Subject: Re: [RFC net-next 2/4] ynl: add the schema for the schemas

From: Jakub Kicinski <[email-masked]>
Date: Tue, 27 Sep 2022 14:56:22 -0700

On Mon, 26 Sep 2022 11:10:56 -0500 Rob Herring wrote:
> On Wed, Aug 10, 2022 at 07:23:02PM -0700, Jakub Kicinski wrote:
> > A schema in jsonschema format which should be familiar
> > to dt-bindings writers. It looks kinda hard to read, TBH,
> > I'm not sure how to make it better.  
> 
> This got my attention in the Plumbers agenda though I missed the talk. 
> It's nice to see another jsonschema user in the kernel. I hope you make 
> jsonschema a dependency for everyone before I do. :) Hopefully we don't 
> hit any comflict in required version of jsonschema as I've needed both a 
> minimum version for features as well as been broken by new versions.

I'm a complete noob on this, my jsonschema is really crude.
But thanks to this it's unlikely to depend on any particular version? :)

> I would avoid calling all this 'YAML netlink' as YAML is just the file 
> format you are using. We started with calling things YAML, but I nudge 
> folks away from that to 'DT schema'.

Good point, I'll try to stick to Netlink schema as well.

> Also, probably not an issue here, but be aware that YAML is much
> slower to parse than JSON. 

Fingers crossed. Worst case we can convert formats later.

> > Signed-off-by: Jakub Kicinski <[email-masked]>
> > ---
> >  Documentation/netlink/schema.yaml | 242 ++++++++++++++++++++++++++++++
> >  1 file changed, 242 insertions(+)
> >  create mode 100644 Documentation/netlink/schema.yaml
> > 
> > diff --git a/Documentation/netlink/schema.yaml b/Documentation/netlink/schema.yaml
> > new file mode 100644
> > index 000000000000..1290aa4794ba
> > --- /dev/null
> > +++ b/Documentation/netlink/schema.yaml
> > @@ -0,0 +1,242 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +%YAML 1.2
> > +---
> > +$id: "http://kernel.org/schemas/netlink/schema.yaml#"
> > +$schema: "http://kernel.org/meta-schemas/core.yaml#"  
> 
> In case there's ever another one: meta-schemas/netlink/core.yaml
> 
> Or something similar.

Ack!

> > +
> > +title: Protocol
> > +description: Specification of a genetlink protocol
> > +type: object
> > +required: [ name, description, attribute-spaces, operations ]
> > +additionalProperties: False
> > +properties:
> > +  name:
> > +    description: Name of the genetlink family
> > +    type: string
> > +  description:  
> 
> It's better if your schema vocabulary is disjoint from jsonschema 
> vocabulary. From what I've seen, it's fairly common to get the 
> indentation off and jsonschema behavior is to ignore unknown keywords. 
> If the vocabularies are disjoint, you can write a meta-schema that only 
> allows jsonschema schema vocabulary at the right levels. Probably less 
> of an issue here as you don't have 1000s of schemas.

Ack, let me s/decription/doc/
 
> > +    description: Description of the family
> > +    type: string
> > +  version:
> > +    description: Version of the family as defined by genetlink.
> > +    type: integer  
> 
> Do you have the need to define the int size? We did our own keyword for 
> this, but since then I've looked at several other projects that have 
> used something like 'format: uint32'. There was some chatter about 
> trying to standardize this, but I haven't checked in a while.

It's 8 bits in theory (struct genlmsghdr::version), in practice it's
never used, and pretty much ignored. The jsonschema I have on Fedora
does not know about uint8.

> > +  attr-cnt-suffix:
> > +    description: Suffix for last member of attribute enum, default is "MAX".
> > +    type: string
> > +  headers:
> > +    description: C headers defining the protocol
> > +    type: object
> > +    additionalProperties: False
> > +    properties:
> > +      uapi:
> > +        description: Path under include/uapi where protocol definition is placed
> > +        type: string
> > +      kernel:
> > +        description: Additional headers on which the protocol definition depends (kernel side)
> > +        anyOf: &str-or-arrstr
> > +          -
> > +            type: array
> > +            items:
> > +              type: string
> > +          -
> > +            type: string
> > +      user:
> > +        description: Additional headers on which the protocol definition depends (user side)
> > +        anyOf: *str-or-arrstr  
> 
> For DT, we stick to a JSON compatible subset of YAML, so no anchors. The 
> jsonschema way to do this is using '$defs' (or 'definitions' before the 
> spec standardized it) and '$ref'.

I need to read up on this. Is it possible to extend a type?
We really need a way to define a narrow set of properties for "going
forward" while the old families have extra quirks. I couldn't find any
jsonschema docs on how the inherit and extend.

> > +  constants:
> > +    description: Enums and defines of the protocol
> > +    type: array
> > +    items:
> > +      type: object
> > +      required: [ type, name ]
> > +      additionalProperties: False
> > +      properties:
> > +        name:
> > +          type: string
> > +        type:
> > +          enum: [ enum, flags ]
> > +        value-prefix:
> > +          description: For enum the prefix of the values, optional.
> > +          type: string
> > +        value-start:
> > +          description: For enum the literal initializer for the first value.
> > +          oneOf: [ { type: string }, { type: integer }]  
> 
> I think you can do just 'type: [ string, integer ]'.

Works, thanks!