netdev - Re: Netlink specs, help dealing with nested array

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Date: Fri, 21 Jun 2024 08:19:06 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Kory Maincent <kory.maincent@...tlin.com>
Cc: netdev@...r.kernel.org, Donald Hunter <donald.hunter@...il.com>
Subject: Re: Netlink specs, help dealing with nested array

On Fri, 21 Jun 2024 16:15:43 +0200 Kory Maincent wrote:
> Hello Jakub, Donald or other ynl experts,
> 
> I have an issue dealing with a nested array.
> 
> Here is my current netlink spec and ethtool patches:
> https://termbin.com/gbyx
> https://termbin.com/b325
> 
> Here is the error I got:
> https://termbin.com/c7b1
> 
> I am trying to investigate what goes wrong with ynl but I still don't know.
> If someone have an idea of what is going wrong with ynl or my specs it would be
> lovely! 

You're (correctly) formatting your data as a basic multi-attr.
Instead of:

+        name: c33-pse-pw-limit-ranges
+        name-prefix: ethtool-a-
+        type: indexed-array
+        sub-type: nest
+        nested-attributes: c33-pse-pw-limit

use:

+        name: c33-pse-pw-limit-ranges
+        name-prefix: ethtool-a-
+        type: nest
+        multi-attr: true
+        nested-attributes: c33-pse-pw-limit

The indexed array is described here:
https://docs.kernel.org/next/userspace-api/netlink/genetlink-legacy.html#indexed-array
it has an extra layer of nesting, which uses the index in the array 
as the type of the attribute.