serde serializer + deserializer for NvList

[ahrens]

Add a serde serializer that can serialize structs to NvList's.

Add a serde deserializer that can deserialize NvList's into structs.

I'd consider this prototype-quality. I'm looking for feedback on if this would be useful, and how much additional functionality would be needed to get it integrated (or make it useful for folks). Things that are known to be missing:

• error handling (return Errors rather than todo!() on unimplemented functionality)
• finer-grained Error variants (not always falling back on Error::Message)
• deserializer: option to fail on unconsumed pairs?
• deserializer: handle nvlist_array-type pairs
• serializer: handle sequences (arrays, vec's, etc) of types other than Byte and NvList
• serializer: handle tuples
• serializer: handle enums (variants)
• automated testing

[ahrens]

@ahl do you have any thoughts on which of the missing items should be required before integration?

[codyps]

I'm generally in favor of having serde support for NvList. Would make working with some NvList content a lot quicker. Might be worth considering hiding behind a feature because serde is a bit heavy (could be default enabled), but that wouldn't block merging this.

[ahrens]

Thanks! I'll look into having serde be a configurable feature, and improving the error handling at least.

[sempervictus]

@ahrens: does draft status mean this shouldn't be used because its somehow deficient/dangerous, or just that it hasn't been thoroughly used/QA'd?

[ahrens]

@sempervictus We are using this in production (this version to be specific). However, there may be some corner cases where it doesn't work or has confusing results where the nvpair data model doesn't match up with serde's. I would want to document those more thoroughly, and ideally add some unit tests, before this is integrated.