creation > > time as well. > > > > Also the BlockdevCreateOptions is a union, which is specialized by the > > driver name > > which is great for creation, but for update, the driver name is already > > known, > > and thus the user should not be forced to pass it again. > > However qmp doesn't seem to support union type guessing based on actual > > fields > > given (this might not be desired either), which complicates this somewhat. > > Does the idea of a union type with a default value for the discriminator > help? Maybe we have a discriminator which defaults to 'auto', and add a > union branch 'auto':'any'. During creation, if the "driver":"auto" > branch is selected (usually implicitly by omitting "driver", but also > possible explicitly), the creation attempt is rejected as invalid > regardless of the contents of the remaining 'any'. But during amend > usage, if the 'auto' branch is selected, we then add in the proper > "driver":"xyz" and reparse the QAPI object to determine if the remaining > fields in 'any' still meet the specification for the required driver branch. > > This idea may still require some tweaks to the QAPI generator, but it's > the best I can come up with for a way to parse an arbitrary JSON object > with unknown validation, then reparse it again after adding more > information that would constrain the parse differently.
Feels like this would be a lot of code just to allow the client to omit passing a value that it knows anyway. If this were a human interface, I could understand the desire to make commands less verbose, but for QMP I honestly don't see the point when it's not trivial. Kevin
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