On Thu, 30 Nov 2023 21:49:54 +0000 Donald Hunter wrote:
> Add a 'sub-message' attribute type with a selector that supports
> polymorphic attribute formats for raw netlink families like tc.
>
> A sub-message attribute uses the value of another attribute as a
> selector key to choose the right sub-message format. For example if the
> following attribute has already been decoded:
>
> { "kind": "gre" }
>
> and we encounter the following attribute spec:
>
> -
> name: data
> type: sub-message
> sub-message: linkinfo-data-msg
> selector: kind
>
> Then we look for a sub-message definition called 'linkinfo-data-msg' and
> use the value of the 'kind' attribute i.e. 'gre' as the key to choose
> the correct format for the sub-message:
>
> sub-messages:
> name: linkinfo-data-msg
> formats:
> -
> value: bridge
> attribute-set: linkinfo-bridge-attrs
> -
> value: gre
> attribute-set: linkinfo-gre-attrs
> -
> value: geneve
> attribute-set: linkinfo-geneve-attrs
>
> This would decode the attribute value as a sub-message with the
> attribute-set called 'linkinfo-gre-attrs' as the attribute space.
>
> A sub-message can have an optional 'fixed-header' followed by zero or
> more attributes from an attribute-set. For example the following
> 'tc-options-msg' sub-message defines message formats that use a mixture
> of fixed-header, attribute-set or both together:
>
> sub-messages:
> -
> name: tc-options-msg
> formats:
> -
> value: bfifo
> fixed-header: tc-fifo-qopt
> -
> value: cake
> attribute-set: tc-cake-attrs
> -
> value: netem
> fixed-header: tc-netem-qopt
> attribute-set: tc-netem-attrs
SGTM, could you add all the info from the commit message somewhere
in the documentation? Perhaps a new section at the end of
Documentation/userspace-api/netlink/specs.rst
> @@ -261,6 +262,17 @@ properties:
> description: Name of the struct type used for the attribute.
> type: string
> # End genetlink-legacy
> + # Start netlink-raw
> + sub-message:
> + description:
> + Name of the sub-message definition to use for the attribute.
> + type: string
> + selector:
> + description:
> + Name of the attribute to use for dynamic selection of sub-message
> + format specifier.
> + type: string
We can leave it for later either way, but have you seen any selectors
which would key on an integer, rather than a string?
