On Thu, Jan 23, 2020 at 12:58:45PM -0500, John Snow wrote: > Yes, I agree: Scrap and start over. > > What SHOULD the syntax look like, though? Clearly the idea of qmp-shell > is that it offers a convenient way to enter the top-level keys of the > arguments dict. This works absolutely fine right up until you need to > start providing nested definitions. > > For the nesting, we say: "Go ahead and use JSON, but you have to take > all the spaces out." > > This... works, charitably, but is hardly what I would call usable. > > For the CLI, we offer a dot syntax notation that resembles nothing in > particular. It often seems the case that it isn't expressive enough to > map losslessly to JSON. I suspect it doesn't handle siblings very well. > > A proper HMP-esque TUI would likely have need of coming up with its own > pet syntax for commands that avoid complicated nested JSON definitions, > but for effort:value ratio, having a QMP shorthand shell that works > arbitrarily with any command might be a better win. > > Do we still have a general-case problem of how to represent QAPI > structures in plaintext? Will this need to be solved for the CLI, too?
I don't know if you've ever looked at how Kubernetes/OpenShift exposes its functionality on the command line ? I think it is interesting to note that they largely don't try to solve this problem of flattening JSON for humans on the CLI using their client. Everything in their world is an object described in JSON/YAML, and there are a small set of generic commands that can act on any type of object. These commands primarily input and output JSON or YAML documents directly. As a user you can pick either format since it can do a lossless conversion in both directions server side. So when configuring objects you'll always provide a JSON/YAML doc. They've got some clever stuff for updating objects where you can provide a JSON patch for only the bits which need changing. When querying/listing objects by default it displays only a small subset of their config information in a human friendly-ish format. If you want to see everything then you ask for it in JSON/YAML format. There's also an expression language that lets you extract particular pieces of information based on requested properties, and you can filter the list of objects based on attributes and so on. I think it is fair to say the structure of kubernetes object config is on a par with hierarchical complexity of QEMU. The lack of a simple human targetted data input format does not appear to have negatively impacted the adoption of Kubernetes. It is worth questioning why this is the case, while we feel the human CLI syntax for QEMU is so critically important to QEMU's future ? Part of it is that the machine oriented data input format via QMP suffers from the fact that it came second in QEMU after HMP. As a result, 90% of the documentation that illustrates QEMU will use the human CLI syntax, varying vintages of that. Since all the docs are focused on the HMP/CLI syntax, whenever there's a new feature we feel pressured to expose it & document it in the human syntax too. All this results in a situation where JSON is functionally the best way to configure QEMU, but practically the worse, since very few people understand how to actually use it. This is a vicious circle holding back QMP/JSON and making the human syntax an ever greater burden for users & maintainers IOW, the difficulty with configuring QEMU via JSON is not the fault of JSON itself, it is the lack of knowledge amongst users and docs, compounded by our never ending "improvements" to the human syntax. There are other factors too, such as our only partial coverage of config using JSON - some is only possible via the CLI still. I guess my point is that with a scrap & startover view point, we should arguably completely ignore the design question of how to flatten JSON for humans/command line, as it is the wrong problem. Instead focus on the problem of making use of JSON the best way to deal with QEMU both functionally and practically, for humans and machines alike. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
